My Wahoo!

Wahoo! owner Tom Brennan recently discovered a leak in the fuel tank of his 1989 Wahoo! 1850 Offshore. He’s in the process of replacing it and graciously offered to share his experience. Fuel tank leaks are a common issue in the Offshores, due to their below-deck location and the lack of below-deck air circulation.

So here it is, with lots of great info. Thanks Tom!

(Note: As of this writing (3/17/13), Tom wasn’t completely done with the project (e.g., he hadn’t replaced the deck), so it’s possible this article will get updated with new info.)

Also, for more below-deck and cutaway shots of an 1850, see these great restoration project photos by Joe Bernard.

I live in southern New Hampshire. Prior to owning my Wahoo I had a 14 foot Mckee Craft (Whaler style) that I fished hard. But with three boys and big dreams, I needed a bigger boat. I happened to see an 18 foot Wahoo! Offshore. It was a mess but I knew the design would be perfect for me. So for over two months I hunted Craig’s List from Maine to Florida. Eventually I found a boat in West Virginia that looked promising, selling for just under six thousand dollars. I traveled solo non-stop to see it in person. It was in awesome shape, with a 2001 Yamaha Saltwater Series 150 that ran like new. The title identified it as a 1989 but contained no other information of note. I had it home by Sunday.

Not long after acquiring it I took it for a two week fishing trip on the Ottowa River in Canada. I ran it hard every day with no issues. Great trip–180 fish, 12 species. Wow (i reeled in 3). Returning home, I next took it out in Portsmouth Harbor where we banged around the ocean all day. Back home that evening as I was cleaning up my wife smelled gas. I opened the access ports and the smell was very strong. I knew right then I had a leak. I wouldn’t be taking my kids out in the boat until it was fixed. The tank had to come out.

Getting the old tank out

Now when I bought the Wahoo! I knew it would need a new fuel tank eventually. I’ve changed tanks in a 33 Egg Harbor from that experience know that the constant to moisture over many years will eventually rot pin holes in aluminum (crevice corrosion). However, the way I replaced tanks in the Egg (the right way) is impossible in a Wahoo!.

To replace the tank meant cutting it out of the deck. And the challenge there was figuring out the dimensions of the tank and where to cut. Before doing any cutting, of course, I got every last drop of gas out of the tank. I did not want to remove the whole center console, so I lifted and blocked it as high as the cables/wires would allow.

The final cut Another view

Measuring through the access holes I was able to determine that the tank was 29 inches wide and the drain lines on the floor of the boat centered at 30 1/2 inches. So my first cut would be for width. I laid down tape on the deck and drew my cut lines on the tape. I decided to make the rear width cut first. I wanted it to be as far back as possible, about an inch short of the stringer. (I wanted it an inch shy of the stringer because I planned to later build a two inch ledge for the floor piece to sit back on.)

For the front width cut, I wanted to go as far forward as I could without cutting under the center console. That turned out to be 36 inches from my rear cut. So the dimensions of the opening would be 30.5 by 36 inches.

I made one plunge cut with a vibrating saw and did the rest of the cutting with a jigsaw. The cut didn’t need to be perfectly straight. I’d hoped that 36 inches would be a long enough hole to allow me to  pull tank out. Unfortunately, it wasn’t. In the end I had to cut a section off the back of the tank to get it to come out. To put in the new tank, I’d either have to cut out more of the deck or go with a shorter tank.

The fuel tank cavity: forward view Rearward view

The cause of the leak

After removing the tank I inspected it but could not find a leak. In fact, 99% of the tank looked in great shape. So I took it to a local metal shop. At first the repairman there couldn’t find one either but on closer inspection he said, “There it is,” and pointed to a light white ring of haze, rough in the middle., towards the front on the port side.

Later when I got home I looked at the tank cavity and found a dip in the foam that had trapped moisture (possibly from normal condensation) against the tank. Lack of air circulation below deck would have made it difficult for this moisture to dry out. The leak was high enough in the tank that it wasn’t until I took the boat on the ocean that wave action sloshed the gas high enough to reach it. Considering the way the tank is laid in the belly of these boats, foamed all the way down each side and corner, I’d guess such leaks are common over time.

The new tank

The old tank was 45 gallons but I was willing to live with less.I preferred that to cutting more deck. So I had a new one made a bit shorter and shallower (its capacity is 36 gallons). I kept the width of the  new tank 29 inches so it would fit between the stringers. I sanded down the foam on the sides and dry fit it in. It fit by a hair. So I sanded more to create some breathing room on the sides.Prior to installing the new tank I sanded, chemical etched, and painted it with four coats of Rust Bullet Industrial Coating.  I plan on locking it in place with rows of 3M 5200.

The new tank

To support the deck piece, I plan on building a two inch ledge of mahogany/aluminum plate on all four sides for it to sit on. Then I’ll attach it with countersunk screws and cover the screws and seam with 5200.