Freewheeling propellers: the chopper theory

[Frank Vernet]

Does anyone know? Cathy....

[darmoose]

i for one am fearful of going back into the water, but alas... i cant resist. did i mention the the helicopter alalogy seems appropriate.

i find it very interesting that the so called experts have opinion, but little to back them up. contributers to this thread have offered that the math supports one answer over the other, so why do we need opinions?

i kinda like Gerrs opinion tho, (your not surprised, i can tell) that a freewheeling prop creates less drag than a fixed prop, except when hidden behind something like deadwood.

to me this is like asking does rain falling on your head make you all wet, and someone answers, no (if your under an umbrella)

by the way, does anybody know if J.V. mentioned any of these contradictions or Gerr in his 12/31/06 post titled "In Conclusion" i gonna have to go back and read that. (heh-heh)

darrell

also, thanks for the forgiveness (i need it, no doubt)

[Loren]

My observations from 20+ years sailing a CD27. For the first 12 years Whippoorwill was powered by the YSM8 and a 2 blade 12x6 prop. It seemed clear to me that having the prop locked in vertical position made a difference. The prop was narrower than the keel which is just inches in front of it. (I apologize for another analogy but if you are traveling in your car with an open window and hold your hand just inside the window- then put it out a few inches you certainly would experience more resistance) It may be different if the prop blade is wider than the keel.
In 1998 I repowered with a 2GM20 and a full sized Michigan 12X14 prop. New problem. I feel and have observed differences in boat speed by freewheeling when traveling from about 1-4 knots. It is not a "sail prop" and has wide blades. (it sure has worked niced for miles of powering on 2 extended cruises) At speeds approaching theoretical hull speed I've not observed a difference.
In practice I only occasionally let the prop freewheel because of the noise and possible wear. Usually the transmission is in reverse. I wonder if rpms experienced in freewheeling situatons at 2 to 3 knots reach levels that would cause more drag than the the locked prop. (especially if the blades fill in much of the circle made by the blade tips)
I've enjoyed reading the thread and hope we remember to have fun doing this.

[M. R. Bober]

I have been away. Has anyone changed their position on locked vs freewheeling?

Mitchell Bober
Sunny Annapolis (where tossing a bit of gasoline on embers is an old mid-winter tradition), MD

[bill2]

Being poorly prepared to elucidate even myself I will nonetheless try to summarize :

The participants are in "irons" with the following

Those in a vacuum ( think outer space ) say there's no difference out there but are not represented herein.

The theorists herein are:

the freewheelers acknowledge that under the right combination of factors their position may in fact be true

though

the locked tight group also agree that under the right conditions their position be true.

Meanwhile the realists :

have declared victory that for want of practical application to position a two bladed prop with the keel or get a folding prop for low drag.

And the three bladed prop proponents have consoled themselves that no one has refuted the fact that hull speed is hull speed is hull speed and they use what canvas it takes to achieve it while retaining strong motoring performance.

It would appear that all sides have declared themselves winners !

Of course this "little bit of gasoline to the embers" may be just what's required to allay the impending cold front.

[darmoose]

while i genuinely regret having said some of the things contained in earlier posts, and vow to not repeat that mistake, i cannot, on further thought ignore the plain truth that begs to be heard in the light of day.

Mitch brings us back to our question, and Bill2 makes a pretty good summary while tossing a little gas on the fire.
(actually, mitch gets credit for throwing the first gasoline, excuse me)
i dont know if folks are too tired of this discussion or not. but i want to restate my belief, after having given some additional thought to both the question of J.V.s original analogy, and to the ultimate question of which causes less drag, a freewheeling or a locked propeller.

