12' sailboat design opinions needed

Hi all!

This is a design of a 12' sailboat with a full keel. plywood stitch and glue construction in mostly 3/8", 900 pounds displacement and 50% ballast ratio. I'm wondering if this boat would be sufficiently seaworthy for crossing something like a Canadian great lake.

I calculated the righting moment to be about 1500 lb-ft at best, but I really don't know if it's enough.
Do you think there is something really wrong with this design?

 

Hi Philippe,

Most countries have regulations with regard to the boat length and where they can be used.
For example, in Australia 3.75m (12' 4") is limited to within 5 nautical miles of the coast.

Honestly, seaworthiness is a function of the weather during the crossing.

I have attached a paper on stability for your amusement.

Regards AlanX

 

Your 12', 900 lb. boat with 50% ballast ratio sounds very stable until it takes water. You planning on building it like a submarine? Have you checked out Sven Yervin's designs? They are small, they go to sea, but they don't go anywhere fast. Partly, he under powers them, and partly they are designed for survival at sea, not speed.

Can't wait to see the design.

 

Welcome Philippe;
There are lots of boats out there like that, but for a boat that size seaworthiness is more about the crew and their ability than the vessel (the lakes in a blow having a steeper seaway than most oceans). The question is whether you want an open camp cruiser or an enclosed micro cruiser. Plywood is the proper material for something like this. Check out the Wooden Boat plans and kits or Duckworks for all the typical variations on this theme.
Boat Plans & Kits https://www.woodenboat.com/boat-plans-kits?ssrnd=12177
Plans & Kits - Duckworks Boat Builders Supply https://duckworks.com/plans-kits/

 

Something like this one ?

 

@AlanX : I don't think there is a minimum like that for Canada. that limitation didn't stop Serge Testa apparently!

@Will Gilmore : I checked his designs, I think mine would look somewhat like his 'Anna'. But honestly, for me, Designing and building my own design is half the fun. it's not impossible that id take inspiration from some of his designs if something needs improvement on mine. Yes I'm aware they aren't fast!

@jehardiman : Mine has a cabin, but few of those design have the safe ballast ratio I'm looking for while not being too big.

@Dolfiman : I mean the Scamp is 12' so it's similar in that regard, but mine has a bigger cabin, smaller cockpit, you'll see! (soon hopefully...)

Any idea how long it takes for a picture to be approved? I actually started the thread by mistake thinking I had put the picture successfully...

 

Welcome to the forum. If the picture goes directly with a post, click "Upload a File" under the post reply area and you can add the photo to a post without waiting. Let me add the photo directly to your post now.

 

There is a lot to be said for having a pram bow (like Dolfiman's Scamp above) on a boat of this size, instead of a pointed bow.

And while there is joy and satisfaction in completing your own design, there is also a lot to be said for trying to have as many similar other vessels to use for reference and inspiration (again like Scamp above, and perhaps the two links below).
Here is a neat 4 metre mini cruising yacht designed by Paul Fisher - although she has a lifting daggerboard type of keel, rather than a full keel.
Pocket Cruisers up to 16' https://www.selway-fisher.com/PCup16.htm#MIN
She is a foot longer than your design, and her displacement is just shy of 1,000 lbs, with 300 lbs of ballast.
This implies that her weight ex ballast is approx 700 lbs - while your boat is 12" shorter, are you sure that you can build her to have a hull weight (ex ballast) of 450 lbs?
Have you drawn a more accurate lines plan yet, or are you using the sections shown in the sketch above to calculate your displacement?
Your keel width appears to be very narrow - how are you going to build it, and what type of ballast will make up the 450 lbs?

Here is another interesting design which you could perhaps use for reference - Jay Benford's 14' Happy.
Benford Design Group http://www.benford.us/index.html?pcty/
Note that while she is 2' longer than your boat, her displacement in cruising trim is 1 ton (2,240 lbs), with a 33% ballast ratio.
Her beam is 6' 3" (about the same as yours?) and her 'deep' (relatively!) fin keel draft is 3' 7" (compared to your draft of 2' 3").

 

@bajansailor the beam of my boat would be 5' 6". you raise a good point that I might not be able to build the hull for only 450 lbs if that 4m mini yacht's hull is 700 lbs. It's not said in the plan how many layer of glass and epoxy is to be used if any. that would be useful to know.

Originally I wanted a fin keel but I changed my mind knowing I would probably have to make it following a good NACA profile, something that would be complicated for a plywood keel structure filled with concrete. What I have in mind would be around 3 cubic feet of concrete, the width of the keel would be 3" plus 2 times the thickness of plywood I would use on either side. the keel would taper fore and aft to about 1". I'm aware that concrete isn't really the best material but it would not be touching water and its just much easier to source.

 

Use lead.
It is so much more dense than concrete that you won't have to make it as deep. This means, in the steeper waves of the Great Lakes, there is less chance of tripping in a wave.

I don't know what your keel profile is going to look like, but a problem with deeper keels is when the water below a wave moves in a different direction than the water the hull is sitting on.

Perhaps 12' comes small enough that you don't need to worry about that, but I don't see any advantage to concrete over lead except $. 500lbs of lead is about $4500 as opposed to 500lbs of concrete costing around $10.

-Will

 

@Will Gilmore this boat should cost less than 5000$ CAD to build so that lead would double the price. But the keel as it stands right now is not exactly deep anyway. I think its a good compromise between having a better righting moment ( by having mass lower ) and still less draft than a fixed fin keel.

 

I just looked back and saw your drawing. It looks like you have it about right. Concrete weighs about 150 lbs./cubic foot, so your full keel of approximately 10'x2'x2" = 3-1/3 c.f. = 500 lbs.

What is your total displacement?

At 1200 lbs, your hull would displace a volume of somewhere around 20 c.f. of freshwater. Where would that put the waterline? (Oh yeah, you said a displacement of 900 lbs. Plus crew and supplies?).

-Will

 

I agree with Will, concrete is a very bad idea and lead is a lot better. For the keel wing itself, you can just use a thick enough piece of plywood as you can see here below in the pictures of an amateur building. Just rounded the fore edge and refine the rear edge, no real need of a Naca profile for your project. And the ballast can be then just two pieces of lead bolted at end of the keel wing.
Construction du Toulinguet https://www.vivierboats.com/albumsfr/Voiliers%20habitables/toulinguet/Construction_Gilliocq/index.html

 

Build a model using balsa or basswood. Not only will the model give better visual feedback of the design, but also some insights to the manufacturing processes.

 

How did you calculate the displacement, center of gravity and center of buoyancy? It would help if you posted your calculations. Also, is the displacement light or loaded? A boat will not necessarily float the way you draw it. You need to have all the weights correspond to the drawn submerged areas.