SailNet is a forum community dedicated to Sailing enthusiasts. Come join the discussion about sailing, modifications, classifieds, troubleshooting, repairs, reviews, maintenance, and more!
I'd say the question has been answered definitively. Now you have to do a similar comparison test for folders, feathering, fixed 2 blade, fixed 3 blade, fixed 4 blade. Also, locking a 2 blade vertically behind deadwood.
That would finally put to rest all the various opinions about what's best or lowest drag.
MS, you are a marine mechanical stud. I'm surprised the lady posters here haven't suggested you pose for a calendar.
Way cool test. No questions really, just way cool.
Did you ever do any feathering prop tests? Max-prop procedure is..... neutral, engine off, reverse for a few seconds, neutral. It's a whole different ball game than the purpose of this test. I'm just curious what happens in real life if the feathering prop is left in reverse.
The drag on hem is so minimal that it would be hard to measure differences. MIT has already done it far more accurately than I could and all the folders and feathering props they tested did very well and had minimal drag...
I do have a brand new Flex-O-Fold three blade in my shop that will be replacing a Max on a friends boat. It will be interesting to see if he can tell a difference. This is being done mostly because the Max can still catch pot buoys where a folder can't....
I am installing a two blade Flex-O-Fold on our boat this spring. We'll see how it does. If it vibrates the Campbell Sailor will go right back on & the FOF will be sold........ Our boat has as close to zero vibration right now as any boat I've ever been on so it will be an interesting comparison..
Very clever testing as usual and it seems quite conclusive for 3 blade fixed props.
I'm not sure this test answers the same question for my fixed 2 blade prop that is mounted in the dead wood in a cutaway in front of our rudder. With this configuration we can align the prop with the hull theoretically 'hiding' it from being a real drag.
Do you know of any studies that might have been done on fixed 2 blade props with this configuration?
Thanks in advance, as always.
Pretty hard to test that, and I would guess with a two blade the differences would be less "dramatic", but one thing I have learned is that if the prop begins to spin:
1- It is not as hidden as you thought
2- Is taking the path of least resistance
When we had a Cape Dory 27 with two blade even after I aligned it vertical it would still begin to spin...
For info, Volvo Penta state to allow the prop to rotate with MS2 gearbox.
The Volvo 2000 series with MS2 gearbox Owners Manual states -
"When under sail, the control lever should be in the neutral position if the propeller is a fixed propeller.
If the propeller is a folding propeller, the control lever should be in the reverse position. Start the engine and run it for five minutes every ten hours when on long-distance cruises."
The reason is that if left in forward, it can wear the clutch cones, and if left in reverse, it can jam the cones.
Gee MS, you could have spend thousands more $ to get the same result. You must not work for the Goverment .
Great test and rig and confrimes the arguement I had last summer.
The bottom line is that if the boat is going thru the water and there's enough energy to spin the prop thats how much energy you loose stopping it from spinning
I have never done a test in the water like this. I just have practical experience with airplanes. When we talk fixed pitch prop (non feathering variety) a spinning prop has more drag through the air than a not spinning prop. Example; a single engine airplane. At cruise. Engine failure. Reduce speed to best glide then keep that speed in decent. The engine (recip type) will keep windmilling. As apposed to; cruise, engine failure. Raise nose to slow aircraft. Prop will stop. Lower nose to attain best glide speed. Prop remains stopped (Harder to get a prop/engine spinning then to keep it spinning) glide angle is better with non spinning prop. Both instances at same indicated airspeed. Weird I know. The only variable is the airmass movement which will affect track and speed over the ground. However the IVSI (Instantaneous Vertical Speed Indicator) will show a higher rate of decent with the spinning prop, again with indicated airspeed the same. It is significant. Again I am talking fixed pitch. NOT feathering.
I don't know why air reacts different than water since both are fluids so to speak.
on an airplane the free wheeling prop is not fully free wheeling it is attached to an engine that is at idle or still spinning aganst the engine compression. there is no transmission to put in neutral. also a lot higher differencial in speeds between the still fluid and the moving craft. the drag increase with speed is not linear
Good experiment that one.
I have always locked the gearbox when sailing. It is less noisy that way and it won't make that rumbling noise when it spins.
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Related Threads
?
?
?
?
?
SailNet Community
1.7M posts
173.8K members
Since 1990
A forum community dedicated to Sailing, boating, cruising, racing & chartering. Come join the discussion about sailing, destinations, maintenance, repairs, navigation, electronics, classifieds and more