Loss of power, C30 with a Universal M25 engine

[tshalvey]

Hi all,
I'm a newbie here and thanks for any help you may be. I'm a new sailor and now own a C30. I recently moved the boat to it's winter marina and had a long trip around cape cod to get to cape cod bay. The last leg of the trip was through the cape cod canal at flood as I was going into the bay. The engine had run well for about 9 hours. We had a 7 knot tide and with the engine at 2,000 knots we were making about 11 knots through the canal. The boat felt like it was surfing and difficult to steer. I decided to back off the throttle a bit and also glanced at the transom and noticed the exhaust port was underwater, I couldn't see the normal flow of exhaust seawater. The bow did feel like we were up on a plane. As I did this the engine lost power. Needless to say, I needed to throw the anchor as the canal is not very wide and I had lost steerage. We were towed to a marina and the engine ran fine when we got there and has run fine since. My question, has anyone else experienced this? Could the exhaust port being underwater cause a loss of power? Thanks in advance for any opinions.

 

[Stu Jackson]

Things to check:

Vented loop between muffler and exhaust riser nipple

Screen on intake of fuel hose inside tank - remove it.

Air leaks in hoses - intake hoses won't leak fuel, but air in the lines will stop the engine; when was the last time you checked you fuel hose clamps?

You might be interested in this:

Engines 101 - The BIGGEST & BEST collection of M25 Series Universal Engine Information on the Internet, plus some M35, too

Diesel Engine - c34.org

 

[sailme88]

Sounds like back pressure caused by the submerged exhaust. Same thing happens when the water muffler exhaust becomes occluded from rust inside out.

 

[tshalvey]

Things to check:

Vented loop between muffler and exhaust riser nipple

This has been checked and is good.

Screen on intake of fuel hose inside tank - remove it.

I've asked the marina to do this.

Air leaks in hoses - intake hoses won't leak fuel, but air in the lines will stop the engine; when was the last time you checked you fuel hose clamps?

They are good, but I'll re-look at them

You might be interested in this:

Engines 101 - The BIGGEST & BEST collection of M25 Series Universal Engine Information on the Internet, plus some M35, too

Yep, I've researched this site, didn't see any reference to this issue.

Thanks for your reply!

Diesel Engine - c34.org

 

[tshalvey]

Sounds like back pressure caused by the submerged exhaust. Same thing happens when the water muffler exhaust becomes occluded from rust inside out.

I'm starting to think this was the issue. By backing off the throttle it gave way to have the seawater take over and block the output. thanks

 

[LeslieTroyer]

you should be cruising at 2500-2800 with that much current you needed more revs to maintain stearage not less as you did.
Les

 

[ontherocks83]

I'm voting on back pressure. Remember engines are just giant air pumps and when you pulled back on the throttle the water pressure was greater than the exhaust pressure and killed the engine. Can't move air, can't run.

 

[ontherocks83]

Also do you have a thru hull with a flapper on it? It wouldn't have prevented the engine from dying but after it was off it would help mitigate water from getting pushed into the exhaust going the wrong direction.

 

[Kopite]

As noted, first thing is you need boat speed vs water to have steerage. This would also cause the overheat with water pushing at the stern. I experienced similar overheating with my M18 in following seas and found later that my flapper door had broken off.

 

[tshalvey]

As noted, first thing is you need boat speed vs water to have steerage. This would also cause the overheat with water pushing at the stern. I experienced similar overheating with my M18 in following seas and found later that my flapper door had broken off.

Yes, I agree. Although the tide was running 7 knots and at 2,000 rpm I was adding 4-5 knots on top of that. That should have given me enough to maintain steerage. I'm not sure the engine overheated, it just lost power. I don't have the flapper door, that will be a good addition. I do have the vented loop properly installed. Thanks for the note.