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Old 21-06-2008, 09:47   #1
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New vs. Old Polyester resin

I was reading a thread here last night about Ferro Cement and although the FC does not interest me there was an interesting paragraph regarding polyester resin.

I'm wondering if there is reliable data regarding the strength of Old vs. New polyester? This interest me greatly because I'm looking for a classic plastic boat. Not only are they in my price range they generally have lines that appeal to me. But the question of strength is a reasonable question considering the age these boats are now reaching.

It is my understanding that many of the old glass boats were actually over built. The lay-ups tended to be very heavy and hand laid. But on the other hand I know that polyester resin has changed. Recently I had reason to talk to an informed Chemical Engineer who works for a polyester resin producer. When asking him for advice regarding a totally different application other than boats. He asked me what type of polyester I wanted.

Now, I don't know if there are dozens or hundreds of polyester types. I suspect from a chemical standpoint polyester can be formulated to spec. But I also suspect thirty years ago, polyester was polyester.

So you may see my point. When we say a boat is FRP, and we really mean fibre glass reinforced with polyester (in the vast majority of cases). We may be comparing caulk to cheese when we compare a thirty year old boat to a say five year old boat.

On the other hand these old boats with their very heavy lay-up may be a real steal because we will never see those kind of lay-ups again. Esp. with the current cost of oil.


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Old 21-06-2008, 13:25   #2
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Types of polyester resins and old boats

Learn more at: Blister & Laminate Hydrolysis in Fiberglass Boat Hulls

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Old 21-06-2008, 14:04   #3
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I'm wondering if there is reliable data regarding the strength of Old vs. New polyester?
Given there may be different types and that during the first oil crisis the price of resin shot up. During that period many manufacturers bought bargain basement resin thinking they would save a few bucks and ended up with boats that blistered badly. I don't think there are any reliable data about just the resin since it is used as part of an overall process. The care and quality of the whole process would matter as much as the resin used. I don't think there is any reliable data about what boats used what resins.

The extra thick layup are not alone stronger. The type of layup matters as much as the thickness. So far there is not much data on how long the stuff will even last. It appears that the hulls will outlast all the gear attached to it. There is enough data on that much.
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Old 21-06-2008, 17:07   #4

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The strength is in the glass, which doesn't age. It is like rock.
Given the cost of labour and materials, you couldn't afford to build a boat today as strong and as well built as the older ones. Despite fibreglass boats being around since the 50's, I never heard of osmosis before the early 80's. If an older boat looks good and shows no sign of osmosis, it probably is a far better boat than newer ones, both structuraly and design wise. They didn't trust the stuff back then , and labour and materials were cheap,so they built them strong. On a cruising boat heavily loaded for cruising, Not having todays excessive beam, they didn't tend to capsize at 120 degrees, and stay capsized ,unlike todays boats.
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Old 21-06-2008, 17:57   #5
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There are plenty of good old FG boats out there each boat has to be judged on its own condition. As I see it the major cost and effort needed to renew is considerable and probably only doable if you have the skills and time to do it yourself. wiring , motor, stern gear rudder bearings, rigging, interior, tanks ,fuel lines and both interior and exterior cosmetics maybe sails and canvas. You will be spending a lot of time rebuilding not sailing-Some people find that the perfect formula for happiness one guy I met rebuilt them and had no interest in using the boat.
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Old 22-06-2008, 18:16   #6
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Originally Posted by eyschulman View Post
As I see it the major cost and effort needed to renew is considerable and probably only doable if you have the skills and time to do it yourself. wiring , motor, stern gear rudder bearings, rigging, interior, tanks ,fuel lines and both interior and exterior cosmetics maybe sails and canvas...
I’d say that in the context of resin (and glass) for older boats, cost and time investments are not inordinate so long as one has the basic skills to do an acceptable job at straightforward fiberglassing… quite nominal actually… But I certainly agree; where expense and time can explode exponentially is the cabin interior, rebuilding/adding required systems, changing rigging to something more “modern” (whatever that is…) and adding any desired techno-gizmos… here the sky is the limit and more than a few refurbishments have foundered because the project grew faster than the skills/desire/time/budget/patience of the rebuilder… however, the glass/resin hull itself is modest by comparison – assuming basic skills, and assuming more or less structural hull integrity…

Worry: misuse of imagination…
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Old 22-06-2008, 20:23   #7
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My personal opinion, and it is only an opinion, is that some of the older hulls are far stronger than the hulls built today. Some aren't. The glass fibres in a hull will weaken if they are subjected to repeated crimping or other compressive forces, as they are crystalline structures and once they're deformed, they don't resume their original shape.

The resins that were used in the very early days of FG boat building were not the ultra-sophisticated sompounds used today, but the yards used lots of resin and lots of glass.

This resulted in strong, stiff hulls. It is the stiffness that contributes greatly to the longevity. Because the boats flex less than many of the more recent, lightly built models, the glass fibres deteriorate less quickly.

The early resins were not very UV resistant. Hulls that have not been protected from UV degrade more quickly than those that have been sheltered. The osmotic blistering issue is something that varies from brand to brand. Again, the thickness of the layup is a factor. A thinner hull doesn't have a lot of excess resin to sacrifice. It takes less time for water to work its way into the core and less time to weaken the boat seriously.

Finally, the sheer mass of the thicker hull makes it better able to withstand trauma resulting from collisions, groundings, or other mishaps.

There are millions out the who will disagree, but - heck - there are still a lot of smokers out there too.

Good Luck ! Hope things work out well

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