Bilge Pump Thru-Hull Question

[unbusted67]

I just bought a bilge pump for me little trailer sailor and was wondering about where I should put the through hull. There are two cockpit drains that empty just above the waterline port and stbd. Should I put it next to one of those or should I worry about heeling over? I have a check valve in line. Would it just be easier to put the through hull in the transom?

[spooky alice]

I had the same issue, I went thru the transome just above the water line. I found when using the motor the bilge flooded due to the stern going down a bit. I added a valve and a raised loop at the thru hull and all is fine. Most bilge pump makers say to aviod a check valve. If I had it to do over I'd pumped the bilge to the cockpit so it ran out the regular drains.

[Sailmonkey]

I ran mine on the transom about 6" below the hull/deck joint. Inside there is a loop that goes as high in the cockpit locker as possible. I also use a jabsco diaphram pump instead of the submerged centrifugal pumps.

[Roy M]

You can also put a tee at the transom thruhull and connect the terminal ends of both an electric and manual bilge pumps (both must have their own loops ahead of the discharge). Electric automatic pumps are great, when they work, and then you have a manual as a backup. The cockpit drains that you mentioned going port and starboard, do they actually drain when you are heeled?

[unbusted67]

Originally Posted by Roy M

You can also put a tee at the transom thruhull and connect the terminal ends of both an electric and manual bilge pumps (both must have their own loops ahead of the discharge). Electric automatic pumps are great, when they work, and then you have a manual as a backup. The cockpit drains that you mentioned going port and starboard, do they actually drain when you are heeled?

I don't know. I haven't sailed it yet. I hope so. There is no transom thruhull on this boat. I just got off the phone with someone at a marine store who said he had never heard of putting a vented loop in a bilge pump line. Which one of us is the crazy one? Do I need a vented loop? Can I get away with the check valve. Can I just stick the thruhull a couple of feet above the waterline?

[speciald@ocens.]

Mount the drain as high as possible on the hull. Remember that all the water in the hose will back flow into the bilge when the pump stops.

[GordMay]

Originally Posted by unbusted67

Do I need a vented loop? Can I get away with the check valve. Can I just stick the thruhull a couple of feet above the waterline?

You need a Vented Loop (& Seacock) if the disharge is below the maximum heeled waterline.

Do not install a check valve under any circumstances.

Per ABYC Section H-22, Electric Bilge Pump Systems
➥ http://www.marinesurveyorschool.org/...20Pump0001.pdf

22.8.6 The discharge location shall be above the maximum heeled waterline,
or
22.8.7 the discharge may be located below the maximum heeled waterline if the discharge line is provided with both of the following:
22.8.7.1 a seacock installed in accordance with the requirements of ABYC H-27, Seacocks, Thru-Hull Connections, and Drain Plugs,
and
22.8.7.2 a vented loop or other means to prevent siphoning into the boat. A check valve shall not be used for this purpose.

[rtbates]

don't be surprised if the check valve doesn't work, as in no water flow output...That was my experience when I used Rule drop in pumps. I have since gone to a diagraph pump that's mounted in a remote locker..much much better deal...

[Roy M]

I don't recall using the term VENTED loop. As mentioned by others, you need a simple loop, going as high as possible before exiting the boat through the thruhull. The function is to prevent following seas from "hammering" water into the boat. A vented loop prevents siphon action when the thruhull is generally below water. A thruhull that alternately submerges and drains doesn't generally create a siphon over the top of the loop. You would use a similar arrangement with the exhaust hose from the aqualift muffler of an inboard engine. On rereading some of the other posts I see a possible problem. DO NOT INSTALL THE THRUHULL HIGH ABOVE THE WATERLINE. Make the exhaust hose loop as high as possible then descend to a thruhull above the waterline.

[unbusted67]

Why should I not make the thruhull high above the waterline? I really wish I had read this earlier. Like before I drilled a f*&king hole in my transom.

[nautical62]

Originally Posted by unbusted67

Why should I not make the thruhull high above the waterline? I really wish I had read this earlier. Like before I drilled a f*&king hole in my transom.

I wouldn't worry too much about your high placement. It's just that the longer your hose run, the more water will drain back into the bilge. If it's too much, it can keep triggering your float switch.

[Roy M]

The only reason for locating the thruhull lower is that a following sea can easily enter the discharge hole at its crest, and since it doesn't have to wait for the hose to fill to the top of the loop, that water has a chance of going straight downhill to the bilge. A waterline thruhull takes a while for the crest to fill it to the top of the loop, and by then the crest has passed. That's what I meant by the term "hammering". It's an issue for many engine exhaust hoses that don't have sufficient loop. Successive passing waves gradually fill and push water into the engine manifold via the exhaust hose. Chances are far fewer by having a high point for the discharge loop, and a relatively long final drop overboard. The amount remaining in the hose when the pump shuts off remains exactly the same: the height to the top of the loop from the bilge pump, times the internal diameter of the hose.

[nautical62]

Regarding the height, I should add, I have a Hunter 30 that has a discharge about 3 feet above the waterline and I've never had any problems.

The only issue is it leaves a mild stain on the hull.

[bobfnbw]

Far as I know there is not reason you can't install a check valve in a bilge pump circuit. I did. And am glad of it. Now I would not do that If I only had one pump, I don't. But my primary bilge pump is a jabsco diaphram pump and I installed a one way valve to keep water from returing after the pump shuts off. Works fine.
I also have a loop with a vent. Works fine. I use a strainor inline before the pump and a groco strainer in the bilge as well.
As to the Origianal question, mount the primary on the transom. Double clamp it.

Gord, this to me says not to use the check valve in place of a vented loop, not don't use a check valve at all.

22.8.7.2 a vented loop or other means to prevent siphoning into the boat. A check valve shall not be used for this purpose.

[Sailmonkey]

Originally Posted by unbusted67

Why should I not make the thruhull high above the waterline? I really wish I had read this earlier. Like before I drilled a f*&king hole in my transom.

Fear not, if you have a point that is higher than the outlet that is all that's needed to allow a downhill drain out. If not......well still no biggie the pump will still do it's job. I would think that if you were being slammed by following seas large enough to cause this to be an issue you'd be worried about a lot of other things on you boat.