Designing a Sailboat

[Robert D]

Ahoy All!

My name is Robert Dobbs and like so many others, I'm building a sailboat, wooden of course

Since this is my first post at the WoodenBoat Forum, I thought it best to ask first... Is this the correct area of the forum to post a self-designed sailboat?

If so, I have some rudimentary drawings I'd like to show, all who are interested, and ask for opinions as to how to approach certain aspects of the build.

Perhaps I should introduce myself a bit more. I live in the North Georgia mountains about an 1.5 hours from Lake Lanier, which is where I'm planning my first launch. I've been building custom homes here since 1995. I've also built custom furniture, cabinets, an acoustic guitar, and even an electric guitar combo amplifier. It is my hope that my hands-on carpentry experience will aid in this sailboat building project. Of course, these accomplishments are quite a bit different from building the compound curves of a sailboat hull. Still, I think I'm up for the challenge, and quite honestly, looking forward to realizing a 40 year old dream.

So, here I am, newbie at the WoodenBoat Forum. I welcome any and all comments.

Thanks in advance!

[WI-Tom]

Sure, this is a good place for a thread on building any boat, self-designed or not.

I expect you'll get many opinions as to the wisdom of designing your own boat vs. building from plans drawn by an established designer. Don't let it drive you away--this really is a fabulous place to learn from LOTS of knowledgeable people.

Tom

[Peerie Maa]

I expect you'll get many opinions as to the wisdom of designing your own boat vs. building from plans drawn by an established designer. Don't let it drive you away--this really is a fabulous place to learn from LOTS of knowledgeable people.

Tom

This ^
First of study what works, study, study, study.
Size, shape and scntlings.

Compound curves are not a problem,.
Strip plank is the way to go fore first time build if you want round bilge.
If you are happy to use multi chine plywood, study https://sourceforge.net/projects/freeship/

[cstevens]

Welcome Robert! I'll be one of those people questioning the wisdom of building to your own design, but not because I think an amateur can't or shouldn't do it (I've been designing boats I want to build since I was twelve although I've yet to do anything about it) but because there are so many wonderful designs already available. So it seems reasonable to ask whether you want to design your own boat out of enjoyment of the project, or because you have not found any existing design that meets your criteria? Either way I'll be curious to see what you have in mind.

[John Howland]

Robert,

Welcome to the WoodenBoat Forum.
Good place to find information about a wooden sailboat design and build project.


John

[Rich Jones]

Welcome!
I've built and/or restored 18 boats in the past 50 years as an amateur.
The one boat I designed at age 18 looked and sailed like a pointy ended cigar box.
I've stuck to established designs since then.
I've no idea of your ability to design a boat, but based on your woodworking experience, I've not doubt you'll do a wonderful job building one.

This is a great place for advice. The vast majority is constructive advice, but if members see you building something they think is unsafe, they will not hold back telling you.
But overall, there is not a better place to share your boatbuilding experience.

[wizbang 13]

Bring it on

[Autonomous]

Do a simple dinghy first. It will not only be a good education but will keep you from making as many expensive, time-consuming mistakes on your destination boat.
Good luck!

[wizbang 13]

Models, build scale models

[John Howland]

Building a scale model is a great way to see things that may not be obvious in the first build.
I built a model under 8' 1:4 scale for my boat. 8" Boards are cheap I could make most of the joint in the same manner as the full size boat. Also one can see any frames that are not fair.

[JimConlin]

It’s not hard to design something that looks like a sailboat.
It’s a lot harder to design a sailboat that works well. It’s a lot more technical than many think.
If you’re contemplating anything bigger than a small dinghy, I strongly recommend that you do some study in the mechanics of sailboats. Some suggestions:
Dave Gerr’s book, The Nature of Boats is a good start.
Principles of Yacht Design, by Larson and Eliasson, is more thorough.
The Westlawn Institute of Marine Technology offers an extensive course in yacht design.

[cstevens]

Most of what I know of boat design (not much, admittedly) I got from Skene's Elements of Yacht Design. I have the eighth edition, updated by Francis S. Kinney, which out of print and I believe is quite a bit different than the original edition that is now back in print. It's also just a great book to read if you love boats. The other books recommended here are also excellent, but I always open Skene's first if I have a question on design.

