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lines plan catamaran

  • PERFORMANCE TOPICS

Optimising Hull Lines for Performance

This article was inspired by a question about the rocker line in the new 8.5m cat Design 256 and I want to stick to the point, so we won’t turn it into a book, but I’ll discuss two issues, hull fineness ratio and some aspects of the rocker profile.

When you manipulate the hull form you’re adjusting the lines in three planes, waterplanes (plan view), buttocks (side view including the keel rocker) and the section shapes. So you need to be aware of how the shapes are changing in the other two planes as you manipulate any one of these three, or all three globally as is now possible with computer modelling.

There are two fundamental constants that you start with and don’t change throughout the process. The big one is the displacement or the amount of buoyancy you need.

If you make the hull finer by narrowing the waterlines you have to increase the draft or make the ends fuller to get back to the required displacement number.

If you flatten the rocker line you have to increase the hull width, fill out the ends, or square up the section shapes rather than having a V or rounded V. 

The other constant is the longitudinal centre of buoyancy. You really can’t do any meaningful shaping of the hull form until you have settled on the these two constants.

A third number that we can plug in as a constant if we want to is the prismatic coefficient which describes bow much volume there is end the ends relative to the cross section shape in the middle of the boat, but in sailing boats this is of less importance compared to other factors. 

Lines plan for the Livewire Catamaran

The hull lines for Design 256, 8.5m Cat. It's that hump in the rocker line - right under the back of the cabin that brought up the question and is one of the key points discussed here.

Hull fineness.

Fine hulls are fast, but only in the higher speed range. There’s a misconception I come across quite a bit that you can add weight and windage and you’ll still be fast as long as your hulls are fine.

Well you won’t be. Your boat will simply sink to find the new state of equilibrium. If your transoms are submerged you’ll have more drag. If your bridge deck is too close to the water you’ll have slamming. Much better to be conservative with your displacement figure in the design stage than overly optimistic.

And fine hulls have more wetted area so you have more drag in light air where friction resistance is the primary drag factor. 

I’ve seen promotional material for catamarans stating that the boat has less wetted area because it has fine hulls. For a given displacement the minimum wetted area is described by a sphere (or a semi sphere in the case of a floating object). The more you stretch it out in length, keeping the displacement constant, the more wetted area you have.

The more you make the section shape into a deep V or a broad U with tight corners, as opposed to a semicircle, the more wetted area you have. Add into the equation finer hulls are slower to tack.

So fine hulls are only an advantage if your boat is light and has enough sail area to ensure you’re travelling at speeds where form resistance is greater than skin resistance.

In my view the advantage of fine hulls is often overrated as it applies to cruising cats.

At the other end of the scale the resistance curve is fairly flat up to about 1:9 which is still quite fast in most conditions. From there the resistance rises steeply as the hull gets fatter and at 1:8 and fatter you’re suffering from some serious form drag.

Illustration of buoyancy distribution in catamaran hull

This is the rocker line isolated from the lines plan above (in blue) and and the red line shows a more moderate rocker line that achieves the same buoyancy and maintains the centre of buoyancy in the same position.  The bow is to the right.

In the image lower right I've squashed it up and increased the height to make the difference in the lines more obvious.

The difference in the two lines is quite subtle, but races are often won or lost by seconds.

Rocker Profile

So if we’re looking for low wetted area we would want a rocker profile that was even and rounded, relatively deep in the middle and rising smoothly to the surface at each end. But this would give us a low prismatic which is not ideal in the higher speed range, and it’s not ideal for pitch damping which in my view is the critical design factor that is often underrated. 

Pitching is slow. It destroys the airflow in your sails and the flow around the hulls, and your performance is suffering from slamming loads.

The single most effective way to counter pitching is with asymmetry in the water planes. You can achieve that in the with a fine bow and broad transom. Or you can achieve it with V sections forward and a flattened U shape aft. Or you can achieve it in the profile view with a very straight run forward and a bump in the aft sections. A flatter rocker line is better for resisting pitching than an evenly curved one with deeper draft in the middle.

The final result is a combination of all three of these factors.

On a cat like Design 256 the weight is concentrated well aft so we need to get buoyancy well aft.

The kink you see in the rocker profile helps to do this. It also helps to keep the rocker straight for most of its length and smooth the water flow exiting the hull aft at higher speeds, possibly promoting some planing effect.

If we had a more even rocker line we would slightly reduce the wetted area, but we would increase the pitching and the water would exit the hull aft at a steeper angle, increasing form drag in the higher speed range.

How much of a bump can you put in there without creating a flow separation, and how damaging would that flow separation be? I really don’t know. The way all of these factors interplay in the various conditions we sail in is very complex.

Ultimately a lot of this work is gut feel nurtured by experience, observing things in nature and most importantly experimenting and trying new ideas.

Is the new Groupama AC45 a breakthrough that will influence the form of racing catamarans into the future? I don’t think anyone has a computer that can answer that. We have to wait and see.

Catamaran hull lines showing symmetric and asymmetric waterplanes

Symmetric and non symmetric water-planes. The blue line with grey fill is the DWL from the design above. As is typical with modern cat hulls the bow is long and fine, the stern is full and rounded. This is the asymmetry that has a damping effect on pitching. The red line on the other hand is more like you would see on a double ended monohull and quite a few multihulls have also used this shape in the past. It's quite symmetric about the pitch axis and does not have good pitch resistance.

Lines plan for the Livewire 28 Catamaran

The hull lines of the new 8.5m Sports Cat Design 256

Lines plan for Mad Max Design 101

Mad Max , Previously Carbon Copy . She was designed in 1997 but she's the current (2016) title holder of the Australian Multihull Chamionships (2 successive years) and the fastest inshore racing boat in Australian waters.

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lines plan catamaran

DIY Cruising Catamaran: Complete Building Guide

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A brand-new cruising catamaran can set you back a hefty amount of money. However, a DIY cruising catamaran provides a more affordable way to own your own boat. While building a large boat can be an extremely challenging and time-consuming experience, nothing beats the pleasure of bringing your own boat to life. 

To build a DIY cruising catamaran, buy good design plans, determine your budget and find a working space. Next, choose your hull material, buy supplies and start building the mast beam. Build and sheathe the hull, install bulkheads, the interior, and finally, launch the catamaran boat.

In this article, you will find a complete guide to building your own catamaran. You will also find detailed information on why you may want to consider building your catamaran and approximately how much this project would cost. Finally, we will explore the advantages and disadvantages of building a catamaran from scratch.

Why You Might Want To Build Your Own Catamaran

Most people might think that purchasing a used boat to repair and fix it up would be cheaper than a DIY cruising catamaran. But while building your own catamaran could be an enormous undertaking, it also comes with many advantages over buying something used. 

Other than the unique opportunity to create beautiful memories and experiences while cruising, sailing, and exploring beautiful coastlines, there are a number of benefits that come along with the DIY approach.  

