Engine overheating when motorsailing upwind

[theglo]

Good morning! (Problem with hints below it). I appreciate any assistance!

PROBLEM: My engine is overheating a bit but ONLY when motorsailing upwind and heeled over.

BACK GROUND: I have a 41' monohull with a new ZF15M transmission replacing the previous Hurth transmission. I replaced it myself in Georgetown Bahamas a few months ago and have driven it to Puerto Rico. It's been a lot of motorsailing as its all upwind.

BACKGROUND #2: I crossed the Mona Passage 2 days ago and was motorsailing into about 20 knots of wind right in my face. The boat was well heeled over with a reefed main up and the engine running at normal RPMs. I was averaging 2.5 to 3 knots of forward progress. I was running at night so couldn't see anything but on a few occasions I threw the engine into neutral, then reverse, revved it up for a moment, and then back into forward, same RPMs, and suddenly I'm getting 3.5 to 4 knots of boat speed for, maybe 10 minutes, and then back down to the 2.5 to 3 knots after a while. The boat also was slightly overheated during this time. As in, 5/8 of the way to WAY overheated on my gauge, but not the usual 1/2. At first I thought it was Sargassum weed that I had caught... but?

Then, to make myself KNOW (or at least I'm pretty sure) there is an issue, at about 3 AM I hit the night lee of Puerto Rico and the wind stopped completely and the seas went flat. I was able to point directly at my destination, and rev the engine up an additional 300 RPM. Running flat and calm I was now traveling 4.5 to 5.5 knots and the engine temperature actually COOLED to normal operating temp.

MY GUESS: I aligned the engine to the new shaft coupling. I think I need to align the prop shaft first, to the shaft hole (log?) in the boat. I think that when I am motorsailing (only main up), and the boat is well heeled, the shaft may be hitting the shaft hole and causing quite a bit of resistance.

QUESTION: Anything else I need to look at that I may have effed up?

Thanks CF world!

[Chotu]

Where is your engine intake? Possible that was out of the water at least some of the time when you are heeled over? Or maybe even just sucking a little air?

[theglo]

Originally Posted by Chotu

Where is your engine intake? Possible that was out of the water at least some of the time when you are heeled over? Or maybe even just sucking a little air?

The engine intake is nearly in the center of the boat, just behind the engine. I can't imagine it's sucking air even if I was laying at a 90 degree angle to the surface of the water. I thought this too, or at least that I may have sucked up some sargassum, and checked it at 2AM that night. It was clear.

It also doesn't explain why the boat suddenly runs a knot faster (4 knots) if I throw it into reverse for a moment, and then back into forward. I wasn't able to register any changes in the engine temp by doing this, there could have been, but since it goes back to 2.5 to 3 knots within 10 minutes it's hard to tell. My guess is that if it would keep running at the 4 knot speed I would see the engine temp go back to normal. BUT, I don't know, which is why I'm asking.

I'll keep an eye on the water output of the engine next time I'm heeled in that direction.

Thank you!

[Sailer_Med]

I normally say, "it's the last thing you did no
matter how unlikely it seems."

That aside I don't see the shaft alignment as making sense. Gravity, which is the accusation, when heeled would trivial compared to the forces of the propeller blades working.

I say speed is a red herring, ignore it for now. It makes sense that the temp would climb beating into the wind and remain stable on an easy cruise (Puerto Rico). If this is abnormal, then look at the cooling system. Last maintenance was...?

[rslifkin]

Intake sucking air was my first thought as well, but I'd expect if it was significant enough to cause overheating, it would probably burn up an impeller. Or at least you'd starve the exhaust for water badly enough to get a noticeable increase in noise.

[Rumrace]

Sounds like you have a drag on the shaft heeling ? Cutlass bearing ?

[wyb2]

Fixed prop, or other?

Speed measured by gps, or paddle wheel sensor?

Doesn’t seem illogical for the engine to work harder beating into waves than in calm water.

Side note, why motorsail and pinch at 2.5-3 knts? Take the main down and point dead up wind and make almost the same speed, or bear off and shut the motor down and make 6 knts.

[Shrew]

Is the engine raw water cooled or have closed cooling. If closed, how are the fluid levels?

Is it possible you're not properly circulating AF when healed, or healed on a certain side?

[Stu Jackson]

Originally Posted by wyb2

Doesn’t seem illogical for the engine to work harder beating into waves than in calm water.

What? Could you explain that to us?


At any given rpm the engine simply does NOT know what's going on outside the boat. No more than a tractor cares if it's sunny or snowing when it's workin' the driveway.

[rslifkin]

Originally Posted by Stu Jackson

What? Could you explain that to us?


At any given rpm the engine simply does NOT know what's going on outside the boat. No more than a tractor cares if it's sunny or snowing when it's workin' the driveway.

Not entirely true. Diesels are governed, so if you're requesting 2000 RPM, the governor on the injection pump will vary the amount of fuel injected to maintain 2000 RPM. So it'll work harder and burn more fuel in gear than it would in neutral at the same RPM. And if you make the boat harder to push (or the shaft harder to turn), the engine will see more load at a given RPM. If something is holding boat speed back, the engine likely won't reach rated RPM at full throttle as it won't have enough power to overcome the extra load.

[GreenWave]

on the shaft issue... if you think it gets worse (i.e. drag on shaft) depending on conditions, lean etc then you might check your motor mounts. If one or more are bad then the shaft position can change with boat lean, rpms etc. Ask me how I know.


Aside from that I would be checking coolant levels, raw water intake for debris, and make sure my prop is clean.

[theglo]

Originally Posted by Rumrace

Sounds like you have a drag on the shaft heeling ? Cutlass bearing ?

Yes, I think maybe that. But only while healing??

[wyb2]

Originally Posted by Stu Jackson

What? Could you explain that to us?


At any given rpm the engine simply does NOT know what's going on outside the boat. No more than a tractor cares if it's sunny or snowing when it's workin' the driveway.

But a tractor does care if you are towing a plow vs just puttering across the field.

For the same rpm’s, does a prop transfer the exact same load back to the engine regardless of boat speed? I don’t think so, but couldn’t tell you off the top of my head how big that difference is.

I’m sure different engines, especially across different decades, are governed differently. Maybe my statement was off base for some, but I’d be surprised if it was off base for all sailboat engines.

[theglo]

Originally Posted by wyb2

Fixed prop, or other?

Speed measured by gps, or paddle wheel sensor?

Doesn’t seem illogical for the engine to work harder beating into waves than in calm water.

Side note, why motorsail and pinch at 2.5-3 knts? Take the main down and point dead up wind and make almost the same speed, or bear off and shut the motor down and make 6 knts.

Speed from gps. Would have pointed into seas as well. Boat speed would drop to under 1.5 knots without main sail up.

I could have dropped off the wind and sailed but was really looking for that night lee of Puerto Rico (which did arrive almost 25 miles offshore). Plus wife and kids were sleeping and sailing off wind introduces a LOT of heel on my boat.

[theglo]

Originally Posted by wyb2

Fixed prop, or other?

Speed measured by gps, or paddle wheel sensor?

Doesn’t seem illogical for the engine to work harder beating into waves than in calm water.

Side note, why motorsail and pinch at 2.5-3 knts? Take the main down and point dead up wind and make almost the same speed, or bear off and shut the motor down and make 6 knts.

FIXED PROP.