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Vented loops prevent siphoning but aren't needed when the system can't siphon, like a sink basin that's higher than the water it's draining to. But a bilge pump is another story as the bottom of the pump is lower than the sea water and if the discharge through hull is below the water line, even if only when heeling, the centrifugal pump can allow water to siphon back into the bilge. Positive displacement pumps, like the rubber impeller water pump in the pic (and the raw water pump in the OB for that matter) won't allow water to backflow.

I had a check valve (aka 'backflow preventer' in some circles) in my last boat for the bilge pump because the bilge was so small and deep that the system would short-cycle with the water in the discharge hose. A check valve just beyond the pump prevented that.

But that would make its own problems in that if the pump ran dry, like when heeled, it would have great trouble priming itself as the air bubble between it and the check valve would prevent that, and without the ability to build pressure, it couldn't push past the check valve. That's how it was when I got the boat. A small vent hole drilled in the hose just before the check valve solved that problem by allowing air to vent when the pump started. A little pee stream of water would of course exist but that was no big deal as restart reliability went to 100%, and the pee stream was small compared to the total flow.

Good explenation about the bilge pump. In CE-Countries 2 bilge pumps (1 electrical and one handpowerd) must be installed. And the trough hull for these pumps Roger put 50cm higher then water line...

Well, if the vent thing is not the proper installation then I guess the valve might do the job all by its self alone - I don't know - like I said - all I have are these old Navy books to figure out how to do this stuff.

I guess I could do a gravity system to a holding tank, but I still need a way to pump out the holding tank. I looked at all the pictures on the internet of the holding tanks on the boats and they all had stuff similar to the pictures in the Navy books, so how am I supposed to know any better??

I will keep researching and try to figure this out.

The deal is that I will be installing a shower in the boat - and that shower will require a sump pump and a holding tank.

Just a thought for a bullet prof system if you’re not moving hundreds of gallons every day, consider manual bilge/grey water pump. You’d be able to discharge you’re holding tank when outside the 3nm limit rather quick and have a back up emergency bilge pump just in case. They are easy to operate and move a ton of water pretty easy.

yukonbob wrote:Just a thought for a bullet prof system if you’re not moving hundreds of gallons every day, consider manual bilge/grey water pump. You’d be able to discharge you’re holding tank when outside the 3nm limit rather quick and have a back up emergency bilge pump just in case. They are easy to operate and move a ton of water pretty easy.

What do they look like? Where do you mount such a thing?

https://www.ebay.com/i/152639983084?chn ... 0056485195
No idea on quality make of the above but this is the general idea. Most handles come off for storage. Could be mounted just about anywhere but I imagine in one of the laz’s SB side for the head (M model) A 3 way valve for pickup from head and or ‘bilge’ then a thru hull above the waterline with vented loop, seacock, lockable overboard discharge selection etc.

yukonbob wrote:https://www.ebay.com/i/152639983084?chn ... 0056485195
No idea on quality make of the above but this is the general idea. Most handles come off for storage. Could be mounted just about anywhere but I imagine in one of the laz’s SB side for the head (M model) A 3 way valve for pickup from head and or ‘bilge’ then a thru hull above the waterline with vented loop, seacock, lockable overboard discharge selection etc.

Hmmmmm, it says the body dimensions are 5.5 by 7 inches. That's a very important metric on the MAC 26M boat because there is a pocket just inside the aft dinette seat that also has access to the lowest portion of the boat - it's a small space right between the ballast tank spline and the inner wall of the aft dinette seat and that wall has a outer surface that projects out away from the spline, hard to describe, even harder to draw,




Yet, that small area where the dinette sticks out into the cabin floor might be a great place to put a hatch for a removable handle to a ballast pump like you describe. It could be a lifesaver in a situation where all power is lost and the boat is swamped - (which, by the way - most boats DO lose all power when they are swamped) thus making electric bilge pumps sort of a wast of money.

Hmmm, you give me some serious things to think about bob - you guys up North are pretty smart.

My 222 came with a fossilized bilge pump which I replaced with an automatic switch version. I wonder about moving the through hull to empty into the self-draining cockpit; it would alert me to water entry if I were sailing, would drain through the floor, and would not be affected by heeling. Thoughts?

BOAT wrote:

yukonbob wrote:https://www.ebay.com/i/152639983084?chn ... 0056485195
No idea on quality make of the above but this is the general idea. Most handles come off for storage. Could be mounted just about anywhere but I imagine in one of the laz’s SB side for the head (M model) A 3 way valve for pickup from head and or ‘bilge’ then a thru hull above the waterline with vented loop, seacock, lockable overboard discharge selection etc.

Hmmmmm, it says the body dimensions are 5.5 by 7 inches. That's a very important metric on the MAC 26M boat because there is a pocket just inside the aft dinette seat that also has access to the lowest portion of the boat - it's a small space right between the ballast tank spline and the inner wall of the aft dinette seat and that wall has a outer surface that projects out away from the spline, hard to describe, even harder to draw,






Yet, that small area where the dinette sticks out into the cabin floor might be a great place to put a hatch for a removable handle to a ballast pump like you describe. It could be a lifesaver in a situation where all power is lost and the boat is swamped - (which, by the way - most boats DO lose all power when they are swamped) thus making electric bilge pumps sort of a wast of money.

Hmmm, you give me some serious things to think about bob - you guys up North are pretty smart.

Placement is irrelevant. Just run a pickup hose to the low point. These can also be mounted vertically to reduce footprint. I’d just make sure they’re self priming but most are.

Okay, so it can be mounted anywhere.

So, I guess you already have one? Anyone have one mounted yet?

BOAT wrote:Okay, so it can be mounted anywhere.

So, I guess you already have one? Anyone have one mounted yet?

Yes on the big boat. It’s emergency manual bilge as well allows me to empty the holding tank offshore, simple, reliable and bullet proof. Still looking for a cheap S or D just saying.

I was looking at something like this https://www.ebay.com.au/i/172807759970? ... dispItem=1 for my shower install, which has now been put on a temporary hold

Wow $50! That’s a deal for a shower sump

Cheap as chips on Ebay

DANG! and I thought I found a good deal at 44 dollars, oh well. I guess I'll just keep shopping.

https://www.amazon.com/Shower-Drain-Sys ... Src=detail