Keel on foam boat

Do I need a halyard if I can reach the top of the mast? If latter, I could just hang the yard on a shackle to of some sort.[/QUOTE]


Not all sailing dingies use halyards. Lazer masts are slid into a pocket on the sail's luff before being stepped. I have seen a racing skif whose sails were hand slid along mast while the boat was tipped on edge.

Remember, it is far easier to make attachments on land than afloat especially in breaze pr chop.

I once bought a sunfish whose halyard terminated on its mast. The first time it capsized the mast floated away. Now the halyard ties to a deck cleat. Doing double duty by holding the mast into it's socket.

Paul

 

My objective was to build a very light craft, which I have largely achieved by using foam as building material. From the weight perspective it would be nice to keep both the rudder and daggerboard at the low end, weight wise. What would be the minimal thickness of these elements? I was thinking 1/2" as Sunfish uses 3/4". My reasoning was driven by the sail area - mine is 44 sqft, while the other one is roughly 75 sqft.
Where should daggerboard be placed in relation to sail's center of effort?

 

The foils need to be reasonably stiff for more than one reason. One of the reasons for having a strong dagger board is that you might need to use it to right the boat after you capsize. The usual drill is to stand on the board while it is sticking out of the bottom. There are other scenarios too, that will profit by a stronger board and rudder. The difference between the weight of a half inch board and a three quarter inch board is less than a pound with ordinary wood such as fir.

The stiffness of a board and rudder which takes the form of a cantilever beam when in use, is a function of the third power of thickness. Translated into useful comparison that means that the three quarter inch board will be two and a half times stiffer than the half inch one.

Save weight wherever and whenever you can but do not sacrifice structural integrity to do so.

 

A while later, the boat is finished:
Rigging is from windsurf board. I have carbon fiber two piece mast and two sails. The boat will go into the water this weekend. Will paddle first to see how stable it is ( have a short version of centerboard - 6" depth). Once the stability is deemed satisfactory the next trial is under sail. There are there sail sizes and 2 masts, starting with the 15 foot mast and 4.1 sq meter sail size. The larger one is a 16 ft aluminum mast with 5.4 sq meter fully battened sail.

 

Sorry to bump this thread so late but I am following your post with a lot of interest! I'm following a similar course of investigation and wondered how your boat sailed! It looks really sharp. What did you end up using as the coating? Did you go with glue/paint/cloth or opt for fiberglass? Thanks in advance!

 

Hi there, thank you for the message. I sailed the boat this summer quite a bit. Never used the floats. I have made a few changes, like redone the rudder brackets and built a kick up rudder. The tarp sail I made worked exceptionally well. There were a few challenges while jibing, but after a few capsizes I figured it out. The strongest air I sailed in was about 15 knots.
I ended up with glue and cloth, but added a thin layer of fiberglass bondo filler over the soft spots. Easy to work with and really hard when cured.
Attached a few pictures if you are interested in talking a look.

 

Thanks for the update! That looks awesome and I love that you made it towable by bike. Do you have a final weight approximation? I was going to guess before that you went with glue and cloth just from the pictures of the finish. It looks great but there's a certain look to it that's different from what you typically see with epoxy. I think you end up seeing more of the cloth or something. I am interested in building something loosely based off the "Foam Flier" which is a row boat. . I like the way you enclosed the front deck on this and used it to support the mast. I think my biggest concern is the forces that are involved with gusts of wind so it's great to know you've survived 15kt winds at least!
-Doug

 

The weight of the hull is just under 28 kg. The added weight comes from the mast sleeve which is probable too large, but at the same time it can take quite of bit of abuse. It is made of plywood 10x10x8 inches, layers of plywood separated by foam layers. Added wooden elements, dagger board box, fiberglass wrapped bumper, as well as added 2 6 foot pieces of 1/4 inch ribar stretching from underneath the mast step aft. That was supposed to firm the bottom and prevent any bending due to potentially excessive longitudinal forces. The entire front part is filled with foam scraps and then the gaps filled with insulation spray foam.
In the beginning I spent a lot of time in the water but then I figured it out. Despite the narrow beam, the boat is very stable when sailing upwind. Fast too. Tacking is easy if well timed. Jibing was a challenge in the beginning. Kneeling inside the cockpit was the best way to manage the weight transfer from one side while turning really slowly so there is enough time to adjust the weight distribution.
Filler paste that I mentioned was used only on the 'soft spots' where the foam did not seem to be sturdy enough as well as in some places where I rushed and did not smooth the hull properly.
Lessons learned:
-No wood glue to be used. Foam layers can be glued with insulation foam spray.
-Rocker to be made by bending the bottom piece of foam board. Attaching two of them together will maintain the curvature. My hull was flat originally and then sanded to the acceptable shape.
-Cloth of any kind is fine, but epoxy should be used. You get more strength with a single application.
-More precise foam cuts - less sending/rasping. Too much of the sending tempts you to cut corners and you generally end up fixing them later.