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Rotten plywood in stern hood
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Author:  skidaddytn [ Fri Sep 19, 2014 9:55 pm ]
Post subject:  Rotten plywood in stern hood
Wow.. my boat is only an '07 and I set out to re-stitch a small part of the top seam of the stern vinyl (over the engine) where the threading is coming undone (maybe an inch or so). In order to do a proper seam repair you need to unstaple the vinyl and get at it from the back side. I removed the nylon lock nuts on the bottom of the hatch and pulled off the cushion to find problem #2. The ding dongs over at Four Winns decided it would be a good idea to use plain plywood (repeat... non-treated plywood) inside here! This is an area designed for wet people to lay on and sun-bath, put on the skis, etc... Very cheap of FW. Well... in one place it had rotted so bad that it literally turned funky colors and was crumbling. The staples near the affected edge at the stern no longer have anything left to bite into... The piece of plywood is custom cut (with curved edges and 4 threaded attachment studs with round bases that seem to be glued on with liquid nails. Can I order this piece of plywood or is my only option to make my own?
Author:  NiagaraChillin [ Sat Sep 20, 2014 12:10 am ]
Post subject:  Re: Rotten plywood in stern hood
I would see if you can remove it intact and use it as a template to make your own. Either marine plywood or a thick piece of starboard.
Author:  LouC [ Sat Sep 20, 2014 12:40 am ]
Post subject:  Re: Rotten plywood in stern hood
I had to replace mine too back in '08. The only part that rotted was by the hinges in the back. I uses it as a template and made a new one out of pressure treated plywood. Still holding up well.
If you use PT plywood make sure to insulate the aluminum hinges (if they are alu) from the PT wood because they will tend to corroded faster if its in a damp climate.
You can also use regular exterior ply and coat it with CPES (thinned epoxy) or even regular epoxy. I had to fix my sun pad in a weekend so I went with the PT wood as it was faster.
Author:  skidaddytn [ Sat Sep 20, 2014 12:03 pm ]
Post subject:  Re: Rotten plywood in stern hood
Where would you go to get marine plywood? Is it better than treated plywood from hd or lowes?
Author:  LouC [ Sat Sep 20, 2014 1:04 pm ]
Post subject:  Re: Rotten plywood in stern hood
For this marine ply is really not needed and it's no more rot resistant than exterior ply. It is stronger but that is more for when you are redoing a transom or stringers. PT ply is the easiest thing to use for this project.
Author:  fi.na.tine [ Sat Sep 20, 2014 3:53 pm ]
Post subject:  Re: Rotten plywood in stern hood
I wonder if coating the wood with that never wet paint would help?

http://www.neverwet.com/anti-wetting.php

My guess is that it would protect the wood but with giving that moisture no where to go - it may create mildew or mold in the foam.
Author:  Graham R [ Sat Sep 20, 2014 5:33 pm ]
Post subject:  Re: Rotten plywood in stern hood
LouC wrote:
For this marine ply is really not needed and it's no more rot resistant than exterior ply. It is stronger but that is more for when you are redoing a transom or stringers. PT ply is the easiest thing to use for this project.


Yes, for most purposes marine ply is an extravagance; marine ply is basically ply with a guaranteed lack of voids.
Author:  NiagaraChillin [ Sun Sep 21, 2014 4:42 pm ]
Post subject:  Re: Rotten plywood in stern hood
Graham R wrote:
LouC wrote:
For this marine ply is really not needed and it's no more rot resistant than exterior ply. It is stronger but that is more for when you are redoing a transom or stringers. PT ply is the easiest thing to use for this project.


Yes, for most purposes marine ply is an extravagance; marine ply is basically ply with a guaranteed lack of voids.

The best anti rot treatment for new good quality ply is to soak it in a MDI/ solvent ( acetone or methylene chloride) mix; cruude MDI works fine, it's the isocyanate component of 2 component rigid PU foam. it soaks right through, the MDI bonds to any OH group and the material becomes essentially a flexible thermoset with nothing for fungus to eat !