[John Howland]

Free downloads:

http://protei.org/download/20110417P...20Eliasson.pdf

Eric W. Sponberg Naval Architect BSE, PE (CT) CEng (UK)
THE DESIGN RATIOS A Naval Architect’s Dozen (or thereabouts)
A primer on some basic principles of naval architecture for small craft.
https://www.ericwsponberg.com/
https://www.ericwsponberg.com/wp-content/uploads/2021/09/THE-DESIGN-RATIOS.pdf

[Robert D]

Thanks to all for the warm welcome!

I have to admit, I've been nosing around here for a few weeks and after reading several posts I had a good feeling about this place. Already I'm getting good advice and appreciate all that has been presented by everyone.

So, let me tell you a bit about the sailboat I'm designing. I'll get you some drawings to look at as soon as I convert them to PDF's. It is a dinghy and I've put a lot of thought into it already. I'll admit I've been inspired by so many sailboats that I've seen on the water, online, and ones I've sailed. I'm not really sure what class it fits into, but I think it's going to be a blast to sail. We'll see of course. Just so you know, I wanted to keep the design as simple as possible.

Okay, here are a few details;

Length -18'
Beam 4'-8"
Height - 2' (From Keel to Deck)
Dagger board centered
Open transom
Large cockpit
Freestanding mast
One main sail (No jib)

Construction;

Hull - 1/4"x2" strip planked (Quarter Sawn Hemlock)
Cockpit sole - (3/8" or 1/2" X 2" Black Locust)
Deck - (Still a little undecided, maybe hemlock with vermillion stain)
Rudder - Black Locust
Dagger board - Black Locust
Mast - Hemlock (Hollowed and tapered)
Boom - Hemlock
All Hardware - Conventional block & tackle stainless steel
Sail - (Undecided right now, but will require battens)

Here are a few more details as well.

Approx. Sail Area @ 165 Sq. Ft.
Approx. Hull Area @ 100 Sq. Ft.
Approx. Deck & Cockpit Area @ 65 Sq. Ft.
Approx. Weight (Hull, Deck, Cockpit) @ 300 lbs.
Approx. Total Boat Weight @ 500 lbs.
Approx. SA/Disp. Ratio @ 42
Approx. Disp/WL Ratio @ 38

Well, I guess that's a good start. Let me clean up my drawings and get them converted to PDF and I'll post them here soon. Please be patient with me, my day job is very demanding. I'm still amazed how many people want to build houses in North Georgia.

Thanks again!

[neil.henderson]

Sounds like an exciting design. A couple of questions/suggestions come to mind...................
a) A daggerboard is great if your focus is room in the cockpit - but I'd suggest you inspect your design to verify that you'll be able to swing the boom across with the board up - an 18 foot hull is likely to need a reasonably long daggerboard
b) Just wondering why you would prefer an open transom. Will you ever want to use an outboard (they can be useful), how do you feel about sailing in large following seas, or maybe you're planning to sail on inshore lakes?
c) How many ribs do you think will be needed inside the hull? I've never built a boat with an open transom but I guess that they rely on internal aft structures inside the hull to maintain its rigidity.

Look forward to seeing the design diagrams - this forum is great for ideas & feedback.

Regards Neil

[wizbang 13]

when i read
deck ,hemlock with vermillion stain
i gotta say....keep reading
i won't even put hemlock in the firewood pile

[Thad]

Better not, Bruce, it sprays sparks.

[John Meachen]

The proposal might need to go round the "design spiral" a few times.Obvious question;have you sailed similar boats before?The description points to a rather skinny boat for the size and the sail area seems exceptionally generous.The point being that you might lack the ability to keep the boat under the mast.It might not be a disaster if your local waters are quite warm but on the other hand it could mean losing anything you have with you via the open transom.

Drawings would be helpful and it might be easier for you to take a quick snapshot with your phone as .jpg files (of less than about 400Kb) are quite easy to post.

[John Howland]

The proposal might need to go round the "design spiral" a few times.Obvious question;have you sailed similar boats before?The description points to a rather skinny boat for the size and the sail area seems exceptionally generous.The point being that you might lack the ability to keep the boat under the mast.It might not be a disaster if your local waters are quite warm but on the other hand it could mean losing anything you have with you via the open transom.

Drawings would be helpful and it might be easier for you to take a quick snapshot with your phone as .jpg files (of less than about 400Kb) are quite easy to post.

Principles of yacht design - Larsson, Eliasson chapter 1, fig 1
I have been around it so many times it makes me dizzy just thinking about.
Untitled.jpg

[J.Madison]

1/4" hull planking? Maybe you mean 3/4"? There are boats that size with 1/4" planking, but that is definitely on the thin side.

