Clearance for fittings on water/ holding tanks

[Sailorjack]

In one of the discussions about replacement tanks someone suggested a minimum clearance between the top of the tank and the underside of the locker top. Can anyone remember what the clearance was of in what thread it was?

Thanks

 

[Peggie Hall HeadMistress]

1.5" thread-barb inlet and discharge fittings need at least 5" above the tank. A 1" vent fitting needs at least 3". If you plan to put all the fittings on the top of the tank, be sure to specify a pickup tube on the discharge fitting in your order. Might be a good idea for us to talk about fittings placement in the tank before you spec anything.

I see you're in Newfoundland...I have a good friend who's a Newfie..near St. Johns.

 

[Sailorjack]

1.5" thread-barb inlet and discharge fittings need at least 5" above the tank. A 1" vent fitting needs at least 3". If you plan to put all the fittings on the top of the tank, be sure to specify a pickup tube on the discharge fitting in your order. Might be a good idea for us to talk about fittings placement in the tank before you spec anything.

I see you're in Newfoundland...I have a good friend who's a Newfie..near St. Johns.

Peggie

Thanks for the info. I am replacing my P & S water tanks and the holding tank. All originals are aluminum but I'm going with poly most likely from Ronco. All fittings for the holding tank will be on top. I will have to put the water tank fittings on the end to maximize the capacity. I propably won't get the original capacity in the new tanks. Some hunter owners are going with rigid PVC pipe instead of hose. Does it make a difference?

If your friend is a sailor send a pm about him/her. The sailing community is not that big here so I may know him/her.

 

[Ed Schenck]

I put a 22 gal Ronco in the v-berth locker with less than four inch clearance. And you are right, to get the capacity in our two water tanks we currently have about an inch of clearance. Thanks to connections all coming off the ends.

 

[Sailorjack]

Ed

I am looking at Rocco tank B445 a 35 gal tank that I think will fit. The v-berth is the next big cut I have to make. I will try to take lots of pictures and keep everyone informed of my progress.

BTW this forum is great and many thanks to all who contribute.

John

 

[Ed Schenck]

Looking forward to your water tank project. Still haven't done that.
A 35 fits nicely up front. I couldn't do that because my transducers are in there. I can still reach them with the smaller tank.

 

[Sailorjack]

Ed

I cut the top off the storage compartment in the v-berth. I have 4" from the top of my mock up tank to the bottom of the v-berth top that I cut out. Peggy Hall figures I will need 5 inches clearance to attach the necessary fittings to the tank. Looking at the picture you provided it is hard to judge the clearance you achieved. Do you remember what the clearance is?

Photo 1 Bulkhead removed - v- berth / hanging locker to get tank in to v-berth
Photo 2 Top cut off storage area
Photo 3 Tank mockup in place
Photo 4 Clearance of 4 inches

 

[Peggie Hall HeadMistress]

It's important that you have enough clearance above the fittings to make sure that downward pressure on the berth, settee or whatever is above the tank won't put downward pressure on any fittings. That can crack a female tank fitting.

 

[Sailorjack]

Peggie

Yes. Thanks for the advice. Fortunately the "deck" of the v-berth in fairly stiff and there doesn't seem to be much deflection. Before I order a new tank I want to make sure everything will work.

 

[Ed Schenck]

Yes, I mentioned that in my original post. I have four inches between top of tank and underside of v-berth. You can see in the picture that the elbows don't sit very high. And you are correct, there is no deflection.

 

[Sailorjack]

Hi All

I'd like to update you on my tank project. I have decided to build a custom fiberglass holding tank. I built a plug using thin plywood. I want to fiberglass the plug then cut the top off and add more fiberglass to the inside to a thickness of about 0.5 inches, coat the inside to make a smooth surface and then put the top back on.
The surface of the plug is not smooth so can I cover the plug with polyethylene sheet ( 6 mil plastic) to act as a release?

