Installing black-water tank : questions ???

Tranona said:
Yes, that is correct and how both the tanks I have installed are arranged - and it works. However, some have a dip pipe for extraction so that may not be possible.
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Is one of those boats your Bav 37, Tranona ? I'm thinking of installing a gravity drained waste tank under the side deck outboard of the heads in Sunrunner. The picture shows the location, I reckon I can get a 600x400x250mm tank standing vertically in the cubbyhole with adequate clearance above. This would put the bottom of the tank about 6 inches above the unheeled waterline. For simplicity I thought I'd just connect the heads outlet to the tank inlet and the tank outlet to the existing outlet seacock.

The issue is that Sunrunner can fairly easily put the rail under because of her tumblehome and I wondered whether below the side decks and around 6 inches inboard of the topside will be enough to ensure it doesn't backflood ? With the existing heads there is a loop in the outflow pipe but of course there's a valve in the (Lavac) heads pump so backflow is a bit less likely anyway.

Any ideas whether this arrangement would work ? I know I could always shut the seacock but it would be rather horrible to forget and have the whole tank contents backflow and spill into the boat. :eek:

Boo2

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Boo2 said:
Is one of those boats your Bav 37, Tranona ? I'm thinking of installing a gravity drained waste tank under the side deck outboard of the heads in Sunrunner. The picture shows the location, I reckon I can get a 600x400x250mm tank standing vertically in the cubbyhole with adequate clearance above. This would put the bottom of the tank about 6 inches above the unheeled waterline. For simplicity I thought I'd just connect the heads outlet to the tank inlet and the tank outlet to the existing outlet seacock.

The issue is that Sunrunner can fairly easily put the rail under because of her tumblehome and I wondered whether below the side decks and around 6 inches inboard of the topside will be enough to ensure it doesn't backflood ? With the existing heads there is a loop in the outflow pipe but of course there's a valve in the (Lavac) heads pump so backflow is a bit less likely anyway.

Any ideas whether this arrangement would work ? I know I could always shut the seacock but it would be rather horrible to forget and have the whole tank contents backflow and spill into the boat. :eek:

Boo2
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The tank in my Sadler is a straight-through, gravity drained one similar to your proposal. In our case the tank outlet is very little above the waterline, less than 6 inches. On starboard tack I assume that the tank fills with seawater, with air leaving it via the vent. Our discharge piping loop extends above any conceivable water line so there is little risk of backflooding, which in any case would have to pass the joker valve. I have always assumed this arrangement to be a benefit, as the tank is flushed whenever we are beating.
 
Yes, the tank in my B 37 is in a similar locker behind the wash basin along with the water pump and changeover cock which had to be moved. Like Vyvs it is straight through and outlet just above the waterline with enough fall to drain when static. Inlet is also from the bottom with a stack pipe inside. Pump out access directly above the outlet and a 25mm vent in the topsides. Very similar size to your proposal giving approx 60l capacity. I had it made in Greece but very similar to the one Tek Tanks made for me for my Eventide. works very well.

With the space you have you will need to have a custom tank as the only standard size bulkhead tanks (from Vetus) are too deep front to back.
 
BabaYaga said:
Just out of curiosity: How do you pump out from the top of the tank without a dip tube?
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I doubt very much that you can. The dip pipe on mine doubles as the inlet, extending downwards to about 25 mm above the discharge. The thinking is that when the discharge seacock is open everything goes pretty much straight through without entering the tank. A sideways 'T' connected to this, with the pumpout continuing on upwards, allows a rod to be pushed right through to the discharge in the event of blocking. The inlet goes to the side arm of the 'T'.
 
vyv_cox said:
I doubt very much that you can. The dip pipe on mine doubles as the inlet, extending downwards to about 25 mm above the discharge. The thinking is that when the discharge seacock is open everything goes pretty much straight through without entering the tank. A sideways 'T' connected to this, with the pumpout continuing on upwards, allows a rod to be pushed right through to the discharge in the event of blocking. The inlet goes to the side arm of the 'T'.
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Thanks, that makes sense to me.
I have some trouble visualizing how the set up outlined by Tranona would work, especially the statement in post #10 that a dip tube for extraction might make rodding out difficult (so presumably there isn't one).
Or is a dip tube part of the land side equipment in some places? I have only seen and heard of systems that connects at the deck fitting, not further down. In my wiew, without a dip tube in the tank, pumping out to shore will have to by the bottom drain.
 
BabaYaga said:
I have some trouble visualizing how the set up outlined by Tranona would work, especially the statement in post #10 that a dip tube for extraction might make rodding out difficult (so presumably there isn't one).
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I think that by "extraction" in post 10 he means the pipe which goes overboard, via a pump. Some people prefer that tanks have no holes in the bottom, as it rules out certain classes of leak (imagine the flood if the fitting got knocked off the bottom of a full holding tank :eek:).

As far as I know, openings for shoreside pumpout will always need a dip tube. The shoreside fitting is a sort of rubber cone that just fits into the deck socket, not a tube that reaches into the tank.

Pete
 
prv said:
I think that by "extraction" in post 10 he means the pipe which goes overboard, via a pump. Some people prefer that tanks have no holes in the bottom, as it rules out certain classes of leak (imagine the flood if the fitting got knocked off the bottom of a full holding tank :eek:).
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Might be, but the context was that of a gravity draining arrangement, in which case there must be a hole in the tank bottom.
Perhaps Tranona finds this thread again and could clarify...

I was just a bit concerned about the OP, as he had a black water that was never used before and that he is probably not so familiar with.
One could get the impression from his first post that he thought a connection from the tank to a deck fitting is all that is needed for pumping out.
 
Yes, just to clarify neither of the tanks I have installed are connected up for pumping out, mainly because there are no convenient pumping facilities where I sail. The Tek Tanks one has a screw blanking plug over the access hole and if I did put in a pump out the fitting would have a dip tube. On the Bavaria one, I am pretty sure it has a dip tube in it already welded in as there is only a plain tube on the top face with a plug over it. I have used this tube for rodding after a blockage - using a guardrail wire with a swaged end fitting for the "rod". Just long enough to come in through the loo window and down the tube and it worked.
 
The saga continues - the old un-used tank was rusted and the pressure test revealed at least 1 leak -> dumped.... also it was only 27 litres (my wife uses that in 1 day I am sure)

So we are now getting a proper 75 litre plastic tank , chopping up a cupboard entrance and installing it correctly : I will have a bit of carpentry to do afterwards.

I have made carefull note of ALL the comments and we are doing our best to ensure it all works well. Am relieved we are installing new (even all the hoses are being replaced) as I would have worried about the old one. Now I have less worries and less money

Thanks to all

Kris SV Footprints Latchi Cyprus
 
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