Exhaust water bypass hose

[jgwinks]

I'm replacing the engine water hoses on the new-to-me boat with twin Perkins 6.354MGT's. In the hose from the heat exchanger to the mixing elbow on each there's a tee with another hose going to a separate through hull with an above waterline closed seacock. It seems if the seacock were opened the raw water would bypass the muffler and exhaust pipes and discharge directly overboard. I've never seen this before and can't imagine why one would to do that. Anyone know what this is for and can I safely eliminate it? Thanks.

 

[Ski in NC]

Common way to do wet exhaust. Often done when exhaust backpressure is high due to too much water in the muffler. So some is diverted overboard. Only about 25% of engine cooling water is needed to cool the exhaust.

Might also reduce the whoosh-whoosh sound of water being expelled from the tailpipes.

But you have to actually throttle that bypass valve. If left full open, exhaust may get too hot and that is a problem you do not want to have. Some previous owner might have said "screw it" with regards to modulating that flow. Just closed it and was done with it.

If running engines at light load, back pressure is a non-issue.

 

[jgwinks]

Ok thanks. This is the first larger boat I've owned. None of my commercial boats have this setup and I don't think it's ever done on the smaller engines in sailboats. The seacocks appear to be fully closed, and we didn't see water coming out of those outlets on the sea trial. I think I'll keep the setup as is. The engines are the high hp version and the boat will plane at about 18 know, but I don't intend to run out anywhere near that fast. I'll just leave them closed.

 

[BruceK]

This thread might be of interest: https://www.trawlerforum.com/forums/s6/how-wet-should-wet-exhaust-34924.html

 

[Keysdisease]

Excellent, someone that actually understands exhaust bypass. Human nature leads many an yacht engineer or boat owner to come aboard or purchase a new to them boat, see a valve that is neither fully open or closed, and feel it necessary to "fix" it by either fully opening or closing.

On some boats to eliminate that compulsion after "dialing in" the valve setting using a back pressure gauge the valve handle is removed.

Common way to do wet exhaust. Often done when exhaust backpressure is high due to too much water in the muffler. So some is diverted overboard. Only about 25% of engine cooling water is needed to cool the exhaust.

Might also reduce the whoosh-whoosh sound of water being expelled from the tailpipes.

But you have to actually throttle that bypass valve. If left full open, exhaust may get too hot and that is a problem you do not want to have. Some previous owner might have said "screw it" with regards to modulating that flow. Just closed it and was done with it.

If running engines at light load, back pressure is a non-issue.

 

[kapnd]

Perkins raw water systems don’t move an excessive amount of water, so I wouldn’t think you’d need to bypass any water unless there’s some serious restriction issues in the exhaust.
Perkins Cast iron exhaust elbows (and exhaust manifolds) are a known sore spot, prone to corrosion and plugging up the spray holes with rust, so make sure that this isn’t the reason for the bypass!

 

[jgwinks]

Thanks. I'm planning to take all that apart anyway. Only 600 hours on the 1973 engines, so I'm more concerned with things being clogged up rather than worn out.