Reverse chine and spray rails

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pee wee
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Re: Reverse chine and spray rails

Post by pee wee » Mon Feb 05, 2018 12:15 pm

My thoughts are that the shape is not too bad, although I do think flat would be better (I'd try to rig up a cut on the tablesaw or use a planer), and that it would be okay as a core or filler for a larger chine shape, but it is fairly soft so I'd want to encase it in resin. One thing that just occurred to me is that it is not going to take a curve, you're going to have to kerf it for anything more than the gentlest curve.


Hank

silentneko
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Re: Reverse chine and spray rails

Post by silentneko » Mon Feb 05, 2018 12:39 pm

I plan on encapsulating it in resin, heating the wood first so it will draw it in better. Then wrapping it in 6oz woven. No matter what wood I chose I think kerf would be needed, it's hard to bend a thin and wide piece. The SYP and cedar I played with both cracked without them.

It's either this, or reducing them to 0.5" x 1.5" and using cedar or SYP, it's just a bit more work.
Built: 15ft Skiff, 16ft Skiff, Modified Cheap Canoe.....FS17 coming soon!

Woodenyouknowit
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Re: Reverse chine and spray rails

Post by Woodenyouknowit » Mon Feb 05, 2018 7:29 pm

I'd just cut it into pieces at 45 deg angle on both ends, then matchbook them together to fit the curve alignment. Bond matchpieces together with gelmagic, then fair, sand, and cover with the fiberglass afterwards. No need for steaming or kerfing to make it bend.

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Re: Reverse chine and spray rails

Post by narfi » Mon Feb 05, 2018 8:18 pm

Woodenyouknowit wrote:
Mon Feb 05, 2018 7:29 pm
I'd just cut it into pieces at 45 deg angle on both ends, then matchbook them together to fit the curve alignment. Bond matchpieces together with gelmagic, then fair, sand, and cover with the fiberglass afterwards. No need for steaming or kerfing to make it bend.
Sorry I am too dense to follow what you are describing here..... It is a problem I have been pondering though, you have any napkin sketchs to help me understand better?

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Re: Reverse chine and spray rails

Post by Browndog » Mon Feb 05, 2018 10:52 pm

My interpretation is that you don’t have to use a continuous piece of trim to make the reverse chine. Cut the long length into smaller sections then join them at the curves. That is how I did my rubrails on my brother’s boat.

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Re: Reverse chine and spray rails

Post by BarraMan » Tue Feb 06, 2018 5:59 am

Silentneko, my boat is 22’. My chines/strakes are made from single lengths of timber, bent and twisted to follow the hull without steaming or kerfing, and no cracking of the timber. It can be done!

Unfortunately, I don’t have time to give any details now as I have to drive 1000 miles in the morning to get the boat custom fitted to its new trailer. However, I will give more details of how I did it over the weekend.

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Re: Reverse chine and spray rails

Post by silentneko » Tue Feb 06, 2018 6:45 am

I'm sure it can be done in a single length with a more stout profile, but so thin and wide I'm hearing cracking once I try to stress the small sample sections towards the curve by the bow.

Barra, what kind of wood did you use?
Built: 15ft Skiff, 16ft Skiff, Modified Cheap Canoe.....FS17 coming soon!

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Re: Reverse chine and spray rails

Post by BarraMan » Tue Feb 06, 2018 7:19 am

I used 42mm square stock Hoop Pine No. 1 Clear Timber cut on the 45 degree angle for my strakes and the basis for my reverse chines.

“Hoop Pine is an Australian native pine tree. Araucaria cunninghamii (which is also often called the Moreton Bay Pine) is native to the rainforests of northern NSW and southern Queensland. Hoop Pine also occurs in the mountain regions of Papua New Guinea. It is almost identical to Klinki Pine, a tree native to PNG although its density is a little higher. The trees can grow to 60 metres high, and can live for up to 450 years. At maturity, the seed cones release nut like seeds which are said to be edible. According to "Wood In Australia" by Keith R Bootle, hoop pine texture is very even, gain is straight and growth rings are inconspicuous. It has a green density of 680kg/m3 and an air dry density of about 530kg/m3. It is easy to work, but it does not steam bend satisfactorily. Hoop Pine takes glue well.
We stock DAR (dressed all round) #1 clears in lengths to 6 metres.
Our suppliers definition of #1 Clear is as follows:-
This is the premium grade, Araucaria Clear No. 1 is completely free of defects on all sides except for the occasional blemish that can be machined out. It is free of all defects.
What this definition does not promise is that the grain will be completely straight. If you also require that, then please tell us and we will try to select pieces which meet your requirements. Depending on how much effort is involved, we may have to ask for an extra charge to cover the work involved in doing this.
Our Hoop Pine comes exclusively from plantation grown trees. Hoop Pine is almost identical in strength and flex to Douglas Fir (Oregon Pseudotsuga menziesii ) which is widely used in boat building. Hoop Pine has been extensively used in Australian boatbuilding (and amateur aircraft construction) as it is readily available in high quality lengths.”


Hoop pine is an Australian native timber but I am sure similar wood must be available elsewhere. You have to use the good stuff - with no flaws in it and straight grained.

I radius’d the sharp edge and covered the timber with two layers of 6 oz biax tape - then sharpened them back up with epoxy/woodflour. I built the reverse chines with epoxy/woodflour before taping.

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Re: Reverse chine and spray rails

Post by silentneko » Tue Feb 06, 2018 10:02 am

There in lies the problem, our wood is junk here, lol. As a last effort I drove out to a lumber yard I had used before. Outside of very rough sawn cedar they stopped stocking most woods outside of what the builders like. They had some spruce, but only 1x stock.

I was at a different Lowes this morning and looked at that molding again. It will not take a bend! I flexed a 7ft section about an inch in the middle and it cracked.

As suggested before, if I'm going to buy it and modify it for my use, I guess I might as well just cut them myself. So I'm leaning towards using just pine and making them 1.5" x 5/8".
Built: 15ft Skiff, 16ft Skiff, Modified Cheap Canoe.....FS17 coming soon!

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Re: Reverse chine and spray rails

Post by Fuzz » Tue Feb 06, 2018 2:31 pm

With the problems you are having getting good wood I think I would just plan on kerfing it. It is all going to be glassed in so it should not make any difference.

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