how big is my holding tank?

[ChattingLil]

We've finally got our tank operational and visited the pump out today. Yippee. However we've got no idea what the capacity is. Anyone got any ideas how we can measure it? The pump out has no guage. So apart from filling it bucket by bucket - any other ideas? It's a steel tank built into the hull with no accessible access hatch (it's under the engine). Thanks

 

[NormanS]

Not sure that the actual capacity, measured in litres or gallons, is going to help you very much. It's unlikely that you're going to measure the amount going in. Experience will give you an idea of the number of days it can cope with.

 

[nigelmercier]

Count the pumps until it's full, that is the important measurement.

 

[sailorman]

measure it
then determine what the pump out puts

 

[Davy_S]

measure it

It's a steel tank built into the hull with no accessible access hatch (it's under the engine).

 

[ChattingLil]

Not sure that the actual capacity, measured in litres or gallons, is going to help you very much. It's unlikely that you're going to measure the amount going in. Experience will give you an idea of the number of days it can cope with.

Count the pumps until it's full, that is the important measurement.

Yes thanks. I think that's right. What we need to know is how long it will last person...

Would be interesting to know the capacity though.

 

[NormanS]

Don't know if you are referring to black tank or grey tank. If it is the black tank, it will be filled by xNo of pump strokes. As an experiment, it would be worth filling it, and counting the strokes. That would give you an indication of the number of days capacity. I presume you are able to pump it out again manually. If it's a grey tank, it's not so important. I pump mine out every second day.

 

[prv]

It's a steel tank built into the hull with no accessible access hatch (it's under the engine).

In that case, if it were my boat I'd think twice before pumping it full of seawater and wee! Highly corrosive mixture which shouldn't really be put into metal tanks at all, especially not plain steel, and doubly especially not one you can't get at when it starts leaking.

Pete

 

[Modulation]

Tricky one this. Depends on your views of what constitutes good form. Wee - just pump it straight through - it's a fluid so same as water albeit not QUITE as pure. **** - MUST go to the holding tank - and all the flushing water too. Is it really that difficult to work out if you can see the size of the pump? Maybe not so tricky after all!!

 

[Gwylan]

We've finally got our tank operational and visited the pump out today. Yippee. However we've got no idea what the capacity is. Anyone got any ideas how we can measure it? The pump out has no guage. So apart from filling it bucket by bucket - any other ideas? It's a steel tank built into the hull with no accessible access hatch (it's under the engine). Thanks

Should be able to get an estimate of the dimensions, hence the volume. Volume in litres, knock 25% off for luck and you will be near your capacity.

 

[nigelmercier]

Yes thanks. I think that's right. What we need to know is how long it will last person...

Would be interesting to know the capacity though.

Put 5 litres of water in the bowl, and count how many pumps it takes to empty it. Then count the number of pumps to fill the tank.

 

[ChattingLil]

In that case, if it were my boat I'd think twice before pumping it full of seawater and wee! Highly corrosive mixture which shouldn't really be put into metal tanks at all, especially not plain steel, and doubly especially not one you can't get at when it starts leaking.

Pete

interesting! Does anyone know what other steel boats with built in tanks do? I suppose it's ok if you pump out regularly and don't leave it festering away?

 

[rogerthebodger]

When I built my steel boat the only tanks that were made from mild steel were my built in diesel tanks. My waste tank I built from flat sheet GRP with polycarb access hatched on top to allow visual inspection with needing to remove hatched.

 

[prv]

interesting! Does anyone know what other steel boats with built in tanks do?

Use the tanks for diesel (ok-ish as the oil protects the steel, though there will still be small amounts of water as condensation above the diesel or settled out below it), or for freshwater (tolerable if well-painted at build time with an epoxy system suitable for drinking-water tanks, but I'm still not sure I would). But waste tanks should be plastic, ideally Tek-style welded from 12mm polyethylene.

Pete

 

[nigelmercier]

But waste tanks should be plastic, ideally Tek-style welded from 12mm polyethylene.

Absolutely.

 

[MASH]

It'll take two people fifteen minutes or so to hand buckets down and pump them in. Count buckets and count pump strokes (or count pump strokes for 2-3 buckets and extrapolate). Then you'll know two useful things. Firstly the tank capacity, plus approximately how many uses the head has before the tank is full.

You can't do much about a built in tank under the engine but maybe work out a plan incase it does leak.

 

[prv]

You can't do much about a built in tank under the engine but maybe work out a plan incase it does leak.

It sounds like it's integral with the hull on a steel boat, which means that a leak may be through the shell plating into the sea! No disaster as long as that's all that happens, but by that point the forward and aft tank wall would also be getting pretty weak, and then when that goes you're sinking.

None of this is going to happen next week, we're talking ten or fifteen years, but it's still a crazy piece of design. Did a professional yard come up with this or was it an amateur bodger?

The metal tank on Ariam was perforated and leaking after fourteen years, but that was stainless rather than mild steel.

Pete