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ohaavik 11-15-2007 01:27 AM

Replacing filling caps on deck
Hi all,

Thanks for all advice gleaned so far; much obliged. I recently took over a boat where the holding tank has been converted to water storage (changed tank of course...) but the deck filling cap is still labeled Waste. I got a filling cap from the manufacturer labeled Water, but I am in doubt as to what compound to use to seal the filling cap - deck connection.

I am thinking silicone should do the job, but is this strong enough and will it create a tight seal?

Appreciate any advice on this. Thanks in advance.

Idiens 11-15-2007 07:49 AM

I'm guessing that the new filler is the same dimensions as the old filling cap, just a name change - and that the name is on the rim, not on the plug.

When you take the old one out and clean up the holes (the big one and the screw holes) check that it was properly fitted. If not, you may have to ream out and dry out all the holes, refill with epoxy/filler, drill out again and then fit the new filling cap. Marine silicon would do for the final seal, but others might have more preferred products.

sailingdog 11-15-2007 10:03 AM

I would agree that you should probably make sure the holes are properly potted, if the deck is cored where the filler cap is located. If its solid glass... then you don't have to worry as much.

I would use 3M 4200 instead of a silicone. It will give you a much better seal IMHO.

ohaavik 11-16-2007 12:07 AM

Filler caps
Thanks for the heads up on the holes. I got the cap from the manufacturer (X-Yachts) and it wasn't just the screw on cover, but the whole thing - the cap and the deck mounting. I haven't yet taken the old one off to see if the screw holes match, though I imagine they will seeing as how it's an original part...

It's monsoon season here in Singapore and I'm waiting for a dry day to change over to the new part - I imagine silicone or 3M 4200 will prefer a dry environment to be applied.

Thank you again for the kind advice.

sailingdog 11-16-2007 12:49 AM


Don't use silicone. You'll be much better off using 3M 4200.

ohaavik 11-19-2007 01:02 AM

Thanks for the warning. As it happens, I set about the job Saturday and the new filler cap and tube fit perfectly, once I managed to get the hose clamp out of the hole...9 raw knuckles later, it was a done job. I used silicone with some water repelling stuff added to it, but am wondering whether I got the seal tight enough and can remove the cap again and use 3M when I can get hold of some.

The new cap looks pretty though; all nice and shiny - wonder how long that'll last :)

sailingdog 11-19-2007 07:39 AM

Only nine raw knuckles later... you must have done it wrong, this is a ten-raw-knuckle job normally. :D For future reference, heating the hose with a hair dryer or heat gun or hot water really makes the hoses easier to work with BTW. :D

ohaavik 11-19-2007 09:01 PM

And there I was thinking I was a natural deck filler changer :D I best remove it and get the 3M 4200 so I can take care of the last knuckle. There is what appears to be a tiny hairline crack in the non-skid stretching from one of the screws and about 10mm inboard...should i bore this out and do an epoxy fill job while I'm at it?

I read that 4200 forms a permanent bond - will I be able to change the cap in the future if I have to convert back to holding tank? No facilities for pumping out here in South-East Asia but in case I wanted to head for Australia or something it might be an issue that I don't have a tank...

Thanks again for the advice SD, it's very much appreciated.

sailingdog 11-19-2007 09:34 PM

Umm.. I would clean the area of the crack with Interlux Fiberglass PrepWash 202, open it up a bit, and then fill with thickened epoxy and re-gelcoat. :D

4200 doesn't form a permanent bond... 5200 does. 4200 is fairly workable.

ohaavik 11-19-2007 10:02 PM

Ah, I was wondering what the 5200/4200 difference was :D

I'll see what I can do about getting the Interlux here and have at it. Actually, I notice your location and was wondering if you know of a good chandlers in Boston...heading there for X'mas to see the kids and might combine it with some shopping...

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