Spindrift 12 #1275 - Daggerboard trunk inside finishing

[J. Cote]

Looking for a little guidance on this one. 

The S12 plans say to coat the inside surfaces of the daggerboard trunk with 3 coats of epoxy and a + 1/8" designed space clearance.

The CS 15 video suggests glass taping these inside surfaces.

My buddy Thrilsbe suggested the sketches shown below for strength where it counts.

 

What recommendations do you have for finishing the inside surfaces of the trunk & what space clearance is needed for that finish?

I haven't trimmed the kingposts to thickness yet, so any recommendation is still viable.

 

Thanks.....

[PeterP]

I have not done a 12 but I built a 10 a while back. This is how I would do it: you have your dagger board I presume. Build the case dry and clamp/ screw it together to see how how the board works  inside. An eight of an inch clearance sounds OK but 3/16 would be something I would personally go for. Whatever Graham recommends. When you're happy take it all apart. You will have two ply faces and two posts. Glass both  plywood (entire) panels on what will be the inside face.  Glass the inner face of your posts.  Even 2oz cloth fully coated is going to be a whole lot tougher than neat epoxy. With 4 oz you will never have to worry about the inside.  Flood coat the glass. Cure it and try everything for fit one more time. Scuff the glass where the posts will go onto the plywood. Glue the posts down on one panel. Run a nice fillet.Cure it. Glue the other panel on. Fillet the last  joints with a long stick and you are done. Good luck PeterP

[Designer]

Peter gave you good advise. Having built these boats for over 40 years or more, my usual standard was to coat the inside of the trunks on Spindrift's with three coats of resin and call it done . On bigger boats I always glass the inside of the trunk sides before assembly.

 

Alan pointed out a while ago that it maybe quicker to glass the the trunk insides than do three coats. It can never be bad to have better abrasion resistance. So the upshot is that, coating or glassing works, but glassing should be better.  

 

The other issue is glass taping the trunk to the bottom. Again this is a complicated issue. It is always better to glass both sides of a joint. The problem is that, as been pointed out, it is hard to taper around the inside of the trunk bottom slot so that you do not narrow it and do not get any bubbles in the glass as it does not like to go around tight corners. I decided that it was too hard for home builders to do well without a lot of pain, so I decided to eliminate the inside corner taping and double up on the fillet and inside taping. I stagger the two layers of 3" tape by 1/2". We ended up with a pretty competitive S10 racing fleet so instead of cutting the bottom slot to the trunk rectangle we cut out the bottom to match the profile of our dagger board to have less turbulence. This would be impossible to tape inside without a lot of work.

 

I have never seen a failure in one that was done this way so far.

 

 

 

 

[Hirilonde]

The only thing I have to add is graphite powder in the epoxy used for both the board and the inside of the trunk. The tolerance for my board fit on my Lapwing is minuscule, yet is glides up and down.

[Don Silsbe]

I told Jan in a text that the d/b is supported very well on this boat.  That must be a big factor in never seeing a failure.  I advised her to save the tapered, glassed joint for a repair procedure, if needed, in the future.