Black water tank in engine room?

[Lomax]

Hi everyone,

I'm currently planning the refit of a 44' steel barge and have a million questions! It's a challenge to find room for all the equipment required for comfortable aboard living while using as little precious living space as possible. One such item is the dreaded black water tank... My boat happens to blessed with a large engine room (diesel), with plenty of space for a good size tank - on my drawings I have fitted an 88L Vetus along one side, which has the benefit of placing it within inches from the head (electric macerator type, right on the other side of the bulkhead), but I'm worried that the often high temperature in the engine room may promote "interesting" biological activity in the tank. What's the common wisdom on placing black water tanks in the engine room?

 

[Ian_Edwards]

I don't have any experience of fitting back water tanks in the engine room, mine are fitted under the floor, next to the heads.
However, I think that your hunch is more than likely to be correct, a warm environment is more likely to generate nasty smells, but if you don't have any leaks and fit a carbon filter to the vent, it may well be practical.
Having experienced a leaking back water tank under the forward berth on a charter boat in New Zealand last year, a leaking black water tank is something to be avoided at all cost.

 

[vyv_cox]

How often will you be running the engine alongside a full holding tank? In my case it would be almost never, as we dump the tank contents as soon as possible after leaving a harbour or anchorage. So for me it would not be an issue. However, 'barge' sounds more like inland waterways, in which case it may be different. I imagine it would take a great deal of motoring to warm up the tank contents significantly, so it still may not be an issue. Can a thermal barrier be installed?

 

[Trident]

My friends Halbery Rassey 44 had two tanks, one in the engine room and one forward - they gave up using the rear heads with the tank in the engine room as it blocked so many times. It may have been plumbing related but certainly he was convinced the heat dried out the solids causing blockages.

 

[Bi111ion]

My aft heads pump and part of the pipework goes through the engine room. I wonder if that does contribute to solids drying out and clogging. In the Netherlands this summer we didnt use the aft heads as the tank is on the forward one, and we motored a lot in land. When I used it again out of Dutch territorial waters it was blocked. Next time I will flush it thoroughly with vinegar before going in to Dutch waters.

 

[Fendant]

I would use only stainless steel for a black water holding tank. For Controlling the level inside the tank I only use a ultrasonic sensor from Philippi.

 

[alanch]

If you are looking to use your barge mainly for inland use then I would consider as large a tank as possible. My inland only 30ft motor cruiser has a 320lt tank. It takes about a month to fill it.

 

[vyv_cox]

I would use only stainless steel for a black water holding tank. For Controlling the level inside the tank I only use a ultrasonic sensor from Philippi.

Urine, faeces and seawater is a very aggressive mixture. Many who have tried stainless steel have been disappointed with the result. Plastic is the way to go, HMWPE being the choice of most. Tek Tanks or Lee sanitation but there are plenty of others. The material is translucent so the level can be checked by shining a torch down from the top. The cost of the purpose made gauges is unbelievable - £150 to tell you it's full

 

[Lomax]

Many thanks for the interesting replies - I'll take that as a resounding "perhaps" Yes, the boat will mainly be used on inland waterways - though coastal jaunts, and even trips across the channel, should be possible. It is not, however, a sailing barge, so engine will be running whenever it's moving, which may be for many hours. I expect engine room temperature could easily go above 40 degrees. The tank would be installed within a couple of feet of the engine, so radiated heat might also be a problem - though some reflective heat insulation should take care of that. Since there is so much space, I would also like to place my main battery bank in there - so I guess what I should be doing is looking at ways to keep the temperature down as much as possible. Forced air ventilation (suck and blow), and a heat exchanger on the fuel return lines (the diesel tank is also in there) might help? There is room to fit a pair of substantial vents on the aft deck, where noise and smell are less of a problem, and forced air could enter at the bulkhead, where the batteries would be situated. The fans can be quite powerful since they'd only be needed when the engine is running, and the alternator provides all the power needed. If there is an issue with the tank contents drying out, that could easily be dealt with by topping it up with water?

 

[Lomax]

Urine, faeces and seawater is a very aggressive mixture. Many who have tried stainless steel have been disappointed with the result. Plastic is the way to go, HMWPE being the choice of most. Tek Tanks or Lee sanitation but there are plenty of others. The material is translucent so the level can be checked by shining a torch down from the top. The cost of the purpose made gauges is unbelievable - £150 to tell you it's full

Yeah, I've already settled on plastic - I've heard too many horror stories about stainless tank welds beginning to leak after a while! High-density polyethylene has all the benefits; durable, odour impermeable, cheap, light. Metering will be needed though, at least with a 1/4, 1/2, 3/4, 4/4 resolution. There may be ways to do this without having to spend too much money. This is the tank I've used in my drawings.

If you are looking to use your barge mainly for inland use then I would consider as large a tank as possible. My inland only 30ft motor cruiser has a 320lt tank. It takes about a month to fill it.

Wow, 320 litres! One month with how many people living aboard? I would be the only occupant most of the time, and would be happy if I could go ten days or so between pump-outs - though I fully intend to use land based facilities whenever available... Do you think I'll need a bigger tank?

 

[Bi111ion]

I was just thinking with your idea of contents drying out. I used to live on a narrow boat inland on a residential mooring with mains power. I had to empty the chemical toilet regularly by hand and it was a pain. I considered fitting one of those toilets that evaporates all the water from the waste leaving only a powder. When you think of all the heat you are making and that you can run a big alternator is that an option? Then the waste drying out becomes an advantage not a problem?

