Yachts/ Catamarans with solid GRP decks

Imagine an I beam ( RSJ) that was solid rather than a scalloped web between two plates . It would be impossibly heavy, barely self supporting- and expensive .

But. You want solid grp where the deck attaches to the hull overlap/flange /shelf .
Not all builders figured that one out at the same time iirc ?
All boats get bumped , modified , strained . That’s when coring considerations count

I once looked at a Canadian Contessa26 that had( wet) coring in the cabinsides extending down into the deck and behind an inner grp moulding . Worst of the worst scenarios to sort without major surgery ..
 
Blueboatman said:
I once looked at a Canadian Contessa26 that had( wet) coring in the cabinsides extending down into the deck and behind an inner grp moulding . Worst of the worst scenarios to sort without major surgery ..
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Good example of poor design. Many decks now do not have any fastenings going through the cored part or even through the deck itself but screwed into aluminium plates bonded into the moulding. Of course that can get ruined as in some model Bavarias where they held the teak down with temporary selftappers in the seams which inevitably pierced the core. Relied on the seam sealant to plug the holes. Fortunately they realised pretty quickly that it was a bad idea and then vacuum bonded panels on.
 
What I am looking for is people with definite knowledge. There has been a couple of I think answers. I owned or sailed on the examples I put in post 1. I do not mean to sound rude or ungrateful and would like to say thankyou to those who have responded so far. (y)
 
bill bligh said:
This is a curiosity question more than anything else. I am trying to compile list of sailing boats between 26ft and above with solid glassfibre decks. So far my list is as follows. Catalac 8m catamaran. Rival 32 and 34. Contest 29 and 33. Halcyon 27. Trintella 29? Wauquiez Centurion 32? I am trying to keep to boats you would find for sale on the UK market. If you can add to this list please do. I have put a question mark after the ones I am not sure of . Over to you knowledgeable people.
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As a point of accuracy I think the Catalacs had solid grp fore, side and rear decks but a cored cockpit floor that may be balsa or ply?
 
It's worth noting that comparing a cored deck to a solid deck, the cored deck is way stiffer. If you take a solid 12mm grp deck and compare it to a cored deck of 6mm grp inner, 25mm core and 6mm grp out layer, the cored construction will be 37 times stiffer. The same amount of grp is used in each construction. In reality the cored decks grp build up would likely be about half that mentioned and still be way stiffer than the solid grp deck resulting in a lighter stiffer deck than the solid deck
 
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Blueboatman said:
Imagine an I beam ( RSJ) that was solid rather than a scalloped web between two plates . It would be impossibly heavy, barely self supporting- and expensive .

But. You want solid grp where the deck attaches to the hull overlap/flange /shelf .
Not all builders figured that one out at the same time iirc ?
All boats get bumped , modified , strained . That’s when coring considerations count

I once looked at a Canadian Contessa26 that had( wet) coring in the cabinsides extending down into the deck and behind an inner grp moulding . Worst of the worst scenarios to sort without major surgery ..
Click to expand...
Our cored section of the hull stops about a foot from the toerail. The portlights are in the solid grp section below the toerail. Beneath the portlights is a moulded in grp bumper rail with teak capping and a stainless trim/bumper. Similarly, the cored deck finished about a foot from the toerail. The genoa tracks are in the solid section. The deck and hull are glassed together then a substantial aluminium toerail bolts through the deck 1" in from the edge of the deck. 150 M8 bolts down each side. Somebody really thought about the construction. All headlining panels are removable to access every deck fitting
 
C08 said:
As a point of accuracy I think the Catalacs had solid grp fore, side and rear decks but a cored cockpit floor that may be balsa or ply?
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My 9m Catalac has reinforcing cored sections on the foredeck, cabin top, cockpit and aft deck. I suspect that the 8m is the same as the deck areas are very similar.
 
Some decks are solid but not necessarily glassfibre thru and thru. some are plywood and then glassed over giving the impression of a GRP deck. but they are not. One of my Twisters was of this construction.

Steveeasy
 
steveeasy said:
Some decks are solid but not necessarily glassfibre thru and thru. some are plywood and then glassed over giving the impression of a GRP deck. but they are not. One of my Twisters was of this construction.

