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Old 16-07-2015, 16:44   #1
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How to replace core in recessed area?

I need to replace the rotted plywood core in a recessed anchor well area of the foredeck as per the pic below:



I'm assuming that the entire lump of plywood will need to be replaced. the thickness of the ply is somewhere between about 1/2" to 3/4". I plan to cut two or three inches in from all sides to facilitate reattaching the old skin (or maybe even laying a new one as I want to shift the position of the winch while I'm at it) which will probably mean that the ply will extend beyond the area of the cutout.

What's the opinion on the best way to replace the ply if the cut away opening is smaller than the area. I'm thinking scarfed sections or building up using layers of thinner play with non overlapping joins??

All advice appreciated.
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Old 16-07-2015, 17:32   #2
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Re: How to replace core in recessed area?

Do you mean the core inside the triangular foredeck piece? I would try it from inside if possible. Often the core up there starts maybe 3" from the toerail.
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Old 16-07-2015, 18:20   #3
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Re: How to replace core in recessed area?

I'd use a die grinder with a cut off wheel and cut through the top lam. Peel it off and maybe try to save it as 1 big piece. Next cut through the ply a few inches in from you first cut throught the lam, dig the old ply out leaving the bottom (inside) layer of lam intact. Scarf the old ply core edge with a angle grinder back 2-3 inches to the lam edge. Put in a new piece of ply with the same scarfed edge angle, gule the old top lam back on......
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Old 16-07-2015, 18:35   #4
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Re: How to replace core in recessed area?

Reefmagnet,

It seems it's time for the ice pick. I'd really want to learn what the wood there by the hawse hole is like. If that's just plain plywood, Guy's method won't work, as there is no laminate there.

If you're concerned about the strength of the repair after you're done, you could epoxy in strong cleats at the fore and aft edges of the anchor locker, up under the old, but still solid timber. Also, I'd epoxy cleats inside from the toe rail, both sides, which will give you somewhere to screw as well as glue in the new piece. (Hope, hope). So, youre first task is to determine how far the rot extends. Can you tell if it was marine grade ply that went in there? (It has more plies, and is stronger, and usually does not have any voids at all.)

In any event, I hope there's enough solid ply left for a small replacement, with a hawse hole liner in your future.

If the repair cannot be effected using the old ply, talk to someone who knows what they're doing--at that point the help and advice of a professional would be welcome.

Good luck with it.

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Old 16-07-2015, 20:27   #5
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Re: How to replace core in recessed area?

Thanks guys. While it would be nice to do from underneath, the anchor locker door is too small for me to get through (I need to go on a diet!). It doesn't worry me doing it from the top as I have to repair the bottom and top layers anyway because the current winch wasn't the original and the hole is one big mess (hence the offset piece of wood sitting on top). I've got the fibreglass bit covered, I just want to make sure the core remains rigid enough to support the winch under load (which "bounces" currently as the anchor is raised due to the links running over the small anchor roller and rotten core) and won't likely separate as a result of this loading in the future.

That's why I'm assuming I'll need to replace the whole lot as I suspect there's a nice triangle of iffy plywood in there because when I replaced the foot switch a while back, the wood was mushy around it as well.

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Old 16-07-2015, 20:30   #6
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Re: How to replace core in recessed area?

There are tremendous forces placed on the windlass so build it strong.
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Old 16-07-2015, 20:35   #7
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Re: How to replace core in recessed area?

Yes, it's one of those old school winches that has no problem skull-dragging the boat. The manual says you only need to give it a rest if the motor stalls. Wife was worried it would head for the deep whilst raising the hook with her on the end of the switch lol.

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Old 16-07-2015, 22:15   #8
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Re: How to replace core in recessed area?

Quote:
Originally Posted by Reefmagnet View Post
I need to replace the rotted plywood core in a recessed anchor well area of the foredeck as per the pic below:



I'm assuming that the entire lump of plywood will need to be replaced.
Were it me, I'd replace it all, as long as you're going do be doing major surgery. Might as well only have to open it up once.
Plus odds are, even if some of the perimeter section of wood isn't rotten now, it'll at least be damp, as well as filled with spores (the precursors to rot).

the thickness of the ply is somewhere between about 1/2" to 3/4". I plan to cut two or three inches in from all sides to facilitate reattaching the old skin (or maybe even laying a new one as I want to shift the position of the winch while I'm at it) which will probably mean that the ply will extend beyond the area of the cutout.
Your plan for where to cut sounds reasonable enough, assuming that:
- It's not solid glass laminate in the area which you're proposing to cut.
- If there is wood out that far, that you have a way for removing it (all), through the sized cut which you're intending to make.