Knowing Your Boat

Building your own catamaran provides you with intimate knowledge of your boat. You will know every corner, including where to find every bolt, wire, bulkhead, rib, hose, and support as you installed them yourself. This knowledge will enhance your confidence while at sea since you will have entrusted your life to a boat whose history you are aware of and deeply connected to.

Pride of Ownership

The satisfaction you get from crafting something with your own hands is immense. As a result, the knowledge that you built your boat from scratch will fill you with absolute pride and an immense sense of achievement. Furthermore, as an owner-builder, you get to keep and enjoy the boat for as many years as you wish.

Substantial Cost Savings

Building your catamaran will work out cheaper than buying a new or even gently used boat. Though you will likely require some additional labor since doing some things will require an extra pair of hands, if you are particularly good at DIY, you will save a significant amount of money on labor costs as a whole. 

Freedom To Create Your Own Designs

If you decide to buy a catamaran boat, it might not be easy to find one that meets your unique needs. However, instead of choosing from production boats that bear traditional and outdated designs, you can come up with an ultra-modern design or style for your catamaran. You also get to pick your layout, size, and equipment based on your taste and budget.

Great Learning Experience

Building your own boat will help you pick up numerous skills that will come in handy later when sailing your boat. As much as you might still require an expert to help you with specialized skills like carpentry or wiring, your new skills will serve you well. This will also be beneficial when it comes to your boat’s maintenance and fixing things for yourself. 

What To Look For in Catamaran Boat Designs

When deciding on the type of catamaran boat to build, you may want to choose a design that’s simple and easy to build. This is because doing so will allow you to spend a shorter time building the boat. 

You also need to have a set of requirements to guide you in choosing your design or what you might call an ideal cruising catamaran wish list. This is essential because, ultimately, you want to build a boat that offers outstanding qualities such as:

  • Delivers good speed
  • Affordable to own and operate
  • Agile, strong, and easy to maintain
  • Has a high resistance to capsizing
  • Great for sailing and cruising
  • Delivers a comfortable and easy motion underway
  • Good handling ability and high performance under sail
  • User-friendly embarking and disembarking
  • Provides ample living and accommodation space 
  • Presents a reasonable resale value

It’s worth noting that, in general, catamaran boats tend to offer a fair resale value mainly because of scarcity and the high price accorded to production models. So, if you build a well-constructed catamaran, you are bound to get a return that’s much higher than the cost of materials upon resale.

It’s also good to consider whether the design you settle on is from an established designer. This is significant because documentation of the building process is just as valuable when it comes to selling the boat.

How Much Would It Cost To Build Your Own Catamaran?

The cost of building your cruising catamaran will depend heavily on the size of the boat you plan to build and the skills you bring to the table. To give you an idea of probable costs, a professionally built 40 foot (12.1 m) long cruising catamaran could go for up to $300,000. 

Though building it yourself will undoubtedly be cheaper, most DIY boatbuilders tend to underestimate the expected costs. Your final costs should cover not only the cost of material and equipment but also the labor and time it would take to come up with the final product. 

If you were to build a 40-foot (12.1-meter) catamaran, your cost of materials would range between 20-30% of the total cost. Therefore, for $300,000 total, the boat’s materials would range between $60,000 and $90,000. The hull tends to range between 15-35% of the total build. Again, this depends on the finish and furniture.

But before you even start working on the DIY project, you will need to figure out where to do the work. If your home has ample space, then you can opt for a backyard building. But if you live in a small apartment, then you might want to consider renting a small garage at first and then move on to a boatyard later. This is one of the significant costs involved in building your multi-haul.  

What You Will Need

To get a clearer picture of how much the entire project would cost, let’s have a look at what else you will need to purchase.

  • Good design plans
  • Working space
  • Ground tackle
  • Matting and roving
  • Equipment such as the engine, windows, rudders, deck fittings, mast, and rigging

In addition to the above, you also need to install plumbing and electricals. You may also want to consider going electric rather than using diesel. Not only will this drastically reduce your maintenance costs, but you get to use the regenerated power for all of your housing needs while sailing. 

Some catamaran boat designs help you save costs by advocating the use of less expensive corpus materials. Most of the material goes directly into making the boat, which means there is hardly any wastage on vacuum bagging . With this method, there are few molds and temporal building forms and fewer fillers to grind off as waste. All these factors reduce the time and cost it takes to build your catamaran boat.

That said, building a boat of any kind is a huge financial undertaking. As such, you still need to have the financial ability to keep building; otherwise, your project will stall or take much longer than anticipated. Instead of enjoying yourself and making memories cruising to faraway lands, you might end up spending all your time building a seemingly never-ending boat.

To reiterate, this project is more of a labor of love, given that it involves a tremendous amount of manual work. Calculating an hourly rate on the time spent building the boat and adding this cost to that of materials may make it seem a very pricey exercise. However, it is vital to understand that your time matters, and every hour you spend working for “free” should be included. 

With that in mind, you need to ensure that you are fully devoted to the boat construction project and are sure you want to do it before you begin. Stopping halfway because it seems like too much work would be incredibly costly.

How To Build a Catamaran

When it comes to building a cruising catamaran, you have 3 main options:

  • You can buy an old boat and refurbish it.
  • Purchase a bare hull plus deck molding for a home-boat building.
  • Start from scratch and build everything, including the hull, on your own. 

As mentioned above, renovating an existing boat may end up being more costly than starting from scratch. To build a catamaran boat from scratch, follow the below step-by-step guide.

Prepare the Essentials

Before you jump into such a large project, there are several important aspects to consider:

  • Buy your plans from an established catamaran designer. You can also get inexpensive, easy-to-build catamaran designs online.
  • Get access to a large working space or build a shed . Depending on your climate, you may need to opt for climate control to avoid an excess of moisture in humid areas. 
  • Decide on your choice of hull material. This could be fiberglass, aluminum, steel, wood, or ferroconcrete. 
  • Start working on a bill of materials estimate. Include everything that you think you need to get a better idea of the initial costs.

Build the Mast Beam

Using wood and epoxy, cut and glue together the pieces of wood that will form the mast beam. Most of the work at this stage can occur in a garage since it involves building small parts. Still, the work could take up to 4 months, so be prepared to put in long hours.

Build the Boat Hull

Now, it’s time to build the boat’s hull. A catamaran comprises two hulls which are connected with a deck. Below is a short video showing how to build a hull mold:

This work requires a larger facility, so you might need to move out of the garage and into a boatyard. If you don’t have access to a larger workshop, consider building a shed where you can work as you do the construction. Make sure there’s enough room to fit the boat and also allow you to work comfortably. To cover the shed, you can use opaque white tarps. 

Sheathe the Hull

Get all the materials you require for this stage in the construction, such as lots of resin, fiberglass, and foam for use in the hull cores. You’ll also require matting and glass roving to sheath the hull . 

Sheathing helps to make the hull impervious to water and other marine borers. But first, you need to prepare the hull using a rotary sander. To make it as smooth as possible, use light, sweeping strokes. This is a very dusty task so be prepared to wear a facemask and safety goggles. 

