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Old 12-10-2015, 05:07   #1
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Grp over ply

I'm considering buying an older cat which has a hull made of grp over ply and a deck made of glass over ply.

Does anyone have a view on this set up please?
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Old 12-10-2015, 05:17   #2
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Re: Grp over ply

Difference in GRP and glass?

I mistrust any core, but an argument can be made if it's older and the core is still dry, then it obviously worked?

Best let some experts chime in though, I'm no expert.
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Old 12-10-2015, 05:36   #3
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Re: Grp over ply

Good question! I haven't spoken to the owner yet but this is how it was described in the ad.
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Old 12-10-2015, 07:13   #4
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Re: Grp over ply

Is the binding resin made with epoxy or polyester? Older polyester boats experience delamination of the resin from the substrate after many years. My WEST System boat doesn't have that issue, even after 40 years. If you mechanically tap the surface of the glass with the butt end of a screwdriver, you may be able to hear either the solid rap of bonded substrate, or the hollower sound caused by a "bubble" of air separating the FRP and the ply. If repairs are extensive, it will be expensive in time and treasure. Eventually the "bubble" cracks, allowing fresh water to enter and begin the cancer of dry rot, This often happens from impact damage, say, dropping a winch handle on the deck. With epoxy, it may result in a "star fracture", radiating cracks eminating from the impact site, and less likely to lead rapidly to further damage, but still needing eventual repair. After all these years, I have been totally refinishing my entire boat and found some evidence of star fractures, but none of dry rot in the deck surfaces.
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Old 12-10-2015, 07:59   #5
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Re: Grp over ply

Thanks Roy.

I'll ask when I speak to the seller. The current owner has been living onboard for the last five years so I'm hoping they've kept on top of maintenance.

Having said that you never know! A very good survey will definitely be required if I proceed.
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Old 13-10-2015, 03:41   #6
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Re: Grp over ply

Also ensure the inside was painted with epoxy paint, not house enamel. Rot can start from the inside too.
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Old 13-10-2015, 05:14   #7
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Re: Grp over ply

Pretty common technique in French home built boats. I think RM took it to the mass market level in monohulls.

They tend to be 'heavy' (compared to balsa and foam cored composites). They will have positive buoyancy (in case of a multi) of the hulls.

Your main concern is the condition of the wood. Water ingress plus sub-prime wood material may spell early death.

If only an outer skin was applied, such boats are quite easily repairable too.

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Old 13-10-2015, 08:37   #8
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Re: Grp over ply

barnakiel, I am confused by your comment regarding coating the interior skin with epoxy. My experience has demonstrated that it is because the entire surface of the boat has been sealed with epoxy, followed by paint, that the boat has endured for so many years in excellent condition. Sure, there is some additional weight that results, but it is certainly negligible in the large context, and the tradeoff is superior lifespan and moisture protection (and termites are definitely disadvantaged in gaining a foothold).
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Old 13-10-2015, 11:56   #9
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Re: Grp over ply

GRP (Glass Reinforced Plastic) and 'glass (fiberglass) are the same thing. Glass over plywood is a good, cheap way to build. And was particularly favored by home builders. So quality varies greatly.
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Old 13-10-2015, 12:11   #10
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Re: Grp over ply

Quote:
Originally Posted by Roy M View Post
barnakiel, I am confused by your comment regarding coating the interior skin with epoxy. My experience has demonstrated that it is because the entire surface of the boat has been sealed with epoxy, followed by paint, that the boat has endured for so many years in excellent condition. Sure, there is some additional weight that results, but it is certainly negligible in the large context, and the tradeoff is superior lifespan and moisture protection (and termites are definitely disadvantaged in gaining a foothold).
Yes. I was not too clear.

What I meant is that when the interior is epoxied it may be at times harder to judge the condition of the wood. (Depending on what kind of epoxy was applied).

I would be in two minds whether I prefer to have a visible damage from moisture or an invisible one.

This in turn leads to implications of (our choices of) what class of plywood was used so that it needed sealing/painting on the interior side. There are various grades of plywood and in my opinion only the top grade should be used for grp over ply (for marine / offshore use). This grade may be painted over for aesthetic reasons but face sealing it is not required otherwise.

Very likely coating in clear and UV stable epoxy ticks all the boxes.

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