Ah, & - Plan on tossing the old, top skin.

One other thought in terms of putting a new "lid" back on, once you're done replacing the wood. Is to think through whether you'd be willing to extend the replacement glass layers out a bit further than just where the new lid, technically "has" to be. And to also add on a couple of extra layers of glass above & beyond what's called for as well.

My thinking is that since that part of the boat's such a high load area to begin with, & that glass & resin are inexpensive... Plus you get a much wider bond line/bonding area for the new material by "overbuilding" it that way.

What's the opinion on the best way to replace the ply if the cut away opening is smaller than the area. I'm thinking scarfed sections or building up using layers of thinner play with non overlapping joins??
This sounds like a fairly decent idea to me. And if you want to pretty much make the new wood which you're laying in "immortal". Get some 1/8" (3mm) Marine Ply, wet it out with epoxy, & then put it under vacuum until the epoxy cures.

I say 3mm ply, as it's easier to bend, if you have to flex & contort it a bit In order to get it into the hole. But thicker stuff 4mm - 6mm+ can work too.
Although, with thinner woods, you can pretty much pull epoxy completely through the wood. And in so doing, saturate all of the fibers with resin. It helps with moisture resistance, plus makes it a good bit tougher & stiffer.

Also, if you want to take the time & make it bullet proof. It wouldn't hurt to put a layer of heavier weight woven cloth, or Triaxial cloth, in between each layer of wood.

BTW, have you checked the integrity & moisture levels of the/any core near where you know that there's something obviously wrong? Say, within a few feet, give or take. Ditto on the integrity of the skin to core bonds in other deck sections in that general vicinity.
- Such could be especially important, given that you state that the deck pumps when hardware there is put under load. Which could, cause some skin de-bonding elsewhere. And that gives moisture an easy pathway to travel down.
I hope not, but, it bears checking.

All advice appreciated.
PS: On the triangular section being fixed. It'd also likely be a decent idea to both, make a template of where everything is located now, in detail. As well as to make yourself a drawing/"blueprint" of the current layout, with measurements on the locations of, & sizes/dimensions of everything also.
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Old 17-07-2015, 10:40   #9
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Re: How to replace core in recessed area?

When performing similar work, we have found a Fein Tool
Multimaster (vibrating saw) to be very useful.

The Fein tool or one of the copies of same is capable of
making flush cuts through or under an angled joint, something
no other tool, to my knowledge, can do.
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Old 17-07-2015, 15:07   #10
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Re: How to replace core in recessed area?

I would cut the whole triangular section out and throw it away. Then in the comfort of a workshop or garage I would fabricate a new triangular section using core material of choice. Then bond the fabrication into place with several layers of double diagonal tape around the perimeter. Make sure the edges of the core material in the fabrication are not exposed.

Very important is to also protect the core material at any bolt holes. Before installation use a 1" hole saw from underneath to remove the core material at bolt hole positions leaving the top skin in place. Then fill that 1" hole with high density epoxy filler.
Then drill the smaller bolt holes through the filler. You will see the positions where the pilot hole was.

Use only epoxy systems such as West. I've done prefabrications like this and it is far easier than trying to fiddle around on the boat. I've used balsa core with success but make sure the core is not exposed whatever core material is used.

Read WEST SYSTEM guides available online
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Old 17-07-2015, 17:21   #11
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Re: How to replace core in recessed area?

Thanks again guys. Fortunately the rest of the boat is solid glass utilising strategically placed foam cored reinforcements and stringers to stiffen the deck which is pretty much bullet proof in respect to resisting water ingress damage.

I'll get to look in the anchor well shortly to see if the ply is a nice triangular piece. Good advice about checking that I don't cut beyond the edges of the ply! From the info here, I reckon I'll go with the layers of thin structural ply glued with slightly thickened epoxy and separated with a layer of light weight cloth if I need to go the segment piece path.

Re the multi-tool. I have one in the toolbox and in the last week I used it for removing old sealant, breaking the sealant bond between various pieces of deck hardware and the deck, removing crumbling fireproof material (which was actually a ceiling tile) from the engine compartment, cutting out a rotten plywood shelf in the galley, breaking the seal around a portlight, cutting a seized stanchion mounting bolt passing through the deck and right beside a bulkhead and, finally, delicate cutting of some addition fibreglass and coring on the underside of the deck to allow the fitment of decent sized reinforcing plates (to replace the original penny washers) for the stanchions. A most handy tool indeed!
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