Install the Bulkheads

Next is installing the plywood bulkheads . You might need to call in friends to help turn the hulls or use a crane. In this step, you will need to laminate the hull sides on the molded hull panels and bond them above the bulkheads. Ensure the bulkheads are snug and sealed in place.

Construct the Interior Structure

Over the next couple of months, the boat work will involve joining the hulls together with the beams that you had made back in the garage. Then, install the cuddy cabin, decks , and the cockpit . Soon the boat will start to take the shape of a catamaran.

Next, proceed to construct the major structural components such as stairs, hatches, mini-keels, and the interior. Then comes the work of fairing the boat, which is quite labor-intensive. 

Finally, it’s time to apply primer on the catamaran boat and start the paintwork. Before painting the boat, you will need to do additional sanding to finish off the two layers of primer as well as fill all the pinholes. Since it’s a large boat, the catamaran has lots of surface area; thus, the sanding could get extremely exhausting—mentally and physically—at this point.

The painting can take a while, too. The hulls are the easiest to paint, but the topsides, non-skid, as well as masking and prepping could seem never-ending. 

The final stretch involves working on the center bridge deck cabin and other final touches like installing the engines, electricals, and plumbing. This is also the time to fix the rudders, rigging, mast, windows, and deck fittings.

Launch Your Cruising Catamaran

After many months or years of hard work, your cruising catamaran is finally ready to test the waters. After lowering the boat into the water, check carefully in case there are leaks. If none, you can set up the sails and take your catamaran out for your first cruise. 

Below is a short video that takes you through the entire boat-building process:

If you don’t have deep pockets, don’t despair. It’s also possible to build an inexpensive catamaran boat, as shown in this post from the coastal passage .

The Pros of Building a Catamaran

Though it will be a costly endeavor, there are so many things to look forward to should you decide to build your own catamaran:

  • It can be lots of fun.
  • You get to have a new boat.
  • It’s an excellent hobby for DIY enthusiasts.
  • The effort is rewarding.
  • It offers a great learning experience.
  • You get the exact kind of boat you want.
  • You can alter building plans and tailor the boat to suit your specific needs.
  • It might be cheaper than buying a new boat.

The Cons of Building a Catamaran

Though there are a number of positive aspects to a DIY build, it is just as important to keep in mind that it won’t always be easy:

  • Maintenance costs can be quite high.
  • It’s both mentally and physically exhausting.
  • It might require some technical know-how.
  • It can take many months or even years to complete.
  • It requires a lot of commitment to finish the DIY project.
  • It might be challenging as well as expensive to get insurance.  
  • You will spend almost all your free time building the boat. 

DIY Cruising Catamaran Tips and Tricks

If you are new to boat building, it would be a good idea to build a small boat first. This would give you a good indication as to whether you’d enjoy tackling a more extensive project like building a catamaran. Again, if you are the handy type, fixing your own electronics could also save you a significant amount of money. 

Here are more tips and tricks to get the most out of your DIY cruising catamaran:

  • Lower your costs. Bring down your costs even further by sourcing for parts and supplies at marine surplus outlets, Craigslist, eBay, or wholesale suppliers. 
  • Enhance your resale value. Most home-built boats are not easy to sell since they tend to be too customized. To enhance your resale value, it’s advisable to work with a standard design from a well-established naval architect.
  • Follow the design instructions. Make sure to follow the designer’s instructions regarding the type of materials and tools to use during the build to avoid making costly mistakes.
  • Maintain your original budget. Avoid any additional customizations once you have started building the boat. Using good plans and sticking to them ensures that your budget doesn’t spiral out of control.

Final Thoughts

Building a catamaran is about more than saving money. It’s fun, exciting, fulfilling, and can be a great learning experience. While it might take many months of back-breaking work, comparative shopping and sourcing for materials will help you save a lot of money. Still, at the end of it all, you’ll have a beautiful catamaran boat, all ready for your first cruising adventure.

However, if you have neither the time nor the energy to build your own catamaran from scratch, refurbishing an existing hull might prove faster and easier. It also works out much cheaper than buying a new boat.

Owner of CatamaranFreedom.com. A minimalist that has lived in a caravan in Sweden, 35ft Monohull in the Bahamas, and right now in his self-built Van. He just started the next adventure, to circumnavigate the world on a Catamaran!

One thought on “ DIY Cruising Catamaran: Complete Building Guide ”

Hello, I am a French Quebecer who is original, imaginative, creative and who finds that all boats and catamarans have a huge flaw and a very big lack of logic. I would have a brand new concept…. I am sending this message to any catamaran creator – designer to make those who have the opportunity and the intelligence to want to know about my innovative idea which will finally upset the market much richer. An idea that will totally change the concept of sailing, navigation and save so much worry!! All I would ask for is a small percentage of each sale of the new product. To be able to make me produce one when I have enough!! It is certain that like that, you just want to tell me: come on Mr. Lessard give us your idea but do not take your word to help me in return! But, if you are the kind of man to have only one word and maybe have a proof of your good faith if the realization of the project would make it… I will be very happy!! Giving it to everyone wouldn’t bother me either…. all I would like is to be able to find flax fiber (too expensive carbon) to be able to try to make my catamaran myself. Because not rich! Have a nice day and looking forward to having a message!!

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catamaran offset table

Discussion in ' Projects & Proposals ' started by Mojtaba , Apr 9, 2012 .

Mojtaba

Mojtaba New Member

hi i'm looking for some catamaran offset table for my project i couldn't find any useful offset in internet , can you help me find some ? thanks  

gonzo

gonzo Senior Member

What kind of a project is it?  
It`s a student project, Me & my friend work on effects of changing geometric parameters of catamarans. we put offset in software and then change it & analysis its hydrodynamic behaviors. we worked on a simple sample but our teacher said its better to work on a real model.  

negin

negin New Member

hi.. how can i get catamaran offset table?  

adam_designer

adam_designer Junior Member

negin said: ↑ hi.. how can i get catamaran offset table? Click to expand...

upchurchmr

upchurchmr Senior Member

Offsets are a large part of what you pay a designer for. I don't know of how you will get offsets from a production design.  
I used samples of delftship. you can download samples & free version of delftship from http://www.delftship.net then you can get the offset from program!  
are all the offset belonge to catamaran?  
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How to Build a Catamaran Boat? (Step-by-Step Guide)

lines plan catamaran

Building a catamaran boat from scratch is a rewarding and challenging endeavor.

It takes a combination of skill, dedication, and hard work to craft a seaworthy vessel.

In this step-by-step guide, you’ll learn how to design and size your catamaran, gather the necessary materials, cut and assemble the pieces, lay fiberglass and apply epoxy, make finishing touches, add hardware and paint, and rig the boat.

With the right tools, planning, and patience, you can make your dream of sailing in a catamaran a reality.

Table of Contents

Short Answer

Building a catamaran boat requires a lot of patience and skill.

The first step is to choose the right materials for the hull, such as fiberglass, wood or aluminum.

