1985 OUTRAGE 18 Water Under Fuel Tank

[rhino18]

My [1985—always use four digits for years] OUTRAGE 18 still has its original fuel tank and [cockpit] deck.

The deck is rotting and will need to be replaced in the next season or so, along with the original fuel tank. In the meantime, I am trying to get at least another season out of the boat.

When there has been rain, water builds up below and behind the fuel tank, and [the water] can be seen when removing the deck plate. [See Figure 1, below.]

Fig. 1. View of fuel tank through a circular removable pry-out deck access plate showing area where water accumulates after rain.

fuelTankWaterLocation.jpg (94.09 KiB) Viewed 13443 times

I replaced a few deck plates that were no longer water-tight but rain water still builds up in this area.

Q1: where and how is this water getting into the [fuel tank cavity]?

Everywhere else seems to be dry.

[Blackduck]

Water can and does get in around the port access cover where the fuel fill and vent lines enter the tank cavity. The designers felt that water running over the top of the tank and back to the rear sump was fine, as the foam used to fill around the tank was waterproof. Of course, time has shown the foam not to be waterproof, and therefore this gives water a place to enter and fill the tank cavity. You can block, or dam up around the cover to divert water around this entry point.

[jimh]

The fuel fill and vent hoses are usually on the Port side.

The normal static trim of a Boston Whaler boat is to be with a slight list to Starboard. Rainwater on the deck should not be draining to Port and flowing into the fuel tank cavity in the channel where the fuel filler hose and the fuel tank vent hose are run.

[einspritzer]

I've had the same [problem in ingress of water under the fuel tank] with my 18-footers. I put in new deck plates and that didn't work. I re-caulked the edges and that didn't work. I sealed the overflow to the bilge and that didn't work.

I ripped out the foam I had sprayed in there.

I decided to live with [intrusion of water onto the top of the fuel tank on my 18-footer].

In the off season I open all the [deck access plates] so that [the below deck area surrounding the fuel tank on my 18-foot] can air out.

I also [bored] out all the foam aft of the fuel tank. Then I stuck a short hose or tube down there. Now I occasionally connect the hose or tube to a squeeze ball pump, and I operate the pump to lift out any water that collects in there.