Old vs New Fiberglass Sailboats Hulls

[smurphny]

Originally Posted by daddle

30 year old balsa cored FRP hull here. Glass is thin. Long race history. World cruiser. Zero problems. If she gets holed, which is way down on my worry list, she has a liferaft and all the safety gizmos. Proper maintenance easily prevents the core rot. She rocks.

Sure, if you have owned the boat and have taken care of it, no problem. But, many boats have been transferred lots of times and are unknown quantities. An unsuspecting guy where I found my Alberg bought this really sleek looking 40' space-shippy sailboat only to find out that the entire (very thin) core was rotten. It eventually went to the dump.

I spent a month replacing deck core, which is a messy but fairly easy job. Balsa is still the best core material. The main problem with most rotted core is that it was never saturated properly. Boats like Pearsons were mass produced and filling the core was apparently not on the agenda.

[minaret]

Originally Posted by smurphny

Sure, if you have owned the boat and have taken care of it, no problem. But, many boats have been transferred lots of times and are unknown quantities. An unsuspecting guy where I found my Alberg bought this really sleek looking 40' space-shippy sailboat only to find out that the entire (very thin) core was rotten. It eventually went to the dump.

I spent a month replacing deck core, which is a messy but fairly easy job. Balsa is still the best core material. The main problem with most rotted core is that it was never saturated properly. Boats like Pearsons were mass produced and filling the core was apparently not on the agenda.

Having repaired acres of rotten balsa core in decks and hulls over the years, I would never own a boat that had any balsa in it anywhere. It is absolutely the worst of all core materials. They still use the stuff at some manufacterers because it's light, but if you do some panel testing you will find that if you actually fill the gaps between balsa blocks with resin it's substantially heavier than a foam core, and still dramatically less rot resistant. If you do an actual layup on a curved surface, which causes the blocks to splay on the weave, you'll see that it takes many gallons of resin to fill the gaps. Straight resin is very heavy and brittle. This is why most cored boats have gaps in the core everywhere, which turn into natural channels for water. You can go to great lengths to avoid this, but youre still putting spongy wood below your waterline. Never a good idea.
When we built Carl Schumacher's last design, the 77' VLDB "Cascadia", they spec'd balsa core for the whole boat, deck and hull, below the waterline as well. I fought them tooth and nail on this, but noone would listen to the lowly guy who actually builds the boats, only the NA and chemical engineers. We bagged all core in epoxy, and bagged all laminate in carbon fiber and epoxy. 12.8 million dollars later, the owner took her for trials in Prince William sound and got 4 days aboard her before the hired skipper put her on a rock at 17 knots. We had to cut out the entire outer skin below the waterline and recore the entire hull from WL down, at a cost of over a million dollars. I laughed a lot...

[felixqld66]

Originally Posted by minaret

Having repaired acres of rotten balsa core in decks and hulls over the years, I would never own a boat that had any balsa in it anywhere. It is absolutely the worst of all core materials. They still use the stuff at some manufacterers because it's light, but if you do some panel testing you will find that if you actually fill the gaps between balsa blocks with resin it's substantially heavier than a foam core, and still dramatically less rot resistant. If you do an actual layup on a curved surface, which causes the blocks to splay on the weave, you'll see that it takes many gallons of resin to fill the gaps. Straight resin is very heavy and brittle. This is why most cored boats have gaps in the core everywhere, which turn into natural channels for water. You can go to great lengths to avoid this, but youre still putting spongy wood below your waterline. Never a good idea.
When we built Carl Schumacher's last design, the 77' VLDB "Cascadia", they spec'd balsa core for the whole boat, deck and hull, below the waterline as well. I fought them tooth and nail on this, but noone would listen to the lowly guy who actually builds the boats, only the NA and chemical engineers. We bagged all core in epoxy, and bagged all laminate in carbon fiber and epoxy. 12.8 million dollars later, the owner took her for trials in Prince William sound and got 4 days aboard her before the hired skipper put her on a rock at 17 knots. We had to cut out the entire outer skin below the waterline and recore the entire hull from WL down, at a cost of over a million dollars. I laughed a lot...

a lot to be said to listening to the experiences of those who actually "do" love the technical thoerists...I laughed alot at that as well

[sarafina]

Honestly, except for the case by case argument, looking at an individual boat and determining her hull quality, I don't think it makes a rat's ass difference...

Puts me to mind of a quote from an long time USCG guy...

something like;
"Every day wooden boats die premature deaths from carelessness or neglect, while FRP boats that should die a decent death have to be forcibly put down."

Lots of things cause boat failure, but it seems that rarely is catastrophic hull failure, due to condition of the 'glass, the cause of the failure. Stringers and interior structure supports, chainplate beddings, core failure due to bad bedding (not general 'glass failure), collisions, hatch failures etc all seem to account for the failure of a boat far more often.

[smurphny]

Originally Posted by minaret

Having repaired acres of rotten balsa core in decks and hulls over the years, I would never own a boat that had any balsa in it anywhere. It is absolutely the worst of all core materials. They still use the stuff at some manufacterers because it's light, but if you do some panel testing you will find that if you actually fill the gaps between balsa blocks with resin it's substantially heavier than a foam core, and still dramatically less rot resistant. If you do an actual layup on a curved surface, which causes the blocks to splay on the weave, you'll see that it takes many gallons of resin to fill the gaps. Straight resin is very heavy and brittle. This is why most cored boats have gaps in the core everywhere, which turn into natural channels for water. You can go to great lengths to avoid this, but youre still putting spongy wood below your waterline. Never a good idea.
When we built Carl Schumacher's last design, the 77' VLDB "Cascadia", they spec'd balsa core for the whole boat, deck and hull, below the waterline as well. I fought them tooth and nail on this, but noone would listen to the lowly guy who actually builds the boats, only the NA and chemical engineers. We bagged all core in epoxy, and bagged all laminate in carbon fiber and epoxy. 12.8 million dollars later, the owner took her for trials in Prince William sound and got 4 days aboard her before the hired skipper put her on a rock at 17 knots. We had to cut out the entire outer skin below the waterline and recore the entire hull from WL down, at a cost of over a million dollars. I laughed a lot...

As stated previously, I think putting a wood core below the waterline is inherently a bad idea. Regardless of the relative strength issue, sooner or later it is going to absorb water because balsa can't be totally saturated with resin and the prospect of recoring a hull is almost unthinkable.

In recoring my decks last year, it was apparent that Pearson had not adequately sealed the balsa. Nevertheless, IT LASTED 40+ YEARS and failed only because the previous owners let it drastically deteriorate. If the boat had been maintained, as many are, there would have been no problem. IMO the workability and light weight of balsa makes it a great material for deck construction. It is not possible or even advisable to totally saturate 3/4" balsa because it would require thinning the epoxy and, as you say, increase weight. It just needs to be encased in resin with no voids. If you're careful in filling the area with balsa there is not much left to fill. A balsa cored deck composed of two layers of glass and 3/4" core is well over an inch thick, very light and very strong. No other material I know of can achieve this kind of strength to weight ratio. I investigated other synthetic core materials before doing my decks and found they were all subject to a host of strength and delamination issues and were mostly experimental products.