Blackwater discharge above the waterline?

[Cool Hand Luke]

Originally Posted by Montanan

I perceive the issue of the blackwater discharge being above or below the water line to be of less an issue than if the blackwater discharge is located adjacent to the below water freshwater intake supply line for your watermaker.

Haha... now that's something one should definitely consider. I wouldn't trust that watermaker 100% at that point

[a64pilot]

I Installed a macerator pump to empty my black water tank, it discharges well above the water line, but if I direct discharge it’s under the water line.
When I empty the tank by using the macerator pump, it does stink, but hasn’t stained the hull.
You also can’t dump the tank and be stealthy either, it’s real obvious what your doing with the stream of brown water, but just don’t empty the tank where you shouldn’t and that won’t matter.

[GILow]

Originally Posted by David B

Frankly I cannot think of any good reason to do this. Holding tank well above the waterline, gravity discharge straight out of the bottom via a short length of large-bore hose.
Holding tank is filled via macerator right at base of toilet, up to the top of the tank, so no potential for significant back-flow if the check-valve leaks.

Clean, out of sight below the waterline, no smell, and you can empty via the usual deck fitting to dock suction, when where discharge is not appropriate.

The single large through-hull with seacock is of course checked as part of regular maintenance, and has a bung tied to it as a safety back-up.

And that's the point, right there. ANOTHER potential point of failure, and, also, the single largest through-hull on the whole boat.

Sure, you check it regularly, but the very fact that it needs to be checked AND you consider a bung needs to be tied to it is admitting that it is a risk to the boat.

A manageable risk, sure, but, to my mind, an altogether AVOIDABLE risk is better than a manageable risk.

[GILow]

Originally Posted by a64pilot

I Installed a macerator pump to empty my black water tank, it discharges well above the water line, but if I direct discharge it’s under the water line.
When I empty the tank by using the macerator pump, it does stink, but hasn’t stained the hull.
You also can’t dump the tank and be stealthy either, it’s real obvious what your doing with the stream of brown water, but just don’t empty the tank where you shouldn’t and that won’t matter.

I'm guessing you added the macerator discharge to an existing system? If that is the case, would you do it differently if you were starting from scratch?

I have the opportunity to start from scratch, hence asking this question, and my current thinking is to macerate into the holding tank (electric toilet), with a gravity drain from the holding tank above the waterline, hence eliminating a through-hull that has the potential to sink the boat.

I will have a deck level pump out fitting, but I do not foresee the opportunity to use it where I am going. It may never be used, but I figure it is worth having just in case.

[GILow]

Originally Posted by Montanan

I perceive the issue of the blackwater discharge being above or below the water line to be of less an issue than if the blackwater discharge is located adjacent to the below water freshwater intake supply line for your watermaker.

Actually, that is a really important point, and relevant to me because my watermaker is a low output variety so will run for extended periods.

I have positioned the intake on the opposite side of the hull, but I would still make sure it was switched off when emptying the holding tank. Probably easiest to put a sign next to the holding tank drain tap, just to remind me.

[David B]

Originally Posted by GILow

And that's the point, right there. ANOTHER potential point of failure, and, also, the single largest through-hull on the whole boat.

Sure, you check it regularly, but the very fact that it needs to be checked AND you consider a bung needs to be tied to it is admitting that it is a risk to the boat.

A manageable risk, sure, but, to my mind, an altogether AVOIDABLE risk is better than a manageable risk.

Ummm - don't we all have bungs tied to every below waterline seacock on our boats as standard practice in good seamanship?

No admission of any issues on my behalf …………………..

[GILow]

Originally Posted by David B

Ummm - don't we all have bungs tied to every below waterline seacock on our boats as standard practice in good seamanship?



No admission of any issues on my behalf …………………..

Of course we do. But you are kind of missing the point. If the seacock/through-hull is not below the waterline then it is no longer a threat to the boat.

[Supers0nic]

My uncle discharged above the waterline. It’s much safer.

[Belezar]

In St Lucia earlier this year a race/adventure boat was docked nearby. Their discharge was above the water line. Disgusting to be nearby if head was pumped. Didn’t see much stain though.

