Hull Twist- Backlash

[Rich Jones]

I put the the main bottom on my Backlash hull the other night and when I unclamped it, there is a 1/4 in twist. If you are viewing from the transom, the right side lifts up about 1/4 in. When you push it down the right sponson lifts up as the boat flattens out. I think the issue stems from having to correct the front end veering off center and having to push it over and clamp on the center line before glueing. I made precise measurements and drew pencil lines to use as a guide. The boat sat as flat as could be on the building board. I used thin ca to attach the bottom because the mating surfaces were just perfect. I would then seal with epoxy after erasing the lines.

Anyway, with that background out of the way, I don’t really want to tear anything apart. I’ve read on these boards that the twist can be corrected when attaching the decks. At first, I thought just clamping to the board and attaching with epoxy would do it. But I read something about OVER compensating. I‘d appreciate if someone could walk me through this. On the side of the transom that’s touching the building board, put a 1/2 (2x distance of the twist) in drill bit (or whatever) under, Then clamp or weight everything down. Then attach BOTH tops with the drill bit there? Or attach the right decking, unclamp and remove drill bit, reclamp, and attach left deck?

These are obviously the issues of someone that hasn’t built a boat in 20 years. In hindsight I probably should have filed some of the slots as they went together pretty tightly and I assumed the front was as square as the rest of the boat. This is no reflection on the kit, laser cutting is awesome.

I appreciate any help you guys can give.

Rich

 

[brad nichols]

If the deck is off you can try clamping the boat down with the shim and using a heat gun warm the hull and leave it overnite. The sealing epoxy will soften with heat.

Brad

 

[Rich Jones]

There’s no epoxy on it yet. I used thin CA to attach the bottom to the frames.

Rich

 

[Charles Perdue]

If the deck is off you can try clamping the boat down with the shim and using a heat gun warm the hull and leave it overnite. The sealing epoxy will soften with heat.

Brad

Dampen the hull with water, warm and clamp down overnight with the shims.
After it is completely dry (a day or two), release the clamps, let the hull relax and this will tell you how much more you need...if any.
If straight then attach the deck. If not then repeat until it is straight. It will straighten up.

Charles

 

[Rich Jones]

Brad and Charles:

Thanks for your replies. This all makes sense. Anyone else have any words of wisdom?

Rich

 

[Rich Jones]

Just an update. I dampened the hull with a spray bottle, heated up with a heat gun, and clamped overnight with a drill bit twice the size of the twist under the opposite side of the transom. Again I have built this hull with Ca to this point, no epoxy. I did this a total of 3 times over the coarse of a few days. Each time it improved the twist a bit, and I was able to shim with progressively smaller bits. At this point there is still a little bit of a twist but pretty negligible. I believe when I clamp the hull down and attach the decks with epoxy that it should completely go away. Thanks again for the help guys!

 

[Bob Blazer]

Do not worry about the twist with the decks off. Repeat, do not worry about the twist with the decks off. The hull at this point is like a wet noodle. After you put the decks on it will become a brick. I always put both sides on at the same time. I put the hull on a flat build board that the width is smaller than the transom then use large rubber bands that go around the entire hull. I also put blocks (1"X1"X1 1/2")on the deck close to the engine rails so the rubber bands holds that inward side of that deck down. Incapsulate the blocks with box tape or use waxed paper to prevent any sticking to the hull where the epoxy runs out. You're welcome.

 

[Tom Foley]

Don't forget to seal with epoxy before you deck her over .

 

[Ray Sametz]

Don't forget to seal with epoxy before you deck her over .

And flotation.

 

[Rich Jones]

Do not worry about the twist with the decks off. Repeat, do not worry about the twist with the decks off. The hull at this point is like a wet noodle. After you put the decks on it will become a brick. I always put both sides on at the same time. I put the hull on a flat build board that the width is smaller than the transom then use large rubber bands that go around the entire hull. I also put blocks (1"X1"X1 1/2")on the deck close to the engine rails so the rubber bands holds that inward side of that deck down. Incapsulate the blocks with box tape or use waxed paper to prevent any sticking to the hull where the epoxy runs out. You're welcome.

Good tips thanks Bob!

 

[Rich Jones]

Don't forget to seal with epoxy before you deck her over .

Will do Tom. Do you seal the inside of the hull with straight up epoxy or do you thin with Denatured Alcohol? What I was going to do, since I’ve used entirely CA to this point is put filets in all the joints( epoxy and the silica filler) , let that cure, then seal the rest of the inside with thinned epoxy, wiping out any excess after letting it soak in. Does that sound like a plan or would you just brush straight epoxy in there and don’t worry about the filets?

 

[Rich Jones]

And flotation.

No kidding Ray that would be bad to forget that! Thanks!

 

[Tom Foley]

I would just brush it in . I have done it both ways and ended up having to double coat it when I thinned it . West Systems is what I use but lots of good stuff out there .

 

[brad nichols]

Straight epoxy and clamp it down with the deck off will take the twist out before you deck it.

Brad

 

[john v]

what bob said, nobody builds more backlashes than bob, was at ed tokiens house today and saw the latest build from bob, absolutly beautiful

 

[Sam Augspurger]

I put the the main bottom on my Backlash hull the other night and when I unclamped it, there is a 1/4 in twist. If you are viewing from the transom, the right side lifts up about 1/4 in. When you push it down the right sponson lifts up as the boat flattens out. I think the issue stems from having to correct the front end veering off center and having to push it over and clamp on the center line before glueing. I made precise measurements and drew pencil lines to use as a guide. The boat sat as flat as could be on the building board. I used thin ca to attach the bottom because the mating surfaces were just perfect. I would then seal with epoxy after erasing the lines.

Anyway, with that background out of the way, I don’t really want to tear anything apart. I’ve read on these boards that the twist can be corrected when attaching the decks. At first, I thought just clamping to the board and attaching with epoxy would do it. But I read something about OVER compensating. I‘d appreciate if someone could walk me through this. On the side of the transom that’s touching the building board, put a 1/2 (2x distance of the twist) in drill bit (or whatever) under, Then clamp or weight everything down. Then attach BOTH tops with the drill bit there? Or attach the right decking, unclamp and remove drill bit, reclamp, and attach left deck?

These are obviously the issues of someone that hasn’t built a boat in 20 years. In hindsight I probably should have filed some of the slots as they went together pretty tightly and I assumed the front was as square as the rest of the boat. This is no reflection on the kit, laser cutting is awesome.

I appreciate any help you guys can give.

Rich

This is terrible. Go back to the jig and maybe flex it the other way

 

[Rich Jones]

This is terrible. Go back to the jig and maybe flex it the other way

Any amount of twist that remained disappeared when decking the hull. I’ve been running the boat the last two summers.