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-   -   How thick does a hull need be? Or is more glass always better? (http://www.sailnet.com/forums/sailboat-design-construction/65634-how-thick-does-hull-need-more-glass-always-better.html)

sailingbud 06-15-2010 02:16 PM

How thick does a hull need be? Or is more glass always better?
 
I am refinishing a Nantucket Clipper built in 1971. The gelcoat has been removed, ground off, and I am deciding how best to redo the hull. There are some blisters in the bulge of the hull below the water line, less than 20, 1" blisters per side, reason for stripping. It has been in a barn for 10 years and is now very well dried out. I have been told that using an epoxy barrier coat below the water line would be good to protect against more blisters. I have also been told the late original owner had plans to lay up biaxial cloth/mat with Vinylester resin to finish the hull.
What would be the benifits of more glass when the hull is already 1" to nearly 1/2" thick where the blisters are. I am tempted to lay up glass along the rough sections of the hull, fair it off and add barier coats of a 100% epoxy product I have used before called Durapoxy.

tommays 06-15-2010 02:24 PM

I would try and keep as close to orginal as i could as the grey area is how much strenth its has lost over time

JimsCAL 06-16-2010 06:04 AM

If only gelcoat was removed, I don't see the need to add more glass. Boats of that era were gnerally ovebuilt by todays standards. Interprotect 2000 seems to be the most common barrier coat. i've used it and would recommend it.

futureshock999 07-20-2010 09:39 AM

I agree with JimsCAL - this is an area that I had experience with when I bought my 1966 Nicholson 32 (they are prone to blistering). As I was told by an employee of the boatyard where she was built - "we didn't know how long this plastic stuff would last, and epoxy was very, very cheap - we just kept putting it on until we got bored." The problem is that they were not particularly GOOD epoxies and matts compared to today's. That's why boats of that era really deserve a thorough drying and as many coasts of epoxy treatment as you have time and budget for (my shipwright insists there is nothing gained after 5, but I will probably go 6 or 7 when I redo my boat). Interprotect is well known (it was what was used on mine), but Blake's is also good (now Hempel perhaps), and when I queried around seems to get higher ratings by those that use it. I would also try to get a moisture meter reading on her hull and all appendages - despite being out of the water for a decade, there could still be trapped water in a rudder or somewhere. (Probably not, but if you can do it...).

But I would not increase the hull thickness - you would be adding weight, possibly substantial if you totalled it all up, and it may affect other things such as her balance.

sailingbud 07-20-2010 02:36 PM

finishing to original
 
The more I have inspected this hull the more I believe it could use another layer of glass to bring her to the original thickness. It appears that more glass has been taken off. Looking at the layers, you see the top layer gelcoat then a layer below which has the same color and mat in the layer then below that no color. In the no color layer there are still some blisters and if I completly remove them it will penetrate deeply into the hull. As an alternative to taking so much out, I am going to fill all blisters with thickened epoxy and rough fair all surfaces. Then I will lay one layer of 1708 with epoxy resin and fair again then I will paint with epoxy paint, I am told I have enough for 6 coats below the water line then I will use epoxy paint over the entire hull probably 2 coats then bootstripe and bottom coat with anti-fouling.
That is my plan as soon as I get a couple of thru-hulls filled that I don't want.
I'll be building a new rudder so there aren't any more appendages to hole water.
I could use some temperatures in the 80s, we have hit the dog days (95+ in the shade with too much humidity to evaporate), I don't think I can spread epoxy fast enough in this heat. I'm concentrating on getting good patches set in during these hot weeks.

bikedaft 10-10-2010 01:59 PM

nantucket clipper is sister boat to halcyon clipper 27, which i own. they are 3/4" at waterline, and 2-3" at keel. overengineered, great! (offshore yachts)

there are two nantucket clippers in the bay where we moor (scotland)


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