where does bilge water come from in a plastic boat?

Burnham Bob

Burnham Bob

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I can understand a wooden boat taking in water and needing the bilges pumped but why do we get water in grp boats? My boat seems to be getting more water in the bilges than usual - although it's still not enough to worry about. It's salt - I've tasted it. None of my sea cocks are leaking. The engine cooling water and exhaust don't seem to be the problem. As far as I can see that leaves only the stuffing box. I've refilled the greaser and pumped some more grease in so I'll see if that works.

As I said the volume in a week is not enough to worry about - but in general if the stern gland isn't leaking why do we get bilge water in grp boats?
 
You have identified the main sources. If it is fresh then it could come from all sorts of fittings - chain plates, cleats, hull/deck joints, mast if keel stepped, windows and so on.

If it is definitely salt then you need to dry the bilge completely and then sprinkle talcum powder all over. This will show the path of the water and help you trace back to the source.

If you have a conventional stuffing box it could need adjusting to reduce the drip - but you can see if it is dripping excessively by watching when the motor is running.

Be prepared for a lot of frustration if the amounts are small and not coiming from an obvious source.
 
If it's not the skin fittings, shaft or plumbing, then it's either wet people, sails etc going below or rain leaks, or hull/deck joint, or a keel bolt or ...or...or....

On one boat, when it rained water came down the mast. When you pumped it out, half the water slowly leaked back from the bilge pump plumbing. Rain leaks from cockpit locker hinges are another favourite.

It's worth tracking these things down before the damp and mould autumn gets hold.

Good luck.
 
Burnham Bob said:
As I said the volume in a week is not enough to worry about - but in general if the stern gland isn't leaking why do we get bilge water in grp boats?
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what volume are you talking about? as Tranona has said tracing tiny amounts is really tricky especially if intermittent. I have half a cupful or so a month and searched high and low. Eventually tracked it down to the anchor locker which drains into the bilges and not overboard. Also in rough seas I get a bit of leakage around deck fittings on the steps down to the bathing platform. might be worth a look.
 
Rudder tube, stern gland, sea water pump on engine, hull to deck join, anchor locker from wet chain, ditto fed by water through hawse pipe, ditto from water in 'sealed' anchor locker getting past the bulkhead because it doesn't drain fast enough (Moody favourite that one), engine exhaust system, anti -syphon, waterlock. Plus of course every skin fitting, seacock and hose clip.

It may not be salt, just salty fresh. So now look at freshwater tank, pumps and taps, calorifier pressure valve overflow (frequent culprit), every deck fitting and there are dozens.

I like bilges to be dusty and water to be in it's place on the outside!
 
Cockpit drain tubes. If they leave the cockpit as a skin fitting/plastic pipe/outboard skin fitting there are four joints per drain that could leak salt water in from the outside. Per drain. Unless your outboard skin fittings never submerge that is. Could even be a chop when on a mooring.
If it's these then you will also getting fresh water leaks when it rains.
Been there etc....
 
small roof hatches too

planteater said:
On mine it's a weep from the sterngland when motoring and a minor flood from the lockers when raining. New locker doors is the priority project for this winter - complete with cam fasteners and compressed foam seals.
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Leaks ditto + from small galley etc roof hatches, run between roof & headlining- takes a while to find out where it's coming from!
 
How much might build up from condensation inside? My boat can be very damp with dew on a cold misty morning and some of it does run down in trickles. Not much, but it could be added to every day, even when you are not there.
 
I have spent a lot of time and effort trying to find out where the water came from that accumulated in the bilge sump, but only when sailing, never when in harbour. I rounded up all the usual suspects as follows:

Stern gland, Volvo rubber seal, a paint tray placed beneath it showed that it did not even drip.

Exhaust system. I suspected a leak from a crack in the plastic exhaust box, and replaced it. No change in the water ingress.

Fridge. Yes it did spill a little out of an improperly sealed drain plug, but only after turning it off and letting it all thaw, and that was not the source. drain plug now sealed.

Leaks through deck. None can be found and everything above bilge level is bone dry.

Freshwater system, including calorifier dump valve. All looks OK.

Finally I noticed that although the engine is Yanmar, the raw water strainer was one of those Volvo ones with a wing nut holding the lid on, and that there was a bit of salt deposit on the outside of it. I changed it for a Vetus one with a big O ring seal and screw on lid, and the problem appears solved.
 
Meandraft...

I suspect you have the same problem I had last year.

The keel boats had loosened a tad from the boat being on the hard for an extended period; I was puzzled at first but deduced the problem was caused at the keel as the boat was fully dry before and became slightly wet after a hard sail.

So I took out my "super duty" torque wrench and retorqued the keel boats with a bit of non drying "something" applied between the large washer and the hull.

Presto, no more seepage.

GL
 
well a fill of grease in the remote greaser and a good few turns has cured the problem - must have had an airlock in the previous grease.

Mind you I found a cockpit drain that was leaking slightly - but that must have been rain as no waves made it to the cockpit in the last few weeks
 
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