Suitable Sized Diesel

[GordMay]

Originally Posted by denverd0n

57 hp is MORE than enough to drive that boat to hull speed, even into the wind. Trying to drive it beyond hull speed is almost entirely an exercise in wasting fuel and creating noise. Personally, I would not even consider the larger engine.

I'd guess that the 57HP is the minimum adequate size for that vessel.
I'd also guess the the 57HP & 80HP are the same basic engine; one normally aspirated, and the other turbo'd.

[Cheechako]

57 would likely be fine in a Bene. My heavy-ish 44 had the Perkins 4-108 which was 51 HP and I never ran it above 2500 rpm. In PNW high currents etc it was great. My 47 footer had an 80 hp mercedes. It was a very heavy boat. I'd take naturally aspirated over a turbo any day.

[Sailor 99]

Originally Posted by GordMay

Yes.
An oft-quoted rough Rule of thumb for determining Horsepower Required for a Sailboat:
One horsepower per 500 pounds ( ± 50lbs ) loaded.
Westerbeke Corporation suggests 2 hp for every 1,000 lb of displacement for coastal cruising, and 2.5 hp per 1,000 lb of displacement for offshore.
In their book "The Gougeon Brothers on Boat Construction", the authors suggest a good rule-of-thumb is 1 hp for every 500 lb of displacement.

This seems like to much engine. I had an 85 Perkins 4236 in my 50 ft Beneteau which likely goes 45,000 lbs all up cruising weight. Wide open we were blowing blacks smoke and the burying the stern. Waste of fuel.

With too much HP. I also don't think you can load them up enough to prevent glazing without over consumption of fuel and noise. A Kubota engineer told me that your minimum all day cruising engine speed is 60% of max rpm/hp.


It's not so much the expense of the fuel, its the quantity and how much you can hold. Sure who cares if you can carry 500 gal, how many can do that? If you only got 100 gal and your burning at 2 gal an hour, your very range limited.

Originally Posted by GordMay

Some people suggest 1 hp for every ft. of boat waterline length.
Some people suggest 3 - 5 hp (continuous rating) per long ton (to calculate the boat's weight in long tons divide the displacement by 2,240).

1 hp per foot of water line gives me 39 hp on a 45,000 lb boat. Not enough.

3-5 HP gives me 60 to 100 hp. I have a beta 75 which actually according to Kubota is only 66 and we can push into 6 ft waves at 6-7 knots, getting knocked back to as low as 3 in the steep and deep waves of Lake Ontario. At that speed we are using 85% of hp.

No matter what I would avoid turbo engines. If the turbo goes you are left with an engine that can not go much above and idle. In other words no engine. Others will disagree and thats fine, but not for me.

[Dymaxion]

Turbo will throw more heat into the engine compartment, if that is a factor/concern.

[oslokid]

Originally Posted by malbert73

Furthermore there is now good technical material written on Morgan’s Cloud that shows that overpowering too much leads to a chronically under loaded diesel which causes glazing etc. with an 80 hp diesel you’d need to be burning a ton of fuel and digging a big hole in the water on a regular basis to adequately load it up

I second malbert73's opinion. The folks at Morgans Cloud put out some great articles (subscription, but for me worth it). Plus, chances are you will have more room in engine compartment and maybe less heat. Probably easier and less costly to maintain. You may also get longer range. Go with the lower HP.

[capt jgw]

Originally Posted by malbert73

Furthermore there is now good technical material written on Morgan’s Cloud that shows that overpowering too much leads to a chronically under loaded diesel which causes glazing etc. with an 80 hp diesel you’d need to be burning a ton of fuel and digging a big hole in the water on a regular basis to adequately load it up

That's exactly the problem we have on the dinner boat I run. Mechanic says run the Detroit's at 1700 RPM all the time, but at that speed the guests are spilling their drinks all over the deck. We run at 1000 for a smooth ride but it's hard on the engines. Boat was originally a Mackinac Island ferry, and they run out balls-out all the time so it was not a problem for them.
Extra power is not always a good thing.

[Mainebristol]

There are other factors at play. On my little old Bristol 32, I have a yanmar 2gmf. It makes 18 horses at full throttle. Everybody in my harbor tells me I'm underpowered, and should have the three cylinder version.

Nope.

This is a SAILboat. Yes, occasionally I have to motor, but my little two banger gets me where I need to go slowly and efficiently. I get more than two hours at full throttle for every gallon of diesel. I fly for a living, and my boat is where I decompress. I don't want more power.

If we wanted to be fast and practical, we would not own sailboats. Get the simpler, smaller engine that will do less damage to your blood pressure and your wallet, and you will be happier. Perhaps you will hoist your sails more often. Isn't that great?

