Yachts/ Catamarans with solid GRP decks

[steveeasy]

Tylers moulded my previous boat an Invicta 26 in 1965, similar construction to the Twister, good solid GRP construction.

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.

Tylers did do a good job on the decks of Twisters, BUT not as good as a Contessa s though!!

Steveeasy

 

[Malish]

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.

not an issue that is widely highlighted on 'mature' Rivals either

 

[Trident]

Most early Prouts like the Snowgoose 35 and 37 had solid GRP decks - only later did they go cored BUT, they use the same moulds as I understand it so simply laid up a thick GRP deck that had previously been solid, then added a balsa core and then a thin GRP layer below so even if the core is gone the upper deck is still the same strength and thickness that the solid earlier decks were so just as strong...
Sadly I only found this out after repairing a large section of deck from the inside underneath to fix a wet balsa core. Surveyors who do these boats a lot say its not really worth the bother because they are strong enough anyway

 

[geem]

.

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.

What is your definition of an old boat? Our 42 year Airex cored hull and deck is in perfect condition. We have seen a balsa cored modern production boat in the yard in Madiera with the whole deck stripped due to bad construction. Sometimes builders of old boats get it very right. Sometimes builders of modern boats get it very wrong. You would think over the years construction practises would improve but that is not always the case.

 

[geem]

Most early Prouts like the Snowgoose 35 and 37 had solid GRP decks - only later did they go cored BUT, they use the same moulds as I understand it so simply laid up a thick GRP deck that had previously been solid, then added a balsa core and then a thin GRP layer below so even if the core is gone the upper deck is still the same strength and thickness that the solid earlier decks were so just as strong...
Sadly I only found this out after repairing a large section of deck from the inside underneath to fix a wet balsa core. Surveyors who do these boats a lot say its not really worth the bother because they are strong enough anyway

That wasn't the case on the 37. We had one for 11 years. The balsa cored deck was not skinned with a lot of grp. Probably just what you would expect on any modern boat.
A friend had an earlier 35 and that core was knackered. It was like walking over a matress. He never bothered fixing it but it was a bit alarming.
The solid glass hull had limited stiffening. The heads hull section in the front port hull would pant when going to weather because it was solid glass. We added a couple of longitudinal stringers that solved the problem. It would have been a different issue if they had built the hull out of core

 

[Trident]

That wasn't the case on the 37. We had one for 11 years. The balsa cored deck was not skinned with a lot of grp. Probably just what you would expect on any modern boat.
A friend had an earlier 35 and that core was knackered. It was like walking over a matress. He never bothered fixing it but it was a bit alarming.
The solid glass hull had limited stiffening. The heads hull section in the front port hull would pant when going to weather because it was solid glass. We added a couple of longitudinal stringers that solved the problem. It would have been a different issue if they had built the hull out of core

Weird, according to Prout none of the 35s were ever cored decks ...

My 35 was solid as were all the 37 (non-elite) I looked at and my Quasar is cored but has about 10mm glass, then 10mm balsa and then 4mm glass.

I guess like many UK companies at the time they just did what they had available or tried things out as a one off . Its been a lot of work to repair the soggy core around hatches and fittings on the Quasar but the SG35 was a dream - terrible maintenance from the previous owner but with the solid deck it was easy to remove and re-bed everything.

 

[geem]

Weird, according to Prout none of the 35s were ever cored decks ...

My 35 was solid as were all the 37 (non-elite) I looked at and my Quasar is cored but has about 10mm glass, then 10mm balsa and then 4mm glass.

I guess like many UK companies at the time they just did what they had available or tried things out as a one off . Its been a lot of work to repair the soggy core around hatches and fittings on the Quasar but the SG35 was a dream - terrible maintenance from the previous owner but with the solid deck it was easy to remove and re-bed everything.

Mt Snowgoose 37 was pre-Elite. Built in 1981 for one of the directors at Prout. Maybe they did something different but we definitely had a cored deck. I suppose once you the have first layers of grp in the mould there is nothing to stop you adding a balsa core. I am certain of this as we cut a new deck hatch so exposed the core.

 

[Tranona]

.

What is your definition of an old boat? Our 42 year Airex cored hull and deck is in perfect condition. We have seen a balsa cored modern production boat in the yard in Madiera with the whole deck stripped due to bad construction. Sometimes builders of old boats get it very right. Sometimes builders of modern boats get it very wrong. You would think over the years construction practises would improve but that is not always the case.

Not just "modern" boats. There was a series of articles I think in YM a few years ago covering the replacement of the teak deck on a not very old Vancouver 38. An object lesson in how not to build a boat. The deck was glued onto a cored deck then all the fittings were bolted through. Seem to remember there being something like 160 holes going through the sandwich, not all of them through ply inserts. In one area around the chain plates the ply had been moulded in the wrong place and fastenings went through the core with inadequate sealing. A large area of the deck had to be removed and rebuilt. An expensive "hand built" boat is not necessarily a better boat - just more opportunities for things to go wrong in construction.

