Bilge pumps cycling while underway

[Pluto]

I’m on my way to Florida from Charleston. I have a 2004 390, one of the last ones built. I’ve always had a problem with bilge pumps cycling while under way. Mostly mid. I pulled the hatch and saw water coming in thru the stringer hole into the mid bilge pump well. I have no idea where the water is coming from. On the hard you can’t see anything that would allow the water in.
Ive had the boat for 6 years but it still mystifies me sometimes.
Any thoughts?

 

[CharlieO.]

Shaft seal or packing. Same with rudder.

 

[Delta Riverat]

Mine was shaft packing. Spinning those shafts with the water feed also coming in cleans them out real good.

 

[RT Firefly]

Greetings,
Mr. P. You have a leak somewhere. Keep in mind as with most water leaks above and below the waterline that the source can easily be at a location quite remote to the source.

I am not familiar with Mainship so any source would be a WAG. Shaft/rudder stuffing box? Through hull or seacock? Leaking hosing to, from or on the engine?
What volume do you think is coming in and what is the frequency of the pumping cycle? Is the mid bilge the lowest section?

 

[Comodave]

I start by putting colored paper towels around the bilge. Then see which ones get wet and start tracing the problem from there. Even if the paper towels dries up you will still be able to tell it was wet. Then just moving in the direction that the towels indicate.

 

[Group9]

Shaft seal or packing. Same with rudder.

This.

 

[Benthic2]

It seems odd that it is only when you are underway. Could it be engine coolant ?

 

[SteveK]

cycling?
On the hard I noticed the bilge pump spit out some water every 1-2 minutes. Bilge water was making its way aft. Still did not seem right. Turns out the pump had gone bad. Would run long enough to fill the discharge hose which would drain back and start cycling even though the float was raised (by hand). New pump installed.

 

[tachyon]

I had a water leak in the starboard stern drain collector box and the generator exhaust thru hull. Both leaks drained forward to the mid-bilge, and the pump there would regularly cycle while underway.

 

[slowgoesit]

My bet is on shaft packing, or shaft log itself. Hopefully it's the packing, and NOT the log.

 

[twistedtree]

There was an issue with one or more Mainship models where underway water would leak in from the swim platform. I delivered one once from Maine to Mass and encountered this. It was pretty disconcerting to have the bilge pump run every couple of minutes. The leaking was only while underway. Note sure if the 390 was involved, but someone here probably knows.

 

[tachyon]

There was an issue with one or more Mainship models where underway water would leak in from the swim platform. I delivered one once from Maine to Mass and encountered this. It was pretty disconcerting to have the bilge pump run every couple of minutes. The leaking was only while underway. Note sure if the 390 was involved, but someone here probably knows.

Yes, the 390 model started out with a foam-filled swim platform that turned out to be a bad idea…..the foam would get saturated with water, causing structural issues in some cases, especially the more northern boats that faced total freeze-up while in storage. Mainship’s fix was to dig out the foam, then put a limber hole thru the transom to allow the swim platform to drain forward to the aft bilge. Some boats had a separate bilge pump installed inside the swim platform.
Our 2003 model has the limber hole fix ; we’ve had no issues with it, and the aft bilge pump rarely turns on.

 

[Comodave]

His is apparently one of the last ones built so hopefully Mainship had the problem fixed by then. I still say line the bilge with paper towels and see which ones get wet. That will help narrow the problem down.

 

[jbbmillar]

Our 390 bilge AFT pump cycles while underway. I think it is from the dripless seal or rudder shaft and really should take the time to find out, but haven't. Kind of like the roof only leaks when it rains. I'm pausing this writing to add to my to-do list for 2023.

Verify that your aft bilge pump and float switch are operational.

There was one crossing where the mid-bilge pump started cycling instead of the aft pump. I discovered the aft pump had stopped working. On Mainia the mid-bilge area drains aft under the engine pan to get pumped out by the aft-pump. The mid pump only runs when I flood the bilge with a hose while cleaning. In order of relative level in the bilge its: aft, mid, fwd, high water. The fwd pump is in it's own well and on Mainia it never auto runs; however, from time to time there's a bit of water that pumps with a manual activation (we don't have AC). Not sure where that comes from either.

 

[garmstro55]

Are you running your air conditioning while underway? I often do in the middle of the summer and the mid-bilge pump light goes on from time to time. I was concerned that I had a leak but eventually realized that the condensate pump was cycling.

 

[slowgoesit]

3 days, one post, and the OP hasn't been back . . . . Doesn't appear to be to concerned with figuring out the problem!

 

[SteveK]

3 days, one post, and the OP hasn't been back . . . . Doesn't appear to be to concerned with figuring out the problem!

Glad others are noticing this new trend in opening posts.

This OP may not have starlink hooked up.

 

[tachyon]

[/QUOTE] The fwd pump is in it's own well and on Mainia it never auto runs; however, from time to time there's a bit of water that pumps with a manual activation (we don't have AC). Not sure where that comes from either.[/QUOTE]

Check your hot water tank pressure relief valve. Our 390 had a drain hose connected to the valve that emptied into the fwd bilge. A bad valve can go undetected for quite some time since the hose end sits underwater, and the leak from it may be
intermittent......(ask me how I know: for awhile I was convinced we had a leak thru the hull!)

 

[Cold Duck]

See my post MS350/390 drainhole in keel 7/11/2022.

 

[rgano]

Leaks can be above the at rest waterline

Over seven years of ownership I have found many less than satisfactory Mainship factory booboos. So I was not surprised when I found that the source of persistent bilge water was the unbedded 2-inch emergency bilge pump mushroom through hull well above the waterline except when moving at my preferred 15 knots.

 

[J.T kearney]

Pluto
Need more clues!! Is water fresh or salt? clear or colored? Is your macerator thru hull left open while under way?
J.T.