How many engines is ideal?

I finally have the time to research this age old trawler question and add to the body of knowledge of this wonderful site!

Sold my twin Yanmar Mainship 34 a couple months ago.


Since there are already plenty of threads debating one versus two engines, thought I'd explore twin versus ZERO engines. So I went ahead and bought a Hobie kayak!


Will post fuel, consumption, range, rpms, and other data in a couple months!

I always thought 8 was about right...

Like these

How about going from one engine to three. We met this house boat owner at Columbus Lock on the TennTom southbound and cruised together to port St Joe, Florida one winter cruise. The outboard controls mounted on the bow and he could steer with all three. Planned to get rid of the old single out drive eventually because it wasn’t near as fuel efficient as the outboards.
Rafted up at Bobby’ Fish Camp, best and only catfish in that area of the waterway.

Four? Lazzara 92 with 4x900hp Volve pods. 136#k boat. 25kts @ 90gph. Not bade efficiency all things considered.

Three. One main engine, one generator engine, and one dinghy engine.

Whatever is working to move you through the water is enough.

Two mains, two generators, one water tender and one land tender (motor scooter) for a total of 6.

Once flew with a crusty old USCG fixed wing pilot that told me when I asked about engines....." I wanna look right and see nothing but engines as far as I can see...then look left and see the same....."

Crossing an ocean I might feel the same, for the rest of boating it just depends....

One of the boats I have inspected: Over 60'. Started with twins, but after its first season, due to not getting the top speed expected, a third engine was added, ahead of and between the original pair. same size, so added 1/2 again the hp. I assume he was satisfied, as he still has the trio, 15 yrs on.

Those crazy 4-6 engine setups are cool until Maintenance is due. It’s ridiculous. 4 engine commercial aircraft are dinosaurs. Too costly per hour ( with long term maintenance) included. Great during the maintenance honeymoon and certainly look cool.

1 main engine
1 generator engine
1 electric outboard for the dinghy

Ted

mvweebles said:

Four? Lazzara 92 with 4x900hp Volve pods. 136#k boat. 25kts @ 90gph. Not bade efficiency all things considered.

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Somewhere there's a prop repair shop salivating about the possible money to be made fixing EIGHT props...

Two outboards.
Or two inbd. Diesels straight drive.

wkearney99 said:

Somewhere there's a prop repair shop salivating about the possible money to be made fixing EIGHT props...

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We had a boat with twin Volvo Duo Props in it. We hit a submerged log and took out all 4 props at once. That was my worst underwater damage ever.

One. That requires only a fraction of the maintenance.

From someone who has had a boat with a single and now a boat with twins, one is the ideal number

Four - Twin inboard straight drive / one gen set / one o/b on tow behind runabout!

So, is an engine a motor, or is an electrical motor an engine?

Are we allowed to count thrusters, as electrical motors, in this survey?

motion30 said:

From someone who has had a boat with a single and now a boat with twins, one is the ideal number

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From someone who had a boat with a single and now has one with twins, 2 is way better than one.

One industrial duty motor to push the boat , one noise maker to create hyd power and also push the boat in an emergency .


Hyd would also be provided by main engine to power AC needs and DC needs underway in addition to other hyd users.

jimdavi said:

Those crazy 4-6 engine setups are cool until Maintenance is due. It’s ridiculous. 4 engine commercial aircraft are dinosaurs. Too costly per hour ( with long term maintenance) included. Great during the maintenance honeymoon and certainly look cool.

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Twin engine passenger planes can fly and land with only one engine, I doubt they can take off with one engine only. Each engine must be very powerful.

I see plenty of go fast opencockpit large fishing boats with 4 outboards, those people want speed. It all depends what kind of boating you want to do, what you can pay for.

The 4+ outboard setups aren't done just because they're cool, but because at that power level, it's cheaper and easier than building 2 or 3 very high powered inboards (that are squeezed in and hard to service). On the other hand, if you blow an outboard, you take it off and put on a new one. And a 400hp engine is much cheaper than a 1000hp engine.