 

[geem]

Not just "modern" boats. There was a series of articles I think in YM a few years ago covering the replacement of the teak deck on a not very old Vancouver 38. An object lesson in how not to build a boat. The deck was glued onto a cored deck then all the fittings were bolted through. Seem to remember there being something like 160 holes going through the sandwich, not all of them through ply inserts. In one area around the chain plates the ply had been moulded in the wrong place and fastenings went through the core with inadequate sealing. A large area of the deck had to be removed and rebuilt. An expensive "hand built" boat is not necessarily a better boat - just more opportunities for things to go wrong in construction.

That sounds like raging incompetence.

 

[Supertramp]

I recall the frightening flexing in so called solid decks on smaller boats and enjoy the solidity of my current cored (without problems) decks. I've also seen old solid fibreglass shatter and crack.

There is a wide range of possible material choices to build in and in interesting combinations (Allures alu/fibreglass) but more importantly the knowledge and building techniques used to apply them seem as or more important than material choice. Cleats and fastenings without reinforcement pads in solid fiberglass are as poor as unsealed holes in cored decks. I suspect many owners neither care nor worry about it until the day they have to embark on a minor repair (such as replacing mast foot cable fittings or clutches/cleats) and discover cracking, moisture, compression etc. .

If I was specifying my own new boat then I would expect some choices and reassurance of detail building techniques. I'd like to think that's what you get from the top end builders but I sense they sell on design and image.

My choice a few years ago was a new or newish boat (Winner from Holland was a possible) but in the end I chose a 30 year old decent quality build (Blondcell) and look after it carefully.

Its well made, and uses simple, good quality materials. But even so I have removed fittings, discovered unsealed deck core (and remedied it). But no soggy core so far.

So choosing simple materials is one thing, but you really are at the mercy of the construction quality and how it performs over decades. I miss the days where yards built (wooden) boats, repaired them, and refined and optimised the design and construction because the materials allowed it. Tranona makes good arguments for modern materials and mass production but the devil and key to longevity is in the detail.

 

[doug748]

I recall the frightening flexing in so called solid decks on smaller boats and enjoy the solidity of my current cored (without problems) decks. I've also seen old solid fibreglass shatter and crack.

Really? Never seen that.

The difficulty with all of these contentious things is that folk get giddy and like to portray them without alloy. Bow thrusters, furling sails, oblong shaped modern boats boats all have their strong points and their drawbacks. As do the alternatives.
People pick what they like, what suits them and their sailing and then bluff it's virtue out to the death.

In the case of cored structures they are wonderfully stiff but have less impressive impact resistance which gets even worse when internal bonds start to shear as the core is compacted. Wet cores we all know about, Youtube is full of people fixing them. You can help solve that problem with plastic cores which, unfortunately have less bond strength than balsa and are weaker. Very seldom do you get an innovation that, everyone will agree, has no drawbacks whatsoever; if I had to chance a suggestion I would say Dacron sails. Though even there someone will say they are very slippy, were expensive and the stitching stands prone to damage.

So if bill bligh does want to avoid cored boats (rather than just fan a good row) he has good reason to do so. Similarly if he wants the advantages of a composite structure, crack on. Alas if he wants a boat larger than about 10 metres he is probably not going to have a choice.

The significance of my earlier remarks about old boats is that they are the ones likely to have multiple owners, all armed with self tapping screws. So you do have to shop with care in that market.

The Marieholm Folkboat is solid GRP but even there I suspect the foredeck contains plywood glassed onto the finished moulding to improve stiffness.

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[Supertramp]

Really? Never seen that

.

Westerly Centaur, 1973, sailed hard would lift the cabin moulding via the cabin mounted lower shroud point. And the coach roof would deform under the weight of a person in places.

Problem? Not really, boat covered 20000 miles+ with no structural failure but overtightening the rigging not advised. Great boats but don't expect solid fiberglass to create a miracle structure.

Its more about understanding what your boat is made of and how the material behaves.

 

[bill bligh]

Really? Never seen that.

The difficulty with all of these contentious things is that folk get giddy and like to portray them without alloy. Bow thrusters, furling sails, oblong shaped modern boats boats all have their strong points and their drawbacks. As do the alternatives.
People pick what they like, what suits them and their sailing and then bluff it's virtue out to the death.

In the case of cored structures they are wonderfully stiff but have less impressive impact resistance which gets even worse when internal bonds start to shear as the core is compacted. Wet cores we all know about, Youtube is full of people fixing them. You can help solve that problem with plastic cores which, unfortunately have less bond strength than balsa and are weaker. Very seldom do you get an innovation that, everyone will agree, has no drawbacks whatsoever; if I had to chance a suggestion I would say Dacron sails. Though even there someone will say they are very slippy, were expensive and the stitching stands prone to damage.

So if bill bligh does want to avoid cored boats (rather than just fan a good row) he has good reason to do so. Similarly if he wants the advantages of a composite structure, crack on. Alas if he wants a boat larger than about 10 metres he is probably not going to have a choice.

The significance of my earlier remarks about old boats is that they are the ones likely to have multiple owners, all armed with self tapping screws. So you do have to shop with care in that market.

The Marieholm Folkboat is solid GRP but even there I suspect the foredeck contains plywood glassed onto the finished moulding to improve stiffness.

I defiantly had no intention of fanning a good row. I originally asked the question for my own interest or for anyone who might want to know what is out there. I have learnt a few things from this thread and hope others have as well.