[CAVOK]

Some personal feedback, after I decided to go with the Yanmar 57 and motoring for over 200 hours.
We were time constricted (due Covid delays) and were into some quite strong 30+ headwinds and an occasional big sea as well.
On the calm days the 57hp gave us more than enough speed (6+kts) with a comfortable 2000rpm.
On the big headwind days there was still plenty of power and as several people pointed out earlier, the swell determined our speed more than anything. Keeping your boat from smashing off waves, especially cross swells had us slowing down rather than speeding up. Our yacht is a fairly light displacement at approx 11,000kg.
For what it’s worth, I’m more than happy with our choice of power. Hope the feedback helps.in the discussions, as for newbies to cruising (us) there are a lot of decisions to be made, that you really have little experience on.

[PerfectPirate]

Something that I am curious about: in this thread nobody has discussed the power-to-prop-size issue. On my Ontario 32 I am running a Yanmar 2QM20 with a 15-inch, three-blade MaxProp. It is a lovely combination and I am very happy with it. Incidentally, the 20 HP engine to 10,000 pound displacement is an exact match to the 500 pounds per HP guideline. However, I have noticed that it is possible, even in smooth water, to ramp up the RPM to near full power and induce cavitation without any actual increase in speed.

Now, the Yanmar specs on my engine/gearbox combination say that I could be running a 17-inch prop, but the prop shaft/strut setup on my boat does not provide clearance for anything larger than the 15-inch prop. So, when people keep advising us to get bigger, more powerful engines, I am assuming that they also think you can fit on a suitably larger prop to match the engine power. Even so, there is still a physical limit to how fast the boat is able to move.

As a side note, on my prior C&C 27, I had a 30-hp Atomic 4 driving a 2-blade Martec folding prop. At idle speed there was still so much thrust that my boat would do 2 to 3 knots in harbour. At 1/4 to 1/3 throttle, the boat would be moving at hull speed. If I cracked the throttle anywhere past 1/3 of maximum, the prop would simply cavitate and thrust would become virtually nonexistent. However, I did love my Atomic 4. A simple, reliable engine that was easy to maintain and fix. They deserve a much better rep than they tend to get in these forums.

[CAVOK]

I agree with you about the importance of matching a prop to the diesel engine and yacht. In the end that came into my thinking, where I thought going with the lower powered diesel but matching it with a 4 blade prop such as Maxiprop. Hopefully that would reduce cavitation. Ideally a variable pitch prop would give the best of all worlds. I’m not sure they even make them and would hate to think of cost and complexity if they did. They are the norm on most light aircraft.

[oldcal46skipper]

My Cal Cruising 46, Satori has a 85HP Perkins 4.236 at 85HP. At 1550 RPMs I cruise at 6.2 knots and consume 1.1 gallon per hour diesel fuel. I have tankage for 380 gallons, which satisfies Naval Architect Bill Lapworth and Cal Boats builder Jack Jensen's plan to be able to motor across the high pressure areas with little wind. I can motor over 2,000 NM if needed.


I have had my boat since 1982, 38 years, living aboard and cruising full time 14 years, so am pleased with the Greatest Naval Architect ever, Bill Lapworth. I replaced the original engine 13,000 hours in 1987 with a new Perkins 4.236. Now have 3,600 hours and she is perfect as she has gotten high quality care.



After advanced age and several health challenges, I've had to stop cruising, so Satori is for sale. I have a Florida LLC rebuilding Perkins 4.107 & 108's, over 200 "Rebuilds" in the last 12 years.



I would never put a Turbo in a cruising sailboat or use one of the high RPM engines. Details on request PM for address

[CAVOK]

This is a late update on my decision to stay with the 57 HP Yanmar.
After nearly two years of using our boat I’ve found 57 HP to be more than ample. It pushes our yacht along with ease in all the conditions we’ve encountered. Ther have been a few “encounters” & I never wished for more horsepower. I love the Yanmar engine. Totally reliable for us so far.

[Rumrace]

The new common rail 57 is a mavel. Congrats on the pending Benni the 46 is a doll. I’ve read in tests the larger engine is minimal and low RPM turbos are not as much fun as say Audi. Range may be very close but I’m sure the 57 will get you around 600 k miles in a perfect day and larger motor may not. As to speed I think it’s less than a knot faster. Something to be said about sea entry conditions in your area. If you have to jump surf heck ya go big.

[flightlead404]

I just want to know if it will plane with the turbo

[Rumrace]

The 46.1 gets on plane around 12 knots of wind.
Now if you add the hydrofoil keel attached with genuine Saskatchewan Seal Skin Straps you can plane sooner.