Then, you will need to build the frame of the boat, which includes the crossbeams and the main hull.

After that, you will need to install the decking, the rigging, and other components.

Finally, you will need to paint and varnish the boat, as well as install the outboard motor and other accessories.

Design & Size Considerations

When it comes to building a catamaran boat from scratch, the first step is to determine the design and size of the boat.

This should take into account the intended use of the boat, such as sailing, fishing, or leisurely cruising.

The size of the boat will depend on the number of passengers and the type of activities the boat will be used for.

For instance, a larger boat may be needed if passengers will be standing or participating in watersports.

The design of the boat is also important and should be chosen based on the intended use.

If you are looking to build a sailboat, you will need a design that is optimized for sailing.

On the other hand, if you are looking to build a fishing boat, you will need a design that is optimized for fishing.

There are a wide variety of boat designs available, so it is important to research and choose the one that best suits your needs.

In addition to the design and size, you will also need to consider the materials used for construction.

The most common materials for building a catamaran boat are wood, fiberglass, and epoxy.

Each material has its own advantages and disadvantages, so it is important to research them and determine which one is best for your project.

Finally, you will need to consider the cost of the project.

Building a catamaran boat from scratch can be a costly endeavor, so it is important to have a budget in mind before you begin.

The cost will depend on the type of materials used and the complexity of the design.

It is also important to factor in the cost of any tools that may be needed for the project.

By taking into account the design and size, materials, and cost of the project, you can be sure to build a catamaran boat that meets your needs and budget.

With the right amount of patience and attention to detail, you can build your own catamaran boat in no time.

Gathering Materials

lines plan catamaran

Gathering the materials needed to build a catamaran boat from scratch can be a daunting task, but it is essential for creating a sturdy and safe vessel.

Before starting the building process, it is important to have an accurate and detailed plan for the boats design and size.

Once a plan is in place, it is time to begin sourcing the necessary materials.

The most common materials used to construct a catamaran boat are wood, fiberglass, and epoxy.

When choosing wood, it is best to select a species of timber that is strong and durable, such as mahogany, teak, or cedar.

Additionally, the wood should be clear and free of knots, splits, and other defects.

Fiberglass is a lightweight fabric that is resistant to water and provides additional strength to the boats hull.

Epoxy is a waterproof adhesive that is used to seal the boat and ensure that it is watertight.

It is important to ensure that the materials are of high quality, as this will help to ensure the boats longevity.

Additionally, it is important to purchase the necessary materials in the correct amount and size.

Too little or too much of a material can be a costly and time-consuming mistake.

Finally, it is important to keep any leftover materials for future repairs or modifications.

With the right materials gathered, the next step is to cut the wood and begin the assembly process.

Cutting & Assembly

Cutting and assembly are the most important steps when it comes to building a catamaran boat from scratch.

The first step is to decide the design and size of the boat.

This will determine the type of materials you need to gather and the amount of effort that needs to be put into the project.

After deciding on the design and size, you will need to cut the wood to fit the design.

This includes cutting the wood to the desired size, as well as cutting any additional pieces that may be needed to complete the design.

It is important to ensure that all the pieces fit together correctly and securely, as any mistakes could lead to a weak boat.

Once the wood has been cut, it is time to assemble the pieces together.

This involves attaching the pieces together with glue, screws, and nails, and ensuring that the pieces fit together securely.

It is important to be careful and patient when assembling the pieces, as any mistakes could result in a weak and unstable boat.

Once the frame is ready, it is time to lay the fiberglass, and apply the epoxy to seal the boat.

This is an important step, as it will make sure that the boat is waterproof and durable.

Finally, you can add the finishing touches, such as the hardware, paint, and rigging.

With the right amount of patience and attention to detail, you can have your own custom catamaran boat in no time.

Laying Fiberglass & Applying Epoxy

lines plan catamaran

When laying the fiberglass and applying epoxy, it is important to take your time and be precise.

Fiberglass and epoxy are key components of a catamaran boat, as they provide the strength and waterproofing necessary to keep the boat afloat.

Start by laying the fiberglass over the frame of the boat.

Make sure to cut the fiberglass to size and overlap the edges for a strong seal.

Once the fiberglass is in place, mix the epoxy and begin to apply it.

It is important to apply the epoxy in a thin, even layer to ensure a proper seal.

Make sure to move the epoxy around to get it into all the nooks and crannies of the boat.

Allow the epoxy to cure and then you can begin to add the finishing touches.

Finishing Touches

Once the frame of the catamaran boat is built, it is time to add the finishing touches.

This includes adding the necessary hardware, painting, and rigging the boat.

Hardware: Before adding the hardware, it is important to ensure that the frame is stable and secure.

Add the appropriate hinges, screws, and nails to the frame.

Make sure that the screws and nails are the correct size and do not exceed the recommended load capacity of the frame.

Painting: Once the hardware is added, it is time to paint the boat.

Choose a paint that is suitable for the materials used in the construction.

Make sure that the paint is applied evenly and that the frame is completely dry before applying the next coat.

Rigging: The last step is to rig the boat.

This involves attaching the sails, running rigging, and standing rigging to the masts and booms.

Make sure that the rigging is properly tensioned and secured.

Once all of these steps are complete, your catamaran boat is ready to sail.

Hardware & Paint

lines plan catamaran

The last step in building a catamaran boat is to add the hardware and paint.

This step is often the most rewarding, as it is the finishing touch.

Depending on the design of your boat, there are various types of hardware you may need.

Some of the most common items are cleats, winches, fasteners, and decking.

After selecting the required hardware, you will need to install them on the boat.

It is important to use the correct type of screws and bolts, and to secure them tightly.

Once the hardware is installed, it is time to apply the paint.

The type of paint and color you choose will depend on the design of your boat.

It is important to use a high-quality marine grade paint that is designed to handle the extreme environment of the ocean.

If you are up to the challenge, you can add some custom artwork or detail to your catamaran boat.

Adding the hardware and paint is the final step in building a catamaran boat.

With patience and attention to detail, you can create a beautiful and unique boat that will last for many years.

Be sure to take your time and enjoy the process of constructing your own boat.

Once you have finished the frame, fiberglass, and epoxy of your catamaran boat, you will need to move onto the rigging.

This is a crucial step in the construction process, as it will keep your boat safe and secure on the water.

When rigging a catamaran, there are a few key components that must be taken into account.

First, you will need to determine the type of rigging you will be using.

Typically, catamarans use a combination of standing and running rigging.

Standing rigging consists of cables and lines that stay in a fixed position to provide stability and strength to the boat, while running rigging consists of lines that are used to adjust the sail and mainsheet.

Additionally, you will need to choose the right type of rope and hardware for your rigging setup.

The rope should be strong and durable, and the hardware should be made of stainless steel and be corrosion-resistant.

Once you have chosen the type of rigging and hardware, you can start assembling the rigging lines.

This process involves carefully measuring and cutting the lines to the proper lengths, and then attaching them to the mast and boom.

