Underwater exhaust not working !

[folieadeux]

The underwater exhaust on both of my Cummins 380QSB engines and the Onan genny are not working. The engines use the above water exhaust when starting so the engines do not have to push against the water pressure at start up. Once the engines start gaining power, they should automatically switch to the underwater exhaust.

The genny does the same thing as the engine and for some reason this weekend none of the power plants switched to the underwater mode.

Any suggestions would be appreciated.

 

[Sandy]

Could the boat perhaps not been used for long enough allow U/W exhaust flaps to foul in place or the pipes foul? Or sea otters got stuck???
Is the system set up so the switch is strictly non-mechanical- i.e., much straighter flow to U/W exhaust and smaller sharp Y-bend back up to A/W/Ex for back pressure relief when starting or idling?

 

[folieadeux]

Sandy

The switch from above-water to under-water is non-mechanical. The above-water is only used when starting or idling so it relieves any back pressure. Dive just cleaned last week and problem was discovered this past weekend, diver is returning and I plan to be on the boat while he is there so all systems can be checked.

 

[tugboat kevin]

crank the rpm up in neutral the boat will shake from the bubbles under the boat

 

[PascalG]

I don't know how meridian sets it up but usually all you have is splitter between the underwater and above water pipes. At low speed, the end of thunder water piping is too low underwater and the exhaust naturally flows into the above water pipe. On plane, with the hull rising and suction, it flows below the boat.

Are you saying that you don't see any water coming out? Some boats have a valve to send cooling water into the above water line pipe, maybe that was closed, or the hose is clogged. I don think there is anything the diver can check for, those pipes are pretty big and not likely to be clogged... Trace the raw water hoses to see what the set up is

As to the Genset, what set up do you have? I ve never heard of underwater and above water exhaust. You probably have a water separator which sends th water below water line and the gases to a different thru hull above waterline. This drastically reduce notice but personally I don't like them as you can't visually check for water flow. Note that the underwater water discharge likely as a sea cock, make sure hath was not closed.

 

[Capt. Bill1]

Some thing does not make sense. As you speed up the water flow passed the underwater exhaust just pulls the exhaust out.

If you are saying at rest they don't switch to the underwater even if you rev them up a bit, that would be normal.

 

[jtybt15]

That's the question Bill.
And the time frame since last running.
The thought of something crawling up there also crossed my mind