We selected a 12 gallon Moeller permanent inboard fuel tank to replace our corroding steel tank.
The WEASEL was built with a steel tank suspended beneath the cockpit floor, held against two glassed in stringers with nylon straps. With this configuration the deck-fill fitting was on the cockpit floor and all of the hose connections to the tank were in the extremely tight place between tank, the stringers and the cockpit floor. The steel tank had never been polished and even the exterior was rusting badly. It made no sense to pull the engine and leave the old tank in place only to clog future fuel filters or worse damage the new engine with contaminated fuel.
The old fuel tank mounts with the nylon straps cut away and the tank removed.
The first step was to remove the old steel tank. This proved rather simple Dave merely undid the hose claps on the vent and fill hose and cut the nylon straps. Dave was able to remove this singlehanded and when I arrived at the boat found it sitting on the dock box.
The next part was the scary part. We emptied the tank into a jerry can. We had a funnel with a filter and I was surprised to see the amount of sludge and rust that poured out. I shuddered to think of that making its way into our new engine. We then disposed of the empty tank and took the contaminated fuel to the Marina Office where Mike helped us dispose of it into their chemical reclamation area. NOTE: I do not recommend doing this with a jerry can you value since all the sludge gets sucked into the tank and unless you want to spray it out with a hose and spill diesel water everywhere it contaminates the can.
We selected a polymer replacement tank; a Moeller 12 Gallon internal permanent tank. This unit came as a complete unit including all the fittings and the sender included. The dimensions of this unit were not far from the original tank so we thought it would be simple. There were a few things we needed for this project:
- 3/8 Withdrawal fuel hose for the engine (approximate length 3”)
- 3/8 Barbed fitting for the fuel withdrawal hose
- (Yellow) Thread Sealing Teflon tape
- 4” of 1 ½ inch fuel fill hose
- Diesel Deck Fill Fitting (the old one was a 2” diameter hose)
- Duplex 18 Gauge Marine Wire for the sending unit
- Hose Clamps (Various high tension clamps)
- Steel Straps and bolts/washers/screws
- 1”x1” Weather Stripping Foam
This first attempt at mounting needed to be reworked. The venting hose configuration would changed, as would the mounting harness and wood blocks were added to keep the tank on a slight angel and allow room for the hoses.
I have to say this project I thought would take about 2 hours, in the end it was 8 hours and one trip to the marine hardware store. Additionally we would have to make additional changes when the engine came to be installed.
First step was to remove the old fill cap. CS in all its wisdom had a cored cockpit floor except where the fuel fill cap was so we had no core rot issues to address. We removed the fill fitting and cleaned the area.
The Dahl metal stripping painted with rust paint. Note the ill fated screws.
Next we dry fitted the tank to see where we needed to mount the straps. A few things occurred here that made us pause. We realized that the fill spout on the tank and the vent barb were far to long. In addition the new seadog fill fitting had to wide a flange and too long a down pipe in conjunction with the tank. We turned the tank upside down and bucked off the excess 2” off fill spout and the barb. It was important to cut these upside down since we did not want the debris going into the tank. Next we cut down the seadog deck fill fitting and re-dry fit everything. This all looked good except the vent hose was too kinked. We opted to put the tank on a slight incline by spacing the front end down about 1” to give the vent hose a nice bend. We also pre wired the sender so we could add a fuel gauge at a later date. NOTE: In the end the engine would need a return fuel line to the tank and the vent hose would be too kinked in the space so Alex would install a horizontal two-barbed fitting.
The withdrawal hose and wired sender. It would have been easier to put the withdrawal hose on prior to mounting the tank.
The fill hose and original vent configuration.
So now for the easy part, simply strap the tank in place and put the hoses on right; not so much. The problem with every project on a new boat is that it is never as simple as popping off one piece of hardware and subbing in the new one. Nope it is a McIver like series of bastardizations. We used Dahl’s plumbing hold down steel stripping. I opted for the galvanized stuff but new that would start rusting out anyway so I coated it in 2 coats of Tremclad’s Rust paint. Honestly I would next time do it with a brush in precut lengths and make sure it had four coats. Still with the new PSS Shacft seal and the coats I gave this stuff will last as until the next idiots removes the tank.
This strapping has nice holes big for bolts and small for screws alternating down it. We had the new tank in position by one of us being wedged over the prop shaft and the other hanging upside down in the lazerrette. This job cannot have too many hands but we made do with two. We bore out four new holes for the bolts in the stringers and with the engine out of the way bolted in the two straps which we had already cut with tin snips into a rough length. It is important to note that we double backed the metal straps so that the bolts went through two holes and used washers and lock washer/nuts on the other side of the existing stringers. This part was easy; we made the mistake of thinking we could use the same combination on the other side. Of course this was not to be. We could not get a tool in the tight space to tighten the bolts. Instead we used heavy duty stainless steel screws with washers. After 5 stripped screws we settled on the right sized pilot hole and tensioned the band up as much as we could. NOTE: The screws would not work in the end. Before the engine install we took them off and redid the project with bolts. We did this by cutting two 6” strips of the steel straps and bolting those in place with the tank out of the way. Then with smaller bolts we connected the two pieces of strap. This idea came from Alex and worked beautifully. We felt kind of stupid at the time.
Moeller recommended putting some kind of shock absorbing material between the tank and the mounts so we used adhesive backed weather stripping high density foam. This was pretty easy to install and we doubled up the front 1/3 of the tank so it was on a slight incline to allow more room for the venting hoses. NOTE: This also did not work as there was too much give. We used 2”x4” wedges (painted) and screwed/strapped into place with the same metals trapping material.
Weather stripping foam was used between the tank and the stringers to prevent any abrasion.
Now we made a fairly amateurish mistake by not attaching the vent hose and the withdrawal hoses prior to installing the tank. With many a bashed knuckle we finally got the hoses on. The fill hose was meant to be last. We in fact had it sticking through the hole on the deck and onto the spout on the tank to keep it aligned. We removed it and then put the deck cap in and measured the distance. We then cut it to length put the hose clamps loose over the pipe and put the deck fill fitting on. We used our old friend 3M 5200 Fast Cure Sealant. With that sealed and screwed into place we tightened the hose clamps and sat back and looked at a fully installed tank.
The modified vent/return hose barb. This is a horizontal configuration as opposed to the original vertical mount.
The new engine and tank give each other a lot of clearance.
The one thing we did not install was a new primary fuel filter/water separator (such as a Rancor) we planned on leaving this to Stem to Stern.
The rancor fuel filter mounted above the raw water strainer in the starboard lazerette.
As if this project wasn’t enough Stem to Stern strongly recommended that we replace our old battery switch with a new one that would protect our alternator if the batteries we’re changed while running. This was a pretty straight forward swap out. We opted for the Perko with the locking feature since our new Volvo was a keyless start model and this provided some poultry security measure.
The old battery cables were replaced to ensure clean runs to the battery and engine.
The locking Perko battery selector switch.
Moeller 12 Gallon Tank Diagram