Home build Sailboat Design

Hi,


I am designing a small family friendly cruising sailboat for a home build. Not sure if I will actually build it but will enjoy the design process. I have a few questions on sourcing components as this will drive a lot of the design. Custom everything seems time and cost prohibitive. Building a mast also scares me a bit.

*Caveat: I am new at this so I am sure I have missed many many critical things.

A little bit about the boat:
Goal: A fast family cruiser. The accommodations don’t need to be fancy since it will be akin to a weekend camper. I would like it to be a planning boat to get more speed.

Note: I really like the Mini 6.5 sailboats but they are too wide to trailer and seem downwind focused. I think a little less beam and a more traditional bow will help upwind?

-Targeting 25ish feet to make it trailerable but can adjust to the rig. I am planning for a mono-hull but see some advantages to a trimaran.
-Beam less than 8’6” as my understanding is that any wider requires a wide load permit in America. Canting the boat on the trailer seems complex but allows more beam.
-Ideally, ramp launchable but flexible on this one.
-Spinnaker on bow sprit as it makes shorthanded sailing easier.
-Seaworthy: I’d like to build it for offshore sailing but this may be prohibitive.
-I am planning to use a hybrid of carbon/s-glass but a plywood hull like the Dudley Dix designs is tempting.
-Any thoughts on adding t foils to the rudders (either on the bottom of the rudder or I-14 style near the waterline)? It seems like there may be some speed and ease of handling benefits.

-The Beneteau First 24 is not a bad match but its expensive and not as much fun as designing your own.

Rig questions: I am engineer and am able to design/fabricate the hull. The sails and mast are items I would like to outsource or buy stock but I a struggling to find options.

-Any ideas on how to economically source mast, boom, and sails? I have struggled to find masts/booms for sale.
-Any ideas on the cost of a semi-custom setup? Maybe it’s not a pricey as I expect.
-Can I stick a Mini 6.5 rig on a slightly larger hull? Any insights on how to source one and what cost might be?
-Ideally, it's carbon mast but aluminum is not a bad option either.

Keel: While I can build a keel, I am little nervous as this is a highly stressed part with safety implications. I lean towards retractable to ease the ramp launching process.

Request help in thinking through the design and sourcing of parts.

Thank you all!

 

If you are able to design/fabricate the hull you are also able to do the same for the rig and keel. Designing for the expected local and global loads is an important part of the process.
Sails are a different thing because you probably aren't a textile engineer and don't understand the material and how to use it.

The only "economical" way is buying second hand. Everything else is custom made, either completely from scratch or assembling commercially available products. Boats are such low numbers products that even the most popular classes don't qualify for "series" status in the modern sense.
You can indeed design the hull to fit a rig from another yacht (like for example a Mini 6.5) in order to take advantage of the second hand market.
Most rigs are built around commercially available parts such as aluminum extrusions and fittings, with only the chainplates beeing truly custom. Carbon rigs are usually made on order, using the desired layup on an existing mandrel.

 

Ply is a bit heavy choice to use with carbon, you get cheaper and lighter with strip planked or cold molded with biax glass. Get Dave Gerr's book Elements of boat strength to calculate the scantlings, another book to get is Larsson Eliasson Principless of yacht design..

 

Your description is a bit of a hodgepodge of other designs. Also, you are going from a monohull to a trimaran. That is an indication that you need to first focus on what your needs are. It is easy to get enamored with a variety of designs that don't fit your needs. Also, the design should meet your building skills, tools you own, and space to build it. Calculate from 4 to 8 years. Considering your experience and the cost to build a boat, buying a design from a reputable designer is your best bet. Some of the items like a spinnaker on any kind of mount for short handed sailing is a terrible idea. Spinnakers are mainly good to beat a racing rule. However, you live in the USA. $3000 will get you a nice enough boat to go sailing and discover if you actually like it.

 

Francois Vivier has been building some hulls with 2 skins of ply, much in the fashion of the Ashcroft method, and states it is faster and cheaper than strip planking. Carbon on ply seems a bit of a mis-match given the difference in modulus, E or S glass is more than adequate, though it may have a place in local reinforcement; I believe RM yachts do just that.

 

Check out the NZ Ross 780, Elliott 780 etc for inspiration - old designs now but still excellent cruiser/racers.

The Int 14s have T foils for specific reasons, as did Moths and A Class cats before they went foiling. Why do you want them? They add wetted surface and unless you are very high-powered for your size and suffer from nosediving they would probably mainly be drag.

 

With respect, many of us love spinnakers for short handed cruising and racing. They make sailing downwind a lot of fun.

Spinnakers aren't there mainly to beat racing rules - classes that don't limit sail area have them too. The simple physics are that you need more sail to go fast downwind than you can normally carry upwind, so pulling up a kite works brilliantly.

 

Well that and the difference in wind speed with VMG increasing it upwind and reducing it downwind.

 

Depends of the local prices but have not seen anywhere marine ply being cheaper than wood adequate for strip planking. Time.. it took me 200h to strip plank 35' hull including sawing the strips. If weight is more an issue PVC foam beats ply and works with carbon too the problem being after cure.

 

I think in Francois case he might be talking about not having to sheath both sides. Certainly I can source local larch, fir or spruce for strip building cheaper than "marine" grade ply. Sheathing and epoxy is a big expense, but that is the difference between "strip built" and "strip plank" that is usually thick enough alone not to need any structural fabric.
I like the idea of using strips for chines, and ply for larger areas, not all "exterior" grade ply is junk.

 

Thank you all for the feedback.

-Good info on the t foils. I thought they might be help in shaping stern wave formation but sounds like extra surface area isn't worth the effect I don't plan on a nose diving boat.
-Fair point that I am waffling on design approach and just look for a used boat.
-For build skills, I am a composites engineer. However, I lack a lot of tools/time at home.
-To an earlier post, I am not a textile engineer so appreciate the feedback that sails are beyond my scope.
-Appreciate the book recommendations! This whole project may be purely digital but even I never build it designing is fun.
-I've raced sailboats for years and currently wingfoil. As kids are getting older, I want to include them. So my sailing skills aren't fantastic but I can handle a boat.
-Thank you for the 780 recommendations, those are good inspirations.
-Good info on core/fiber miss-match. Plywood makes for easier molding but I can see were carbon is overkill. I am a big s-glass fan but am also eying uni e-glass and some of the satin weaves.

I have some info to digest and appreciate feedback (always welcome as it can save a lot of effort). I think this next step is design and build a 3ish foot model to work out the bugs and better understand the scope of the project.

-WannabeNavArch

 

An asymetrical is as efficient and much easier to handle. The clew can be attached to a bowsprit, retractable or fixed, that simplifies handling.

 

Aahhh, that explains it. The difference is that around here, and as far as I know in most places, an assymetric IS a spinnaker; it's a breed of spinnaker rather than a separate sort of sail. That's also what Andrew Buckland and Julian Bethwaite, who introduced the assymetric as we know it, call it.

 

I guess we are in agreement then . In the dark ages there was a similar sail called a drifter.