Twisted hull? How to fix it?

[fmjnax]

How do you tell if your hull twisted on you (during the tear-down phase)? I've got my 16' boat on the trailer and I am doing a full restore. I've got the cap off, the deck pulled, all the foam removed, etc. Basically, the only thing left in the hull is the 3 stringers (which would practically crumble if you as much as blow on them) and the transom. I had put some angled blocks between the bottom chine and the trailer at various spots to keep the shape, but I guess I made them wrong (or the kids were playing in the garage and I didn't know it!) because they have all fallen out since I last worked on the boat (about 2 weeks ago). When looking down the hull from the top of the transom towards the bow, the right side of the bow is slightly higher than the left side. It doesn't look like the sides of the hull have bowed out, though (measurements still match to the references I made with the top cap). However, I'm worried that my hull has twisted on me.

That said, if it has twisted on me, at least I am still at the stage where hopefully I can correct it without much effort. My problem is that I don't know how to correct it... or how to confirm that my hull really has twisted. Any advice?

 

[JDA1975]

Re: Twisted hull? How to fix it?

I let mine do what it wanted while tearing down, Finished grinding this weekend and will be flipping the empty hull tomorrow to do some bottom prep work then building a stand for it when i flip it back over. like this thread http://forums.iboats.com/showthread.php?t=287390 , Figure if you flip hull and make it level at certain points then build your stand to match shape, you should have a perfect shape for re-decking. Been wondering where you disappeared to, I was following your thread cause our hulls were so similar in design

 

[fmjnax]

Re: Twisted hull? How to fix it?

Thanks JDA, and sorry for the drop-off. Work kicked my butt the last couple of weeks so I haven't had any time to work on the boat. I got out there today and took measurements on everything and drafted up a [pretty much] scale representation on some graph paper. I then pulled up the remaining deck and foam and cleaned it all up. I won't have much time during the week, but I should have enough time to finish up my pre-griding preparation and get my thread updated with pictures. I'm hoping I will be able to start ordering my supplies this coming week, but next week may be more realistic. I still haven't started any major grinding, so I'm not nearly as far as you are. I've been following your thread, though.

I like the idea of building the stand like in the thread you referenced. I think I will go ahead and do that as it will not only help keep the hull shape, but it will also allow me to bring the hull to a height more manageable while working and will allow me plenty of time to work on the trailer as well.

 

[JDA1975]

Re: Twisted hull? How to fix it?

yeah, plus I plan to paint the Hull, I'm fond of forest green so doing forest green hull with a tan or yellow(wife wants orange which looks good with green but i hate that color) on the trim. Flipping hull will make that prep plus trailer work so much easier. Grinding sucks, cleaning up is worse,,,I had to enclose my carport because neighbors complained about the dust so i had like an inch of dust covering everything! If I disappear from the site call the authorities because my wife will kill me when she finds out I am using her shark vacuum cleaner to pick up the dust....those things don't lie when they claim "no loss of suction" blows my shopvac away lol

 

[oops!]

Re: Twisted hull? How to fix it?

hang on here guys.......

this isnt right.

the top of the sides of the hull arent anything......thats just how they cut it coming out of the mold. if the kid dipped the saw too much or was too high....it will look funny after the cap comes off. there is also optical illusions that can totally fool you unless you know what to look for.

the plaining surface is everything.
that can be determined by stringlines.

just make sure the hull is properly supported from the bottom in a long bunk type rack.....and let the weight of the hull comform to the bunks.....if the bunks are right......the hull will be.

if you are twisted or hooked.......screw the hull to the bunks.....after the stringers, deck and foam are back in.....then you can un screw it.
i didnt flip my hull till i had the strings glassed in to the hull so the hull would not move. then it was easy to see any imperfections in the planing surface.

 

[fmjnax]

Re: Twisted hull? How to fix it?

Thanks oops! Can you elaborate on checking with string lines? My bpat is only a 16 footer and is on a bunked trailer so maybe I am just being paranoid?

 

[oops!]

Re: Twisted hull? How to fix it?

run a stringline from the transom to the forward keel.....measure the distance of drop between the lifting strakes.

from the forward hull to the transom between the lifting strakes....on the flat area......

and if you can on the inside make an "X" from back to front......you will find out if its crooked.

 

[JDA1975]

Re: Twisted hull? How to fix it?

when i said level i might have misrepresented what i meant, when hull is flipped the bottom should be level/straight across so once you get it leveled there and build a perfect fit stand it should be ok, i know the cut lips are far from level or straight, I just hope to keep my keel straight with my other 2 hulls. I think it will all work out in the end, even without the stringers/deck the tri-hull seems to remain pretty rigid.

 

[oops!]

Re: Twisted hull? How to fix it?

tri hulls are a bit different.....this is due to the amount of curves in the hull and the 3 rigid keels.....

however...the premise is the same.....if the hull sits on the cap edge....like this

you have to level the keel and the chines....you can shim it....do what you have to to get it straight on the planning surface.
if you glass it with out making it straight......you will have handling problems on the water.....some of these might be quite severe

 

[JDA1975]

Re: Twisted hull? How to fix it?

ok, looks like we were saying same thing, just my lack of boat lingo made me question if I understood what ya meant or if you misunderstood me....Im such a newb!

 

[fmjnax]

Re: Twisted hull? How to fix it?

Sorry for reviving this thread, but I'm getting to the stage where I will be pulling the hull off of the trailer and need to make sure I understand this correctly. When I run the stringline, do I run it from the bottom of the hull or from the top? If I run it from the top, I would run it from the top center of the transom to the center of the bow (to the bow eye)? I would then measure from that stringline down to the outter keels on each side? And I would expect that the distance should pretty much be the same for each side at each point I measure? If I am way off base, please let me know!

My plan is to check [hope] that the hull sits proper on the trailer. Once confirmed, I will pull the hull off the trailer and begin my trailer work (rewire, paint, new bunks, ets). I will go ahead and paint the hull while it is off and flipped. Once both are done, I will put the hull back on the trailer and let it conform back to its shape before continuing with pulling the old transom/stringers and replacing with the new. Of course, if my hull isn't sitting true while on the trailer, I will rectify that as needed. Any concerns with this plan, and if so, I'm open to suggestions.

 

[oops!]

Re: Twisted hull? How to fix it?

your concern is the planing surface.....the outside bottom of the boat........where it rides on the water.

measure from the transom lowest point to the front lowest point.......it should be almost straight.......a smile is ok....but a frown is not. a frown is a hook....(space between the string and the hull)

then do it again on the outer chines.

click the link in my sig......i think i used stringlines in the first 4 pages

 

[fmjnax]

Re: Twisted hull? How to fix it?

As funny as it may sound oops!, the "smile" vs "frown" just made it all make perfect sense! I'll go back through your thread tonight after work and find that section. I read most of it from work and our web filtering here blocks out most of the pictures so I probably missed a lot of good information.