I need to replace the holding tank on my boat. Tanks that I've found on the web (and elsewhere) don't seem to fit very well, and I am considering building my own out of fiberglass. I can find very little on how well fiberglass holds up as a holding tank and was wondering if anyone here could comment. Thanks,
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If you use epoxy you should be fine
Go for the epoxy instead of polyester resin. Epoxy is immune to the blistering and does not react to just about everything. GuyT has a good point, how are you going to build the tank. If you want to "fill an existing void" space then you will need to epoxy the hull that will be used as part of the tank and then just build flat walls that you can build into a tank with glass tape. If you are going to build the tank and then install it then you still would want to build flat walls and then construct the tank from them using glass tape. Just don't build something you can't get into the space because of the access to it. A 6'x6' tank top will not fit through a 5'x2' door no matter how you turn or bend it. Also it is best to build the wall then drill a hole for the fitting that you glass in instead of building the wall and fitting at the same time. Don't forget about baffling if you have a tank that is "long" along the length of the boat. Baffling will keep the sloshing down and keep the smelly stuff from running out the vent etc. You will want to leak check it BEFORE you try filling with the real McCoy. Since the tank will never see anything above 0 PSI just apply a little lung power on a full tank to check for leaks and then some sea trials to make sure she doesn't flex unexpectedly. When you get done get us some pictures so we can go "OOOOOH" and "AHHHHHH"
Go for the epoxy instead of polyester resin. Epoxy is immune to the blistering and does not react to just about everything. GuyT has a good point, how are you going to build the tank. If you want to "fill an existing void" space then you will need to epoxy the hull that will be used as part of the tank and then just build flat walls that you can build into a tank with glass tape. If you are going to build the tank and then install it then you still would want to build flat walls and then construct the tank from them using glass tape. Just don't build something you can't get into the space because of the access to it. A 6'x6' tank top will not fit through a 5'x2' door no matter how you turn or bend it. Also it is best to build the wall then drill a hole for the fitting that you glass in instead of building the wall and fitting at the same time. Don't forget about baffling if you have a tank that is "long" along the length of the boat. Baffling will keep the sloshing down and keep the smelly stuff from running out the vent etc. You will want to leak check it BEFORE you try filling with the real McCoy. Since the tank will never see anything above 0 PSI just apply a little lung power on a full tank to check for leaks and then some sea trials to make sure she doesn't flex unexpectedly. When you get done get us some pictures so we can go "OOOOOH" and "AHHHHHH"
I would post pics but I never took any and
it is buried in the bowels of the bilge. There are no seams it was built over an aluminum form and fitted to the curve of the bilge. The waste line and the vent line were installed after the tank was otherwise complete. I pressure tested it to six feet of water column and then measured the volume of water when I drained it. 12 gallons. The same line that brings waste in also takes it out because it enters the tank from the forward end at the top and stops at the aft end at the bottom. The vent enters the tank at the forward end and is routed at a constant slope to a vertical run.
it is buried in the bowels of the bilge. There are no seams it was built over an aluminum form and fitted to the curve of the bilge. The waste line and the vent line were installed after the tank was otherwise complete. I pressure tested it to six feet of water column and then measured the volume of water when I drained it. 12 gallons. The same line that brings waste in also takes it out because it enters the tank from the forward end at the top and stops at the aft end at the bottom. The vent enters the tank at the forward end and is routed at a constant slope to a vertical run.
I'm even more confused by that.
The inlet and discharge SHOULD be completely separate...inlet at--or on--the top...discharge at the bottom, either via hose at the bottom, or a pickup tube inside the tank TO the bottom. I cam't quite manage to visualize any way to combine 'em that isn't likely to cause more problems than it solves.
The inlet and discharge SHOULD be completely separate...inlet at--or on--the top...discharge at the bottom, either via hose at the bottom, or a pickup tube inside the tank TO the bottom. I cam't quite manage to visualize any way to combine 'em that isn't likely to cause more problems than it solves.