Not quite on topic, but (my) experience proves it is good to have a spare dinghy motor for extended long distance cruising. You can be extremely limited if your dinghy engine will not start, perhaps because it was dropped in the water!!! Only good thing about the experience was that we had a spare dinghy and a spare motor on board, and the engine dunking happened at the mother ship and not at some remote shore line

Chrisjs said:

Not quite on topic, but (my) experience proves it is good to have a spare dinghy motor for extended long distance cruising. You can be extremely limited if your dinghy engine will not start, perhaps because it was dropped in the water!!! Only good thing about the experience was that we had a spare dinghy and a spare motor on board, and the engine dunking happened at the mother ship and not at some remote shore line

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On a turn... I dunked a near new 3 hp Johnson o/b; back in the early 60's... hadn't turned transom clamp tight enough. Small anchor snagged it for retrieval. Pops was not happy!! Had it up and running that afternoon.

That was back in the day of simple 2-strokes. Easy to pull apart, no electronics, no emission controls. The "good old days"!!

Chrisjs said:

That was back in the day of simple 2-strokes. Easy to pull apart, no electronics, no emission controls. The "good old days"!!

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Yup! I still enjoy owning many of the oldies. Carburetors and all!!

- 1967 Buick Wildcat with 430 cid, 500 fpt, 400 hp... original engine. Was rated at 360 factory hp. Bout 5 years ago [when it had 125K on it] top to bottom rebuild by racing car engine rebuilder... a real knowledgeable "old Boy". That "Sunday drive" car and engine is sure FAST n' Fun!! Only 13K miles on her since rebuild. Just getting broken in - LOL! Have to be careful not to "Light Up" them rear tires! Passing gear on the hwy is an acceleration rush. Special exhaust system sound makes people pay attention!!

- 1975 Johnson o/b on 14'8" 1975 Crestliner, four seater runabout

- Twin 1977 350 cid, 255 hp Mercruiser i/b's in our Tollycraft tri cabin

- 1977 Kohler 7.5 gen set

- 1985 350 cid, 325 hp in 1985 1T, 4WD, 4 spd, mech transfer box, 4" rise, pwr everything 1985 Chevy Silverado

- 1989 Mercruiser 350 cid, 260 hp i/o in a 1989 18' Bluewater cuddy cabin ski boat

- 1995 model 454 Chevy with TBI [super simple "after carbs" stuff] in 25' 1996 Tiffin Allegro RV

I carry a Leatherman "Surge" knife/tool with me at all times. Fulfills a lot of sudden needs on those old baby engines!

We also have 1998 Explorer SUV and 2014 Lincoln MKT - SUV. Those two go to the mechanic for most repairs. I do repairs on the six mentioned above. Sometimes they do need to go to mechanics.

For Cruising: 1 inboard engine
For Efficiency: 1 inboard diesel
For Maneuvering: 2 inboard diesels, or one diesel and one bow thruster
For Pocketbook: 1 inboard diesel
For Maintenance: 1 inboard inline diesel, NA, and not oversized for boat

For EGO . . . well, just not interested in that. The only person I have to impress is ME!

"Twin engine passenger planes can fly and land with only one engine, I doubt they can take off with one engine only. Each engine must be very powerful."

A modern turbo jet must be able to take off (after V1) on a single engine as well as climb out over obstructions on one.

In addition should one engine fail at altitude over the ocean the operating engine will maintain altitude and keep the aircraft able to complete the flight.

My worst case was when I had 4 engines including 2 cantankerous old generators. However I suppose I should consider the battery bank/inverter as a generator as well. Eight of those big 8Ds coupled with a transformer style 3kW inverter was very robust.

So my ideal boat would be 1 main + 1 inverter bank + tons solar. But that's without aircon.