All of this is a result of me thinking I was being clever and not following the plans. Michael Storer, the designer, specifies that the chinelogs should end 50mm short of the bow-end of the hull sides. But I noticed that the stem is significantly less deep than that so you end up with a gap. Silly designer, says I, I'm going to extend the chinelogs all the way to the stem and make it all pretty. Well, if you do that what happens is that the two chinelog ends hit each other as you bend the hull sides around the first bulkhead, doh!
I took the pull saw and viciously hacked away chunks of the offending chine logs. THAT will teach them and nobody will see the butchery since all this is inside the floatation chamber. The hull went together beautifully. Except now with the chinelogs not touching each other the hull sides are not quite fair just aft of the bow and the gap between the chinelogs allowed the chinelog to split away from the hull side. How much do you want to bet that if I had cut the chinelogs 50mm from the hull end, as instructed, they would have come together and just touched thereby preventing that slightly unfair hollow and since they would be touching each other they could not separate from the ply. Silly builder.
BTW, the chinelog that pulled away from the hull side was a secondary joint since that hull side was epoxy coated all over, without masking the joint areas. The epoxy was well sanded with 60 grit, in the glue joint. It looks like it's mostly the wood and not the epoxy that failed but it's a little hard to tell. The side which did not fail had the joint areas masked before epoxy coating so that joint is wood to wood. Coincidence or is that side a stronger joint? You decide.
The chinelog on the left has separated from the hull side while the one on the right has only a bit of a crack. It is mostly hanging on but is causing an unfair hollow just aft of the stem.
So the solution is to separate the other chinelog from the hull side by the same amount. I used a small steel scraper, as a wedge, to shear the cedar away from the hull side.
I taped the underside with some packing tape to form a dam and filled all of the cracks with slightly thickend epoxy. It's ugly but stout.
Total time to date: 207hrs
Good fix! You are not the first to not position the chinelogs for enough aft, I had to bevel mine too, but not after I cracked the ply in the bow! I just filled it with epoxy and then Quick Fair before painting, but I had the same issue.
ReplyDeleteA good fix.
I am suspect of gluing on components on already epoxy coated surfaces-- I always can seem to chip off an epoxy blob easy if it cures on an already epoxied surface, even if it's sanded, but I always pull up ply if the blob lands on untreated wood. Taping off, or sanding to the wood, is essential in my opinion.
From my blog:
ReplyDeleteWhen I was dry-fitting the boat last week for the first time I heard some ***crack***ing noises, and since I didnt' see anything, I figured it was some epoxy somewhere settling or what-have-you. NOPE it was the chine logs right where they abut the stem. You'll notice the taper I put in to give them some room to fit together, and you'll also notice where the wood actually separated from itself. The glued face stayed firm to the plywood, which makes me feel like my gluing jobs are satisfactory. I'm bummed the wood split, but again, this whole area will be filled with epoxy and all will be good with the world again.
For pictures: http://gisamateur.blogspot.com/2009/11/filling-stem-gap-w-fillet.html
I somehow missed your blog post about the fun with chine logs. Too bad cause it might have turned on a light bulb in my dim brain.
ReplyDeleteI think you are right on the secondary bonding being weaker but it is used in big boat construction all the time. It's simply unavoidable. While the raw wood to wood joint is stronger I suspect the secondary is also plenty strong. It's a question of what's good enough. I'll find out since my boat is a mixture of both joints.
I think it's a question of surface area. If the entire bulkhead is glued in position on roughened epoxy, it's going to be fine because there's so much area. If its a small gluing area that is going to incur a lot of stress, it would probably be better to get it down to the wood, one way or another.
ReplyDelete