110hp engine on a 42ft boat - repower?

[TiPegleg]

So my new boat came with a 110 hp 6 cylinder MWM 229-6 diesel turning a 22.5" prop. This thing is immaculate, I can basically eat off of the the engine room, and I have several tons (almost literally) of spares. Here's the kicker - the boat is only 42ft on deck, 16 tons, and a waterline of 37ft... It's a damn big engine.

The backstory goes that the original owner/designer built this boat specifically to go to weird places safely. One of these places was a journey UP the Amazon river with a generator and a large cold plate running to the engine.

That said, I don't really have those plans in mind. So... do I pull it? Replace it with something more appropriate in the 50-60hp range? What would my realistic fuel consumption be for this engine (I already looked at the consumption curves but they assume a fully loaded engine).

Right now it's turning a fixed prop and while I always thought my first "upgrade" was going to be a feathering prop, this whole thing throws me for a loop.

Opinions greatly appreciated.

[more]

Originally Posted by TiPegleg

So my new boat came with a 110 hp 6 cylinder MWM 229-6 diesel turning a 22.5" prop. This thing is immaculate, I can basically eat off of the the engine room, and I have several tons (almost literally) of spares. Here's the kicker - the boat is only 42ft on deck, 16 tons, and a waterline of 37ft... It's a damn big engine.

The backstory goes that the original owner/designer built this boat specifically to go to weird places safely. One of these places was a journey UP the Amazon river with a generator and a large cold plate running to the engine.

That said, I don't really have those plans in mind. So... do I pull it? Replace it with something more appropriate in the 50-60hp range? What would my realistic fuel consumption be for this engine (I already looked at the consumption curves but they assume a fully loaded engine).

Right now it's turning a fixed prop and while I always thought my first "upgrade" was going to be a feathering prop, this whole thing throws me for a loop.

Opinions greatly appreciated.

why complicate life, if engine work don't do anything. enjoy in sailing-motoring. consumation with 50 hp engine maybe be more from this engine.,who know

[more]

But for you can be an easy change order MWM D229-4 for 5-6000$ and install on place MWM D229-6.
i now change 2 solar panel from 2x100W to 2x150W
only 10 meter solar cable. new inverter and MPPT
2 meter marine cable 95mm fuse and battery switch 300A
for now only i spend 1500€
my boat is only 10 km from my house only for now drive 500 km maybe be finish fo 2 weeks.

[tkeithlu]

Hmmmm.

First, engine swaps to a different engine are known nightmares. The mounts, hoses, seacocks, cables, and electrical connections are all in the wrong places.

That is a pretty generous engine for a 16 ton boat.

But then, the difference in fuel consumption in a big engine that is loafing and a smaller engine that is working hard, both doing the same work, is not great. Both will use about 0.4 pounds of fuel per hour per horsepower. Diesel weighs about 7.2 pounds per gallon. I'm inclined to say that you'll have to cruise a very long way to displace the cost of fuel difference after paying for the new engine.

Beyond those considerations, there's a rule of thumb that seems to be popular on the forum: Don't make changes for one year. Of course, that's one year of use, not sitting at the marina. It's just time in which to get the needed changes firmly in mind, sort of like my putting bright ideas I have on my Amazon wish list rather than in my shopping cart. If it still has that alure later, then I buy it.

[Bellinghamster]

Wow, that's a big engine for a light boat!
Of course, the easiest is to leave it as-is but I think you'll find you run around just cracked above idle to make near hull speed which is not good for a diesel. It'll carbon up over time. They like to run ~80% of rated load. You can mitigate the carbon buildup a little by running it hard periodically which will suck some fuel. I agree with the previous poster.. you can buy a LOT of fuel for the cost of an engine change.

[TiPegleg]

I should mention that I spent some time in trawler forums before posting here to figure out what the folks cruising the ICW on twin 250hp beasts are doing when they're slinking by at 8kts. Turns out that just about all diesels are ok to run at 10% of rated HP as long as you take care to bring them up to revs religiously every few hours.

So the second part of this question is, folding prop... I want that light air performance so I don't need the engine to just get by?

[more]

Originally Posted by Bellinghamster

They like to run ~80% of rated load. .

No,you are wrong. Diesel engine like 70-80 rated RPM and power less better for example 75% rpm and 50% rated power be nice and prefer.

[Stewie12]

I would rather have an engine that is too big. You never know when you might need that extra horsepower. Dragging an anchor in gale force winds would be one example.

[sail sfbay]

If you need to re-power get an engine that matches the boat's displacement and weight AND make sure it is accessible for maintenance. By comparison, my Hunter 46 that weighs about 15 tons has a 75 hp Yanmar. Boat achieves hull speed under motor.

[cottonsail]

My boat is a 15,000 lbs sailboat. The new engine is a 50HP Volvo Penta. That's slightly more than 3 HP per 1000 lbs. It's perfect. The old engine was a 37 HP Westerbeke. Best was abut 6.3 at 1 GPH. Now I am doing 6.9 kts at the same 1 GPH. IMHO 3+ HP per 1000 lbs is perfect.

[Elie]

I would'nt touch a thing. An old French saying pretents that too strong has never failed. If the boat sails well, a few pounds is not that bad. You also will apreciate the power in case of real emergency . Maybe a significant inprovement would be a feathering propeller that would reduce the fixed prop. You would see the performance result right away.

[ThereAndBack]

Another vote to leave it alone. The only thing I might change is a folding prop if you don't already have one and intend to sail since that is a big prop. But if the engine works, I wouldn't mess with it. It is a big project and life is short.

[sailormed]

“ So my new boat came with a 110 hp 6 cylinder MWM 229-6 diesel turning a 22.5" prop. This thing is immaculate, I can basically eat off of the the engine room, and I have several tons (almost literally) of spares.”

So the engine is in pristine condition, taken care of religiously and you have thousands of dollars of spare parts? Just leave it as is and keep it in that condition. Change the prop if that better suits your use of this boat.

[MicHughV]

I've never ever come across any sailor "wishing" he had less power...
on the contrary, the usual " wish" is...." wish I had a bit more power"...

Yep, considering changing the prop to a max prop or similar....is smart....that is a pretty big blade to carrying around...

sailors motor far more than they readily admit it.....

[Cadence]

Originally Posted by TiPegleg

So my new boat came with a 110 hp 6 cylinder MWM 229-6 diesel turning a 22.5" prop. This thing is immaculate, I can basically eat off of the the engine room, and I have several tons (almost literally) of spares. Here's the kicker - the boat is only 42ft on deck, 16 tons, and a waterline of 37ft... It's a damn big engine.

The backstory goes that the original owner/designer built this boat specifically to go to weird places safely. One of these places was a journey UP the Amazon river with a generator and a large cold plate running to the engine.

That said, I don't really have those plans in mind. So... do I pull it? Replace it with something more appropriate in the 50-60hp range? What would my realistic fuel consumption be for this engine (I already looked at the consumption curves but they assume a fully loaded engine).

Right now it's turning a fixed prop and while I always thought my first "upgrade" was going to be a feathering prop, this whole thing throws me for a loop.

Opinions greatly appreciated.

If it ain't broke don't fix it. Run her at a relatively low RPM and she will probably serve you forever and give you reasonable fuel consumption.