Thru hull for macerator, above or below waterline?

J

jtsmlarson

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Joined
Jul 7, 2002
RO Number
9256
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411
I have everything I need to add my macerator except the thru hull. I'm trying to figure out a way to do this either with existing thru hulls or without having to add a new one below the water line. Can I pump this out through the toilet freshwater thru hull? Can I shoot this out through an above waterline thru hull or should I just bite the bullet and add a new thru hull?
 
If you're talking about the Macerator outlet, I think you definitely want this as an underwater seacock. Can't imagine having macerated waste pouring out the side of the boat. Mine has a dedicated thru-hull and I think most do.
 
Mine discharges through a dedicated thru hull above the waterline. I like it like that since it is separate from any other system in the boat. .since I only use it when off shore and underway it works out OK.

Bob
 
quote:
Originally posted by rnbenton

Mine discharges through a dedicated thru hull above the waterline. I like it like that since it is separate from any other system in the boat. .since I only use it when off shore and underway it works out OK.
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Mine is also above the waterline. This eliminates the need for a seacock and vented loop. A far simpler installation and it works just as well.

You cannot share the thru hull with the head intake or any other use.
 
Definitely don't use the head's intake through-hull; you'll be pulling that nasty water back into the toilet when you flush it, basically turning your head into a recirculating head. You won't like the results. It needs to be a dedicated through-hull.

While the others have said that they prefer it to be above the waterline, and I understand their reasons why, I tend to disagree. It ain't the prettiest thing to look at, it can stain the side of your hull, and it will SMELL!!! My preference would be to have it "just below" the waterline, maybe 4" or so.
 
i'm with vic on this one unless yours is a 50+mph high speed application.

yes it does require a seacock but I would not install a vented loop unless your macerator pump is below the water line as well.
 
Mine, which I no longer use and which is capped off, is as Vic says - just below the surface. It's such that at rest, if you open it up, no water will come out. i.e. the valve body and fittings rise up a few inches and come above the waterline.
 
Below the water line, can't with smarts see it anyway else.
 
Ok, I can't resist. YGTBSM. This is obvious. BELOW!!

The only reason a mfg. would put it above is to discourage use. And rightfully so if you are nearby pump outs.
 
quote:
Originally posted by boatbum

Ok, The only reason a mfg. would put it above is to discourage use.
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Or to be cheap. Plastic above waterline thru hull is cheaper. Mine was like that, apparently, from the factory.

Bob
 
quote:
Originally posted by rnbenton

Originally posted by boatbum

Ok, The only reason a mfg. would put it above is to discourage use.
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Or to be cheap. Plastic above waterline thru hull is cheaper. Mine was like that, apparently, from the factory.

One question though; If you discharge out of a thru hull below the waterline or under the boat, wouldn't that make it suseptible to be sucked in by your cooling water intake or A/C intake?

Bob
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I can see both sides of above and below. The advantage to being above the waterline is obvious, but yes I would have to contend with the mess. I'm looking at a point that is about 1" above the waterline and right where the bottom paint ends at the very back of the boat. It's something that will only be used for one or two weeks a year when we're cruising in the San Juans. I think at that point, enough water would slosh in and out of the through hull that I wouldn't have to wash it after every use but I've never had a macerator before!?! I don't want a TP stripe either! The rest of the time we have it pumped out since we're on inland lakes. I definitely want it on the side of the boat so that I can dump it at RV dump stations between uses.
 
The 87 340 DA discharge is through the bottom just forward of the starboard rudder. Gets plenty of prop wash to disperse waste pumped out underway.
 
The above water line version is going to stink IMHO.

Besides, shutting down appliances while pumping over is not a big deal.
 
An above the waterline holding tank discharge will smell as you're discharging sewage. So what? If the boat is moving, you're moving away from the smell. You’re also able to hear more easily when the tank has been emptied.

My boat is now ten years old and has an above the waterline discharge. There is no stain. There's a stain from the AC cooling water discharge, but not from the holding tank discharge.

It's less expensive for the manufacturer, but this is one of those situations where a relatively large expense provides a relatively small benefit. Before I owned one, I might have said that it should be below the waterline. Having now owned a boat with an above the waterline discharge, I have no problem with it and if I were installing a system in a boat, I would save the cost and trouble and do it just like the boat I have.
 
quote:
Originally posted by jtsmlarson

I can see both sides of above and below. The advantage to being above the waterline is obvious, but yes I would have to contend with the mess. I'm looking at a point that is about 1" above the waterline and right where the bottom paint ends at the very back of the boat. It's something that will only be used for one or two weeks a year when we're cruising in the San Juans. I think at that point, enough water would slosh in and out of the through hull that I wouldn't have to wash it after every use but I've never had a macerator before!?! I don't want a TP stripe either! The rest of the time we have it pumped out since we're on inland lakes. I definitely want it on the side of the boat so that I can dump it at RV dump stations between uses.
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Stop right there - You can't use your boat's macerator to pump out at an RV dump station. It would shoot out all over the ground.

You need to suck it out of the deck fitting. That's the difference between a marine pumpout station and an RV dump station. RV holding tanks can be emptied by gravity. Boat tanks cannot.

I've posted this before, but this is what I used to empty my previous boat's holding tank into my home sewer. It would work just as well at an RV dump station:

203062913.jpg
 
quote:
Originally posted by boatbum

Ok, I can't resist. YGTBSM. This is obvious. BELOW!!

The only reason a mfg. would put it above is to discourage use. And rightfully so if you are nearby pump outs.
Click to expand...

As I pointed out in my other responses, placing the discharge above the waterline saves the cost of a seacock and vented loop and the cost of installation, bonding, etc. That's one less below the waterline penetration. It's also one less thing to operate when discharging sewage.
 
I prefer above waterline. Unless you are a disguting law breaking sob you will always dumb at least 3nm offshore where chop will rinse the hull side as you dump

Plus this allows you to check for flow so you know it s pumping and also let you see when the tank is empty so you don't burn those cheap impeller macerators

And cost aside that s one fewer sea cock to worry about
 
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