Deck Rebuild- 17’ Roth Bilt

Quik Fix 16

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Weight on a small boat adds up. Make it a little stronger than it needs to be , but don't get carried away... They ain't trying to weather the perfect storm, its just a day boat outboard
Ditto and I might add, IMO, Roth Built are quality boats. I've built over 1000 small boats and never anything as nice as a Roth Built. Never got their price either.
 

GLA

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that looks like what was happening with a small novi I had once, it had composite deck , but the framing below was spruce
it didn't have any ventilation and started to rot pretty quick

maybe on the rebuild put some vents in to let it breath some, or use all composite, even then it needs to breath
 

centreville75

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I finished my 24 tcraft deck and transom last year. It had wide box-like fiberglass stringers like yours...but not quite as wide. I used half inch, epoxy coated bottom, and glassed the top. The span between stringers is so close and the stringer is so wide that I have no deflection at all. Turned out fine. But, if I were to do it again I'd use one inch nida core. Just saying

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Dorado

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I decided on 3/4 marine ply. It’s not a rocket ship and I think it’ll benefit from having a thick and solidly built deck.

Given the size of the skiff and lack of airflow I plan to coat underside in resin. If that’s a horrible idea, I’d love to hear it soon!
 

Maze

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The 6 year old and I decided to tear into our Roth project today. The deck only had a couple soft spots. Kind of hysterical given what we uncovered...

I will say the stringer system is more than I expected. I was prepping myself for a few rotter 2x6s.

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Yeah I agree...I’d prolly go 1/2 if it were mine ... maybe with some extra support under the large spans in middle.
That's exactly how my Finestkind17 looked when i cut the deck out except my stringers were broken off the hull and saturated with water
I glassed the bottom of the new floor marine3/8ply with csm and poly still haven't got them in since I moved on to flipping the boat and working on the outside to leave some wait off to make it easier to flip over
 

Cool Boat

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At IBEX show a few years back and went to one of the major core manufacturer's presentations on laminate schedules. One of the tidbits that stuck in my mind is that the stiffness of a panel varies with the cube of the thickness, such that doubling from a 1/2" core to a 1" core (same glass on both sides) increases the stiffness approximately 9X. The attending and presenting experts had quite a discussion on that but finally noted that although the stiffness increased, the ultimate fail strength did not. I note that we replaced a cedar/ply/glass deck on a 28' Herreshoff Rozinante two years ago, went with 1/2" Coosa Bluewater 26, two layers, ounce and a half mat between the layers (assembled wet) and mat plus 1708 on top. This layup schedule was lighter than the original and that wooden boat will see no more deck leaks for the rest of its life. When we were building the Bluewater Baby yacht tenders we had 3/4" Nidacore (actually Polyumac air comb Polyumac | Air-Comb ) with glass on both sides. Virtually bulletproof and even lighter than the Coosa Bluewater 26 which we used in the transoms for extra stiffness. Air comb is a fraction of the cost of the Coosa too. For the small amount of area I would suggest going back with either composite, properly glassed on both sides, and have a permanent deck, never to rot again. We are currently doing exactly that on a 23' DE hull ourselves, as time and energy permits. For any plywood users out there, I believe the Herreshoff Rozinante plywood deck failed due to improper edge sealing. If the edges are allowed to absorb water, the lifespan will be reduced.
 

centreville75

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Perfectly said Cool Boat. For the time and money spent, Coosa or Nida Core, depending on the situation, are the way to go. I'm just a backyard boat junkie and have no professional build experience but many many (just ask the admiral) completed project boats.
 

Cool Boat

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Thank you. Probably not perfect. Going with heavy plywood also adds a performance penalty. Even if a boat isn't a speeder, less weight usually burns less fuel. Centerville, do you have any of your projects posted? Working slower these days, give more time to study other folks projects!
 

cdevil

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They should have used plywood with literally anything covering the underside or foam boat or nidacore.

