Loo outlet location

[Hartley18]

The latest threads on Loos and Poos have got me thinking.. (anything to stop we worrying about the engine!)

Our head outlet (yes, I know you're not supposed to use it.. yadayadayada.. ..and we usually don't - in fact, haven't used it since we bought the boat) was kinda right on the waterline and, having removed a lot of crap off the boat since the pic below was taken, is now pretty much always above it!

I'm assuming the outlet is supposed to be below the waterline - otherwise it's blooming obvious when you use it - if not, is this a problem??



Thanks,
Cameron

[JohnRPollard]

Cameron,

What do you have against poo? Poo isn't so bad, is it?

Here in the States we can only use that direct-discharge thru-hull when we are well off-shore, beyond any coastal waters. So, ours never gets used on Chesapeake Bay.

That said, ours is well below the waterline, and quite a bit inboard toward the fore/aft centerline of the boat. That's where I'd want it, so that when/if it was being used while sailing off-shore, it would not be high and dry on one tack or the other.

[sailingdog]

Yes, you'd be wise to move it to under the waterline, rather than at the waterline... unless you plan on only emptying the tank while you're sailing on a starboard tack...

[SlowButSteady]

Modern sailboats almost always have the head outlet below the static waterline. But, this is more for aesthetic reasons than anything else. It also allows the discharge hose to drain regardless of the heel of the vessel (within reason); which is why greywater outlets are also usually below the static waterline. Ships usually have the outlet well above the waterline, for safety reasons; if a valve and/or hose fails the boat isn't likely to sink.

If I had my druthers, I would locate all outlet thru-hulls above the waterline and put a little "spout" on the outside to keep the hull clean. Just use the holding tank in port and give the thru-hull a rinse with wash-down pump when needed. However, I realize that this scheme might not be practical with all sailboats, particularly smaller ones. (and I'm too lazy to move mine from their manufacturer-installed locations)

The location of the outlet in your pic might as well be below the waterline. It isn't really high enough to protect the boat. However, if you treat it as if it is below the static waterline (i.e., make sure it has a proper valve/seacock, that you keep closed when not in use) it shouldn't be a problem.

[oceanscapt]

I'd rather have it below the waterline. The venturi effect of water passing over the thruhull creates a bit of negative pressure allowing the 'product' to move more easily. I also tend to think the product will affect the bottom paint less than the bootstripe or hull. Of course, if you're on the other tack, the rules are off.


I've seen this proven on boats where the chain locker drains were below the waterline. You could hear the suction at speed and the locker was generally dry.

[tdw]

You really do go looking for ways to spend money don't you ?

"Oh look...I'm all neurotic about my engine but I've got a spare minute or two so I'll find something else to worry about."

Cameron, if you didn't have a worry in the world.....you'd be worried about not having anything to worry about.

btw....yes it is too high. Should be well below waterlevel. Remember that when you install that holding tank (money money money) and you want to empty it when you are the requisite 15nms off shore, you won't want the outlet to be above water, particularly if you are down wind....

Originally Posted by Hartley18

The latest threads on Loos and Poos have got me thinking.. (anything to stop we worrying about the engine!)

Our head outlet (yes, I know you're not supposed to use it.. yadayadayada.. ..and we usually don't - in fact, haven't used it since we bought the boat) was kinda right on the waterline and, having removed a lot of crap off the boat since the pic below was taken, is now pretty much always above it!

I'm assuming the outlet is supposed to be below the waterline - otherwise it's blooming obvious when you use it - if not, is this a problem??

Attachment 6249

Thanks,
Cameron

[Hartley18]

Originally Posted by tdw

You really do go looking for ways to spend money don't you ?

"Oh look...I'm all neurotic about my engine but I've got a spare minute or two so I'll find something else to worry about."

Cameron, if you didn't have a worry in the world.....you'd be worried about not having anything to worry about.

Weeell.. You know me! It's only that I'm due to haul the boat out in the next month to fix a few other problems..

I'll talk to the boat-builder and see what he thinks, but I am not all that keen to blow holes in the hull of a 50 year old boat just for something that hardly gets used. We still own a Hartley TS with a Porta-potty, remember? - if you've ever had to crawl-carry a full PP the length of the cabin of an 18-ft TS, you'll understand our "in-grained reluctance" to use a marine head!

If it was REALLY a problem, I'm guessing a few more lead ingots would the easiest fix but in the end, I suspect we'll just leave it as is.. I was just curious to know whether or not it's in the wrong spot.

Question answered. Thanks, guys!

[remetau]

Originally Posted by Hartley18

having removed a lot of crap off the boat since the pic below was taken, is now pretty much always above it!

Is that literal?

[Hartley18]

Originally Posted by remetau

Is that literal?

Fortunately not!

[SlowButSteady]

Originally Posted by oceanscapt

I'd rather have it below the waterline. The venturi effect of water passing over the thruhull creates a bit of negative pressure allowing the 'product' to move more easily...

Come to think if it, that may be why the thru-hull is so close to the waterline. The Venturi effect isn't all that large, unless the outlet is shaped just right (which plain old "mushroom" thru-hull ain't), and it is almost certainly less than the water pressure on a thru-hull a couple of feet below the static waterline. Putting the thru-hull near the waterline would let it utilize Venturi w/o having to overcome the water pressure (at least when the boat isn't heeled). This location also means that if the thru-hull, valve, or hose fail there will be less pressure forcing water into the boat, giving one a bit more time to get things under control (or check the status of ones insurance coverage).

However, my guess is that this was just a convenient place to put the thru-hull and still have it at least nominally hidden below the waterline.