Open transom? So a big planing dinghy is what you are after? A reasonable way to come up with a design is to find several existing boats that "bound" your ideal boat and then gently merge them into a new design. If there is a boat that mostly meets your requirements but you want some feature to be different, that is also a reasonable way to come up with a new design. Niether method is without pitfalls of course.

Either way, start by studying what works for similar boats, and if you aren't familiar with construction details buy a set of plans for a similar boat to educate your scantling and construction choices.

[John Meachen]

To help put the proposed parameters into some kind of perspective,this is what happens with 10 sq metres of sail on an unstayed rig and a hull about a couple of inches wider.Having 70% more sail area might get very interesting.I don't totally agree with the comments about hemlock-it makes satisfactory pallets.

[WI-Tom]

So, let me tell you a bit about the sailboat I'm designing.

Length -18'
Beam 4'-8"
Dagger board centered
Open transom
Large cockpit
Freestanding mast
One main sail (No jib)

Approx. Sail Area @ 165 Sq. Ft.
Approx. Weight (Hull, Deck, Cockpit) @ 300 lbs.
Approx. Total Boat Weight @ 500 lbs.

Interesting. 4' 8" is mighty slim.
165 sq ft of mainsail on a mighty slim boat will be... interesting. How interesting will depend on the hull shape, firmness of the bilge, etc.

For comparison, my boat is 18' long and 4' 8" beam. It's designed as a two-masted lugger (85 sq ft mainsail, 49 sq ft mizzen) with a total of 134 sq ft of sail. It weighs about 300 lbs. Planking is 1/2" strip-planked, edge-nailed and epoxy glued. No structural glass.

Thoughts:

Once the wind gets above 5 knots, my boat moves just fine under mainsail alone (85 sq ft). Since it's a cruising boat and I really don't want to capsize in remote areas with cold water, I use only the mainsail, stepped in a center mast step. With the full 134 sq ft of sail, by all reports, light-air performance is very good. But "reef early and often" is the rule.

With only 1/4" planking, I'm guessing you are using the wood as a core, and will use glass on both sides for structural strength?

Freestanding mast--does that mean you'll have a lugsail of some kind?

165 sq ft seems like a lot of sail. Might be just the thing for a racing boat. I'm no racer, so I wouldn't know. But it seems other posters are a bit surprised by such a large sail area as well. Will it be reefable?

Tom

[Robert D]

Hey All,

First, let me apologize for taking so long to get back with all of you. Like I said, my day job is a bit demanding right now. I'm actually looking forward to winter, it's about the only time of the year when I'm free to be in my workshop, which is nice and warm for a sailboat building project...

Okay, there were a few details I failed to mention, which should answer some of your questions, and shed some light on the reasoning behind my choice of materials as well.

The 1/4" planking is very common for canoe's and kayak's, which keep these crafts very light. It was my hope the same would be true for my sailboat. I will be using fiberglass inside and out. Right now I'm thinking 1 layer of 4oz CSM for the inside and 2 layers of 4oz CSM for the outside. This should make the hull quite durable, yet still fairly light. It certainly will not be impenetrable, but it will be tough enough to bring her up onto the bank on a regular basis. When I sailed my Prindle cat, sunfish, and laser, this is how I came to shore all the time. Of course, there really wasn't much choice when you launch off the east coast Florida beaches.

Anyway, I know most boat builders prefer well known and well proven materials such as D-Fir and Eastern/Western Red Cedar. I'm very familiar with these species of wood and I'll admit they are excellent choices. However, Hemlock was long used in the house building industry due to it's structure properties. You don't here about it much anymore because spruce is so easy to grow hectare's at a time and Canada has pretty much cornered the market in that regard. No complaints by me though, spruce is a wonderful material to work with. It makes a great wall stud and is perfect for framing a roof as well. Not to mention, as it ages it gets very hard.

