Condensation dripping on fuel tank fittings

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IFish4Tuna

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I have a 1999 Bimini 306. When ever I pop off the cover of the access holes above the fuel tanks I find they are wet on the inside cover with condensation build up - all summer & fall.. Also it drips top of the tank. There is always a puddle on top of the tank around the fittings both front and rear tanks. I resealed the fittings last year so its not leaking around the mounting area. Also fresh o-rings. These are pop-top fixtures.

Looking for other people's experience on this. Is that just the nature of the pop-top port hole fixtures. It's made me wonder if I have excessive moisture where the fuel tanks are.

So I bought an endoscope on amazon for $30 and ran it down the rear of the rear tank to the lower deck that the tanks sit on. I did not see any puddles. BTW the endoscope works awesome for $30 (records and takes photos and has a light). Did same on the front side on the front tank. No puddles down below. Wondering if there is just enough condensation build up from the aluminum tanks to draw moisture from the bilge area.

I also reached inside the access hole and felt around on the underside of the deck and did feel some moisture in a few areas. The water on top of the tank is localize to the port hole areas despite some areas being moist on the underside of the deck. Also not sure if that's condensation or if the the center floor panel may need to be pulled up and rebuilt.

Anyway I really am trying to avoid standing water on top of the fuel tank fittings. Any advice welcome on experiences w/ this.
 
It's not all condensation. The pie plate access ports are leaking. If liquid is discolored it's probably a rotted deck panel (leaking coffee colored water from deck core). Pull the ports out and caulk them in with 3M4000. Then replace the o-rings. Use a good grease on the o-rings. I also put a piece of 10-mil plastic over the tank sending unit under the port. This photo is of my deck panel that I rebuilt with Coosa board coring. Tanks were replaced later.

2 Tanks uncovered.jpeg IMG_0273.png IMG_1107.jpeg

Beckson Deck Plate o-rings
These were sized off new Beckson deck plate.
www.McMaster.com
9452K515 Dash number 359 $8.66/5-pack 3/16" x 5 3/4" x 6 1/8" - OEM size.
9452K514 Dash number 358 $8.30/5-pack 3/16" x 5 5/8" x 6" - One size smaller - plates go in and out better. My choice.

Harbor Freight Super Lube 3 oz. clear synthetic grease $8.99
 
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My 2011 Canyon does the same as almost all other boats on the market to that when the round access plates start to leak.
The one over the fuel tank sender and elbows is the most obvious one as the water make a poodle there and i still don't understand why tank manufacturers doen't make the tank top a tiny bit curved so that water flow away and don't poodle there.
However, there way be also condensation from humidity condensing on the cooler tank outside but thats not really concerning for the tank, while the poodle around the fuel sender area is concerning.
My bilge is bone dry even if she is in a slip and i did not noticed obvious condensation, if you are sure that the tanks have condensation on their walls then you may leave the access plates open if on a trailer or check if you can get your bilge dryer.

As Hookup1 wrote, replace the round access plates with new ones, caulk them correctly and use a thin film of silicon grease after you removed them and reinstall them again. The silicone grease is not a sealant, but it will reduce wear on the o-ring.

Chris
 
Pulled the two floor panels last weekend. The large one covering the tanks was saturated. Once I put it on it's side water began pouring out of it. I'll be having them redone by the same person who did my rework this spring.

Thoughts on replacing the lift top port holes with screw in style. Are they any better at preventing leaks?

IMG_3485.JPG
 
My 2007 306 did the same thing. Replaced all the access covers, resealed, the works. Nothing helped. To be honest, the 306 is a pretty dry boat, especially at the helm area.

What I did was thoroughly dry it out with the yard blower, then a hair dryer. Sprayed copious amounts of Corrosion X on it, although Boeshield T-9 of LPS-3 (waxy one) would be at least as good.

Reseal the access pie holes, and live your life. They make rotomolded ABS tanks as a replacement when the corrosion compromises tank, which will happen. If I recall, the tank company was out of Miami, and it was $1500 for both tanks.
 
In comparison, yeah, the screw in deck plates are a bit better. But, in reality, it still comes down to sealing (re-sealing) the screw-down part every so often and making the sure o-ring is good - and they both have those two parts to keep up on. If you keep up on that, then either style is fine.
 
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The deck ports are ok if you replace the o-rings (McMaster part numbers in another post here). Lube them with silicone. Clean annually.

These port are only caulked in with regular silicone. It does not stay sealed and they leak. Use 3M4000 on them.

The last option is since these ports are rarely opened caulk the lid with regular GE silicone. Just the gap around the lid. It's easy to remove.

The saturated hatch core is from the screw holes that secure it to the boat. They expose the coring. When it is rebuilt overdrill the screw holes in the core from the underside and completely fill them with resin and filler. Then re-drill them from the top.
 
Some own experience with screw-in pie plates.
my dive panga had them and they always locked up and i had to weld a lever to fit the finger holes to be able to screw off the plate. What i am not sure if the scre-on is really water tighter then a press-in ones.
The most important thing is sealing, the o-ring on the plate and the sealing between deck and the pie plate "frame".
I bought long butyl rubber strips (also available in cartridges) to give them a try, they are used for example to seal RV Trailer sides and roof and are UV resistant, sticky but removable. Otherwise just use PU caulk like 3M 4200 as it will adhere most to deck and pie plate frame.
Yes, i know that it bonds rather well, but on a pie plate it can be cut loose with a cutter when pie plate cover is removed.
I used many many cartridges of PU caulk and never had any debonding if degreased well, but had debonding using silicone stuff and anywhere, in my house on boats, etc.
The only thing not to do is using 4200/5200/Sika PU caulks or adhesives to seal things where a cutter blade or cutting string/wire does not arrive to cut the two surfaces free. Dong so will lead to break the two surfaces free and that mostly leads to damage, even if heated up.

Chris
 
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