Depending on the type of rigging setup, you may also need to attach the lines to the hulls and deck.

It is important to inspect the rigging lines and hardware regularly to ensure that everything is secure and in proper working order.

Rigging a catamaran boat can seem like a daunting task, but it is essential for the safety and comfort of your vessel.

With the right tools, materials, and attention to detail, you can successfully and safely rig your catamaran boat.

Final Thoughts

Building a catamaran boat is a rewarding experience that requires patience and attention to detail.

With the right plan, materials, and steps, you can build your own boat in no time.

Now that you know the basics of how to build a catamaran boat, why not grab your tools and get started on your very own project? With the right motivation and dedication, you can make your dream of owning a catamaran boat a reality.

James Frami

At the age of 15, he and four other friends from his neighborhood constructed their first boat. He has been sailing for almost 30 years and has a wealth of knowledge that he wants to share with others.

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Catamaran Design Formulas

  • Post author By Rick
  • Post date June 29, 2010
  • 10 Comments on Catamaran Design Formulas

lines plan catamaran

Part 2: W ith permission from Terho Halme – Naval Architect

While Part 1 showcased design comments from Richard Woods , this second webpage on catamaran design is from a paper on “How to dimension a sailing catamaran”, written by the Finnish boat designer, Terho Halme. I found his paper easy to follow and all the Catamaran hull design equations were in one place.  Terho was kind enough to grant permission to reproduce his work here.

Below are basic equations and parameters of catamaran design, courtesy of Terho Halme. There are also a few references from ISO boat standards. The first step of catamaran design is to decide the length of the boat and her purpose. Then we’ll try to optimize other dimensions, to give her decent performance. All dimensions on this page are metric, linear dimensions are in meters (m), areas are in square meters (m2), displacement volumes in cubic meters (m3), masses (displacement, weight) are in kilograms (kg), forces in Newton’s (N), powers in kilowatts (kW) and speeds in knots. 

Please see our catamarans for sale by owner page if you are looking for great deals on affordable catamarans sold directly by their owners.

Length, Draft and Beam

There are two major dimensions of a boat hull: The length of the hull L H  and length of waterline L WL  . The following consist of arbitrary values to illustrate a calculated example. 

L H  = 12.20      L WL  = 12.00

lines plan catamaran

After deciding how big a boat we want we next enter the length/beam ratio of each hull, L BR . Heavy boats have low value and light racers high value. L BR  below “8” leads to increased wave making and this should be avoided. Lower values increase loading capacity. Normal L BR  for a cruiser is somewhere between 9 and 12. L BR  has a definitive effect on boat displacement estimate.  

B  L / L In this example L  = 11.0 and beam waterline B  will be:
Figure 2
B = 1.09A narrow beam, of under 1 meter, will be impractical in designing accommodations in a hull. 
B  = B  / T  A value near 2 minimizes friction resistance and slightly lower values minimize wave making. Reasonable values are from 1.5 to 2.8. Higher values increase load capacity. The deep-V bottomed boats have typically B  between 1.1 and 1.4. B  has also effect on boat displacement estimation.
  
T  = B  / B 
 T  = 0.57		Here we put B  = 1.9 to minimize boat resistance (for her size) and get the draft calculation for a canoe body T  (Figure 1). 
 Midship coefficient – C 
C  = A  / T  (x) B  We need to estimate a few coefficients of the canoe body. where A  is the maximum cross section area of the hull (Figure 3). C  depends on the shape of the midship section: a deep-V-section has C  = 0.5 while an ellipse section has C  = 0.785. Midship coefficient has a linear relation to displacement. In this example we use ellipse hull shape to minimize wetted surface, so C  = 0.785
Figure 3
 
C =D / A  × L where D is the displacement volume (m  ) of the boat. Prismatic coefficient has an influence on boat resistance. C is typically between 0.55 and 0.64. Lower values (< 0.57) are optimized to displacement speeds, and higher values (>0.60) to speeds over the hull speed (hull speed    ). In this example we are seeking for an all round performance cat and set C  := 0.59
 
 
C  = A  / B × L where A  is water plane (horizontal) area. Typical value for water plane coefficient is C  = 0.69 – 0.72. In our example C  = 0.71
  
 
m  = 2 × B  x L × T    × C  × C  × 1025 
m  = 7136		At last we can do our displacement estimation. In the next formula, 2 is for two hulls and 1025 is the density of sea water (kg/m3). Loaded displacement mass in kg’s
  
 
L  = 6.3		L  near five, the catamaran is a heavy one and made from solid laminate. Near six, the catamaran has a modern sandwich construction. In a performance cruiser L  is usually between 6.0 and 7.0. Higher values than seven are reserved for big racers and super high tech beasts. Use 6.0 to 6.5 as a target for L  in a glass-sandwich built cruising catamaran. To adjust L  and fully loaded displacement m  , change the length/beam ratio of hull, L  . 
  
 
m = 0.7 × m
m = 4995		We can now estimate our empty boat displacement (kg): This value must be checked after weight calculation or prototype building of the boat.
  
   
m = 0.8 × m 
m = 5709		The light loaded displacement mass (kg); this is the mass we will use in stability and performance prediction:
 
 The beam of a sailing catamaran is a fundamental thing. Make it too narrow, and she can’t carry sails enough to be a decent sailboat. Make it too wide and you end up pitch-poling with too much sails on. The commonly accepted way is to design longitudinal and transversal metacenter heights equal. Here we use the height from buoyancy to metacenter (commonly named B  ). The beam between hull centers is named B  (Figure 4) and remember that the overall length of the hull is L  .
 
Figure 4
  
 Length/beam ratio of the catamaran – L 
L = L / B If we set L  = 2.2 , the longitudinal and transversal stability will come very near to the same value. You can design a sailing catamaran wider or narrower, if you like. Wider construction makes her heavier, narrower means that she carries less sail.
  
B  = L / L  B  = 5.55Beam between hull centers (m) – B 
  
BM  = 2[(B  × L x C  / 12) +( L × B × C  x (0.5B ) )] × (1025 / m )

BM = 20.7		Transversal height from the center of buoyancy to metacenter, BM  can be estimated
  

BM = (2 × 0.92 x L   × B   x C   ) / 12 x (1025 / m  )

BM = 20.9  		Longitudinal height from the center of buoyancy to metacenter, BM  can be estimated. Too low value of BM  (well under 10) will make her sensitive to hobby-horsing
  
B  = 1.4 × B We still need to determine the beam of one hull B  (Figure 4). If the hulls are asymmetric above waterline this is a sum of outer hull halves. B  must be bigger than B  of the hull. We’ll put here in our example:
  
B  = B B B  = 7.07Now we can calculate the beam of our catamaran B   (Figure 4):
  
Z  = 0.06 × L   
Z  = 0.72		Minimum wet deck clearance at fully loaded condition is defined here to be 6 % of L   :
  
 EU Size factor
SF=1.75 x m  SF = 82 x 10 While the length/beam ratio of catamaran, L  is between 2.2 and 3.2, a catamaran can be
certified to A category if SF > 40 000 and to B category if SF > 15 000.
  
