High density foam for battens on soft wing sail?

Actually, I think the CNC would work and almost no sanding. They run the CNC across the width, so a 1/2” cutter takes say 25-30 passes a foot or 120 passes per piece. The cnc could also spot/cut the mastholes with precision.

They’d be done with them before you had time to buy the materials for making the mould.

You ought to do a bit more homework on the hole. I don’t know if the force on the hole calculation needs to account for an unbalanced one. I’d say that calculation drives the foam choice. As foam density increases, generally so do the properties that resist damage..

Also, simply bonding the two halves with epoxy putty may result in a thin, brittle zone; the okume shear web would prevent that, but I’m hoping a few others comment. Mainly rx, who is a solid composites engineer and even I have been lucky to know the man.

Bonding the tube in the hole must also be done right. Maybe you leave a 1mm margin and seal the bottom and just pour clear epoxy and hope it doesn’t overheat or run a fan on it..

ps - if you end up building these with a cnc, my reward would be a picture of the output here

 

Yes, 2 part mold made of thick plywood with the front cut out which would be facing up. The initial state is a pretty runny liquid so it would fill out the sharp end nicely. There would be small holes throughout on the edges to let air escape and hopefully prevent voids. I would overfill it so it would ooze out the top and generally create more pressure which would help with filling out the mold completely, in theory. The top would then be sanded to shape by hand using a template. Then the whole thing would be sanded lightly the to help with adhesion of the epoxy. I would certainly experiment first to make sure it will work as envisioned.

To be honest I'm not especially concerned with warping. If mixed well the material should be very uniform. The lack of major temperature variations and there being little variation in load in it's thin dimension should help as well.

Rather than add the complication, I'd opt to increase the density of the foam.

In reality the forces would be much less than what I am designing for, so I'm not too concerned; any deformation of the foam around the mast would not be catastrophic to the functioning of the sail. Perhaps nylon tube would make a good sleeve, it is strong and slippery, and could be easily epoxied into a hole in the batten. using a sleeve would evenly distribute the loads to the foam and assure plenty of strength.

This project must be done on a reasonable budget, as I'm not wealthy. I'm going to do as much as possible myself not only to save money but because I enjoy the process. Part of the whole point of this project is to test and build upon my skills. I already have the skill and tools to do everything with adequate precision.

Thank you for bringing this up, it is certainly something I will be keeping in mind. I have been experimenting with epoxy and additives so will have a good idea what mixture to use by the time I build them. Perhaps it would be a good idea to use a slow hardener to limit the heat buildup.

Absolutely. I will be documenting everything and posting it. I'm probably going to work for another year before I start building, so it might be a bit of a wait. The designs will be coming much sooner though.

Thank you very much for all your input, lots of good food for thought there.

 

The CNC would just be far quicker is all. All the half shells would be made in like 4 hours or so. All the parts would be done and built in less time than you’ll spend building the mold.

 

At 8.6” wide, you’d get 5 pieces per sheet and so you would face costs for 3 foam panels. And yes, the faster and easier method would cost 1-2k. I think 8# foam will suit, based on not worrying about deformation.