Sorry I dont have a link...that was back in the 1980s so assume they have got better. Maybe search for waterless electric toilet.

 

[alanch]

Wow, 320 litres! One month with how many people living aboard? I would be the only occupant most of the time, and would be happy if I could go ten days or so between pump-outs - though I fully intend to use land based facilities whenever available... Do you think I'll need a bigger tank?[/QUOTE]

We don't live aboard. Only 2 of us for about 3 weeks at the most. I have a high level alarm set at 80% and have never had it go off (yes it does work!) We have a jabsco manual toilet but you will have the benefit of an electric macerator which will use much less water. You should be able to calculate from the macerator specs what the water use is and how often you are likely to use it to check how often you will need to MT the tank. Be warned. Pumpouts can be expensive!

 

[Lomax]

I was just thinking with your idea of contents drying out. I used to live on a narrow boat inland on a residential mooring with mains power. I had to empty the chemical toilet regularly by hand and it was a pain. I considered fitting one of those toilets that evaporates all the water from the waste leaving only a powder. When you think of all the heat you are making and that you can run a big alternator is that an option? Then the waste drying out becomes an advantage not a problem?

Yes, I've seen those, it's an interesting option. So is a composting toilet. In the first case you need a lot of electricity, and in the second a much bigger bathroom (current layout allows for only 120x70cm!). In both cases you'd still need somewhere to dump the waste - although there will me much less of it, and it will be less unpleasant to deal with. Then there are Marine Sanitation Devices; effectively miniature sewage treatment plants, which should render the waste harmless and legal to pump out in most places. I may be tempted by such options later, but for simplicity's sake the current plan is electric macerating toilet straight into a black water holding tank.

We don't live aboard. Only 2 of us for about 3 weeks at the most. I have a high level alarm set at 80% and have never had it go off (yes it does work!) We have a jabsco manual toilet but you will have the benefit of an electric macerator which will use much less water. You should be able to calculate from the macerator specs what the water use is and how often you are likely to use it to check how often you will need to MT the tank. Be warned. Pumpouts can be expensive!

Ok, good info there, thanks. I could fit a slightly longer/taller tank, but the width will have to be about the same as the 88L I've based the drawings on. No chance to fit anything as big as your 320L tank. From what I've read in the specs for the loos I've looked at they use about a litre of water with every flush - if you're happy to hop ashore and tinkle in the bushes when possible then 88L ought to take quite a while to fill?

 

[alanch]

At my age a tinkle means every 2 hours!

 

[vyv_cox]

Ok, good info there, thanks. I could fit a slightly longer/taller tank, but the width will have to be about the same as the 88L I've based the drawings on. No chance to fit anything as big as your 320L tank. From what I've read in the specs for the loos I've looked at they use about a litre of water with every flush - if you're happy to hop ashore and tinkle in the bushes when possible then 88L ought to take quite a while to fill?

Unfortunately there is a down side to low volume flushing, in seawater but perhaps less of a problem in fresh. The hose between the toilet and the tank almost always contains a mixture of water and urine, resulting in salt deposition at the top of the bend. This will completely block the hose in time, for me about two-three years. The only way to fix it is to remove the hose, so I suggest you plan your layout to allow this.

 

[Lomax]

Here's a quick render of the layout, top down view - the cabin/engine room bulkhead divides the image in half horizontally, outline of bathroom top right, with the black water tank just below. The brown-red blocks to the left of the tank is the main battery bank. I think this is an efficient use of space.

 

[Lomax]

Unfortunately there is a down side to low volume flushing, in seawater but perhaps less of a problem in fresh. The hose between the toilet and the tank almost always contains a mixture of water and urine, resulting in salt deposition at the top of the bend. This will completely block the hose in time, for me about two-three years. The only way to fix it is to remove the hose, so I suggest you plan your layout to allow this.

Interesting. I plan to only use fresh water for flushing though. Having talked to a few live-aboards I've included a 750L fresh water tank in the bow - sounds like a lot to me but everyone complained about not having enough fresh water on board.

 

[Lomax]

At my age a tinkle means every 2 hours!

After a few beers it's more like every 20 minutes for me!

 

[Birdseye]

Hi everyone,

I'm currently planning the refit of a 44' steel barge and have a million questions! It's a challenge to find room for all the equipment required for comfortable aboard living while using as little precious living space as possible. One such item is the dreaded black water tank... My boat happens to blessed with a large engine room (diesel), with plenty of space for a good size tank - on my drawings I have fitted an 88L Vetus along one side, which has the benefit of placing it within inches from the head (electric macerator type, right on the other side of the bulkhead), but I'm worried that the often high temperature in the engine room may promote "interesting" biological activity in the tank. What's the common wisdom on placing black water tanks in the engine room?

Didnt you ever light farts as a kid? The gasses coming off that tanks can be explosive particularly if you eat lots of beans and curry.

 

[Lomax]

Didnt you ever light farts as a kid? The gasses coming off that tanks can be explosive particularly if you eat lots of beans and curry.

Not successfully, though I've heard it's possible. Maybe we weren't trying hard enough. Certainly gas captured from sewage is used for its flammability in energy production. However, in a marine waste water system I would expect this to be vented harmlessly* over board via the tank ventilation hose? It may be that gas production increases so dramatically with temperature that it poses a problem - I doubt it, but I don't really know, which is why I posted the question. So far the potential drying out of waste, and the clogging this can lead to, would appear to be the only problem with my plan?

*) As long as you're not within smelling distance of the outlet!