'85 tricabin fresh water tank replacement
Posted: Wed Dec 04, 2013 8:12 am
When I bought my boat, there was no fresh water tank level sensor. Being a mechanical engineer and fond of data, not to mention wanting to know whether I could complete my shower, I set out to fix that by installing a Wema level sensor in my factory aluminum water tank. Here is my tale...
I needed a threaded fitting in the tank in which to screw the new sensor. Since I didn't really want to weld two feet away from 220 gallons of gasoline, I bought a half-nipple and a piece of aluminum plate from my favorite store on earth, http://www.mcmaster.com. I cut a hole in the plate, rolled it to match the tank curvature, and welded the nipple to the plate. Since I was going to be cutting a hole in the tank, I figured that I'd take the opportunity to make the hole big enough to serve as an inspection port while I was at it.
Here is the tank before I really got started. The tank is enclosed in some built-in cabinetry, which has been removed. The hole is laid out. The plate and nipple were used to mark the proposed hole.
The new plate is attached to the tank by bolts, which can be removed when the need arises to access the inside of the tank in the future. They are threaded into 1/4" x 1" 6061 aluminum flats that were riveted in place inside of the tank. One flat is already installed inside of the tank, and is visible on the right side of the picture. I used tape as a cofferdam to catch debris so it didn't disappear into the bilge.
I also took the time to install a water tank vent that discharges overflow outside the boat, where it gives an indication that the tank is full, and keeps you from spilling water inside of the boat each time that you fill the tank. The factory vent discharged into the bilge when the tank was full. Really? I inspected the vinyl vent hose, tried to puncture it, and decided that it was in much better shape than anything that I could buy new.
Having made a new large hole in my tank, I was able to see inside for the first time. Uh oh. What is that? It looks like a baffle plate that was formerly welded in place inside the tank. It is floating around free now, and it could interfere with the new float. That's either got to come out, or get bolted back in place.
Mmmm. That doesn't look to good either. It is where the baffle was formerly attached to the tank. Looks like this one wasn't the last weld to break -- one of the other tabs acted as a hinge while the baffle rubbed on the tank after it broke here. I'm drinking water that is contained by this mess?
I decided to remove the tank, and coat the inside with food-grade epoxy tank liner. When I got the tank home, I was able to more closely inspect the tank. After further review, a new tank was in order.
After the factory tank was removed.
I was fortunate to find a tank that would not only fit through the door, but would fit within the geometric confines available in the tank area, and had more capacity than the factory tank. It was the same width, but was a pentagon in cross-section, instead of a circle. I think that I picked-up 6 gallons in the deal.
Here is the tank space part way through the installation of the support for the new tank, looking aft. New 2x material was sistered onto the existing supports, then additional 2x material was laid on top in order to provide complete support for the new plastic tank. Note the rectangular hole in the upper-left bulkhead. When I got the boat, there was a tiny hole there. The first time that I removed the night stand, I made the hole as large as it could be, so that there might be a chance of getting an arm in there to work on something in the future if need be. Also visible to the left on the bottom of the hull is the new fiberglass backing plate for the outside leg of the V-strut. I beefed-up the original arrangement the first time that I pulled my boat.
And another shot a little farther along, looking forward. The 2x4 that you see on the right is just tacked in place in order to provide a reference for the supports. Not too much in this area is plumb, level, or square, so I had to provide a datum.
The new tank support in place. Why do the inside of the hull and the pressure-treated wood which will likely never be seen by me again need to be painted? They just do....
Polyethylene foam provides a modest cushion for the tank, and protects against asperities in the supporting structure.
A wire runs along the forward bulkhead of the compartment. It is protected by a spacer, which keeps the wire from being pinched in the event that the tank slides forward for any reason. Why does it have to be level? It just does....
The new tank is held in place with new stainless strapping.
Here is the wiring all buttoned-up and ready for some self-fusing tape over the connections. Abrasion resistant covering on the sensor wires protect them from the stainless strapping, to which it is tied to resist fatigue. Some extra wire is coiled along the bulkhead to left, so that there is a chance of working on the wire in the future and having some slack in it.
All that future stewards of my boat will see to let them know that something happened here. My original plan was to install the rolled plate and nipple arthroscopically, so I carefully cut a door in the existing plywood underneath of the drawers. Ha!
