Bilge pump water intrusion?

[family affair]

Does your bilge pump have a check valve or a vent loop?
I ask because I suspect that water in my bilge is coming in from my thru hull and back down my bilge discharge. I only have water when it gets rough and the boat rocks more significantly. I've checked for water along the every thru hull I can access and and everything appears to be dry. Calm days the bilge stays 100% dry. If I'm out in bad chop, it's the worse. Thankfully nothing significant (maybe a quart of water on the worst day of hellacious chop) but I'd prefer to keep it dry.
Should there be a loop or a check valve on the discharge line? Is this typical with some boats?

 

[Hookup1]

Does your bilge pump have a check valve or a vent loop?
I ask because I suspect that water in my bilge is coming in from my thru hull and back down my bilge discharge. I only have water when it gets rough and the boat rocks more significantly. I've checked for water along the every thru hull I can access and and everything appears to be dry. Calm days the bilge stays 100% dry. If I'm out in bad chop, it's the worse. Thankfully nothing significant (maybe a quart of water on the worst day of hellacious chop) but I'd prefer to keep it dry.
Should there be a loop or a check valve on the discharge line? Is this typical with some boats?

Both bilge pump exhausts on the Islander are mounted high off the waterline (about 18"). There are no check valves. I have broken both plastic thru hulls off at different times. You should check that as a source of your water.

The aft one broke when I stored my power cord and dock lines in the compartment under the tub. It was fixed immediately so it was no problem.

The forward one was a dangerous one. The hose and plastic thru hull are located under the sink. To get to them you have to remove the refrigerator and crawl into the hole. It failed in rough sea conditions on a long trip. The bilge light/pump kept cycling while underway. Because the hose was laying inside the boat the pump exhaust water never got out of the boat. The bow spray water was coming into the broken thru hull up high.

The anchor locker also drains into the bilge.

All above water thru hulls were replaced with GemLux stainless ones when the hull was painted in 2022.

 

[family affair]

The 270 uses bronze thru hulls and look like new. I suspected the bilge discharge up front till a few days ago. I had a little water in the aft bilge, but zero up front. Because the front of the hull is lower than the back, I would think that indicates the water has to be coming from the back, somewhere. I've considered taping off the aft bilge thru hull in chop to see if the bilge stays dry.
IMO another clue is mold growth. Behind my deck liner is extremely clean - virtually no growth. I would think that if I have a leak somewhere away from the bilge, I would have noticable mold growth. I have almost none.

 

[Hookup1]

There are so many places that could leak that are hidden. Could be rub rail, windows, scupper hoses, it’s a long list.

There is a 1/2” pvc pipe in aft bilge that could be plugged to isolate fwd/aft bilge. May help you troubleshoot.

 

[Hookup1]

The long 1/2" pvc runs from fwd to aft bilge. It can be plugged as mine was to keep water (or leaking fuel) from getting to the fwd cabin.

The other two circled areas are 3/4" pvc couplings that serve as limber holes. They allow whatever is in the compartment the fuel tanks are in to drain back to aft bilge. My boat sits in such a way the bilge is dry but water is "stored" underneath the fuel tanks. When the boat goes up on plane sometimes the aft bilge pump will trigger (light on dash) as the water underneath drains back.

 

[family affair]

I appreciate the ideas.
I don't suspect I have water sitting in the tank area. I've pulled the pie plates and the tank is spotless - like new - zero funk from moisture.
I think plugging off the tubes to isolate water entry is a good start.

 

[everwhom]

Another common leak area is the hull to cap joint under the rub rail. There's screws that can loosen and caulking that can fail. You only notice in rough seas.

 

[Sardinia306Canyon]

Should there be a loop or a check valve on the discharge line? Is this typical with some boats?

There should be a loop and i dislike check valves as they can plug or stick open.

If you get water only when it's rough then probably as above, the cap joint or something in the bow, anchor locker drain or - if you have it - the anchor storage cut-out in forward keel.
Water entry in chop comes mostly from midship to bow and there mostly bow area as there she plows thru the water.
Chris

 

[family affair]

There should be a loop and i dislike check valves as they can plug or stick open.

If you get water only when it's rough then probably as above, the cap joint or something in the bow, anchor locker drain or - if you have it - the anchor storage cut-out in forward keel.
Water entry in chop comes mostly from midship to bow and there mostly bow area as there she plows thru the water.
Chris

There is no loop. Considering the hoses for my black water tank were plumbed backwards, it wouldn't surprise me if all of this is from a lack of a loop.
We often get nasty chop in these parts. I'm confident water goes into the thru hull in these conditions. I also get it when pulling the tube at low speeds with sharp turns. I thought it was from water brought in from swimmers. Turns out when I have swimmers and/or wash the deck, I have no water below.
I'll try a couple more tricks to narrow it down.

 

[wspitler]

Depending on how much water you’re talking about, there are numerous places that rainwater can gather and never reach the bottom of the bilge until the boat rolls. The outboard side of the strakes can trap water, not a lot. My 330 will have freshwater in it after the bilges have been completely dry on the lift and then we go out for a day or so with no rain. I will then find freshwater in the bottom of the bilge and no leaks in either of the water systems. I suspect it comes from trapped freshwater in places on either side of the strakes. If you’re seeing an inch or 2 inches of water after being offshore then that may be coming from your through hulls.

 

[Ekea]

i put in a new bilge pump this spring. i did add a loop just for this reason. i didnt install the included check valve because it reduces the flow rate of the pump. with the way my loop is, id have to almost submerge the gunnel to get water to back flow into the bilge.

 

[family affair]

i put in a new bilge pump this spring. i did add a loop just for this reason. i didnt install the included check valve because it reduces the flow rate of the pump. with the way my loop is, id have to almost submerge the gunnel to get water to back flow into the bilge.

Did you not have a loop before? If you didn't have a loop, was water getting in?

 

[Automated14]

I appreciate the ideas.
I don't suspect I have water sitting in the tank area. I've pulled the pie plates and the tank is spotless - like new - zero funk from moisture.
I think plugging off the tubes to isolate water entry is a good start.

If you want to plug off a through hull, I suggest swimming pool rubber plugs. you can buy them online. you can get them from size "00" which is real small all the way up to "15" and beyond. If I had to guess, I'd say a #4 or #6 would be close. #9 1/2 will fit inside 1 1/2" pvc pipe for reference.

 

[Ekea]

Did you not have a loop before? If you didn't have a loop, was water getting in?

there was no loop prior. i only had two years with the boat before replacing it and with now 5 and 3 year olds, i try to avoid the crazy conditions.