Fuel economy

[motion30]

Just thinking. (I know often dangerous) has anybody pulled one propeller and just ran on one motor and what were the effects of fuel economy?

[Comodave]

Originally Posted by motion30

Just thinking. (I know often dangerous) has anybody pulled one propeller and just ran on one motor and what were the effects of fuel economy?

PassageMaker Magazine had a story where a guy did that on a transit from Hawaii to the west coast. Don’t remember what the details were but you might be able to find it online somewhere. I believe it was maybe a GB 42.

[motion30]

I have been unable to find that article if anyone has a link I would greatly appreciate it

[RedRascal]

I've heard of a couple with a Bayliner 38 that I believe pulled a prop to get more range for making longer jumps in the Caribbean. The 38 was what they had and running 1 engine gave them the range to get where they wanted to go. Maybe one of the guys from the Bayliner forum will have more details. It was a great tale of making what you have work.

[Pete Meisinger]

I think it would make little or no difference.

pete

[O C Diver]

Originally Posted by motion30

Just thinking. (I know often dangerous) has anybody pulled one propeller and just ran on one motor and what were the effects of fuel economy?

While I think it would improve your economy slightly, typically most twin engine boats have smaller rudders. Before I tried that, I would try maneuvering and docking with one engine to see how that worked out.

Ted

[Comodave]

The guy that did the Hawaii trip stopped midway and put the prop on the other engine and pulled the original prop…

[rslifkin]

Unless the rudder drag penalty is severe, running on one with the other prop removed should save a little fuel on most boats. Chances are, it won't be enough to justify the reduced maneuverability and loss of redundancy. Plus, depending on how the boat is propped and its top speed, you might be significantly speed restricted to avoid overloading the running engine.

[Comodave]

Originally Posted by motion30

I have been unable to find that article if anyone has a link I would greatly appreciate it

I don’t have any of the old PMMs anymore and the new ones aren’t that worthwhile IMO.

[tiltrider1]

The Hawaii transit guy did it so that he could run the engine more loaded. He could have made it running both engines but the engines would have been just above idle and not making the appropriate heat.

One gallon of diesel makes about 20HP for one hour in most diesel engines. It takes a fixed amount of HP to move a boat through the water. Doesn’t mater if you get all the HP out of one engine or Half out of two.

Now some HP does get absorbed by the internals of the engine. By using only one engine you will gain some marginal economy, you unfortunately will give this back with rudder drag when you compensate for a crabbing boat. In almost all twin engine boats there is no economy gain by running just one engine, prop or no prop.

Now some one is going to pipe up about how they shut one engine down and got 15% inprovment in fuel economy. What they will fail to mention is that they slowed down on one engine. The act of slowing down is what gave them the economy. It goes something like this. “I normaly cruise at 1500 RPMs. I found when I ran just one engine at 1500 RPMs I saved a bunch of fuel.” This is true but what else is true is that they traveled at 7.5 knots on two engines and 5.9 knots on one engine. Had they throttled both engines down to 5.9 knots they would have saved the same amount of fuel.

[Delta Riverat]

If I was worried about saving 5% on fuel cost I wouldn't have bought a boat.

Prop on, prop off. Rinse and repeat. What's that worth in time and effort?

Hire a diver? Haul and remove? Put it back on?

Be my guest, I'm not doing it.

[RedRascal]

I think I found the couple that tried using just 1 prop on their Bayliner 38. They wrote a few books about their travels which are on Amazon. They must have worked something out because I think a 38 has about a 300 mile range and it's ways to Honduras and Guatemala.

https://www.amazon.com/Diamond-Lil-D...=UTF8&qid=&sr=

Blog here but I didn't surface anything quickly that spoke about the range of their boat. Diamond Lil's Adventures Maybe someone that is better at search can get the story if running one prop gave them materially better range.

[North Baltic sea]

Hi,

Litle bit this topic "articel."

https://www.passagemaker.com/lifestyle/strategies-for-long-range-cruising-with-twin-engines-2

I think best way saveing consuptions is low cruising speed 2-3 knots under you hull speed.

NBs

[markpierce]

Run the boat like it was designed.

Lots of previous posts.

Reduce speed to increase efficiency, At six knots, my boat's fuel consumption is half that at seven knots.

[mvweebles]

Originally Posted by Comodave

PassageMaker Magazine had a story where a guy did that on a transit from Hawaii to the west coast. Don’t remember what the details were but you might be able to find it online somewhere. I believe it was maybe a GB 42.

It was many years ago, but I remember that article. Was indeed a GB42. It seems unbelievable, but my memory is that he removed one prop and loosened the other. To balance engine hours, he dove on his boat and swapped props. I believe he was a single-hander.

The reduced drag of removing a fallow prop would be significant. Would definitely make enough of a difference on a trans-Pacific trip.

Even though I read the story with jaw on floor, I find my recounting above incredulous.

OP - why do you ask?

Peter

[rslifkin]

If you were planning to run like this regularly, folding or feathering props might be worthwhile. Much easier then removing a prop, plus it leaves the second engine able to be used if needed.

[Portage_Bay]

To find out if a given twin engine boat will burn less fuel by running on one you just have to try and see if it works. Some people claim it does. Tiltrider1 explains very clearly why it probably won't.

My very small data set of two boats says it's not worth the trouble. One had modern instrumentation that indicated % load and fuel consumption. The savings were not enough to matter and the % load on the running engine was far too high at anything more than minimum speed. The other boat is older with no such instrumentation but was clear within minutes the boat was all but unmanageable. Extreme rudder required to keep a good heading and crabbing through the water.

In both cases we did not pull the idle prop. It was a first effort to see if running on one was worth any theoretical fuel savings.

On the boater who swapped props mid transit to Hawaii. I recall reading the article and couldn't believe he did that. The risk / benefit calculation on that decision was in my opinion far out of balance. Apparently his goal was to run the single harder for proper engine loading at low speeds. I think there are better ways to address that concern. Either run on one engine to Hawaii and the other on another long passage or find a way to carry more fuel. It would not require a lot of extra fuel to run the boat at minimum speed and two or three times a day run her hard for 15 - 20 min.

Regarding economy. If one is looking to have a less expensive boat to run the fuel burn difference between twin and single is not a major savings. It's maintenance and repairs. For example I currently have twin CAT 3208s. It's time to replace the exhaust risers. I've got 4 to buy and install where a single inline 6 would have 1 riser.

[AlanT]

I recently had to run my boat on one engine for a day. One thing to bear in mind is that the offset rudder angle required to compensate for offset propulsion constantly changes with changes in engine speed and, I suppose, current. At low idle my small rudders were unable to compensate for offset and I was only able to turn in one direction and when trying to drive straight the boat would crab somewhat. With increased engine speed rudder has more bite and therefore less angle required and it was possible to turn in both directions.
~A

[wrm95]

U S navy would routinely on long cruises.

[tiltrider1]

Originally Posted by wrm95

U S navy would routinely on long cruises.

Yes but why, I doubt it was for fuel consumption. More likely it was to do maintenance.