A cross-section of the old tank. Yes, that yellow thing is a pit that extends two-thirds of the way through from the inside.
The old tank has been re-purposed. Crabs anyone?
I needed a threaded fitting in the tank in which to screw the new sensor. Since I didn't really want to weld two feet away from 220 gallons of gasoline, I bought a half-nipple and a piece of aluminum plate from my favorite store on earth, http://www.mcmaster.com. I cut a hole in the plate, rolled it to match the tank curvature, and welded the nipple to the plate. Since I was going to be cutting a hole in the tank, I figured that I'd take the opportunity to make the hole big enough to serve as an inspection port while I was at it.
Here is the tank before I really got started. The tank is enclosed in some built-in cabinetry, which has been removed. The hole is laid out. The plate and nipple were used to mark the proposed hole.
The new plate is attached to the tank by bolts, which can be removed when the need arises to access the inside of the tank in the future. They are threaded into 1/4" x 1" 6061 aluminum flats that were riveted in place inside of the tank. One flat is already installed inside of the tank, and is visible on the right side of the picture. I used tape as a cofferdam to catch debris so it didn't disappear into the bilge.
I also took the time to install a water tank vent that discharges overflow outside the boat, where it gives an indication that the tank is full, and keeps you from spilling water inside of the boat each time that you fill the tank. The factory vent discharged into the bilge when the tank was full. Really? I inspected the vinyl vent hose, tried to puncture it, and decided that it was in much better shape than anything that I could buy new.
Having made a new large hole in my tank, I was able to see inside for the first time. Uh oh. What is that? It looks like a baffle plate that was formerly welded in place inside the tank. It is floating around free now, and it could interfere with the new float. That's either got to come out, or get bolted back in place.
Mmmm. That doesn't look to good either. It is where the baffle was formerly attached to the tank. Looks like this one wasn't the last weld to break -- one of the other tabs acted as a hinge while the baffle rubbed on the tank after it broke here. I'm drinking water that is contained by this mess?
I decided to remove the tank, and coat the inside with food-grade epoxy tank liner. When I got the tank home, I was able to more closely inspect the tank. After further review, a new tank was in order.
After the factory tank was removed.
I was fortunate to find a tank that would not only fit through the door, but would fit within the geometric confines available in the tank area, and had more capacity than the factory tank. It was the same width, but was a pentagon in cross-section, instead of a circle. I think that I picked-up 6 gallons in the deal.
Here is the tank space part way through the installation of the support for the new tank, looking aft. New 2x material was sistered onto the existing supports, then additional 2x material was laid on top in order to provide complete support for the new plastic tank. Note the rectangular hole in the upper-left bulkhead. When I got the boat, there was a tiny hole there. The first time that I removed the night stand, I made the hole as large as it could be, so that there might be a chance of getting an arm in there to work on something in the future if need be. Also visible to the left on the bottom of the hull is the new fiberglass backing plate for the outside leg of the V-strut. I beefed-up the original arrangement the first time that I pulled my boat.
And another shot a little farther along, looking forward. The 2x4 that you see on the right is just tacked in place in order to provide a reference for the supports. Not too much in this area is plumb, level, or square, so I had to provide a datum.
The new tank support in place. Why do the inside of the hull and the pressure-treated wood which will likely never be seen by me again need to be painted? They just do....
Polyethylene foam provides a modest cushion for the tank, and protects against asperities in the supporting structure.
A wire runs along the forward bulkhead of the compartment. It is protected by a spacer, which keeps the wire from being pinched in the event that the tank slides forward for any reason. Why does it have to be level? It just does....
The new tank is held in place with new stainless strapping.
Here is the wiring all buttoned-up and ready for some self-fusing tape over the connections. Abrasion resistant covering on the sensor wires protect them from the stainless strapping, to which it is tied to resist fatigue. Some extra wire is coiled along the bulkhead to left, so that there is a chance of working on the wire in the future and having some slack in it.
All that future stewards of my boat will see to let them know that something happened here. My original plan was to install the rolled plate and nipple arthroscopically, so I carefully cut a door in the existing plywood underneath of the drawers. Ha!
A cross-section of the old tank. Yes, that yellow thing is a pit that extends two-thirds of the way through from the inside.
The old tank has been re-purposed. Crabs anyone?
