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[ukmike]

HI.
I have just made, well 3 weeks ago, a keel 50 inches long, (1.27mtrs ), which was perfectly straight when completed from 2 laminations of 5mm birch plywood.
My problem is that it has developed a bow in the middle.
How can I straighten it ?
Any suggestions will be most appreciated.
Mike.

[hammer]

Soak it in water for at least 24 hours.  Pack up the ends weight on middle. Keep looking at it when it as gone just passed straight, remove weight. It should move back slightly to straight.  I am afraid it will be a bit of trial & error. Or you could cut it down the joint a reglue it.

[Umi_Ryuzuki]

Take a nice level board, I'm sure they exist,... and draw a straight line down the center.
Tack your keel to the board using dowels, screws, or blocks of wood.

Stand and place your frames, then sheet the boat.
Once you have enough sheeting on the boat, it will keep the keel straight.

 

[ukmike]

Take a nice level board, I'm sure they exist,... and draw a straight line down the center.
Tack your keel to the board using dowels, screws, or blocks of wood.

Stand and place your frames, then sheet the boat.
Once you have enough sheeting on the boat, it will keep the keel straight.

 

Thanks for that Umi but it would not be possible to do that as the keel is fitted after the frames are attached to the gunwales.
It is built upside down.
Mike.

[TailUK]

Working from the middle outwards towards the bow and stern.  Glue scrap blocks either side of the keel between where the frames will fit and push the keel straight.  After you've fitted the frames and/or stringers you can begin planking at which point the keel should remain straight. 
Or cut 2 new keel pieces and fasten each down to the build board.  Add the frames and/or stringers to one side and plank it.  Do both sides then glue the 2 halfs of your keel together.

[John W E]

hi there
I would strongly recommend that you use a building board - think of something like steel right angled brackets that you can screw onto your frames onto a perfectly level building board and then, fasten your keel in - once your frames are set square and true.  If you are unable to do that the only alternative would be to somehow fasten a piece of aluminium angle iron or straight steel temporarily to your keel to hold it square.   However, I think it would still distort, even when you have your deck edge supporting in.   I presume this is your build which I have had a look at - the other problem to be concerned with building this size of model without a building board is when you skin the model, that may twist the keel if it's unsupported.

http://www.modelboatmayhem.co.uk/forum/index.php/topic,58394.msg609307.html#msg609307

john

[ukmike]

Working from the middle outwards towards the bow and stern.  Glue scrap blocks either side of the keel between where the frames will fit and push the keel straight.  After you've fitted the frames and/or stringers you can begin planking at which point the keel should remain straight. 
Or cut 2 new keel pieces and fasten each down to the build board.  Add the frames and/or stringers to one side and plank it.  Do both sides then glue the 2 halfs of your keel together.

Thanks, but again the construction will not allow me to use that method.

The bow seems to be along the whole length of the keel, not confind to a particular area, just a gentle curve not unlike a beer barrel stave.

Has anyone had any success using water and a heat gun ?

Here's a photo of it.

Mike.
.

[ukmike]

hi there
I would strongly recommend that you use a building board - think of something like steel right angled brackets that you can screw onto your frames onto a perfectly level building board and then, fasten your keel in - once your frames are set square and true.  If you are unable to do that the only alternative would be to somehow fasten a piece of aluminium angle iron or straight steel temporarily to your keel to hold it square.   However, I think it would still distort, even when you have your deck edge supporting in.   I presume this is your build which I have had a look at - the other problem to be concerned with building this size of model without a building board is when you skin the model, that may twist the keel if it's unsupported.

http://www.modelboatmayhem.co.uk/forum/index.php/topic,58394.msg609307.html#msg609307

john

Many thanks John and yes it is the build that you have viewed.
I have a building board which I have levelled in both directions a little longer than the 50 inches or so and have bought some right angle brackets to do as you suggest, ( none of the brackets are square but have reshaped them to be a close as I can get them.
Have screwed them to the board and they do indeed straighten the keel but when I fit the frames and remove it with frames fitted the bow re appears, as it would, due to there being no full length stringers. It's a strange plan with an equally strange construction method, also, all of the notations are in French !!
I do have a 5ft length of Aluminium 2inch angle but that also isn't true.
Frying pan and fire springs to mind.

Hope you are keeping well John.

Mike.

[Onetenor]

Steam or ammonia the keel then clampit  between two lengths of straight timber and leave to dry overnight. If that doesn't work do it again with a thin piece of wood stood in the middle so it bends a bit the other way and let it dry again then when released it should spring straight

[tigertiger]

If I just the keel, with nothing attached yet, I would consider remaking it.

I am assuming that the pieces of ply are in the same orientation. See pic. If this is the case I would flip one piece after cutting, before gluing. See pic. Any tensions balance out. This will be a lot simpler, and maybe even cheaper, than a work around.
I have done similar things cutting long square sections into 4, and re-gluing (before shaping), to make masts that stay straight; no matter how much humidity/temperature/etc. change.
One thing I have learned is that door skins seem to have cupping and bowing built into them, which may or may not be useful. I will not use them, even though off-cuts are an almost free source of wood for me.