 Engine Power Requirements
P  = 4 x (m /1025)P  = 28The engine power needed for the catamaran is typically 4 kW/tonne and the motoring speed is near the hull speed. Installed power total in Kw
V  = 2.44 V  = 8.5Motoring speed (knots)
Vol = 1.2(R / V )(con x P ) Vol = 356motoring range in nautical miles R  = 600, A diesel engine consume on half throttle approximately: con := 0.15 kg/kWh. The fuel tank of diesel with 20% of reserve is then
  • Tags Buying Advice , Catamaran Designers

Rick

Owner of a Catalac 8M and Catamaransite webmaster.

10 replies on “Catamaran Design Formulas”

Im working though these formuals to help in the conversion of a cat from diesel to electric. Range, Speed, effect of extra weight on the boat….. Im having a bit of trouble with the B_TR. First off what is it? You don’t call it out as to what it is anywhere that i could find. Second its listed as B TR = B WL / T c but then directly after that you have T c = B WL / B TR. these two equasion are circular….

Yes, I noted the same thing. I guess that TR means resistance.

I am new here and very intetested to continue the discussion! I believe that TR had to be looked at as in Btr (small letter = underscore). B = beam, t= draft and r (I believe) = ratio! As in Lbr, here it is Btr = Beam to draft ratio! This goes along with the further elaboration on the subject! Let me know if I am wrong! Regards PETER

I posted the author’s contact info. You have to contact him as he’s not going to answer here. – Rick

Thank you these formulas as I am planning a catamaran hull/ house boat. The planned length will be about thirty six ft. In length. This will help me in this new venture.

You have to ask the author. His link was above. https://www.facebook.com/terho.halme

I understood everything, accept nothing makes sense from Cm=Am/Tc*Bwl. Almost all equations from here on after is basically the answer to the dividend being divided into itself, which gives a constant answer of “1”. What am I missing? I contacted the original author on Facebook, but due to Facebook regulations, he’s bound never to receive it.

Hi Brian, B WL is the maximum hull breadth at the waterline and Tc is the maximum draft.

The equation B TW = B WL/Tc can be rearranged by multiplying both sides of the equation by Tc:

B TW * Tc = Tc * B WL / Tc

On the right hand side the Tc on the top is divided by the Tc on the bottom so the equal 1 and can both be crossed out.

Then divide both sides by B TW:

Cross out that B TW when it is on the top and the bottom and you get the new equation:

Tc = B WL/ B TW

Thank you all for this very useful article

Parfait j aimerais participer à une formation en ligne (perfect I would like to participate in an online training)

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Catamaran Design Guide

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performance, yet desire high daily averages and passage times, which should be as short as possible. When choosing a large multihull, sailors look, above all else, for safety and comfort, long before the consideration for flat-out speed comes into the discussion. Nevertheless, performance is a highly important design consideration. No catamaran sailor wants to sail slower than a same length ballasted keelboat. Below are some EVALUATION & COEFFICIENTS useful coefficients, which will help compare monohulls and multihulls objectively.

Bruce Number (BN)

below "Indigo," a magnificent Wormwood 70, sailing in sparkling Caribbean waters.

Wormwood Catamaran

Various multihull characteristics and design features can be expressed in mathematical formulas. Their results are crucial and will give prospective owners a basis of comparison between different types of catamarans. These numbers are important, as they eliminate ambiguity and clearly display various advantages or concessions of a design, which would be hard to quantify any other way. Mathematical coefficients not only will provide insight into a boat's performance in varying conditions, they also reflect concerns about loads to be carried safely, speed and stability.

We have already mentioned the Displacement/Length and Sail Area/ Displacement ratio in our chapter on Multihull Advantages, illustrating the point of a multihull's efficiency. Let's look at some other coefficients that give us an indication of a boat's performance.

What is performance and how do we really measure it? Most people who buy a cruising catamaran are not really interested in racing

The Bruce Number is very similar to the Sail Area to Displacement ratio although the formula is slightly different. It is the square root of the sail area in feet, divided by the cube root of the boat's displacement in pounds:

SA = upwind sail area (mainsail and 100% jib)

Displ = weight of the boat in pounds

Similar to the Sail Area to Displacement ratio, the higher the coefficient the faster the boat and better is its performance in light air. Typically a BN of 1.1 will be the threshold between fast and more sluggish multihulls. A heavy displacement monohull might have a BN of .7, whereas a modern cruising catamaran shows a BN of 1.3. Offshore multihull racers can have BNs of 2.0 and higher. The BN will also tell us about a catamaran's ability to withstand stronger winds before reefing. A boat with a higher BN is usually overcanvassed in strong conditions and will have to be reefed earlier than one with a lower coefficient.

On the other hand, they will be able to produce more "power" than their counterparts in lighter winds and perform better.

Sail Area to Wetted Surface (SAWS)

SA/WS = Sail Area Wetted Surface Coefficient

SA = upwind sail area

WS = total underwater surface area (hull and appendages)

This formula simply divides the upwind sail area of the boat (mainsail and 100% jib) by the wetted surface. This coefficient will give us a statistical indication of the multihull's lightair performance since in low wind conditions skin friction becomes an important factor. Monohulls can have coefficients of at least 7% more than multihulls.

Hull Fineness Ratio (HFR)

The Hull Fineness Ratio, known as the hull's beam-to-length ratio, is an interesting number. It is derived by simply dividing the waterline length of the hull by the waterline beam of the hull.

Max. WL/Max. Beam WL = Hull Fineness Ratio Max. WL = length of the hull at waterline in ft. Max. Beam WL = beam of the hull at the waterline in feet.

Monohulls, when compared to multihulls, have low hull/fineness ratios. In Part 1 of this

Catamaran Proportions

book, discussing "Efficiency," we saw that ballasted keelboats are limited to Archimedes' principle of hull speed (1.34 x VWL). Multihulls do not have these theoretical barriers, because their hulls are narrower.

The thinner the hull the faster it will be able to travel through the water. But, attention! It will also carry less unless you are on a mega cat. Typically, a 40' cruising catamaran's HFR will range from 8:1 to 10:1. Dennis Conner's above While sailing under spinnaker and experiencing virtually no roll at all, guests will always find a comfortable spot to relax on the foredeck, an impossibility on a monohull.

There are various methods of calculating the transverse stability of a catamaran. One of the simplest and most utilized techniques is establishing a relationship between the height of the Center of Effort (CE), displacement, beam and sail area. Multihull designer, James Wharram added safety factors of 20% to compensate for gusts and the dynamic environment of the ocean. Another method is described in the text below.