Peggie, Picture two separate tubes placed side
by side. One runs diagonally from the top, forward end of the tank to the aft, lower end of the tank. That tube carries the waste into and out of the tank. The second tube is for the vent and just penetrates the wall of the tank at the forward end at the top. The waste enters the tank through the first tube. (actually a 1 1/2 inch PVC pipe) and is removed by the same tube simply by shifting a valve that connects the tank to either the head or to the pump out port. The head can not pump over board or out the pump out port. The vent is completely independent of the pump out lines and port. If this still leaves questions I will endeavour to answer them. Ross
by side. One runs diagonally from the top, forward end of the tank to the aft, lower end of the tank. That tube carries the waste into and out of the tank. The second tube is for the vent and just penetrates the wall of the tank at the forward end at the top. The waste enters the tank through the first tube. (actually a 1 1/2 inch PVC pipe) and is removed by the same tube simply by shifting a valve that connects the tank to either the head or to the pump out port. The head can not pump over board or out the pump out port. The vent is completely independent of the pump out lines and port. If this still leaves questions I will endeavour to answer them. Ross
I get it Ross, but I couldnt imagine why!
Your intake waste is pushed down to the bottom of the tank. Your discharge waste is sucked out throught the same tube. The problem is that you must raise the height of the tube to allow solid waste to pass and to not get clogged between the exit of the tube and bottom of tank. By doing this you never fully evacuate the bottom of the tank when you discharge -or- If you lower the tube to get the contents from the bottom of the tank during discharge, then you run the risk of clogging. By getting the design to one hose, you dont get the same performance as two lines.
Your intake waste is pushed down to the bottom of the tank. Your discharge waste is sucked out throught the same tube. The problem is that you must raise the height of the tube to allow solid waste to pass and to not get clogged between the exit of the tube and bottom of tank. By doing this you never fully evacuate the bottom of the tank when you discharge -or- If you lower the tube to get the contents from the bottom of the tank during discharge, then you run the risk of clogging. By getting the design to one hose, you dont get the same performance as two lines.
The end of the waste tube is cut left and right at
a 45 degree angle so that the waste that is pumped down through the tube is ejected either left or right at the bottom end. Therefore when I connect to the pump out all that went in must be able to come out through the same pipe. The quality of the suction at pump out is not less than 10 PSI on the vacuum. That is probably equal to the pressure of the force applied by the pump in the head.
a 45 degree angle so that the waste that is pumped down through the tube is ejected either left or right at the bottom end. Therefore when I connect to the pump out all that went in must be able to come out through the same pipe. The quality of the suction at pump out is not less than 10 PSI on the vacuum. That is probably equal to the pressure of the force applied by the pump in the head.
How can a tube that runs through the tank
Do anything except pass waste through the tank? If it weren't for your assurance that there's no way to dump the tank I'd think it was a highly creative way to install a tank that's "all for show, not for go." It's not a design I'd recommend for a bunch of reasons: a) it requires valves that wouldn't be needed if the tank had separate inlet and discharge lines...b) it requires at least one unnecessary valve...c) if it ever clogs you can't pump out OR flush the toilet...and d) there doesn't seem to be any way to rinse the sludge out of the tank.
Do anything except pass waste through the tank? If it weren't for your assurance that there's no way to dump the tank I'd think it was a highly creative way to install a tank that's "all for show, not for go." It's not a design I'd recommend for a bunch of reasons: a) it requires valves that wouldn't be needed if the tank had separate inlet and discharge lines...b) it requires at least one unnecessary valve...c) if it ever clogs you can't pump out OR flush the toilet...and d) there doesn't seem to be any way to rinse the sludge out of the tank.
Consider tank location
I'm guessing that Ross's tank can't have another fitting as the location is "down low" in his boat. He would have to drill a hole in the hull to get access to the bottom of the tank or install a second tube that just stops at the top of the tank. I don't see the point in putting a second tube at the top just to dump stuff in when you are going to pump the stuff in. If you gravity fed the tank then that might be a requirement but even then I doubt it. I like the way you think Ross, I'm gona keep my eye on you!
