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  1. #31
    Join Date
    Dec 2005
    Location
    Far S. Cornwall
    Posts
    13,344

    Default Re: Use a ball valve on the exhaust outlet?

    I would have a flap, S/S with a rubber pad, adjusted to give a pretty good seal. If the transom is raked, then a simple counterweight, studding with a small weight on the end, will keep it tight and can be adjusted. You can, of course, get a fitting with external spigot to take the drips away from the gelcoat, this can be cut to face slightly upward.

    Oh, the rubber is to avoid the endless clatter when ticking over.

  2. #32
    Join Date
    May 2005
    Location
    Loch Snizort, Isle of Skye
    Posts
    4,926

    Default Re: Use a ball valve on the exhaust outlet?

    I was taught to always, always, always, go straight to the stern and check the water flow every time the engine was started up. No exceptions.
    Is this not common practise? It has saved my bacon at least once that I can remember, when the raw water pump belt was slipping and the engine wasn't pumping water.

    Maybe it's a bit like 1-2-both switches, which some people reckon are a recipe for drained batteries, whilst everyone else just gets on with life and uses them quite happily.
    Moody 39- Deb 33- Wayfarer- Wanderer

  3. #33
    Join Date
    May 2007
    Posts
    38,235

    Default Re: Use a ball valve on the exhaust outlet?

    Quote Originally Posted by Kelpie View Post
    I was taught to always, always, always, go straight to the stern and check the water flow every time the engine was started up. No exceptions.
    Is this not common practise? It has saved my bacon at least once that I can remember, when the raw water pump belt was slipping and the engine wasn't pumping water.

    Maybe it's a bit like 1-2-both switches, which some people reckon are a recipe for drained batteries, whilst everyone else just gets on with life and uses them quite happily.
    Exactly so.
    I guess it's a bit like people with modern cars not being able to cope with operating the traditional manual handbrake.

  4. #34
    Join Date
    Jun 2019
    Location
    Scarborough
    Posts
    628

    Default Re: Use a ball valve on the exhaust outlet?

    Quote Originally Posted by Kelpie View Post
    I was taught to always, always, always, go straight to the stern and check the water flow every time the engine was started up. No exceptions.
    Is this not common practise? It has saved my bacon at least once that I can remember, when the raw water pump belt was slipping and the engine wasn't pumping water.

    Maybe it's a bit like 1-2-both switches, which some people reckon are a recipe for drained batteries, whilst everyone else just gets on with life and uses them quite happily.
    More foolproofing of systems leads to enhanced foolishness of their operators..
    I concur it's a reflex action to check water is coming out when the engine starts, it's the only way to be sure, and applies on all kinds of vessels not just yachts!

  5. #35
    Join Date
    Jul 2002
    Location
    Farnham, Surrey
    Posts
    21,406

    Default Re: Use a ball valve on the exhaust outlet?

    Quote Originally Posted by doug748 View Post
    I have one such valve. If you leave it shut it busts your engine.
    No it doesn't - as lots of other people have pointed out.

    Quote Originally Posted by Rocksteadee View Post
    One day someone will forget to open the valve (kids, wife, new owner).
    Engine may start on first turn of the key (exhaust would initially be at zero pressure)
    Back pressure could build up and force cooling water back into engine.
    Back pressure could blow off exhaust pipe or split it. This may not get noticed.
    Engine compartment now filling up with exhaust fumes and cooling water.
    Consequences are possibly now obvious
    With the engine running I don't believe for one millisecond that water is going to be forced back into the engine against the pressure of the exhaust. It's more likely that the exhaust pipe will be forced off a fitting and the boat will start filling up with water and exhaust fumes. I also think most people would notice what was happening at this point...

    Quote Originally Posted by Kelpie View Post
    I was taught to always, always, always, go straight to the stern and check the water flow every time the engine was started up. No exceptions.
    Is this not common practise? It has saved my bacon at least once that I can remember, when the raw water pump belt was slipping and the engine wasn't pumping water.

    Maybe it's a bit like 1-2-both switches, which some people reckon are a recipe for drained batteries, whilst everyone else just gets on with life and uses them quite happily.
    Exactly. I always do it and always get the crew to practice doing it if they start the engine. We also have a tell tale water stream from a fitting midships that its easy to go and check is steaming appropriately.

    I don't expect it's any surprise to anyone that I admit that we have a large good quality ball valve on our exhaust skin fitting. I fitted it because a couple of times, in the right conditions and when it's rough enough, wave slap up the counter of the boat (where the exhaust comes out on our boat) has forced seawater back up the exhaust and hydraulic locked the engine. This is despite having a larger than standard water trap, and a gooseneck as high as possible up inside the stern of the boat and a high rise water injector on the exhaust of the engine. When the engine has hydraulic locked I have had to remove a preheater element and spin the engine over to blow the water out and then start the thing as soon as possible to dry it out to prevent cylinder and piston damage. (I've rebuilt the engine once due to this problem and I don't want to have to do it again!)
    Semper aliud

  6. #36
    Join Date
    Oct 2002
    Location
    Plymouth
    Posts
    8,604

    Default Re: Use a ball valve on the exhaust outlet?

    Quote Originally Posted by john_morris_uk View Post
    No it doesn't - as lots of other people have pointed out.



    With the engine running I don't believe for one millisecond that water is going to be forced back into the engine against the pressure of the exhaust. It's more likely that the exhaust pipe will be forced off a fitting and the boat will start filling up with water and exhaust fumes. I also think most people would notice what was happening at this point...



    Exactly. I always do it and always get the crew to practice doing it if they start the engine. We also have a tell tale water stream from a fitting midships that its easy to go and check is steaming appropriately.

    I don't expect it's any surprise to anyone that I admit that we have a large good quality ball valve on our exhaust skin fitting. I fitted it because a couple of times, in the right conditions and when it's rough enough, wave slap up the counter of the boat (where the exhaust comes out on our boat) has forced seawater back up the exhaust and hydraulic locked the engine. This is despite having a larger than standard water trap, and a gooseneck as high as possible up inside the stern of the boat and a high rise water injector on the exhaust of the engine. When the engine has hydraulic locked I have had to remove a preheater element and spin the engine over to blow the water out and then start the thing as soon as possible to dry it out to prevent cylinder and piston damage. (I've rebuilt the engine once due to this problem and I don't want to have to do it again!)



    People are getting worse on these pages how many are reading past posts? How many are pondering them? We have a nausea of uninformed, opinion.
    These beliefs, thoughts and expectations are of great interest but -

    Read post 30

    So stick to your guns, blind faith is a grand thing in metaphysics, let it justify what you want to do if you wish, carry on.

    However, I am telling the wider readers who are not buffoons that I have direct experience of blown head gaskets due to an exhaust valve being left closed.
    Last edited by doug748; 11-09-19 at 09:02.

  7. #37
    Join Date
    Dec 2005
    Location
    Far S. Cornwall
    Posts
    13,344

    Default Re: Use a ball valve on the exhaust outlet?

    Air, gas, is compressible, water not. Seems fairly obvious to me that forcing gas followed by water, injected close to the engine, into a dead end results in the gas compressing and forcing the water back. In certain configurations this is going in the engine.

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