Or skip the chemistry lesson and get the marine plywood :roll:
http://www.homedepot.com/p/Unbranded-3-4-In-4-Ft-x-8-Ft-AB-Marine-Plywood-726540/202084532
[url]http://www.overtons.com/modperl/product/details.cgi?pdesc=Greenwood-PlyDek-XL-Plywood-Panels-4-x-8-5-each&i=76127&s_kwcid=msnsearch_marine%20plywood_&device=c&network={network}&matchtype=e[/url]
Author:  LouC [ Sun Sep 21, 2014 6:25 pm ]
Post subject:  Re: Rotten plywood in stern hood
Trust me if you coat regular ext ply with CPES that stuff is so nasty that the rot spores will pick up and MOVE AWAY!!!!
I didn't have time to get involved in putting 2 coats of that stuff on when I had to fix mine so I took the easy way out with the PT.
Author:  Graham R [ Mon Sep 22, 2014 2:48 am ]
Post subject:  Re: Rotten plywood in stern hood
Why use marine plywood, which as Lou indicated is no more resistant to rot than exterior ply, and pay more for a product that performs the same in this particular application ? If you want either (both) to rot, don't treat them with anything . "Chemistry lesson" deleted.
Author:  LouC [ Mon Sep 22, 2014 5:37 am ]
Post subject:  Re: Rotten plywood in stern hood
I think the Greenwood XL stuff is treated, so that would be a good choice (Grady White uses this stuff in their boats, one of the few that still uses wood). Like I said, that stuff is fine for structural stuff like decks and transoms, but for a simple sun pad job, just use PT stuff and make sure to isolate aluminum hinges from the PT.
Author:  skidaddytn [ Mon Sep 22, 2014 1:38 pm ]
Post subject:  Re: Rotten plywood in stern hood
Thanks for the advice guys. Fortunately, the design is such that there are 2 layers of plywood. The bottom layer (which connects to the hinges) has a black (probably flame resistant) layer of material stapled so that the staples are not visible from the engine compartment. There is a middle layer of fiberglass for the walk-thru transom side, and then there is another layer of plywood which serves as the backing for the cushions. The 2 layers of plywood are bolted back to back. I did not see any mold on the bottom layer, but it looked to be the same kind of plywood. I guess maybe I should poke around into the fire resistant material near the hinges to double check as it could be hiding on the underside of this layer as well? It is my opinion that the walk-thru transom contributed to the early death of that plywood as having snap in carpet with fiberglass underneath holds in moisture. I hate the walk-thru transom. We almost never use it and the hinges are a knee buster. I'm considering removing the fiberglass/hinges and bolting the walk-thru down. Although I worry the split cushions may not line up flush anymore.
Author:  LouC [ Mon Sep 22, 2014 2:34 pm ]
Post subject:  Re: Rotten plywood in stern hood
Post a pic of what you have. It may be easier to fix than you think. I'm not a fan of those walk thru transoms because it makes the engine compartment very tight for servicing with all that molded in 'glass on the sides. With the old style sunsport seating you can re design it to come apart easily like I did...
Author:  skidaddytn [ Mon Sep 22, 2014 2:44 pm ]
Post subject:  Re: Rotten plywood in stern hood
Don't have a picture of everything mentioned, but I did snap one of the rot. You can see that it is approximately 1/2" plywood, with some water stain (this area is still strong though), and rot at the edge... There is water stain on the bottom layer of plywood as well, but I don't think this is structurally a problem. You can also see the bolts coming through that will need to be put in the exact place on the new piece of plywood. Also you can see lots of unused holes and a few oval cuts, that were put there possibly as a drain, or because they re-purposed plywood that was previously cut for something else.

Image

Here's a photo of what I was trying to repair which will now have to wait:

Image
Author:  Graham R [ Mon Sep 22, 2014 4:13 pm ]
Post subject:  Re: Rotten plywood in stern hood
On my third Four Winns now, generally very good design at the design stage, lovely looking boats but moderate to sometimes good build quality in the application stage .

Starboard as a load bearing material; forget it, nothing bonds to it, it's a thermoplastic and creeps like hell under load. Sorry about the materials science lesson.

Plywood as the "filler" in a high load item sealed item . Great until water ingress is possible as the result of a big unsealed hole. Sorry about the lesson about how to prevent wood rot.

All those awful self tapping screws, undersized often and if not over tightened so they strip out the GRP. or starboard, Sorry about the basic materials science / engineering lesson.

I've had a bad, bad day , no offence meant to anyone here a all !

I thought it was bad before, but combine the mentality in a factory in 2008 when redundancies were on the line, with very odd wiring systems and installing a sensitive Volvo Penta EVC controlled system , well it's a nightmare that deserves a film making about it.
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