I'm guessing that Ross's tank can't have another fitting as the location is "down low" in his boat. He would have to drill a hole in the hull to get access to the bottom of the tank or install a second tube that just stops at the top of the tank. I don't see the point in putting a second tube at the top just to dump stuff in when you are going to pump the stuff in. If you gravity fed the tank then that might be a requirement but even then I doubt it. I like the way you think Ross, I'm gona keep my eye on you!
I think that you are missing a detail here.
If I had a wye valve in the discharge line from the head to the holding tank or the overboard discharge that would be normal. I simply installed the valve in such a manner that I can pump waste into the tank from the head or I can shift the valve and pump waste out of the tank via the on deck fitting. I can run water down the pump out fitting to rince the tank. The configuration of the tank is quite narrow at the bottom and with a substantial slope to the aft end. Edited to add: Bietzpadlin has a deep bilge with internal ballast that is encapsulated with glass. I designed the shape of the tank to fit the bilge and to rest on the keel. The tank is about 3 1/2 feet long, about 10 inches deep at the forward end and about 14 inches deep at the aft end. it is about 8 inches wide at the bottom and about 14 inches wide at the top. The top of the tank is level and is about 4 inches below the cabin sole. The tank is glassed in place to prevent movement but can be removed by cutting the fiberglass tabing.
If I had a wye valve in the discharge line from the head to the holding tank or the overboard discharge that would be normal. I simply installed the valve in such a manner that I can pump waste into the tank from the head or I can shift the valve and pump waste out of the tank via the on deck fitting. I can run water down the pump out fitting to rince the tank. The configuration of the tank is quite narrow at the bottom and with a substantial slope to the aft end. Edited to add: Bietzpadlin has a deep bilge with internal ballast that is encapsulated with glass. I designed the shape of the tank to fit the bilge and to rest on the keel. The tank is about 3 1/2 feet long, about 10 inches deep at the forward end and about 14 inches deep at the aft end. it is about 8 inches wide at the bottom and about 14 inches wide at the top. The top of the tank is level and is about 4 inches below the cabin sole. The tank is glassed in place to prevent movement but can be removed by cutting the fiberglass tabing.
Thanks for responses
Thanks for the responses to my question. I appreciate the ideas and comments. Our boat is a Swallow Craft Swift 33. We plan to put the tank under the starboard settee (where I think a tank used to be, based on old screw holes). The current 5 gallon tank seems to be a legal formality, and we're not comfortable discharging raw sewage after it fills. I think I could fit a 30-35 gallon tank, located about 2' from the toilet. Height is limited to 10", and length to 42". Width tapers from 15/20" (front bottom/top) to 20/24" (rear bottom/top) w/corner hull cutout along the bottom of the tapered side. Access is pretty good, and am planning to build/fit a mockup first. If I build it, I plan add a sump area to allow the dip tube to extend below the bottom of the tank. I will put in baffles. I read Peggy Hall's book, and it didn't seem to cover fiberglass in much detail, so was wondering what the problem was with it, if there was one. I looked at the Ronco Plastics list of tanks and some would fit, but not well. And, the tanks can't be easily modified. I also e-mailed them a week or two ago, but never heard back from them.
Thanks for the responses to my question. I appreciate the ideas and comments. Our boat is a Swallow Craft Swift 33. We plan to put the tank under the starboard settee (where I think a tank used to be, based on old screw holes). The current 5 gallon tank seems to be a legal formality, and we're not comfortable discharging raw sewage after it fills. I think I could fit a 30-35 gallon tank, located about 2' from the toilet. Height is limited to 10", and length to 42". Width tapers from 15/20" (front bottom/top) to 20/24" (rear bottom/top) w/corner hull cutout along the bottom of the tapered side. Access is pretty good, and am planning to build/fit a mockup first. If I build it, I plan add a sump area to allow the dip tube to extend below the bottom of the tank. I will put in baffles. I read Peggy Hall's book, and it didn't seem to cover fiberglass in much detail, so was wondering what the problem was with it, if there was one. I looked at the Ronco Plastics list of tanks and some would fit, but not well. And, the tanks can't be easily modified. I also e-mailed them a week or two ago, but never heard back from them.
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