Steveeasy
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Often plywood is used under a windlass. On screwed down teak decks plywood is often set in the core material to allow the screws somewhere to fix to.
Ply can be as bad as balsa if water gets in due to badly installed deck fittings.
 
geem said:
Our cored section of the hull stops about a foot from the toerail. The portlights are in the solid grp section below the toerail. Beneath the portlights is a moulded in grp bumper rail with teak capping and a stainless trim/bumper. Similarly, the cored deck finished about a foot from the toerail. The genoa tracks are in the solid section. The deck and hull are glassed together then a substantial aluminium toerail bolts through the deck 1" in from the edge of the deck. 150 M8 bolts down each side. Somebody really thought about the construction. All headlining panels are removable to access every deck fitting
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That is well put together Dutch (?) quality
Similarly my last boat was put together and although it had an aging teak deck I was pretty certain that when I came to remove that and add value to the boat . coring would not be an issue and the deck/hull/flange/well glassed over joint /bolted/aluminium rail , compartmentalised coring strips and 3x1 solid teak rub rail would have minimised any unknowns and general use and abuse over the years.. thus it proved ??
Which was … nice
 
Blueboatman said:
I once looked at a Canadian Contessa26 that had( wet) coring in the cabinsides extending down into the deck and behind an inner grp moulding . Worst of the worst scenarios to sort without major surgery ..
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The UK 26 has no core. The space between the deck and inner liner has some cable runs to the mast and interior lights that are impossible to maintain. The deck definitely flexes if you jump on it but this hasn't caused me any problems in the last 50 years. Surveyors will sometimes remark on this which would be a serious problem if the deck was cored.
 
andsarkit said:
The UK 26 has no core. The space between the deck and inner liner has some cable runs to the mast and interior lights that are impossible to maintain. The deck definitely flexes if you jump on it but this hasn't caused me any problems in the last 50 years. Surveyors will sometimes remark on this which would be a serious problem if the deck was cored.
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Yes I forget who built the Canadian ones
Edit : here we go . J J Taylor , who used coremat in the Co32 decks in lieu of solid..
Contessa 32 - Wikipedia
So on the 26,who knows ?
Over there coring came in earlier than over here too I think , as the Americans were further along in learning how to build in grp - they used chopper guns to ‘ spray on’
chopped strand mat /resin early on too .
 
I want to thank all of the contributors to this thread. I am finding it an interesting read. I once owned an 8M Catalac, on the surveyors advice I had to install a bigger backing pad for the babystay. Defiantly no core. I didn't know about the underside of the cockpit.
 
The Rival 34 has areas of balsa (or ply) sandwich across the foredeck and a 'wood core' under the mast. The plans for the R32 are not quite as explicit. The side decks and hull are solid on both though
 
The deck of my 55 year old Twister is solid GRP and there are reinforcing pads of marine ply where necessary. These are bonded to the underside of the deck, and encapsulated.

Over the 25 years of my ownership I have several times had to drill through holes for new deck hardware and I have never found any evidence of softening of the plywood.

I reckon Tylers, who moulded the Twister hull/deck did a good job.
 
Poignard said:
The deck of my 55 year old Twister is solid GRP and there are reinforcing pads of marine ply where necessary. These are bonded to the underside of the deck, and encapsulated.

Over the 25 years of my ownership I have several times had to drill through holes for new deck hardware and I have never found any evidence of softening of the plywood.

I reckon Tylers, who moulded the Twister hull/deck did a good job.
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Tylers moulded my previous boat an Invicta 26 in 1965, similar construction to the Twister, good solid GRP construction.
 
Sandwich construction is great, It saves weight, adds stiffness and insulation.

Not so cool, it also delaminates and gets sogg,y a feature that only emerges in older boats so It's clearly a great idea to avoid sandwich construction if you can on an old un.
 
doug748 said:
Sandwich construction is great, It saves weight, adds stiffness and insulation.

Not so cool, it also delaminates and gets sogg,y a feature that only emerges in older boats so It's clearly a great idea to avoid sandwich construction if you can on an old un.
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No it’s not a great idea to avoid sandwich construction in old boats. Nor is your claim justified or factual fir all old boats. It’s a great idea to be aware of the risk and assess if it is an issue. That goes for any age of boat as well.
 
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