water ingress - Beneteau Oceanis 31

graemeB1

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Hi There,
I recently bought a Beneteau Oceanis 31 fixed keel 2001 which I sail on the lake here in Switzerland. The boat has not been used much by the previous owner, only 130 hours on the engine, and is like new inside the cabin. But, from the outside it has clearly not had a lot of TLC. I have replaced the rigging and had the engine and electronics serviced a few weeks back. With the final arrival of summer I hoisted out the boat to do the antifouling and was told by the Capitain du Port that he had only once in 10 years hoisted out the boat. The undersides were pretty much covered in weed and muscles. After two days of work it was all sanded down and new antifouling applied. An investigation of the undersides by the local chandler pronounced all looked in 'OK' condition so we relaunched looking forward to faster sailing and it goes really well undersail or motor!
However, the next day we arrived at the boar and I noticed water in the bilges which at first I blamed on over-enthusiastic use of the high pressure cleaner I used on the undersides and sides. Thankfully the electric bilge pumps had it drained off pretty quick and an investigation of the engine bay showed some residual water around the rear drive entry through the hull. Not deterred we spent the afternoon sailing but arriving back at port the engine bay was once showing a new collection which we pumped out. The next day same story with water from the engine bay to the sump but well below the floor boards. We pumped that out again today and during the day it did not look like it increased or came back again to the same extent, it definitely seemed less today.
So to my question.When we had the boat out for antifouling it was a record heat wave here in Switzerland with 35 oC. I am pretty sure no servicing was done on this boat prior to my purchase. Is it possible the grease in the stern tube has dried out or needs refilling, and do I have to haul it out again to do that? The engine is a Volve Penta MD2020. There is a watercooling system fitted to the drive prop (on visual inspection it looks good) from the engine on my boat so if the seals dried out will they 'reswell' after a time? Apart from the stern tube I find no other way for water to get into the boat, it doesn't smell wet and other compartments like the heads and forward cabin are dry. I checked the clamps on the cooling system and all are tight and look in good order.
Look forward to enlightenment!
Best
GB
 
The seal is a Volvo rubber seal which relies on lip seals to keep the water out. These need greasing every year, but do not rely on the grease to seal. Suspect they have never been greased and are worn. First thing to do is squeeze the rubber seal and check that water comes out alongside the shaft. This is known as "burping" and expels trapped air from the seal. Then observe the seal when the engine is running in gear. If there is any water coming in then the seal needs replacing. Relatively cheap, around 100 euros, but you need the boat out of the water to disconnect the shaft to change the seal.. Also check the clamp that holds the seal onto the stern tube as that is another potential source of leaks.

I am assuming you have checked for leaks in the engine cooling system and the freshwater tanks, piping etc as these are all potential sources. However, a leaking stern tube seal is obvious as you can see the source quite clearly.
 
The seal is a Volvo rubber seal which relies on lip seals to keep the water out. These need greasing every year, but do not rely on the grease to seal. Suspect they have never been greased and are worn. First thing to do is squeeze the rubber seal and check that water comes out alongside the shaft. This is known as "burping" and expels trapped air from the seal. Then observe the seal when the engine is running in gear. If there is any water coming in then the seal needs replacing. Relatively cheap, around 100 euros, but you need the boat out of the water to disconnect the shaft to change the seal.. Also check the clamp that holds the seal onto the stern tube as that is another potential source of leaks.

I am assuming you have checked for leaks in the engine cooling system and the freshwater tanks, piping etc as these are all potential sources. However, a leaking stern tube seal is obvious as you can see the source quite clearly.

Hi Tranona
thnx a lot, will check it out and let you know
Best
GB
 
When we bought our boat the Volvo shaft seal had not been replaced in years. When we got around to removing the shaft to replace it we found two tiny but neat little grooves worn in the shaft by the lips of the seal. Amazing that rubber can wear away stainless steel like that. We were advised that a new seal would quickly leak because of the grooves and, with the shaft showing minor signs of galvanic corrosion too, we replaced the propshaft. Important stuff that grease!
 
Dear All,
Thanks for all the advice.
I spent a jolly hour yesterday 'sandwiched' into the engine box area to verify where the leak is happening. Definitely water is entering via the stern tube.
Best
GB
 
Hi Slipknot,
Do you have picture showing where you put the straw relative to the steel?
Best
GB

Just slide it along the prop shaft so that it pushes the lip seal up and then squirt the grease in. You can do the same thing with the nozzle of the tube the Volvo grease comes in, but the straw can be better because it is flexible. However, if it is leaking, grease will not stop it as the lip seals are worn or the shaft is worn where the seals run. Hopefully the former as a new shaft is a bigger more expensive job.
 
With only 120 engine hours the shaft is unlikely to be worn. However, the seal is at least 2001, 12 years old & the mfr says they should be replaced at 7 yrs. A new seal isn't expensive and pretty easy to do. Did mine in my Bene last year.
 
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