The Magnus effect

O C Diver said:

It would be interesting to know the increased fuel consumption value (producing electricity for the rotors + drag) as a percentage of normal fuel consumption, to stabilize the boat.

Ted

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I won’t ever have an answer for that question since I have no way to measure fuel use within that likely range of sensitivity.
Old school engine and no flow sensing equipment.
Having seen what rpm produces what speed would suggest the difference will be too small to measure. Again, not nothing I am sure, but quite likely not enough to cause a minute of concern.
I am going to make the 5 hour trip to Anacortes for the boat show on Tuesday so that Magnus can exhibit the installation and sea trial for prospects while I am gone to Mexico. That trip involves the Strait of Juan de Fuca and Rosario Strait so I might get a better trial that day.
For spinning the rotors you could likely compute the fuel,use from the fuel curve after converting 1100 watts to hp. Less than 2 amps is not much power.
Drag would be a total guess. If it does not affect speed at a given rpm, can it be significant?

klee wyck said:

I won’t ever have an answer for that question since I have no way to measure fuel use within that likely range of sensitivity.
Old school engine and no flow sensing equipment.
Having seen what rpm produces what speed would suggest the difference will be too small to measure. Again, not nothing I am sure, but quite likely not enough to cause a minute of concern.
I am going to make the 5 hour trip to Anacortes for the boat show on Tuesday so that Magnus can exhibit the installation and sea trial for prospects while I am gone to Mexico. That trip involves the Strait of Juan de Fuca and Rosario Strait so I might get a better trial that day.
For spinning the rotors you could likely compute the fuel,use from the fuel curve after converting 1100 watts to hp. Less than 2 amps is not much power.
Drag would be a total guess. If it does not affect speed at a given rpm, can it be significant?

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This is a rough estimate, but should be in the ball park. 1100W would be about 0.1 gph if produced using a generator. Using an on-engine alternator to produce the power is about 1/2 the efficiency, maybe not quite that much less, but approximately. So I would estimate 0.2 gph increased fuel burn. If memory serves me, that's about what I have seen on my boats with hydraulic fins. I also can't see any reason why there would be a significant difference between the two, so this seems to pass the sniff test.

klee wyck said:

I
I am going to make the 5 hour trip to Anacortes for the boat show on Tuesday so that Magnus can exhibit the installation and sea trial for prospects while I am gone to Mexico. That trip involves the Strait of Juan de Fuca and Rosario Strait so I might get a better trial that day.
For spinning the rotors you could likely compute the fuel,use from the fuel curve after converting 1100 watts to hp. Less than 2 amps is not much power.
Drag would be a total guess. If it does not affect speed at a given rpm, can it be significant?

Click to expand...

There are no free lunches.

While I don't expect it to require a great deal of energy, arresting wave action has a cost. When talking to people about my efficient hull speed, I tell them that making water stand up (boat wake) requires a significant amount of diesel fuel.

I also can't imagine that 2 horizontal hull protrusions doesn't add drag factor.

My guess is 10%. If you choose to increase the RPM to maintain the previous hull speed and factor in the power consumption for spinning the rotors, 10% will be the increase fuel consumption per mile. To have a stabilized boat, that's a negligible cost.

The other question is whether consumption increases as it takes more effort to stabilize the boat in bigger seas. Logic says yes, but is it proportional or are the rotors only able to produce a certain amount of wave attenuation?

Inquiring minds are expecting more detailed analysis!

Congratulations, it looks to be a meaningful improvement!

Ted

The rotating cylinder is producing lift on one side and drag on the other. It’s not comparable to pushing a non rotating cylinder through the water. The lift is augmented on the side that moving in the same direction as the boat. You only get a Magnus effect when the cylinder is moving relative to the body of water it’s submerged in. Would think total drag would depend upon how fast the boat is moving and how fast the cylinder is rotating.
Potential advantage would be you can vary speed of rotation (and lift) with boat speed. With fins surface area of the fin is chosen by size of the vessel and made optimized for a particular boat speed. So fins work best at one particular speed and are most efficient at one particular boat speed. With Magnus you still need different sizes of rotors of different lengths to match a vessel and you’re limited in the top speed it’s reasonable to use them. But within a small range of,speeds you should be able to get optimal performance all the time.

I got to demo the DMS MagnusMaster at Trawlerfest in Anacortes last week. We were out on a 40 ton steel trawler with two stabilizers. It was a flat day so the DMS owner, Patrick, was using the stabilizers to rock the boat.

In the first video I am propped with elbows on the counter behind the helm to stabilize the phone and was standing on a rug. Within a few seconds of turning on the stabilizers the boat heeled so much that the rug slipped out from underneath me (that's what induced the alarmed look on Patrick's face). This video is a little over a minute and the rocking occurs at the end. There's a second video of using a single stabilizer to rock the boat.

There's a third video that I won't post where I was sitting in a folding chair on the deck in front of the helm with elbows propped on the chair arm rests. Because I was focussed on recording and not balancing I got tossed out of the chair.

Two stabilizers:
https://youtu.be/PjLrRoUbs8o

One stabilizer:
https://youtu.be/VhUudTeqNyc

I'll be getting a single unit on my 20 ton Helmsman 43 when it arrives in a couple months...

I am glad someone chimed in here.
By now I am biased like the manufacturer since I have spent silly money on the equipment.
But....during Trawlerfest and the Anacortes Boat Show, I left LIBRA with Magnus and a capable captain to do some demonstration sea trials. I was not around but am hearing that there were at least 5 sea trials and up to 21 observers aboard at a time. Quite a few folks have now seen these in action on Libra, which is 65 tons by the way. The stabilizers will throw the vessel around with induced roll like it is a paperweight.
I also got a decent trial on the delivery trip in the Strait of Juan de Fuca.
We had conditions which, while not terrible, were banging things around and opening drawers and cupboards before we secured them and before we turned the stabs on.
Once we turned the stabs on the vessel was quiet as a mouse. My wife and cruising partner who was a pretty big skeptic on the spend, is now a very serious fan of the equipment.
I will say again, these things are the real deal, and the low power consumption defies logic.

65 tons and getting rolled that quickly by a single stabilizer. I'm very impressed.