Multihull Stability & Capsizing Moment d - Displacement (kg) x half beam (m) max ~ Sail Area (sq m) x Height of Center of Effort (m)

P max = maximum pressure exerted onto sails

Multihull Stability & Capsizing Moment

Trimaran Center Effort

height of sailplan CE

half overall beam (half hull beam)

racing cat "Stars and Stripes" had a 16:1 HFR. Of course, the larger the boat, the narrower the hulls will become in comparison to its length. For example, the HFR of a 100' luxury catamaran may be 12:1, providing it with a high speed potential. However, monohulls can show HFRs of 3:1, though the comparison is complicated as their angle of heel affects the measurement.

One has to be very careful when analyzing the Hull Fineness Ratio of a cruising catamaran, because other factors such as the actual shape of the hull cross sections (Prismatic Coefficient, PC) can throw the analysis off balance. Go-fast sailors like to think that fine hulls are always fast. That is not necessarily true because a slim hull could have a large underwater volume, thus slowing it down. Consequently, a wide waterline-beam hull could have less drag than a narrower one. It could have a shallow underbody (low PC), which would be beneficial to load carrying (Pounds Per Inch Immersion Number, PPI) and early surfing characteristics at speed.

Stability Coefficient (SC)

This mathematical formula has been devised by the distinguished catamaran designer and sailor James Wharram and his team. This coefficient analyzes a multihull's ability (in a static environment) to resist capsizing due to wind.

( 0.682 VW x (.5 Boa) ) x .555 = CW .00178 x SA x h

W = Wind speed, apparent, in mph CW = Critical Wind Speed to capsize in mph SA = upwind sail area in sq ft. h = height of Center of Effort (CE) of total sail area

Boa = Beam overall

This formula will tell us how much wind it will take to overturn our multihull. By instinct we will know that a catamaran with a wide stance and a conservative sail plan will be very stable offshore. The SC formula will inevitably illustrate that a wider beamed catamaran with a tall sail plan will be as resistant to wind induced capsize as a short-rigged, narrower boat. This is not so if one considers the chaotic environment of waves and the real world of heavy weather sailing. It is interesting to note that a wide beamed boat (regardless of the SC) is more resistant to capsize in seas due to the effects of a higher moment of inertia. In an open-ocean environment, which is everything but static, the SC formula has little meaning. Nevertheless, it serves as a good basis to evaluate stability as a factor of wind force.

below When the wind suddenly comes up, all that is needed is a couple of turns on the jib furler to quickly reduce the headsail size. The catamaran will hardly sail any slower, but feel more comfortable.

Ship Hull Fineness

Wide hulls and a large overall beam will increase the overall righting moment of a catamaran. A word of caution: Excessive beam will reduce the fore and aft stability. Designers strive to compromise hull fineness ratios, place heavy weights towards the CG (Center of Gravity), and engineer hull and overall beam to achieve a seaworthy balance, which is safe, yet provides ample liveaboard accommodations.

Catamaran Stability Considerations

Seaworthy Catamaran

Diagonal Stability & Beam-to-Length Ratio (BLR)

Stability of a multihull, or the resistance to capsize, should be seen as three components. Athwartship Stability is one well-publicized type and the one often talked about. The other much more important types are Fore and Aft and Diagonal Stability. Fore and aft stability is established by the relationship between the boat's waterline length and the distance between the hull centerlines. It will reflect the catamaran's resistance to tripping. This relationship should be in the vicinity of 39% to 42%. For a seaworthy cruising multihull it is important maintain the proper ratio between length and beam, which, in turn, balances equal amounts of athwartship with diagonal stability. The goal should be to prevent the possibility of a sudden discrepancy of powers between fore and aft and sideways resistance. Most of today's multihulls keep these two component forces in equilibrium, making them extremely seakindly and safe.

Some early design multihulls were very narrow, partly due to the material limitations of that time. But things have changed. Contemporary composite construction allows designers to build wider boats without compromising stiffness. Production catamarans of today have a wide stance and have the benefit of greater safety margins in gusty wind conditions than their older cousins. Multihulls are sophisticated structures and true modern miracles. They provide a more comfortable ride and more interior room. Thanks to modern materials they weigh less and perform better than catamarans built only 10 years ago.

Some catamarans, especially production boats, which are very popular in the charter fleets, are growing wider by the year. The businesses who rent these beamy monsters adore them. Lots of room plus open decks are ideal for clients and the bigger (wider) the boat, the more paying guests can share the fees. But there certainly is a limit as to how wide is too wide. Extreme beam can be dangerous. It can lead to instability fore and aft and to excessive bridgedeck slamming, as the relative distance from the bridge deck to the water will decrease with an increase in width. A vessel with excessive beam might seem stable athwartships, but it will compromise overall stability.

We know that multihulls can, in extreme cases of seamanship error in wild storms, be thrown over from any side - front, back and beam-on. The best examples of this phenomenon are racing multihulls, especially Formula 1 trimarans, which have fine hulls for speed and huge sailplans to provide driving power. They are initially extremely stable athwartships (High Beam-to-Length Ratio), but have a tendency to become unstable fore and aft. They will surf down waves and reach a point where the power of the sails, and speed, will exceed the ability to keep the bows out of the water and the boat will pitchpole. This is the reason why catamaran designers usually draw their multihulls with a Beam-to-Length relationship of between 50% and 55%. The longer the vessel the lower that percentage becomes.

I am currently involved in the "Gemini" project, which presents an example. It very well might become the world's largest sailing catamaran. She will have an overall length of 145 feet, yet her beam will "only" be 54.4'.

Stable Catamaran Dingy

Please, don't worry. "Gemini" will not be tender and tip over in the slightest breeze. On the contrary, this monster will be one of the most stable craft afloat, although the beam-to-length relationship is only 37%. The relatively low beam-to-length ratio also involves the fact that the boat would be too heavy and building costs would be prohibitive if she were to have a standard 52% BL relationship. Most importantly, could you imagine turning a 75-foot-wide boat?

above Asymmetric spinnakers on furlers are great inventions. They add instant sail area, yet can be doused in a matter of seconds when the wind picks up strength.

Catamaran Underwing

above Although this Edel 35 was a good-looking and popular catamaran, it suffered from excessive bridgedeck pounding, which was caused by only several inches of clearance between the saloon's underwing and the sea.

Obviously there is a sweet spot in the beam vs. stability question. Designing too beamy a boat will also necessitate more freeboard to preserve bridgedeck clearance which, in turn, will increase windage and complicate maneuvering. Unless sophisticated aramid construction methods are utilized, more beam will also add more weight and stress to the structure. Adding more mass will, to a certain point, help make the boat more stable, but where do we stop? Is it better to add weight or width to make a boat stiffer? Of course, both characteristics are interrelated as a beamier boat normally is also heavier. Just adding weight to a catamaran simply to make her more stable will not pay off. Consequently, making a boat too wide might increase living space yet it will also burden the structure, require a beefier manufacture, and yield an even heavier boat. Needless to say, a boat which is too wide will also create practical restrictions such as maneuvering, the ability to haul the vessel and much higher building costs.

