Stern Tube Bleed Hose

billcole

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Hi All
My First 305 has a bleed hose from the exhaust elbow to the stern tube, but I don't really see what it's purpose is.

The bleed is fed into the stern tube outboard of the Volvo shaft seal. The prop shaft is 25mm diameter, and the internal diameter of the stern tube is 40mm, so the gap between shaft and tube is 15mm all round at this point. The bleed hose is 10mm internal diameter, so I can't see how it can supply enough water to do anything other than exit straight to the sea through the big space around the shaft.

I'm replacing the engine , and wondering whether I still need to connect the bleed hose to the new engine, or whether it would be better to just connect an open ended hose from the stern tube to a point well above the waterline so that air can escape from the stern tube on launching, but eliminating any possibility of back siphoning through the bleed hose to the engine

I know the Radice version of the Volvo seal does have a bleed hose fitting, but there the water is fed to the "cutlass bearing" part of the seal, and presumably aids lubrication and also removes the need to burp the seal, but with my set up I don't think any of the bled water would flow up in that direction.

Can anyone shed any light on what Beneteau's intention for the bleed hose might have been ?

Bill
 

billcole

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No, the cutlass bearing is on a separate P-bracket about 1/2 metre away, the stern tube just has the shaft seal on the inner end, but is otherwise empty apart from the shaft itself
 

Tranona

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No, the cutlass bearing is on a separate P-bracket about 1/2 metre away, the stern tube just has the shaft seal on the inner end, but is otherwise empty apart from the shaft itself

It is there to ensure that there is water in the tube even when underway using the motor. As you move forward water tends to be sucked out of the tube, which is underwater anyway. So the feed is not the main source of water in the tube, but supplementary. Probably not a big issue in a displacement boat so a bit belt and braces. The same system is fitted to Beneteaus but the tube is just a vent rather than a positive feed.
 

billcole

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Thanks, mine is a Beneteau First 305, so I wonder if the hose started life as a vent and then got connected to the engine by someone at a later date
 
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