floor / deck access panel, how best to seal?

[tfret]

I did a complete restore on my ski boat about 5 years ago. Brand new deck, fiberglassed MDO plywood, new expansion foam, and I had a brand new aluminum fuel tank fabriacated. I installed the new deck completly solid without any access panels to the below equipment (I figured I'd never need to get back in there and really really really did not want the floor to ever rot out again). Now it seems I have a hole in my gas tank which requires me to cut the deck in order to pull the tank. I plan to carefully cut the deck so that I can re-install the "panel" that I cut out. Of course now there will be a seam all the way around this panel that will need to be sealed really well to prevent water from creeping into the floor. I could just glass back over it all but I sort of like the idea of having a removable panel in the event I ever need to get back in there. I'm in need of suggestions of how best to seal the edges around this panel so that it remains water tight, as well as how best to secure the panel. The original construction had the panel screwed down with stainless steel screwes and a rubber gasket all the way around it. It didn't work very well. Water crept into the edges of the plywood and it rotted out. Thanks for any ideas.

 

[DeepBlue2010]

I did a complete restore on my ski boat about 5 years ago. ..............., and I had a brand new aluminum fuel tank fabriacated.

This doesn't sound normal unless you did something drastically increased the corrosion rate at one spot (touching another metal) or the weld job on the new tank was a bust. Who made it, a good reputable company or just a guy with a welding torch?

In any event, what did you do to verify you got a hole in the tank? Did you pressure test? The gas leak maybe coming from a different location, have you considered that and checked?

Regarding the panel, what type of finish you currently have on the deck, carpet, paint, gelcoat, etc?

 

[tfret]

The tank was fabricated by a profesional metal fabrication shop. They did a superb job and made the new tank with a metal gauge twice as thick as the original. I foamed it into place, like the original (no screws). The best guess I have is that is has been scooting around and has rubbed a hole in the bottom. I inspected all connections and lines that I have access to and all is normal. I parked the boat after filling it. Two weeks later the tank is empty. The only way the entire tank drained out is with a hole in the bottom. That is rather intuitive. Pulling and repairing the tank, or whatever I discover the problem to be, should be straight forward. What I need to figure out is how best to seal the deck water tight but allow for future access. All of the deck access doors I see online are too small. The deck is water proof (so they say) MDO plyboard, with two layers of fiberglass over it, topped with an industrial polyurethane coating sort of like textured roll on truck bed liner. The floor has been awesome. It kills me to cut into it. I guess i could always just use a ton of silicon caulk to seal the panel that i remove back into place. Thanks anyway......

 

[Grub54891]

Was all the fuel in the bilge?? Or did someone syphon it out??

 

[DeepBlue2010]

Wasn't asking my questions to doubt your intuitions or skills. Just plain old brain storming to examine the issue from different perspectives.

Also, don't foam the tank in, it is not the best way to install an aluminum gas tank no matter what the factory originally did. Read this very carefully and follow the instructions in it, and you should be fine http://www.yachtsurvey.com/fueltank.htm

If you go this route, don't use silicon. It will shrink and deteriorate over time and will allow water to seep under. What you need is 3M 4000 (not 4200 nor 5200). This product has an excellent UV resistance characteristics and will hold up really well.

 

[Scott Danforth]

Was all the fuel in the bilge?? Or did someone syphon it out??

that is where my head went too. if it leaked, you would be able to smell a full tank of fuels worth in the bilge. in fact the smell probably would take years to get rid of.

 

[tfret]

DeepBlue thank you so much for the link to the correct way to install an aluminum tank. Wow, I wish I found that the first time around and none of this would be necessary. I guess just because the OEM did something, doesn't mean it was right. So it will definitely be installed correctly this time. To answer Grub, the entire tank (25 gallons!) drained out into the bilg, and then out the drain plug, which was removed at the time, and onto the garage floor. I'm just grateful the place didn't burn down! So now back to my original question. How best to seal the deck panel that I will be cutting out? DeepBlue suggests 3M 4000. I guess I was thinking clear silicon since my floor is grey, it would be less noticeable. I think the 3M stuff is white. After it cures perhaps I could paint it? Please, give me more thoughts on this.

 

[DeepBlue2010]

You can use anything but silicon. It is not going to hold to UV, deck cleaning, etc. If you want the best option out there, grab a tube of [FONT=verdana, geneva, lucida, lucida grande, arial, helvetica, sans-serif]deck calking for teak decks. Lots of reputable companies makes very good quality ones and some comes in different colors. I would spend some time on Amazon compare brands and read reviews. When you have your mind set on few options, give the factory technical service a call and ask them if you can paint over them. I know you can paint over 4200 and 5200 (did not try 4000 though) and this will alleviate the UV concerns of 4200.

5200 is a strong glue, it defeats the purpose you want to use it for.[/FONT]