Curved Plywood Bow seats -- Rotted & Restored

[wellcraft-classic210]

I have a 1995 SeaRay Signiature 180 that had rotted wood in the curved Bow seats. I searched the internet repeatedly for tips & methods but I was not able to find much on the particular subject.

What I did know was that I needed an 8 inch Radius on my tightest bend and their were other larger radius curves as well. I was also aware that a layered lamination when done properly will tend to hold the exact shape -- VS a steamed bent section of wood will tend to have some spring back.

I own a planer and tried planing a few scraps of Plywood to see how flexible and resilient the were. After some trial and error I found that sections of 3/8 CDX plywood at .150 in thick that has about .100 long grain and .05 cross grain worked well. I chose this material as I already had it on hand.

I could have used marine plywood mainly for cost reasons and knowing a lost of material was going to be wasted. Bending plywood is another option but it would have still required thin laminated layers to meet the radius requirement and provide a stiff substrate when done.

I made a template of the hull section in the bow that the seats needed to mate to and then formed a bending jig for the inside curve that tad the same shape with 1/2 inch removed to allow for the laminated material thickness.

The sections were planed to .150 thick from 2 sheets of very clean 3/8 cdx plywood with no knots in the outer surfaces but they they did have some voids internally.

After selecting 6 of the best sections with the least voids I applied epoxy resin and then peanut butter ( thickened resin ) in the remaining voids. I started clamping in the middle of the largest curve and worked may way out in both directions to reduce gaps in the layers and left the parts clamped for 24 hours. The first one did have a few small separations and some spring back so I added more resin & clamp time on the second which made for a very tight joint.

After using the old cushions as a template and carefully checking the fitment and through bolt locations each one received 3/16 routed edges radius's and 2 more coats of epoxy on the outside and through holes -- Any small gaps in lams were also filled with epoxy. The bolts were 10-24 stainless steel flat heads with 1/4 washers threaded into tee nuts pressed into the opposite side.

The foam was attached to the plywood using 3m #77 spray adhesive. A thin player of plastic sheet was was spot glued using the #77 as well to allow the vinyl to slide on the foam better and avoid wrinkling.

The vinyl was stapled using stainless steel staples. The hand stapler would not drive them all the way & they needed to be hammered into their final resting place.




Some pics below.

ROTTED WOOD



BENDING FORM ( SCRAP MATERIALS )



PLANED PLYWOOD




EPOXY


CURVED PLYWOOD AFTER LAMINATION



READY FOR ASSEMBLY

 

[jimmy wise]

they make bendable ply

 

[Ned L]

Very nice work with great results!

Can't say I've ever thought of putting plywood through a planer before (something for me to keep in mind though). I'm not sure I'd want to take it down to the point of hitting the glue though. That's got to be a bit rougher on the blades than I would like, that resorcinol is hard stuff.

 

[Woodonglass]

Uhhmmm, Have you heard of "kerfing"??? That's the typical and recommend way to bend thicker sheets of plywood and then use thickened resin to fill the kerfs. Lot's less intrusive on your planer blades!!! Looks like it worked out for you though!!!

 

[wellcraft-classic210]

Gents
Thanks for the thoughts -- Its interesting to see how others would resolve this. Each way has its own set of merits & detractors.


I tried a kerfing sample but was not thrilled with the result. It needed a LOT of cuts to make the 8 in. radius and seemed structurally weaker. I suppose filing the voids and using cloth on the outside would help with strength -- But then it seemed to be about the same or more labor with more glue & cloth usage.

FYI --
The planer blades are fine as the steel is much harder than the glue // although I agree it does most likely increase the wear rate slightly--// Cutting laminated boards is a common practice at my shop.

 

[JaCrispy]

Nice job. Luan wouldn't make that bend? And yes, kerfing requires a ton of cuts for it to be uniform, otherwise it can look like a bunch of angles.

 

[wellcraft-classic210]

Good question on Luan -

That was something I looked at also- 1/4 luan will not make an 8 inch radius. I think the main reason is that its 3 layers which give it strength and also limits bending.

I suspect I could have planed & used it in place of the CDX. The CDX decision based on materials I already had on hand.

 

[wellcraft-classic210]

duplicate

 

[Woodonglass]

Hmm, well I never had any issues using the kerf method in over 40 years of woodworking. Matter of fact one of our master builder members just did a similar build using the kerf method. This might be of interest . Just goes to show you there's more than one way to skin a cat and to make a curve. Both ways work fine!!!

 

[jigngrub]

Kerfing is a great way to make saw dust for the rose bush beds!!!

... and it helps bend plywood too!

There's a bunch of different ways to skin a catfish. Some people start at the head, some people start at the tail... some people fillet it first. But in the end you get a nice fish dinner... I like mine with hush puppies, tater salad, and baked beans most of the time. Other times I want cheese grits and cole slaw

 

[wellcraft-classic210]

Gota love Frisco boater -- I admire his gift for explaining things and what seems to be an unlimited amount of energy for projects.

Nothing beats your 40 years of experience and I wish I would have found that video earlier.

( Although I still may have gone the same route.-- As in stubborn Irish )

I did not expect this project to get debated so much -- Just wanted to share it.


Here is some added info on bending woods from Rockler and what I thought was meant by 'the kerf method'

http://www.rockler.com/how-to/bending-wood-part-i/

 

[wellcraft-classic210]

Wood on Glass --Nothing beats your 40 years of experiences and I wish I would have found that video earlier.

Gota love Frisco boater -- I admire his gift for explaining things and what seems to be an unlimited amount of energy for projects.

( Although I still may have gone the same route.-- As in stubborn Irish )

I did not expect this project to get debated so much -- Just wanted to share it.


Here is some added info on bending woods from Rockler and what I thought was meant by 'the kerf method'

http://www.rockler.com/how-to/bending-wood-part-i/

 

[Woodonglass]

Yep, that's kerfing plywood and works prfectlly well. Fill the kerfs with thickened resin and lay some strips of CSM and she'll be as solid as she can be. The tighter the curve needed the deep and closer the kerfs need to be. As stated, There's lots of various methods to accomplish the same thing. Your's worked fine and is perfectly acceptable. Not knocking it at all. That's what's great about this forum. We all get to see and share different methods of how "Git er Dun!!!!" Thanks for sharing yours!!!!

 

[jimmy wise]

wow bendable ply is available and you can bend it and glue it up...

 

[wellcraft-classic210]

Jimmy -- Thanks for your input.

This project had a requirement of 1/2 inch thick plywood bent to an 8 inch radius?

I did see an study this link -- http://www.columbiaforestproducts.co...nding-plywood/ but the min radius is 12".

Are you aware of any 1/2 bending plywoods that will meet that spec? Cost is a consideration also.


added note
I did some more research on the www & found many of the bending plywoods are not rated for exterior use -- have very soft cores and are very prone to rot.