15 foot sports recreational dinghy

The points at each end match to the last digit, as expected, since they were calculated for one end only and simply reproduced in a spreadsheet. One of the plank developments (Garboard) also shows a small asymmetry. It looks as though there is a small error in there someplace. This Summer I plan to use the plank developments - it will be interesting to see which end - or indeed if either end - of the built hull measures correctly . . .

 

You can do it now in very easy manner -- plot the developed picture in large scale using tile printing software on heavy stock material and voila... you can stitch and glue 1/8 scale model.

 

I did just that only 1/12 scale: without using and station forms it went together perfectly. I will probably make a larger model - maybe 1/6 - using model aircraft ply before moving on to full size. I'm still deciding the optimum size; it was going to be a solo but I have a request to build a double . . . the design was converted from lapstrake to smooth hull so I want to model it first, that's not necessary for a known good design.

 

Sea Turtle

http://www.boatdesign.net/forums/at...rts-recreational-dinghy-bum_004_composite.jpg

After I got *two* positive feedback messages for the image above, here goes further work based on the initial hull. I wonder if it is any good. I would appreciate any constructive criticism or a suggestion or two. Thanks in advance.

 

It looks a nice boat to my untutored eye and I think it would be easy to build. I'm a bit surprised at the displacement - it seems a lot for a crew of two. I wonder at the generous freeboard for a boat that would presumably be sailed level, and it should easily carry 50% more sail area if performance is an issue.

How does it utilize the ply sheets - have you planned for the offcuts to be used for decking? Of course it is not planned to be built, so that may not be a consideration but a professional designer would want to optimize economy. The sheer planks may not come out of two standard 8 foot long sheets scarfed together; did you allow for the length of the scarf joint plus a small error allowance?

 

the hull looks decent, but as pointed out a bit deeper than necessary I think. That sail needs battens and more roach, a triangular sail is not very efficient, poor performance. I would also want the jib to go up higher on the mast. both of these will affect the location of the CLR.

time to stop designing, and go out and build something.

 

“coffee table construction”

The carrying capacity and freeboard are envisioned for some extra weight and rough water. If built, this craft will do some exploring. If built, the dagger board would be replaced with a weighted drop center board. Sail area also reflects some safety factor against sudden wind gusts.

My method of building will be constructing a sturdy frame and planking it with ¼” rigid foam sheets. Then light weight FG goes on inside and outside. After that I would re-apply ¼” rigid foam and repeat FG. I would do that to the point when the initial frame is visible no more from the inside. This would give me a smooth shell-like hull ready for anything inside. But again, I would need a decent shop to do that.

Presently I have another idea to tackle – a small/portable craft. I am returning my thought to my original thread http://www.boatdesign.net/forums/sailboats/proof-concept-41301-post517437.html#post517437 because I live in urban environment in very small square footage flat. I have neither backyard nor the shop. So I invent the new method of “coffee table construction.”

Let’s see where it leads me to. Best regards and thanks again.

 

I think the "safety factor" would be greater if you made the boat a little wider. Then you could add side decks and reduce freeboard a little as A.K. suggests.

Except that I think it should have more beam, I like the planform of this boat best of all your designs. In profile I'd make it deeper around station 7 (or in your case, since you have about 13.4 stations along LWL, station 10) so LCB is 53.33% aft (measuring from station 0, the forward point of the waterline, putting it at your station 7.15). [If you want to measure from the transom like powerboat designers then LCB and LCG should be at 46.67% of LWL.]

Note that this boat is similar to a Comet:
http://www.cometclass.com/
http://www.cometclass.com/newComet.html

 

Tidying loose ends which started this thread

I decided to have a crunch on the one model of the first dinghy, which started this thread… I hope that this take is a bit better. I tried to apply whatever information I was able to absorb. I wonder if this boat is better suited for planning. I would appreciate if someone would give me a knowledgeable feedback. I uploaded just one picture, hopefully it is clear for someone to read. If not -- I will post more. Thank you.

 

The simple sharpie style designs in posts 70 and 94 are more to my taste in that I prefer the straighter, more contemporary waterlines at the bow. But the 6' beam and the freeboard on this boat seem about right, and the combination of the upper panel with tumblehome and the reverse sheer is visually interesting.

I think this boat will have weather helm unless you shorten the boom.

I wish I understood the way this program gives LCB. Can someone explain? The convention I'm familiar with regarding station spacing is to divide the waterline length by 10 with station 0 being at the forward end of DWL and station 10 at the aft end.

 

Sahara Dinghy

I also refined a little bit the "Sahara Dinghy." Perhaps I made some gross blunders, if so, would you please let me know? Thank you -- best regards...

 

I'd suggest much wider side decks that form the tops of enclosed flotation tanks so the boat comes up dry from a capsize. You could also or instead go for a cockpit sole that's well above the waterline and large scuppers or an open transom for draining, but if the side decks remain narrow what you'll find, if you're sailing single handed downwind or in light conditions, is that you have to kneel to keep your weight centered. I prefer to sit.

 

A hull like that should plane well, but in rough or choppy conditions that blunt bow will pound and throw a lot of water up in your face. good for lakes on calm days.

I suggest if you want a planning hull (keep it light), than put a finer bow on it. I also agree with stephens comments above.

 

After 100+ posts in this thread, little has been absorbed as far as yacht design. The same obvious flaws still exist, plus new ones. Learning yacht design this way is difficult, ponderously slow and discontinuous at best. Not a very wise approach, to learning what is necessary, to develop reasonable sailing lines, let alone structure. Is there a problem with buying a few books on yacht design, studying them and learning why your doodles are contemptuous, some humorous, to basic design concepts and fundamentals?

 

I think that's harsh, but what I would say is:

• I like the hull in post #16 better than some of the later ones,
• I join others in recommending a finer bow. The laser had a good hull when it was designed, and still does. Spend some time staring at it. http://www.laserwa.asn.au/index.php?id=42