Thanks

 

[Peggie Hall HeadMistress]

Have you checked out the Ronco Plastics Ronco Plastics Marine Catalog tank catalog? They make TOP quality thick-walled rotomolded tanks for a very reasonable price and have more than 400 shapes and sizes, over 100 of which are non-rectangular. And they install fittings in quantity, sizes and locations--including on top with a pickup tube--specified by the customer when they make the tank. I'd bet they have one that'll fit your space...and it's a whole lot easier than making a FG tank!

 

[Jim Legere]

I would doubt that you can get a smooth surface with poly vapour barrier - you will have folds and they will not lie flat. Why not just make your thin plywood plug the 'core' of a glass sandwich tank? There are many different approaches; with a bit of sweat equity they will all get you a holding tank. I assume you have read this article in Good Old Boat?

 

[DianaOfBurlington]

Plastic over fiberglass

Sounds like a heck of a lot of work, Sailorjack. I go with Peggie on this one.

The only application for which I'd consider using fiberglass is an integral tank, building it right into the inside of the boat. And this is best done at the building stage, as-- no matter what you use the tank for (and it shouldn't be for fresh water) --it will require some additional hull layup and a lot of work to fit and 'glass the top properly. We've done this with diesel tanks and holding tanks before. The main issue is making sure there is a throughway for bilge water to get past the tank.

Remember that modern ethanol-blend fuels and fiberglass tanks do NOT mix. If you use gasoline, plastic is your best (and only) option.

A friend has a 1960s boat with integral fresh-water tanks, and the keel bolts come up through the bottom of the fresh-water supply. It was designed this way. This was inexcusable. To inspect or maintain the keel bolts you have to drain the fresh-water supply, remove the lid covers (and their bedding compound), attend to the bolts and then wait for your 5200 to dry before refastening the lid and refilling the supply. Just imagine if the bolts were leaking seawater and you didn't know till you were at sea and having to drink or cook with that tank water. It's absurd-- yet many boats in the '60s were done this way.

As Peggie says, there are hundreds of weird and wild tank shapes to choose from. Ronco and Raritan both supply tanks in light- (fresh water) and heavy- (holding) duty plastic. These are engineer-designed and will pretty much last for ever. Few if any cost over $500. Given the option I wouldn't take out my toolbox for that.

Best of all, if it ever does go bad, since you know you got it down the hatch and into the bilge, you know you can get the old one out and get a replacement back in. Building custom tanks, especially when working inside the boat, can be like building a boat in your basement....

Just my two bits there :dance:

 

[Sailorjack]

Peggie, Jim, JCII & Ed

Thanks you for your advise and comments.

Peggie, I agree that a plastic tank would be the easier choice. I have studied the Ronco and Raritan catalogues and built several tanks using cardboard but the best fit and the biggest tank I could get was with the Ronco B445 but it barely gives me 4 inches clearance for the fittings.

Jim, I have added pictures of the plug that I have built, it fits the shape of the hull. While I like the idea of using the plug as part of the tank the cleats that hold the plug together pose a problem( see pictures). I did read the article in Good Old Boat about using drywall as the plug but you can see from the pictures that the curves would be very challenging. I think I can get a reasonably smooth finish to the inside of the tank as I will have to add another 1/4 inch of fibreglass to the inside to ensure no problems with leakage and get a smooth finish for easy cleaning.

JCII, my plan is to build the tank in my shop an then install it in the boat as if it was a plastic tank. You are right about the price of a plastic tank and I would pay it if I could get the right one.

If I am heading into trouble with my approach please let me know as I do respect your experience and appreciate your advise.


Photo 1 Plug upside down
2 Aft
3 Forward
4 Inside
5 Top

 

[Jim Legere]

Nice plug. (Nice shop too...) What about touching up the plug with autobody filler, then just rolling a couple of coats of cheap polyester resin on the the plug, and several coats of wax? I assume you are going to cut the tank in half after it is constructed, remove the plug and then glass it all back together? (or better yet, make a female mold and start producing tanks for sale to the rest of us!

 

[Sailorjack]

Jim

Auto-body filler and polyester is not a bad idea to seal the plug. I think I'll try it. As for making the mold and producing tanks let's see how this one turns out first. I'm glad the camera. doesn't pick up the mess of my shop but thanks for the compliment. I'll keep you posted on the progress of the plug.