UNTWISTING A BOAT FRAME

[mark couty]

Even though ny Dumas boat is jig built, it still has a slight twist in it. Is there a way to counteract the twist ? All the sponsons, bottom and non trips are all covered. I was about to start sheeting the deck when I saw it. Its not like a pretzel but it is definitely noticable. Thanks.

 

[Greg Wannamaker]

Generally the more perfect your jig is the better your build product will be, during my frame up stage I even tack the hull to the jig itself, another thing to make sure of is the perfection of the surface your jig rests on, I actually build on a really heavy office desk. Solid square building surface, perfect jig all equals a high quality square hull. So if your already past the frame up stage make sure all is square, true and level, go ahead and sheet it but make sure to place lots of heavy stuff on it all, this will ensure he whole hull is square to the table and jig, I think I used an entire set of encyclopedias to weigh it down while the epoxy cured, bang your done. If you end up with a minor twist, maybe a millimetre here or there, tweak it with a sanding block and you should be good.

Good luck with the build!

 

[brad nichols]

Heat will soften the epoxy and rejig it and try a shim on the opposite side, hope you can straighten it out.

Brad

 

[Hydro Junkie]

There are two things I would do before clamping the hull to the jig:

1) Verify your jig is totally flat. I'd put a straight edge on it along both sides and down the center running lengthwise, do the same in at least four places running across the width and then diagonally from corner to corner.

2) Verify that the hull actually was built square. Measure the distance from the hull bottom to sponson bottom at the sponson transom and verify that both sides are the same. If not, you have more issues to deal with than just a slight twist. Dumas kits are not known for being the most exact fitting product on the market

Once you know the jig is flat and have verified you're dealing with only a twist, clamp the hull down and hit it with the above mentioned heat gun.

 

[Bob Blazer]

Mark if you have not put the deck on as of yet and you should be able to twist it now. You should have no problems straightening it out. If it is hard to twist put a small wedge to over compensate for the twist when you deck it.

Hope this helps, Bob

 

[Larry K]

Hey Mark!

You shouldn't have any problem with "twists" once the boat is decked. As Greg says, it should have been pinned to the jig up to this point. That helps you get all the frames and mains square while the skins are attached. And, as HJ says, if the jig is true the hull will be as well. The framework always seems a little floppy when you take it off the jig but once the glue sets with the decks are on, what you see is what you get. Your jig has served its purpose up to this point and you can put the hull back on the jig to do the decks if you wish, but consider this. The only thing your boat is ever going to "know" is where it hits the water. The last few pickle-fork hulls I've built, I dry fit the decks & used 2 or 3 pins just to locate the pieces. Then apply epoxy (slow setting stuff) & set them back in place. I then used masking tape to pull the decks down onto the mains, sheers & non-trips, working fore and aft from the middle. The last step is to set the boat on a flat surface and run a couple of bungy cords or tarp straps over the hull near the transom and the sponson transoms. I strapped mine down on the bed of my table saw. The surface you use MUST be solid, flat & straight. The only thing touching the surface should be the rear edge of the sponson riding surfaces and the hull transom. Once the glue sets, the hull will be rigid - and straight!

 

[mark couty]

I have verified that the jig is true, I think the twist may have occured when I put the bottom sheeting on. I will first try the tacking the hull to the jig and try the heat gun method before sheeting the deck to see what it looks like.

Thanks for the tips guys.

 

[Hydro Junkie]

Any updates?

 

[Chris Thomas]

I usually Screw the boat (Stringers) to the jig. Some #2 X 3/8 sheet metal screws work well. Holes are filled during the finishing process. BE Careful not to sheet over the access to the screws. The air traps are primo spots and are open to view all through the building process. Typically I run 2 screws vertically thru the bottom of the boat, into the jig, just inside the transom. This will keep the rear end square too...

 

[mark couty]

Been working a lot of O.T.

 

[mark couty]

I had time late Sunday evening to tackle my problem. I put the boat on the jig, clamped the transom and tacked the sides down also and hit it with the heat gun. I wasn't sure how much heat to put on all the joints. I couldn't tell for sure how much heat to apply and I was starting to smell the glue, so at that point I stopped applying heat to everything. I will let it set for a few days before untacking and see what happens. How much heat is too much or not enough.

 

[brad nichols]

Should start to feel tacky, I would think?

Brad

 

[glenng]

Mark, I got a 1/8" twist at the transom while glue work was done on chines. I contacted Joe Petro(Zippkits) and he provided a simple solution. Place a 1/4" dowel or drill bit (2X the twist) under the low spot on the transom then pile as much weight into the hull as you can and when sponsons were skinned on the top the twist was gone.

 

[glenng]

Note- the boat was built on flat MDF stock- not on a jig.

 

[mark couty]

Untacked it last night, the twist is gone. the heat gun trick worked. Thanks guys !!

 

[brad nichols]

Great to hear it worked out for you!! Now tack it down and do the rest of the sheeting.

Brad