Beam has a great effect on bridgedeck clearance, which is one of the most vital characteristics of a good cruising catamaran. As standard practice, the well-known rule of 1" of bridgedeck clearance for each foot of beam was a safe way to prevent excessive wave slap. The wider the beam the more the relationship changes and the necessary height of 1" per foot of beam needs to be increased to 1.3" or more. In the extreme case of overly square boats, that number will have to be closer to 1.8" per foot of beam. This will have a negative effect on any seaworthy multihull that has a bridgedeck saloon. The wide beam will necessitate a high cabin sole to remain a safe distance from the waterline. In order to provide standing headroom, the coachroof might be higher than practical, which could result in a boxy, high-windage multihull. Not only will this be unattractive, but also raise the Center of Gravity (CG) which really should be kept as low as possible.

More overall beam on the other hand (given that there is still sufficient bridgedeck height) has a less known benefit, as it reduces the possibility of hull-wave interference, which is particularly important for fast designs. The wave interaction between the hulls can lead to additional resistance, and especially in an agitated sea state, the formation of wave crests can pound the bridge deck. Most early narrow-beamed catamarans suffered from this phenomenon,

Ultimately, a boat's design has a major influence on its ability to stand against the forces of nature, and to keep occupants safe. Manufacturing excessively wide catamarans is like trying to market monohulls with super deep-draft keels. Both are totally impractical. We designers have to make sensible compromises and learn from past experiences of what has worked at sea by balancing the benefits of a wide boat with its disadvantages.

below This narrow-hulled Outremer 64 Light has completed her third circumnavigation with the same owners. Note the smooth underwing clearance, lacking any protrusions or steps.

Outremer Standard

"A great cape, for us, can't be expressed in latitude and longitude alone. A great cape has a soul, with very soft, very violent shadows and colors. A soul as smooth as a child's, and as hard as a criminal's. And that is why we go!"

~ Bernard Moitessier

Catamaran Underwing

Dinghies, windsurfers and every imaginable type of water toy can be stored conveniently on large catamarans and easily launched from the wide transom steps for shore-side pleasures. Note the twin life rafts located in special compartments on the massive aft crossbeam.

Continue reading here: Hull

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Readers' Questions

What length should a stub keel be to waterline length on a catamaran?
There is no set rule for the length of a stub keel on a catamaran in relation to its waterline length. The length of the stub keel will depend on various factors, such as the size and design of the catamaran, intended use, and specific requirements of the boat builder. Generally, the stub keel on a catamaran is designed to provide stability and improve sailing performance, so it is important to consult with a naval architect or boat designer to determine the appropriate length for a specific catamaran.
What is a 16 passenger catarmarn like?
A 16-passenger catamaran is a type of boat or vessel specifically designed to carry 16 people comfortably. Catamarans are multihull boats with two parallel hulls, which are connected by a deck or a structure. They offer stability, speed, and efficiency in the water. A 16-passenger catamaran can vary in size and design, but generally, it will have enough seating or lounge areas for all passengers. It may have indoor cabins with beds or seating areas, as well as outdoor spaces for relaxation or socializing. These boats often come equipped with amenities such as bathrooms, kitchens or galleys for meals, and sometimes even entertainment systems. The catamaran's size can influence its specific features. Some catamarans are designed for day trips or shorter excursions, while others are built for longer journeys or overnight accommodations. Additionally, they can be used for various purposes, such as whale watching, diving trips, ferry services, or private charters. Overall, a 16-passenger catamaran provides a comfortable and stable platform for small groups or gatherings, allowing passengers to enjoy the beauty of the water while ensuring safety and comfort.
Is the catamaran hull floor always on the waterline?
No, the hull floor of a catamaran is not always on the waterline. The design of a catamaran allows for the hulls to be elevated above the waterline, reducing drag and increasing speed. The position of the hulls in relation to the waterline can vary depending on factors such as the weight distribution, load, and sailing conditions.
How close to a catamarans design reefing points should you go?
You should always be careful when approaching reefing points on a catamaran and stay as far away as possible. Generally, you should aim to stay at least 10 meters away.
What keel to length ratio for catamarans?
The keel-to-length ratio for catamarans typically ranges from 0.1 to 0.25.
Is 70% length to beam ok for a catAMARAN?
Yes, it is generally accepted that a catamaran should have a length to beam ratio of between approximately 6:1 and 8:1. Therefore, a 70% length to beam ratio would be within an acceptable range.
What is the waterline length to baem ratio of a typical cruising catamarans?
This ratio will vary depending on the type and size of the catamaran. Generally, the ratio should be between 1:1.5 and 1:2.5, with 1:2 being the most common.

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  • January 18, 2022
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American Cruise Lines to build 12 catamaran cruise vessels

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First two catamaran cruise vessels habve already started construction at Chesapeake Shipbuilding

Guilford, Conn., headquartered American Cruise Lines has unveiled plans for Project Blue—a fleet 12 identical 109-passenger sister ships of catamaran design.

Operating exclusively in the U.S., they will more than double current capacity for domestic coastal cruises.

“Project Blue started as a design challenge to create a boat small enough for New England harbors and stable enough for the Alaska Inside Passage, with a draft shallow enough for the Atlantic Intracoastal Waterway,” says Charles Robertson, president and CEO of American Cruise Lines. “These boats can run almost anywhere, and because there will be 12 of them, they will be deployed all over the United States.”

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Like all of American Cruise Line’s new ships, the entire Project Blue fleet will be built by Chesapeake Shipbuilding in Salisbury, Md. The first two ships are already under construction and are due for delivery in 2023.

Each boat in the Project Blue fleet will accommodate 109 passengers and 50 crew.

They will be 241 feet long, 56 feet wide, and feature a catamaran design that enables both shallow draft access and stable sailing along lakes, rivers, bays, and America’s coastline.

“Together with Chesapeake Shipbuilding, we built the first modern riverboats in the country. Now we are proud to introduce another new ship design for domestic exploration. American has specialized in small ship cruising for over 30 years, and continuing to innovate and expand the possibilities for cruising close to home is central to our mission,” Robertson elaborated.

lines plan catamaran

American Cruise Lines says that the new fleet will feature elegant modern décor by Studio DADO of Miami, Fla.

Each ship will offer 56 spacious staterooms—including a range of large standards, suites, and singles—nearly all with private balconies. Observation and sitting areas will be available at the bow, both inside and outside, and each ship will showcase an expansive forward lounge with 270 degree views. At the stern, the ships will have a new adventure deck equipped with kayaks, tender, and other activity related options relevant to the itinerary. American’s new go-anywhere ships will also feature two dining venues, as well as room service, a rarity for small ships of this size.

The first two ships will debut along East Coast itineraries and will be named American Eagle and American Glory —namesakes of the company’s first two small U.S.-built ships.

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    Optimising Hull Lines for Performance This article was inspired by a question about the rocker line in the new 8.5m cat Design 256 and I want to stick to the point, so we won't turn it into a book, but I'll discuss two issues, hull fineness ratio and some aspects of the rocker profile.

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  12. catamaran offset table

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