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Old 30-10-2009, 00:16   #1
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A Valve in Exhaust System

I can't find my old posts on this subject so will start again with my current thinking.
Old authors of boatbuilding books recommended valves in the exhaust system to keep following seas from drowning your engine. I see a lot of boats but not very many with valves.
I am going to exhaust to the port side of my vessel because of cabin configuration and the engine room. Just no reasonable way to go to the stern with it.
Does your boat have side exhaust? Do you have a valve to keep water from entering the exhaust system when you roll in a seaway? What kind of valve, ballcock, gate, bronze, marelon, stainless?
I don't like the idea of having a valve in the system because if it is left closed when trying to start the engine, the engine floods. If necessary I'll do it. I've studied the North sea system but not certain if that would take care of the flooding issue when the engine is not running.
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Old 30-10-2009, 08:44   #2
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Our exhaust is under the counter but the issue is similar as having one on the side. We have a bronze ball valve (conbraco) in the exhaust line as high up as possible. I'd avoid marelon as I don't know how well it holds up to heat/oil/particulates/etc. in the exhaust.
FWIW, we mostly leave it open and close it only in large following seas.

A slick solution would be a reed switch on the valve handle tied into the start switch as an interlock. I haven't gotten around to doing anything like that though.
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Old 30-10-2009, 10:42   #3
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Steve Dashew (a boat builder) of Setsail.com just recently made a post about this on his website. He invites questions from his readers, he might be a good person to ask.

SetSail Blog Archive Engine Exhaust Line Valves - Are They Necessary?
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Old 30-10-2009, 11:54   #4
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Aloha Scottie and S&S,
I just read the link. He is doing the valve thing for the same reasons that original boatbuilders do it.
I like the idea of a failsafe to make certain that the cooling water intake valve and the exhaust valve are open before the engine can start. I'll have to look at that more seriously. Thanks for the Conbraco valve recommendation. I'm concerned that if the valve handle breaks off in the open position then seawater can enter but even worse if it breaks in the closed position, your engine can't be used.
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Old 30-10-2009, 12:06   #5
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My experience is that engine flooding from following seas seems to be more of a problem of boats with exhaust exits on the transoms. If you have a side exhaust with a loop up under the deck and down to the exit, you are quite unlikely to have a problem. Make the loop so that if you are heeled over with the exhaust underwater, the top of the loop will be as high as possible above the exhaust point.

If you have a transom exhaust, at minimum you should have a flapper valve on the outside.
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Old 30-10-2009, 13:25   #6
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The valves were used primary in the past for systems using a fully jacketed exhaust pipe. These systems did not have the loops and water locks that most of todays systems have. A properly designed system has no need for a valve and on the contrary they can be dangerous. If you attempt to start the engine with the valve closed you can blow a hose off and they you are out of luck till you fix it. I say design the system right and do not worry about it, a valve is just one more thing to trip you up.

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Old 30-10-2009, 13:55   #7
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Quote:
Originally Posted by sailvayu View Post
The valves were used primary in the past for systems using a fully jacketed exhaust pipe. These systems did not have the loops and water locks that most of todays systems have. A properly designed system has no need for a valve and on the contrary they can be dangerous. If you attempt to start the engine with the valve closed you can blow a hose off and they you are out of luck till you fix it. I say design the system right and do not worry about it, a valve is just one more thing to trip you up.

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Easy to say, harder to accomplish in the real world, especially on smaller boats, where there might not be the room to do it right. A gooseneck will give higher backpressure and more volume of water to deal with. Are you going to need a bigger waterlift? etc, etc.

I only shut the valve on the Cal 34 I sailed maybe twice in 20 years, so far never on my Cal 40. I doubt that I'm going to redesign a system that's been in the boat for decades.

If you have the time, money and, space and you think you're going to forget to open the valve then redesign the exhaust system and leave the valve out.



John

By the time we get done doing everything right by today's standards, there isn't going to be any room left for us.
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Old 30-10-2009, 14:22   #8
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From SkiprJohn's original post I get that he is installing his system now. Why not design and install it right so he does not need the valve in the first place? Would make sense to me. And by your own post you do not seem to need the valve you have so why have it? I suppose if it gives you piece of mind then fine but I personally see no reason for it. In 35 years working on and sailing boats I have never heard of anyone getting water into there engine from waves, not to say it does not happen but I am guessing it is rare. Now I have seen lots of other failures of exhaust systems that let water into the engine but that is a whole different thing. Trust me I understand the real world too and have installed many exhaust systems so I know it is not always easy but if you do it right the first time it will be worth the effort. Saying something is hard is a poor excuse for not doing it right.

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Old 30-10-2009, 16:32   #9
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My gen set exhaust out the side I did install a bronze check valve No need to wory about turnin it on
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Old 30-10-2009, 17:14   #10
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Our boat

Side exhaust=yes
Valve=no
High loop in exhaust 2' above engine=yes
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Old 30-10-2009, 17:30   #11
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Yes, installing it now. I'm always imagining the worst possible scenario when it comes to such things and do a lot of mental over engineering. I have a vetus waterlift followed by a vetus gooseneck followed by about 3 feet of hose to the port side at about 6 inches above the waterline. I'm trying to imagine what happens when I get a big wave on the port side while on a port tack and the water enters the exhaust pipe/hose. Will it be forced up through the gooseneck and then down into the waterlift?
I appreciate all your input. I've seen quite a few transom exhausts but the only side exhaust I've seen is one where I know the engine flooded twice. I'm thinking someone left the valve closed while trying to start the engine but am not certain.
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Old 30-10-2009, 18:00   #12
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You should come out of the water lift and rise as high as possible before looping back down and then over to the side. try to avoid any low spots in the hose that will trap water. Water should drain out the exhaust hose to the thru hull or back to the water lock. If you can get the loop out of the water lift about 12 -24" above the waterline you should be ok. Would help if you could do a sketch scan it and post it so I could see exactly what you got. Water does not easily get forced back up the exhaust pipe from outside due to air pressure inside. I have seen boats that have sunk and still had dry exhaust manifolds. Not to say it will never happen.

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Old 30-10-2009, 18:04   #13
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Thanks Sail,
I'm gaining a bit more confidence in my ability to design this thing properly. I'm no artist but can probably give you a good sketch tomorrow when things aren't too hectic around here.
Happy Halloween!
regards
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Old 03-11-2009, 12:27   #14
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Here's the new system design and I've had several suggestions which I will implement. #1 I'll loose the SS tubing and I'm going to glue some pieces of vernatube (fiberglass tube) together to make the proper bends. #2 top of the gooseneck is too high and should be lowered to somewhere between 59" and 35" to the top of the gooseneck from the base of the waterlift.
Thanks to all for your input.
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