There are a few more reason's why I chose Hemlock. First, it grows in my back yard. In fact, I have a 300 year old tree with a trunk girth of about 36". She's a beautiful tree, and I'd never cut her down. But, if she fell, she wouldn't go to waste that's for sure. Of course, it grows fairly abundantly here in the North Georgia mountains, and I have several sources to obtain logs. Unfortunately, they are dying quite often due to the infestation of a tiny little beetle called the "Hemlock Woolly Adelgid". The good news is, they can be saved with treatment, which we spent the money and saved all of ours. Still, it's hard to save them all because so many are deep in the National Forest. Needless to say, I'm happy to use a standing dead Hemlock recently cut, as long as it hasn't been dead too long. Now, just so you know, I've tested the strength and flexibility of Hemlock and it is quite impressive. Also, I've been rather picky at choosing my Hemlock logs. I've been fortunate enough to find some with very tight grain, in the range of 10-12/inch. For conifer's in this area that's pretty good. It would be better if they were more in the 16/inch range, still the Hemlock is quite strong. I guess I should have mentioned that I own a sawmill and have already cut my Hemlock into 5/16" X 2" strips and are airdrying as we speak. Most of it is at about 17% moisture count, so should be ready for use in a couple of months no problem. Also, the strips will planned and then cut to a bead and cove configuration. I really like the idea of interlocking the planks, just seems like the best way to strip-plank a hull, especially with 1/4" material. One more thing, It is a very beautiful wood when sanded and varnished. Well, at least to me it is...

Okay, according to the US Forest Service, Air-Dried weight/species as follows; (Note these are general estimates)

Eastern Hemlock - 28 lbs/cubic foot = 2.33 lbs/board foot. At 1/4" thick, it's about .58 lbs/sq. ft.
Eastern Red Cedar - 33 lbs/cubic foot = 2.75 lbs/board foot. At 1/4" thick, it's about .68 lbs/sq. ft.
Western Red Cedar - 23 lbs/cubic foot = 1.92 lbs/board foot. At 1/4" thick, it's about .48 lbs/sq. ft.
Douglas Fir - 34 lbs/cubic foot = 2.83 lbs/board foot. At 1/4" thick, it's about .7 lbs/sq. ft.

As you can see, the differences in weight aren't much to be concerned about. I'd think that the strength and durability are the most important in regards to hull construction. Having said that, it's nice to be light and strong. You know, like when we I was 21 years old...

Here's a few more details to the construction;

I plan to buy a pneumatic nail gun that shoots plastic nails for attaching the planks to the ribs, which I've not really figured out yet how many to incorporate into the hull. I'm thinking of white ash as the keel and gunwale. However, I believe I'll need to keep the thickness to a minimum for weight concerns. I've already mentioned using Black Locust, which by the way, grows around here along with white ash and easy to get. Black Locust can be compared to Teak in regards to rot resistance. It's rather heavy at 48 lbs/cubic foot, but it is as tough and strong as oak, if not stronger. It's also kind of pretty when varnished. I figure at about 3/8" thick and well supported, it will accommodate the cockpit sole very well.

About the sail area. I know I'm pushing the limits. But, I plan to sail on Lake Lanier and we don't get a lot of strong winds regularly. So, I figure I can sail fairly fast in light winds. Still, I do plan on having the sail maker reef the sail just for those heavy days.

Well, I've gone on quite a bit and I hope I haven't bored everyone with my long rant. Obviously, there are a bunch more details to this build and I've got quite a bit more designing to do. But, here are my drawings so far. They are just line drawings but do give a pretty good idea of what I have in mind. I plan on doing some very detailed drawings on things like, the dagger board, which I plan to build as retractable. Also, get more detailed about the mast and boom.

Anyway, here the are...

Well, I just tried my best to upload 3 PDF files of my drawings. Can't figure out how to do it. Any suggestions?

[wizbang 13]

unclick the green box ?

[WI-Tom]

Well, I just tried my best to upload 3 PDF files of my drawings. Can't figure out how to do it. Any suggestions?

Take a screen shot of the PDF, open in Paint, and save as a jpeg. Then use the "insert image" button (just to the left of the filmstrip icon) in the new post menu to insert it as an image. Might work ok.

Tom

[Rumars]

CSM is not something you want to use for your boat. Most of it is made for polyester resin anyway, and should not be used with epoxy. CSM weight is by square foot while all other fabric weights are given for square yards.
What you want is either a woven fabric or a stiched biax. The best practice is to use a biax followed by a light woven finishing cloth, but small boats do just fine with woven fabrics alone.
The wood thickness decides the stiffness, but you already decided on 1/4" so that's done.
Why do you want to use white ash if you have black locust? And why use something else then hemlock for the keel and stem?

[Robert D]

Hey All,

Is there someone here at this forum that can help me with uploading a PDF file?

[jpatrick]

Hey All,

Is there someone here at this forum that can help me with uploading a PDF file?

I don't believe that you can upload a pdf here. You first have to convert it to a jpeg image, then upload that image.

