Our West Wight Potter 19 came with a 3 gallon portable fuel tank for the outboard. It works fine and stays mostly out of the way at the aft end of the cockpit. For most uses, it holds more than enough fuel. Many P-19 owners fill their tank at the beginning of summer, sail all summer, then pour half a tank back into their tow vehicle.
It worked for us until we started doing longer trips, sometimes in remote areas with few fuel docks. We decided that we needed a larger tank - a minimum of 5 gallons. A larger portable tank would start to be intrusive in the cockpit as well as being even uglier than the 3 gallon tank. It would also conflict with some ideas I was working on for a cockpit table.
Over the last three years, every time I crawled headfirst into a quarterberth, I couldn't help but notice the large unused space just aft of the cockpit. This seemed like an obvious place for a built-in tank. The only downside was sacrificing the handy locker just below the winch.
The dominant issue for any fuel system design is safety, especially when the fuel is gas. I decided early on that any type of below decks tank, no matter how well designed and sealed, was too risky. I didn't want to mess with blowers and complex venting systems, so I settled on a design that made the tank storage area an extension of the cockpit. There would be no air passages between the tank space and the interior of the boat.
Another design goal was to get the fuel line out of the way. It was too easy too catch something on it, it conflicted with the cockpit table ideas and was generally untidy.
I also wanted the option either of filling the tank in the boat or removing it for on shore refueling. With a larger tank, in-boat refueling would be easier, but sometimes the only fuel source is away from the water (i.e. hike to the nearest gas station). Carrying an extra gas can for that purpose was not an option. Some fuel docks have rules against filling portable tanks on the boat, so even though removable, the tank would have to appear "built-in" enough to allow in-boat filling in those cases.
To make the best use of the space, I decided on a rectangular tank. Standard gas cans always have an irregular shape. The envelope of the tank is much larger than the fuel volume. A simple plastic box would be the most space efficient. I selected a 6 gallon waste tank from Todd. They are sold by West Marine and many other marine suppliers. Though not sold as fuel tanks, they are made from the same material and actually have thicker walls than most portable tanks.
Lastly, the new system needed to look better than the ugly bright red tank sitting in the cockpit. The solution to this problem would lie more with the cockpit table than with the tank design.
The first step was to remove the hatch just below the winch. International Marine had used the right type of sealant, so it was an easy job. The cutout for the hatch was slightly wider than the width of the tank, but not enough to cause problems. Next I cut the rest of the opening. Here is a photo after making the cutout. Emily is on the job doing quality control. When sizing the cutout, I filled the tank with water, causing it to bulge, then made the measurements. The difference from an empty tank was enough to matter.
The fiberglass compartment (just above Emily's head) was the next to go. It took some effort, mostly with a hacksaw blade on a plastic handle, one of my favorite tools. I was sorry to be removing this very useful compartment, but everything on a small boat is a tradeoff.
It was now time to build the enclosure. You would think that building a simple plywood box is no big deal. The problem is getting it into place once it is made. It won't fit. In addition, I had blocked access to both aft ends of the quarterberths with compartments for the stern anchor rode and a long stern tie line. The challenge was to build the enclosure with access only from the cutout.
Part of the problem was the size of the tank. At 12" wide, 16" high and 8" deep, it just barely fit in the available space. In particular, the back of the enclosure would be nearly flush with the inside of the transom. I actually had to turn the lower gudgeon bolts around so the heads were inside, to gain an extra 1/8". Because of the table design, it was critical that the tank not extend forward of the aft cockpit surface. I built the enclosure in-place, one piece at a time. All joints have a 3/4 by 3/4 cleat to provide a large surface for sealant. All joints are fastened with screws. The sealant is a weak adhesive, in case I ever need to disassemble things. Here is the sequence.Here is a picture of the completed enclosure after painting. The fuel line exits via a thru-hull at the upper right. The thru-hull passes through the enclosure and the transom without providing an air path to the interior. The small offset panel for the winch intrusion is visible at the top. The screws and the notches from the original hatch give an unfinished appearance, but that will be taken care of by the table.
The tank had three threaded inserts, two at 1.5" and one at 0.5", all NPT threads. The 1.5" openings were in the center and the half inch opening was in a corner. I purchased threaded plugs for each opening and modified them for the fuel line, filler cap and vent.
The filler cap was just a 1.5" plug with a metal bar on top to make it easier to twist on and off.
I drilled a small hole in the second 1.5" plug and attached a thin tube for the vent. The tube runs out the same transom hole as the fuel line. I originally just had a hole under the lip of the plug, but still got some fumes. It wasn't a safety problem, but I hate the smell of gas. Some sort of one-way flap valve might be an even better solution.The fuel line goes through the half inch opening. It needed to be in the corner to provide clearance around the winch intrusion. Here is a photo of the fuel line assembly. The stainless fitting is a standard quick disconnect that matches the one on the original tank.
Here is a picture with the tank and all lines installed. Note how easy it is to see the fuel level. The fuel gauge on the portable tank was pretty crude and after a couple years, the clear plastic cover over the needle went completely opaque from UV. Now you can see why the fuel line needed to be off to the side - it wouldn't clear the winch intrusion. The filler cap just fits under it. The vent tube attachment (not visible) is just behind the filler cap. Before adding fuel, I used a hair dryer to blow hot air through the tank for an hour, removing the last drops of water.
Here is a photo of the fuel and vent lines on the transom. The squeeze bulb is oriented upward to facilitate priming if the line goes dry. It should probably be oriented even more vertically. The bulb is easy to reach when needed but the line is out of the way. I shortened the line on the tank side by about two feet.
Here is the tank in the refueling position. By sliding the tank a bit less than half way out, the filler cap can be removed but the tank balance remains aft. The fuel and vent lines have enough extra length so they can remain attached. After refueling once on a recent cruise, I'm thinking of adding a piece of 1 inch flat webbing around the tank near the bottom to make sliding the tank out easier.
