PK78 all stich together.

svey · Post by **svey** » Tue Jun 17, 2003 9:11 am

I finish stitching together my PK78 last night. Everything went well. I think I might have put more stitch than needed but the instruction and tutorial are giving different information. I've opted to follow the instruction that came with plan (stitch holes every 102MM). I will fair everything tonight and start filleting.

I have a small question regarding the hard spot. I've read that I must try to avoid them but how can I do that? The sides and bottom panels are bend around frame and they are in contact with those frames. Am I supposed to use spacers?

Rick · Post by **Rick** » Tue Jun 17, 2003 11:05 am

Congrats on your PK78!

I didn't get hard spots on my PK78. Did you use 6mm plywood? What kind did you use? It sounds like your ply might have been "bendier" than what I used (which was BS6566 okume).

Good luck. It's fun to work on a boat where turning it over just means picking it up and turning it over!

- Rick Tyler

svey · Post by **svey** » Tue Jun 17, 2003 11:25 am

I'm using Oukoume Marine ply.

Is it my understanding of a hard spot that is wrong? Am I correct to say that all the plywood parts should be "hanging" (less than 3/8") to one other and never touching each other?

Rick · Post by **Rick** » Tue Jun 17, 2003 11:59 am

I probably ought to let Jacques answer this, but fools rush in where angels fear to tread...

Little dinghies like the PK78 aren't subjected to the sames sorts of stress as the planing powerboats. Whether or not the seat frames touch the sides of the boat really doesn't matter. The epoxy fillets and glass tape will spread out any loads there are.

If you are really concerned about this, you could always cut out a few thin spacers (a quarter-inch or so) and insert them between the wooden parts before tightening the wires (or ties). I didn't bother, but it certainly wouldn't hurt anything.

I have learned that if the gaps are a little too big, and your epoxy paste is a little too thin, you can have a *lot* of epoxy squeeze through.

Have fun!

- Rick Tyler

Post by **jacquesmm** » Tue Jun 17, 2003 12:12 pm

Rick wrote: Little dinghies like the PK78 aren't subjected to the sames sorts of stress as the planing powerboats. Whether or not the seat frames touch the sides of the boat really doesn't matter. The epoxy fillets and glass tape will spread out any loads there are.
- Rick Tyler

Correct, thanks Rick.

LarryA · Post by **LarryA** » Tue Jun 17, 2003 12:17 pm

Hard spots are really just another name for a place where the local mechanical properties don't match those of the overall system. In english, that means the plywood against plywood is harder than the plywood against epoxy against plywood, it gives less when a force is applied. This causes the forces to fail to be distributed evenly across the structure, a hard spot, which can lead to fatigue type failures.

Anyway, on a boat like the PK78, I don't think I would stress myself too much about hard spots. (OK, a really bad pun). They really are a problem on boats that slam a lot. The instantaneous forces associated with slamming are quite large in comparison to the normal forces to which a hull is exposed.

svey · Post by **svey** » Tue Jun 17, 2003 1:03 pm

Tx everyone.

I sure hope that my PK78 will not be subject to any poundingl, I want to take my 3 years old boating in a boat that will not cover our conversation. I have a console skiff at the moment with an old 1970 Merc 40hp and that thing will cover any conversation.

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