Jeff

[Robert D]

Well Folks,

I don't know what the secret is to upload a JPEG file, but I definitely have had enough of wasting my time trying. Don't mean to sound arrogant, but it really shouldn't be this difficult. This is not my first attendance at a forum and uploading images. So, I guess you'll never see my drawings and we'll have to go on script description alone.

I do want to thank all who have tried to help though. When I get some more details completed I'll present them.

Anyway, my choices of wood seems to be at odds with some of you. I understand, however I'm a "Think outside the box" kind of guy and I believe it's worth experimenting now and then. Not to mention, just because a particular species of wood is not in the realm of accepted building norms, does not mean it is an inferior material. As I've said, I have tested a bit with Hemlock and it seems to me to be very strong and durable, and the truth is, any wood can be kept from rotting if treated properly. I'll admit though, I plan to do some more extensive testing... keep you posted.

Black Locust also may not be a popular wood to use in boat building, but has many characteristics that Teak has. It is well suited for exposure to the elements. And, yes... I still need to do a little testing on that as well. But, if you didn't know, Black Locust was used as fence posts in this area by old timers. They did nothing to it but stick in the ground. Of course, that alone does not qualify it, but Black Locust is very hard and resistant to rot. More so than oak.

Just so you know, I had already thought of building a model first. But, after thinking about that route, I came to the conclusion, why not just build the boat. Don't mean to sound over confident or even a bit egotistical, but I have no doubts in my abilities to accomplish this first build with exemplary results. I am planning though, to build some test panels with different configurations of fiberglass to better understand the final structure. Also, experiment with, bead and cove, and heat bending different structural members of the hull. It's all very interesting to me, so I think I'm going to have a good time just playing around with the techniques that can be applied in the hull construction alone. Then of course, there is the mast itself, which I believe will actually be quite the challenge to build. The more I've read about the techniques used, the more I realize how intricate the work will be. Still, I feel it will be a rather enjoyable project.

Well, gotta go. Be back soon...

Thanks to all once again!

[wizbang 13]

no, not any wood can be kept from rotting on a boat
rotting rhymes with yachting
hemlock....pffffft

[JimConlin]

There are other people who experiment at measuring the properties of wood species, the Forest Products Lab of USDA. Look up their wood handbook. It’s available online.

[Rumars]

There is nothing wrong with hemlock, it's just a core, the natural durability of the wood is irrelevant as long as you don't have any unprotected holes. You could just as well use balsa and there would be no problem. If you stay with the equivalent weights of your proposed CSM layup (you should not use CSM and polyester on hemlock) you will have 72oz fiberglass in epoxy, 1/4" hemlock core, 36oz fiberglass.
Just be sure any hole into the core has an appropriate epoxy plug, and you will be golden.
Black locust is very good for any non-encapsulated elements, like a rubbing strake or an external stem.

[timo4352]

The bigger the boat, the greater the loss in time and money should a self designed boat be a flop.
It has happened before...right here on this forum.
My last build, a 22 foot outboard skiff, was built to an existing plan.
I don't have a fortune in it, but could not imagine the feeling of wasting even 10 or 12 Grand plus 3 years time on a possible turd.
Questionable materials...? I wouldn't do it, unless you don't care if it lasts more than a few years.
My first little 13 foot sailboat was built from altered plans with cheap plywood...it worked OK and was fun, but I have graduated to using better materials, and un-altered plans since then.
Consider how precious your time and money are to you before proceeding...
I'm not saying "don't build"...just build it wisely and enjoy every minute of it.
Good luck to you.

[P.I. Stazzer-Newt]

Okay, here are a few details;

Length -18'
Beam 4'-8"
Height - 2' (From Keel to Deck)
Dagger board centered
Open transom
Large cockpit
Freestanding mast
One main sail (No jib)




Approx. Sail Area @ 165 Sq. Ft.
Approx. Hull Area @ 100 Sq. Ft.
Approx. Deck & Cockpit Area @ 65 Sq. Ft.
Approx. Weight (Hull, Deck, Cockpit) @ 300 lbs.
Approx. Total Boat Weight @ 500 lbs.

The Hull dimensions are pretty close to those for Uffa Fox's Flying Fifteen
See https://www.flying15.org/The-Flying-...Specifications

But that has an (approx) four hundred pound keel, 10% less sail area and is raced two up.

Double trapeze???

[wizbang 13]

cuz there are so many good balsa core boats sailin around.
or boatyards that are infected with waterlogged balsa wood boats
yes, hemlock is just as good as balsa