Non Cored GRP deck soft...what about this for a fix?

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yourmomm

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Hi. My 50+ year old swedish storfrida 25 has a soft as hell deck. All over, in heavy traffic areas, there's flexing. It's not cored, either with balsa or ply (I've checked). It's just a 6mm grp/csm top layer, 12mm gap, then a 3mm grp cabin roof (no csm). Weird construction. Everything else is heavily built+++, and these boats have happily gone around the world...

So, since accessibility is an issue from down below, and to keep things simple, I was just wondering about this fix:

https://youtu.be/65PoGQ7F7dc

What do you all think?

Thanks for your advice.
 
I think you should summarise what's in the video rather than expect people to sit through it.
 
A minute was enough to show the method. Seems effective so long as the added weight does not cause problems and so long as you are confident that you know of all potential holes in the lower layer.
 
Solid laminate tends to be a bit bouncy. A quick search indicates this might be a common feature of this particular deck design.
I would only go for the fix if I was totally convinced I could not live with it and, perhaps, the outer edges of the panels were showing signs of distress.
 
Unfortunately.. as doug748 says.. solid laminate does tend to be a bit bouncy. I have a similar construction on my 1972 Contest 33, which for those who don't know is a Dutch boat built by Conyplex.

The boat is built like the proverbial brick $h1te house, but not a sq inch of balsa core anywhere I'm afraid. The construction of the deck though is more than adequate, and along with the inner deckhead liner (which is beautifully done) at no time have I been concerned about its construction/strength.

Unfortunately a lot of these older boats had their wiring bonded in between the deck-head liner and the underside of the deck... that's something to consider if planning structural alterations..

The only problem I find is condensation on the liner in the wet winter months in Cornwall if I stay on board.
 
As others have said, common to have slightly "springy" decks on some older boats without balsa or foam cores in decks/coachroof. Assuming no signs of stress cracking, a small price to pay for avoiding the problems core materials can cause. A rotten and saturated balsa core is a truly horrible thing to have to deal with, and is all too common.
 
The other way would be to created some ribbing under the deck, perhaps using glassed in balsa strips or glass fibre rope
 
PCUK said:
Can't you fill it with foam? As long as it's well sealed and water-tight there won't be a problem.
Click to expand...
Expanding foam can exert a lot of pressure over an area - you might find the thinner inner headlining moulding distorting. Also any cables will be sealed in forever, no chance of pulling new cables through later.
 
Thanks all. Yep I agree a minute is all you need.

1. Cardinal yep any amount of weight up high is not good...but i'm thinking the difference in weight between this and gop reinforcement (assuming i wanted to wreck the cabin top layer, to get to the deck from underneath) would be negligible...?

2. Doug748 There's bouncy, and then there's weak! The deck stepped mast has already had a fold in the deck at some point I see, and has been heavily reinforced underneath, with solid mahogany and steel supports. It wont be moving again in a hurry. Thanks for the heads up about looking for distress at the outer panels (I'm thinking you mean the deck/hull join? I'll do this, and then decide whether I can live with it...

3. Thanks saxonpirate. This is my first GRP boat (a Colin archer design though, same as my two wooden boats, before), so perhaps this flexing is normal after all...it doesn't inspire confidence in a storm, though, and it's all I'd be thinking about in a blow. I'll check the deck/hull join for signs of distress, as suggested by doug748 and jwilson.

4. Thanks jwilson, will check for that stress cracking.

5. Savageseadog I'd have to destroy the inner layer to reinforce the deck...something I'm not to keen to do.

6. Pcuk yep I was thinking about this alternative too (I don't think there's any wiring left in the deck cavity, if there ever was any there. It would be good heat insulation too! But I'd worry about eventual water ingress (inevitable in a flexing deck around through deck fittings I would say) and then being stuck with a rotten core which would be very destructive to repair. At least with reinforcing with gop from underneath, you'd kill the flexing...

I think overall, it seems that the best alternative is to look for stress cracking, and make sure it's safe in a blow (maybe get a surveyor to look at it, even if I can't find any cracking: it would still be cheaper, if it meant I can avoid the repair) and then try and get over my anxiety about it...
 
The method in the video will not work with your decks.

Would it be possible to cut strips out of the inner moulding, then fit 12 mm or 14mm thick wood battens to support the deck using an epoxy mix. Then hold the inner moulding in place using decorative teak strips screwed to the battens.
 
I really don't think that fix is appropriate on your boat unfortunately. That void will have years of the dust that inevitably gets in everywhere, and combined with condensation I'd expect to find a bit of mildew as well. Not a good way to get a strong bond.

You don't really need to 'do' the whole roof to substantially stiffen it, so I'd have a look at carefully cutting out a panel in a pleasing shape which can be put back and covered with a fairly simple trim. If you could get as close as say 120mm from the edges, that would be more than good enough. 12mm Airex or similar with 1-2mm of glass would be plenty.

Lastly, I thing Doug748 was actually talking about flexing in the corners where the coachroof rolls off down into the cabin sides (if you think about it that where the bending in the 'flatter' part will stop) - not the hull/deck joint.
 
the deck is there primarily to keep the water out rather than structural. You say the mast compression issue has been solved so the only loads now are from the rigging so if the chain plates are taken to the hull or to bulkheads bonded to the hull then effectively there are no loads on the deck. If you find now stress cracking that in a way confirms it, so your concerns about what might happen "in a blow" are probably unfounded. The boat is 50 years old so any weaknesses in the basic design and construction would have shown up by now.
 
One thing I'd like to add concerning very early use of GRP in boat construction.

As a whole, the majority of boats pre dating the 1973 oil crisis, (when the cost of polyester resin rose dramatically) and even up till around 1980 really were pretty much massively overbuilt. The scantling's on the early boats were still being based more or less on wooden boat construction. That's definitely the case with my Contest 33, and many others I've worked on over the years.

As others have said.. unless there's evidence of structural stress, substrate breakdown, I wouldn't be concerned about your deck in a blow. The weakest links in a deck are the windows, and the hull deck joint. If they are ok, the other weakest link found on many boats in a storm is the guy sailing it.. ha ha.. :)
 
Thanks again.

1. Concerto and anoccasionalyachtsman have nailed the solution I think, although I'd go for Concerto's wood option. If I make the strengthening battens out of cherry, I can oversize them slightly and use them as decorative features around which to fix the new headlining. I like this idea, even if there's no structural weakness...I'm used to wooden boats, and having a firm surface underfoot...

2. Tranona, most seem to share this view, in the absence of stress cracking. I am the load which worries me, though! I just don't like flexing decks, it would seem...

3. Saxonpirate yep this one is overbuilt for sure. First time I've been tempted away from wood! I figured it was because in the days when this was built, they didn't really know much about GRP as a new boat-building material, so overbuilt to be on the safe side. She turned 50 this year, and sailed around Cape Horn, and around the world, so she's seaworthy alright. And with a displacement of well over 3T unladen, in a 25ft boat, I don't think they were looking to make weight savings... (or for any speed!). Hadn't thought that the oil crisis may have spurred on lighter hull builds...
 
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