To core or not to core?

[SwampSailor]

Originally Posted by Rex Delay

You did say 1" plywood, right? To me that implies a structural member, probably a mast support bulkhead. Be very cautious in modifications, it may be a very significant structural member!

The forward section of the roof over the V berth does provide main mast support, there’s a springboard spanning the area but the plywood in that area is in decent shape and since it’s separated by both head bulkheads I don’t think the salon wall is contributing to the integrity of that component. My Mizzen mast is aft of the salon and separate from the salon roof. The only rig component present in the vicinity of the repair area is the main sheet anchor which is a 1/2” eye bolt. I will have to look a little deeper this weekend to see if there are any structural ties providing anchor support to that bolt.

The timber Mariners are an older vintage than mine, they switched to a solid hull and plywood decking after only a few of the timber versions.

[Hardhead]

Originally Posted by coopec43

Lots and lots of fiberglass factories have gone up in smoke!


I wouldn't dump the water on it. I have a rag as well as the bucket of water so I wet the rag in the bucket of water and lay the rag on the glassing to cool it down well before it bursts into flames. I would not do any glassing just before I knocked off for the day as I like to be there as it is curing. (maybe I am a bit too careful)


Oct 17, 2015 - A Melbourne suburb has been blanketed in toxic black smoke by a fibreglass factory blaze. The fire, which erupted on Saturday afternoon, is now under control but residents in Heidelberg West are being adv....

Oct 16, 2015 - Fibreglass factory fire in Heidelberg West. Print Email Facebook ... Black smoke billows out of a fibre glass factory ablaze in Melbourne's north.

Firefighters are dampening down hot spots after a fire at a fibreglass factory in Dunedin ...

Just do a search on "factory fire fibreglass"


https://www.heraldsun.com.au/news/na...e190167cbef230

Thanks - I'm glad you mentioned the actual fire danger of epoxy kicking off in such a way - I never knew it was possible. Very important to know...

That heavy black fiberglass smoke would make one hell of a boat fire at sea.

[OS2Dude]

From other posts I've read, they use a core between fibreglass not only for strength and lightness, but for a bit of flexibility. Solid fibreglass that is thick will break before it bends, and since a boat flexes as it goes thru a seaway, this may be an issue. Depending on size having a difference in flexibility between the cored/non-cored area may result in cracks at the interface as well.

Not to mention any differences in expansion/contraction as the boat goes through the seasons.

Good Luck.

(I'd re-bed the windows as well, silicon is at best a stop-gap for a leaking window.)

[Thumbs Up]

1' thick ply with glass on one side is not plywood core. It is plywood with a protective glass covering. Grind out the rotten ply until you have a nice bevel (scarf) on the good ply. Make a pattern and glue (with thickened epoxy) the new ply into place. It is ok to use two 1/2", or a 3/4" and 1/4" to get your inch of thickness. The repair should be constructed just like the original only this time well coated in epoxy, No need to re-engineer one small part of the boat. It will be lighter, easier, cheaper, and correct. Any other method is just plain wrong (unless you replace the entire cabin top). You will have a nice flat plywood surface to glass onto. Check those other portlights and make sure there is no unsealed plywood endgrain anywhere. Buy a cheap Harbor Freight moisture meter and check the rest of the cabintop. Chances are that you have similar problems around all of the portlights but if you catch them in time they won't be as big of an ordeal.

[captlloyd]

You could do multiple layups spaced Three or four hours apart with no worries.

[SwampSailor]

Originally Posted by Thumbs Up

1' thick ply with glass on one side is not plywood core. It is plywood with a protective glass covering. Grind out the rotten ply until you have a nice bevel (scarf) on the good ply. Make a pattern and glue (with thickened epoxy) the new ply into place. It is ok to use two 1/2", or a 3/4" and 1/4" to get your inch of thickness. The repair should be constructed just like the original only this time well coated in epoxy, No need to re-engineer one small part of the boat. It will be lighter, easier, cheaper, and correct. Any other method is just plain wrong (unless you replace the entire cabin top). You will have a nice flat plywood surface to glass onto. Check those other portlights and make sure there is no unsealed plywood endgrain anywhere. Buy a cheap Harbor Freight moisture meter and check the rest of the cabintop. Chances are that you have similar problems around all of the portlights but if you catch them in time they won't be as big of an ordeal.

This was my original plan (two layers of 1/2”) and still the one I’m leaning towards, but had the brain storm (or other more smelly brain function) and wanted some other opinions before deciding on final path. I do like keeping things original for aesthetic purposes but if hidden by a veneer thought this might give me best of both worlds...

[Boatyarddog]

Originally Posted by SwampSailor

The forward section of the roof over the V berth does provide main mast support, there’s a springboard spanning the area but the plywood in that area is in decent shape and since it’s separated by both head bulkheads I don’t think the salon wall is contributing to the integrity of that component. My Mizzen mast is aft of the salon and separate from the salon roof. The only rig component present in the vicinity of the repair area is the main sheet anchor which is a 1/2” eye bolt. I will have to look a little deeper this weekend to see if there are any structural ties providing anchor support to that bolt.

The timber Mariners are an older vintage than mine, they switched to a solid hull and plywood decking after only a few of the timber versions.

And again in newer versions, no plywood in cabin tops, side decks, cockpits.
Glass is laid up thick and horizontal struts glassed in under decks, handrails, ect.
Mine is a 1979, built after Far East moved to the USA.
Clair Oberly brought molds from Japan, and manufactured them in Long Beach CA.
The Mast support, transfers weight to the structural bulkheads, as well the 4 corners of the v berth, hanging locker and head.
No compression post, means these structural bulkheads must be in good shape to support the weight and tensioning of the rig.
They are pretty well made, I wouldn't want a cored deck Mariner as most of them have issues.
Also, avoid the wooden spars, unless your a shipwright, or have deep pockets.
A very seaworthy vessel for sure.

[roland stockham]

Yes the people who noted that 1" ply may imply that it is structural are spot on. Before deciding you need to get info about the boats design and what that peace does. 5yrs ago plywood was probably lighter, stronger, cheaper and more stable than composite that may not now be the case but you need to know the engineering requirement of the section before being able to replace it with a different structure.