Composite material has been around for a long time. My 1995 Maritime has a composite transom. Even my whaler has mahogany for it's transom
Has mahogany for transom core? Hard oily woods like that and teak are tough to bond to and very expensive. Plus without back cutting I don't know how you could get a hardwood to follow the complex curves of a whaler's transom. I don't know what year or model whaler you have but the one we redid had plywood in the transom and it didn't cover the whole transom. It had an 8"x 8" block around each pad eye and a 2' x 2' area where the outboard is mounted. The rest was just foam. We got the boat for almost nothing because the previous owner added a bunch of improperly bedded accessories and the transom core rotted away and the outboard moved into the transom well about an inch at speed. It was built with 3 and 5 ply plywood and a thin layup of glass that measured out to 2 layers of 1.5 oz. CSM and 1 layer of woven roving. It would have been fine but somebody had done things like used lag bolts to install a fuel/water separator and just screwed a transducer to the outside. I use fir true marine plywood at 7 plies, no unfilled knots, around $120 a sheet, little less for the 5/8" that's right now redecking my son's Ken Craft. As for decks the JC got 3/4" plywood with mat underneath and 2 layers of 1.5 oz. on top. To me the real trick is to seal all end grains with epoxy and any place you open a hole epoxy that. 16 years and no soft spots. The original 15 year old plywood deck only got removed because the fuel tanks rotted away.
All fiberglass boats are composite. Just means made of more than 1 material, like glass and resin.

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Brooksie

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A bit more work but 2 layers of 3/8 ply = 3/4 and let you stagger the jounts so you won't have cracking at the seams. I did my deck many many years ago, 2 layers 1/2" over 3' spans. Still as solid as the day I put it down. Coat the bottom with resin (epoxy) and the edges good, and it will outlive you. Don't epoxy surfaces you are going to use polyester resin on.
 

leaky

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I haven't had good luck coating things in resin, epoxy included. It tends to "check", basically the grain sorta pops out and exposes the wood. Literally had a plywood structure hopelessly rot on me in about 10 years time on my skiff when I did that. I was a kid then, have since learned.

I have had some luck building up plywood edges with thickened epoxy, multiple sessions until you have some thickness there, then sand it flush, and it lasts. But today, after so many more fiberglass projects, I would just round the edges of the plywood and wrap glass around them.

Really with plywood or anything, the right way is laminate your panels top & bottom, doesn't take much - just a loose weave 6 or 8 ounce cloth and you got a moisture barrier that stiffens up your panels too.
 
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Just coating surfaces in resin doesn't work, look at many European boats that try that. Fails almost right away. I glass both sides of any panel. I use CSM up against the panel for bond and then build from there depending on what the piece is doing, deck, bulkhead, stringer. The epoxy is just to seal end grains. Those get glassed in or covered by what you are installing.
 

Brooksie

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Just coating surfaces in resin doesn't work, look at many European boats that try that. Fails almost right away. I glass both sides of any panel. I use CSM up against the panel for bond and then build from there depending on what the piece is doing, deck, bulkhead, stringer. The epoxy is just to seal end grains. Those get glassed in or covered by what you are installing.
Humm, never a problem coating plywood with epoxy here. Suppose it might be better with mat maybe only b/c you would use 4x the resin? I can look up at the bottom of my deck from the bilge and the plywood looks like the day I rolled the 2 coats of epoxy on.
 

Genius

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Take this as opinion because I have had a very different experience. My 40 year old Jarvis Newman (recently sold/surveyed) had bare wood on the underside of the plywood and was like the day it was built. Glass on top, bare wood bottom and good ventilation doesn't allow water to collect and cause rot. This has been my direct experience and I believe it is a much better way of doing vs encapsulating the wood.
 

leaky

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Humm, never a problem coating plywood with epoxy here. Suppose it might be better with mat maybe only b/c you would use 4x the resin? I can look up at the bottom of my deck from the bilge and the plywood looks like the day I rolled the 2 coats of epoxy on.

My assumption he's not talking epoxy. Basically you don't usually use csm with epoxy, not because it doesn't work rather it just isn't needed because epoxy adheres so well everything can be done with straight cloth or woven - which is lighter and stronger. With polyester, and typically vinylester too, that csm layer being resin rich adheres better.
 
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