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Old 15-09-2013, 09:19   #1
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Experience with Deck Prisms?

We have a flush decked Nantucket Island 38 that we're refitting, I'm about to start on the decks this week -- they're solid glass, about 1/2" to 3/4" thick, we're laying cork decks over them. I'm going to be fairing the decks and painting with an epoxy primer this week.....there was a single deck prism (the rectangular kind) at one point over one of the heads that had no other natural light, in general the interior is very dark, I'm considering adding several deck prisms throughout the boat -- does anyone have any experience with purchasing and adding new deck prisms?

Not sure if I want to go with Glass w/ Frame (Davey and Co.) or the acrylic molded with no frame, the acrylic might be brighter and easier to re-bed etc. in the future

see prisms below

SailBoatStuff Fixed Portholes (Deadlights) and Deck Prisms
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Old 15-09-2013, 09:46   #2
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Re: Experience with Deck Prisms?

Hi,
We had the acrylic deck prisms on our 1974 36 ft. flush deck sloop. I loved them. In our boat, they illuminated the galley, the nav station, and the pilot berths.

Our deck prisms came with the boat, and were still in good condition 26 yrs. later, when we sold her. Never had to replace one, but they looked similar to the ones in your post page from the catalog, the rectangular ones. Never had a problem with them. They were bedded with 5200, not the best idea nowadays, but may have been at the time of manufacture of the boat.

Ann
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Old 15-09-2013, 10:10   #3
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Ann, why not 5200?
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Old 15-09-2013, 10:24   #4
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Re: Experience with Deck Prisms?

I have one on my forward hatch. Mine is sealed with 3M 4200UV. 5200 is a powerful adhesive, too powerful for some folk's tastes, but, which can be released and removed with a product called, appropriately, DeBond http://www.marineformula.com/. I have repaired a number of deck leaks in boats using deck prisms which folks left unrepaired. It can lead to some expensive dry rot damage. Old deck prisms can sometimes be found on e-bay or marine junk stores, and were often used in old sailing ships because they could light up dark corners without jeopardizing the deck's security. They were originally sealed in hot tar, but required occasional re-bedding.

Using Debond requires a bit of patience, but it is worth the effort. I have used it to remove 3M 5200 polyurethane sealant on mast gooseneck fittings, cleats, etc. It's better to use the 4200 because it holds up well to sunlight, but is easier to remove, should the unit ever need to be serviced or removed.
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Old 15-09-2013, 10:29   #5
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Re: Experience with Deck Prisms?

If you make the hole well, I think they work great. But definitely one of those adages:

"Want to know where boat leaks come from?"

"Where people cut holes in the boat."

So if you cut the deck properly, epoxy the edges to keep penetration out, then use a good caulking compound (4200, etc), I think you're good to go.
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Old 15-09-2013, 16:28   #6
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Re: Experience with Deck Prisms?

Quote:
Originally Posted by Roy M View Post
I have one on my forward hatch. Mine is sealed with 3M 4200UV. 5200 is a powerful adhesive, too powerful for some folk's tastes, but, which can be released and removed with a product called, appropriately, DeBond MarineFormula Adhesive remover and general cleaner by DeBond. I have repaired a number of deck leaks in boats using deck prisms which folks left unrepaired. It can lead to some expensive dry rot damage. Old deck prisms can sometimes be found on e-bay or marine junk stores, and were often used in old sailing ships because they could light up dark corners without jeopardizing the deck's security. They were originally sealed in hot tar, but required occasional re-bedding.

Using Debond requires a bit of patience, but it is worth the effort. I have used it to remove 3M 5200 polyurethane sealant on mast gooseneck fittings, cleats, etc. It's better to use the 4200 because it holds up well to sunlight, but is easier to remove, should the unit ever need to be serviced or removed.


While 4200UV can certainly still be bought, I'm not sure they are even making it any more. The newer flavor is 4000UV. It has much better UV resistance, doesn't yellow like 4200. Debond and AntiBond work ok for small stuff, but bigger bedded pieces it only helps at the edge and can't penetrate further till you've worked in a tool, which kinda defeats the purpose. It helps, but only a little. Heat is the real secret, where it can be used.


3M 4000 UV Marine Fast Cure Adhesive Sealant



I once had a sweet custom boat that had dead lights (or deck prisms) built out of massive antique crystal grapefruit squeezers, installed upside down. The star shaped cone on the bottom of the squeezers refracted rainbows all over the inside of the boat, even in moonlight. Totally awesome. I found the effect really magnified how much light was put out as well.
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Old 15-09-2013, 17:19   #7
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Re: Experience with Deck Prisms?

Our rectangular prisms came with a bronze frame an bronze screws.
They occasionally leaked. Eventually, I removed the screws, cleaned up well, used Gluvit to turn the teak into plastic, then bedded the prisms in 4200 ONLY, and cut off the screwheads to put into the countersunk holes as feaux-screws. Never had a problem since... Hope this answers your question.
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Old 15-09-2013, 22:25   #8
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Re: Experience with Deck Prisms?

I rebedded all 3 of our deck prisms. PLEASE do yourself a favor. Don't use 5200. Sooner or later, you will need to rebed these again!
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Old 15-09-2013, 22:40   #9
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Re: Experience with Deck Prisms?

Had several in the past, really liked them. As others have said they need proper bedding.
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