Deck Prism

[stuffinbox]

I am chasing leaks right now and though some are straightforward, gaskets for the Bomar hatches, I have one Deck Prism forward that I want to remove, clean-up and properly and re-bed. I have tried to remove the glass by tapping with a rubber dead blow hammer from below with no luck. I used a wooden block and hammer with more force but the results were the same. I am thinking about using a small screw jack to put a light load on the lens and repeating the process. The stainless flange on deck is flush with no lip to pry against so its going to have to come up at the same time as the lens. I hope its age and not 5200 I'm up against.
Any suggestions would be appreciated.

[EagleSailTwo]

Originally Posted by stuffinbox

I am chasing leaks right now and though some are straightforward, gaskets for the Bomar hatches, I have one Deck Prism forward that I want to remove, clean-up and properly and re-bed. I have tried to remove the glass by tapping with a rubber dead blow hammer from below with no luck. I used a wooden block and hammer with more force but the results were the same. I am thinking about using a small screw jack to put a light load on the lens and repeating the process. The stainless flange on deck is flush with no lip to pry against so its going to have to come up at the same time as the lens. I hope its age and not 5200 I'm up against.
Any suggestions would be appreciated.

Or worse yet, bedded with 5200! If it is, your jack idea may be the only one but if you can slip a razor under the flange as it begins to rise and cut little by little going round it should break free........good luck.

[Geoff S.]

Stuffinbox, your question prompts a more general deck prism question for me. Diva, as part of her (now going on 5-year) refit, has had a completely new deck done: beams, ply, glass and plank. Her deck is now bona fide leak-free. I've often thought about bedding prisms in several key places to bring more natural light below, but I'm concerned that I'd be creating potential leak points and maintenance issues in doing so. (I'm aware of my inherent hypocrisy in worrying about maintenance issues when I made a concious choice to go back to teak plank instead of nonskid, but there's no point in adding to my problems someday!)

So, question for the gurus: with modern adhesives, is there a "proper" way to bed a prism such that future leaking becomes a non-issue? Of those on the board with prisms in place, how many have leak problems?

[delmarrey]

An old trick we used on car winshields was to insert a length of piano wire thru under the glass and start see-sawing back and forth working your way around the glass.

If you can get a wire under the flange you'll have a chance. Pushing straight on would be useless, you'd have to start at a corner and hope you don't break the lens..........................................._/)

[Canibul]

I like your screwjack idea. If you put a light upward load on the whole assembly ( a 2x4 strap?) and left it sitting for a while under tension, perhaps the adhesive would eventually let go at one point and that would be your start.

A single edge razor blade around the outside flange edge, perhaps? Would a hot air gun ( hair dryer) help soften the adhesive?

Of course the best way to remove it is to put yourself in a situation where you really dont want it to come out. then of course it will pop out on its own.

[stuffinbox]

I have to admit, It's prism 3 an zero for me. I have 5 of these on Tara and only the one in the forward compartment drips. I am not looking forward to removing the trim and overhead to access this hardware from the inside but it's looking like thats where I'm headed. To answer Geoff, over the years I have learned that everything has the capacity to leak. The way I have been reworking and bedding fittings is removal of the hardware and cleaning both deck and metal surfaces, the cleaner the better, buffing the flange with a fine wire wheel and a dremel works well. Whatever you chose to bed the fittings with plan on re- bedding at least some of them in the future, 3M 5200 is not a very good option. If your using machine screws and back-up plates screw the fittings down gently and after the sealant cures re-tighten them but do not allow the screws or bolts to rotate, tighten the nuts only. If your using just screws don't attempt to re-tighten them. On the subject of prisms, I am still amazed at the amount of light they produce and view them as one of the most impressive features on the boat.

[Canibul]

I see that the 3M 5200 seems pretty popular among people here. I have had good luck over the years sealing things marine with Permatex 66B and one of the DowCorning RTV compounds, they stick really well, totally waterproof, and stay flexible no matter what.

I make underwater viewing buckets with RTV, glass, and a plastic bucket. I know it sticks to the glass so well I have to use a razor blade to get it off.

[Talbot]

The trick with sealing prisms is to make sure that the adhesive sealant has decent UV stabilisation.

[hellosailor]

There is stuff called "5200 solvent" now, which is designed to dissolve 5200 and similar materials. I'd try soaking some of that on before applying the jack, because the jack will move SOMEthing--quote possibly the deck or the prism but not the seal between the two.<G>

[Terry Etapa]

I've used a product called Antibond 2015 on 5200. Using it is like using penetrating oil, except your trying to break a 5200 bond, not corrosion. In my case, I used the Antibond 2015, and a wood wedge to disbond a metal plate.

[chucks]

The glass prism will break if you hammer on it or use a pry bar or jack. I did and it cracked. The glass and bronze trimmed ones are hard to find. Try heating the glass and use a razor knife around the bedding. It should be sealed with polysulfide sealant.

[Brent Swain]

You'll get a given amount of light thru a given size opening whether it has a prism or a simple glass plate in it . Prisms don't increase the light , they simply difuse it, something that the checker pattern plastic from under a fluorescent light will do just as well, for a much lower price.
Brent

[stuffinbox]

Well, after several attempts to remove the prims and flange the little screw jack came thru in the end. I took it easy and re adjusted the compression on the jack and let time work for me. It was bedded in polysulfide and I found the leak was caused by 2 broken corners on the lens itself. I swapped ends on the prism when it was re-installed and used polysulfide to re-bed. We got 5 inches of rain over a two day period with no drips so it's time to move on to the next item on the list...

[FrankZ]

Originally Posted by stuffinbox

Well, after several attempts to remove the prims and flange the little screw jack came thru in the end. I took it easy and re adjusted the compression on the jack and let time work for me. It was bedded in polysulfide and I found the leak was caused by 2 broken corners on the lens itself. I swapped ends on the prism when it was re-installed and used polysulfide to re-bed. We got 5 inches of rain over a two day period with no drips so it's time to move on to the next item on the list...

One leak down, 7 million more to go....