Twisted Slo-mo-sun

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Twisted Slo-mo-sun

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14 November 2010 at 17:49 #28879
Jeremy
Participant
@jeremy15845
Having completed the planking of my Billings Slo-mo-shun, I find to my horror that I have a slight twist in the hull. Resting the boat on a flat surface,one side of the transom is about 2mm above the surface. I have yet to cut out the hatch which might give me the opportunity to force a slight correction but I would appreciate views on whether this distortion will have any significant effect on performance?

I built the keel on a flat surface but, in common with others building this boat, I only fixed the central eight planks on the upper surface before cutting away the keel to allow me to complete and the epoxy the interior of the bottom. The rigitity at this point was clearly not enough to prevent the hull twisting . Photo above. Other photos of the build are in my Slo-mo-shun album.
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14 November 2010 at 17:49 #6027
Jeremy
Participant
@jeremy15845
14 November 2010 at 18:03 #28880
Bob Abell 2
Participant
@bobabell2
Hello Jerry

Nasty!…………….I would cut the hatch opening, right away and over twist the hull with heavy weights

If does twist nicely in the opposite direction….then give it a coat of varnish first.

You will need to check the twist quite often, as the varnish dries, to make sure it stays twisted correctly

Best of luck……Bob
14 November 2010 at 18:14 #28881
Jeremy
Participant
@jeremy15845
Hi Bob

Thanks for your instant advice. I will have a go as you suggest. However, the deck has not yet been veneered – should I steer clear of varnishing before this has been done? The bottom has already been expoxied inside and out.

Jeremy
14 November 2010 at 18:26 #28882
Bob Abell 2
Participant
@bobabell2
Hello Jerry

I meant, varnish inside…….Place cross planks across the top of the hull and apply weights to get the twist out.

Make sure the “over twist ” is not permanent

Keep the hull flat at all times, during the veneering…..the veneering should help the retain the new realignment

Can you twist the hull now, just by your hands?…….If not….think about plan “B”

Bob
14 November 2010 at 18:43 #28883
Jeremy
Participant
@jeremy15845
Bob

Thanks for clarifying that. In answer to your question, hand pressure on the hull flattens it down and that’s before cutting out the hatch. Hopefully, it will work out but, if it doesn’t, what is plan “B”? Hopefully not the breaker’s yard!

Jeremy
14 November 2010 at 19:06 #28884
Bob Abell 2
Participant
@bobabell2
Hello Jerry

I knew you`d ask that!…….Mmmmmmmm!

I think you`ll sort it

Bob
14 November 2010 at 19:29 #28885
Jeremy
Participant
@jeremy15845
Hi Bob

And I guessed there wouldn’t be an answer! The boat is now strapped down straight and true. Tomorrow I will cut out the hatch and take it from there. It’s just nice to know that there’s somwehere out there who sympathises with my predicament! I will let you know how it goes. Failure is not an option.

Jeremy
14 November 2010 at 20:05 #28886
ashley needham
Participant
@ashleyneedham69188
Personally I would not worry about 2mm. It is unlikely to make a jot of difference to the “go”, or at least, nowt that cant be trimmed out!

The only time I worry about any sort of imbalance, be it twist, uneven curves or skewed superstructures is if someone is likely to notice.

By and large all my boats have something wrong with them, but absolutely no one has ever noticed. Job done.

Ashley
15 November 2010 at 07:58 #28888
Bob Abell 2
Participant
@bobabell2
If the twist can be put right without too much aggro…..might as well gerron with it!

There`s nothing more narkin` than a cockeyed hull…….early in the build

But I agree……it would hardly have any effect

Bob
15 November 2010 at 18:56 #28890
ashley needham
Participant
@ashleyneedham69188
Jeremy. You should worry about 2mm. When I built the “Toyboata”, out of long bendy bits of lite-ply, despite some serious holding down when gluing up, it was about 6 or 7mm askew corner to corner at first !!

I had to put a diagonal across the hull underneath the bonnet and extra bits at the back to get it anywhere near straight. It eventually came good after cabin bits and the roof had been fixed in place.

Its a good job I didnt have a plan to adhere to or I may have scrapped it !

Ashley
15 November 2010 at 20:56 #28893
Jeremy
Participant
@jeremy15845
Ashley. That’s the trouble with written English – should I worry or shouln’t I worry – it all depends on how you say it!

Hatch now cut out and ready for the cockpit, engine cowling, exhausts etc which I will build using the excised piece of decking.

One suggestion which may be useful to those trying to eliminate a twist. If weights are not available, force on the requisite part of the hull can be exerted by strapping down front and back on a workmate and then increasing the tension by opening the jaws. Care neeed of course not to risk crushing the hull after which the breaker’s yard might be the only option.

I will leave it strapped down as I apply the veneer and see what that does. If nothing, I will live with it. I would never noticed the discrepancy in the first place until I put the hull on its stand.

Jeremy
16 November 2010 at 15:47 #28898
Paul T
Participant
@pault84577
Make a steam chest out of an old box, strap the model firmly in the correct position on a firm rigid board and place it it the steam chest.

Connect the steam chest to the outlet pipe of a wallpaper steamer and let the steamer run for quarter of an hour.

Disconnect the steam and let the chest cool down before removing the model.

Works for me every time.

Paul
16 November 2010 at 19:54 #28900
B B
Participant
@bb42502
To take out a twist in the hull try this method. get a thick piece of wood place the hull on the wood center line. Drill holes through the thick piece of wood fairly close to the edges of the hull. Now take some threaded rod put a washer and a nut on one end and push it throught the wood. when you are finished you will have a few threaded bolts sticking up next to the hull. Now take a few pieces of wood and drill holes so that the threaded bolts can be slid through the wood. Now put washers and nuts onto each of the threaded rods. Take wedges and put them at the transom end so that it is level and tie the nuts gently so that the rear end of the boat can not move. In the mid section you do the same but here you tie up the nuts so that you start to introduce a slight opposite over twist in the direction you want. tie up all the nuts so that the hull is solid in possition and will not be able to move. Now for the magic. Take some luke warm water with a 50/50 mix of Scrubs Ammoniac and with a cloth wet the hull with this mixture. Not sopping wet but just wet enough. now leave the hull to dry out completely and release from the piece of wood. The hull should come out perfectly without a twist. The amoniac in the wood makes the wood very plyable. I have used this for planking where the hulls have serious curves in it.
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