[Knotical]

Originally Posted by Montanan

I perceive the issue of the blackwater discharge being above or below the water line to be of less an issue than if the blackwater discharge is located adjacent to the below water freshwater intake supply line for your watermaker.

Some boats we saw during boat shopping had their head intake thruhull right behind the overboard discharge one, and you can't just flip the hoses as their sizes are different.

[a64pilot]

Originally Posted by GILow

I'm guessing you added the macerator discharge to an existing system? If that is the case, would you do it differently if you were starting from scratch?



I have the opportunity to start from scratch, hence asking this question, and my current thinking is to macerate into the holding tank (electric toilet), with a gravity drain from the holding tank above the waterline, hence eliminating a through-hull that has the potential to sink the boat.



I will have a deck level pump out fitting, but I do not foresee the opportunity to use it where I am going. It may never be used, but I figure it is worth having just in case.

Yes, when I replaced my waste tank, I had another bung added that I plumbed to the Macerator. My reasoning was that I didn’t want to leave for the Bahamas with a half full tank, and no way to empty it for months.
To install the discharge below the waterline would have required pulling the boat, and also of course a thru hull with a valve, so a lot more money.

I very rarely use the macerator to empty the tank, in the US we almost always pump out, and when elsewhere you direct discharge of course.

But if I were planning on using it often I would probably have used a diaphragm pump as they are more robust and last longer, and may have gone for underwater discharge, because pumping out does stink, unless sailing downwind, then there is no smell of course.

But for occasional use I like it the way it is. As is, I may use it three times a year.

We macerate into the tank also, but an above water line gravity drain wasn’t possible as the bottom of my tank is below waterline.

I think that if a gravity drain was possible, that would be the way I would go, gravity doesn’t break like a macerator can.
If it plugged I’d use my shop vac to blow into the pump out hose to clear it, surely a tank can hold a shop vacs pressure?

Oh, and if your starting from scratch, toss that tiny 5/8” vent. I went with a 1” vent. Actually I have two one inch thru holes side by side, one is the discharge, the other the vent. You can’t have too big of a vent.

[Shrew]

Originally Posted by Belezar

In St Lucia earlier this year a race/adventure boat was docked nearby. Their discharge was above the water line. Disgusting to be nearby if head was pumped. Didn’t see much stain though.

This is a good point. I suspect there is a difference between discharging directly from the head and discharging from a holding tank.

The holding tank has significantly more water, holding tank chemicals to both deodorize and break down solids. It also has the benefit of time for solids to break down.

You get none of this in a direct discharge from the head setup.

Mine was the former and not at all unpleasant. But then again, we discharged underway and it allowed to visually see when we were done offloading.

[senormechanico]

Originally Posted by navdi

Some boats we saw during boat shopping had their head intake thruhull right behind the overboard discharge one, and you can't just flip the hoses as their sizes are different.

I am OK with recycling things, but that's ridiculous!

[GILow]

Originally Posted by a64pilot

...

But if I were planning on using it often I would probably have used a diaphragm pump as they are more robust and last longer, and may have gone for underwater discharge, because pumping out does stink, unless sailing downwind, then there is no smell of course...Yes, there is that...

....

If it plugged I’d use my shop vac to blow into the pump out hose to clear it, surely a tank can hold a shop vacs pressure?

....Great idea!

Oh, and if your starting from scratch, toss that tiny 5/8” vent. I went with a 1” vent. Actually I have two one inch thru holes side by side, one is the discharge, the other the vent. You can’t have too big of a vent.

Now that is an interesting observation. My charcoal filter came with two pipe sizes, from what you are saying I should use the larger, which I think is one inch. Is this about making the tank easier to empty at pump-outs or some other reason?

[Uncle Bob]

Originally Posted by GILow

Now that is an interesting observation. My charcoal filter came with two pipe sizes, from what you are saying I should use the larger, which I think is one inch. Is this about making the tank easier to empty at pump-outs or some other reason?

Hi, I once asked our intrepid headmistress the same question and if I remember correctly the larger hose, without filter, to allow maximum air flow into the tank which improves aerobic bacteria action. (if I remember it correctly)