i was trying to come up with other analogies to either support or negate Johns original. it occurred to me that when one is flying a kite, one is holding the kite against the force of the wind, much like a propeller being pulled through the water. the kite, if left unencumbered by restraints, will take the path of least resistance. it will spin and decend to the ground. how do we stop that from happening? we stop the kite from spinning by tying a tail to it(we introduce controlled resistance). EUREKA! our freewheeling propeller will take the path of least resistance, if unencumbered, through the water. IT WILL SPIN. it will spin as fast as the boat is moving through the water except for whatever resistance is applied to slow it down. (this is VERY IMPORTANT as it proves that our freewheeling prop is merely taking the path of least resistance by spinning). other analogies that i believe apply are a mainsail, if unrestricted by the sheet will take the path of least resistance, it will swing out and dump the wind. so will a rudder if not restricted by the helmsman. the greatest resistance is created by placing the sail or the rudder perpindicular to the wind.


in the helicopter analogy, while the blades do need to spin to have the potential of slowing the choppers descent, they must also have resistance applied by the pilot and the mechanism of the rotor.
by reversing and then adjusting the pitch of the blades he is slowing the rotors to a rpm that is slower than the rotor would spin if left unencumbered. it is this resistance that allows the pilot to have some control over his descent by CREATING DRAG.

Matt, in his several explanations of how helicopters fly, and how they can resist falling when the power goes off, indeed did answer our question. i was not paying proper attention at the time.

Matt wrote:

" What John failed to recognize in the original post was that he was comparing a powered state on his model to an unpowered state of a freewheeling prop. The powered state on his model is equivalent to sailing with the engine running and the transmission in reverse"

i believe, and Matt please correct me if i am wrong, that the "powered state"refered to is the helicopter in autorotation mode descending toward the ground. the power is provided (since the motor is off) by the wind rushing up and forcing the blades to spin. and , if the pilot does not control the rate of spin by adjusting pitch (applying resistance) the blades will spin as fast as the wind rushes up, there will be little or no resistance, and the helicopter will fall like a rock.

our freewheeling propeller, if unencumbered by drive train friction, will spin as fast as the boat is sailing (or close to) and create little or no drag. its only when we introduce more resistance to slow down the propeller rpms that we increase drag on the boats motion. the amount of drag created by the propeller is proportional to the difference between the rpms that the propeller would achieve without applied resistance and the rpms resulting from applying frictional resistance. the larger this difference, the greater the drag. i dont see why this wouldnt apply to all ranges of propeller speeds.

since the greatest resistance applied to our freewheeling propeller is when it is locked tight, it can only follow that a locked propeller creates more drag than a propeller spinning at any rpm. now there may (i say may) be anomalies that come into play when the propeller is stopped, as many have claimed, i dont know. and i am open to seeing evidence to that effect, but until then, this analysis seems very reasonable to me.

it will be easy for "proplockers" to distract our attention and try to deny the obvious logic behind this analysis. i think this would be a mistake if they are indeed looking for the truth. far better to poke at it, ask questions, offer differing views for scrutiny, if they dare.

so there it is, i am out there once again. i cant help but conclude once again that:

1.) john's helicopter analogy is not applicable to a sailboat sailing and freewheeling its propeller.

2.)a freewheeling propeller creates less drag than a locked down propeller.

it is all about the propeller, and how it acts in its environment. a freewheeling prop or a rotor on a helicopter will take the path of least resistance, if allowed to, it will spin as fast as it can (all the way up to the rpms that match the boats speed, all we need do is remove any frictional resistance). since "spinning" is the path of least resistance, it cannot create more drag than a stopped propeller.

go ahead, have at me.

darrell

[Neil Gordon]

I have been away. Has anyone changed their position on locked vs freewheeling?

Yes, Mitch, each side has through cunning logic convinced the entire other side and so the free wheelers are now locking their props and the lockers are now spinning.

[Carter Brey]

http://www.amazon.com/exec/obidos/tg/de ... ver-std-20

[Neil Gordon]

http://www.amazon.com/exec/obidos/tg/de ... ver-std-20

Thank Carter for finding the Amazon link!

By the way, as a special this week, Amazon is also including for free a six volume set of this thread.

[Dick Barthel]

http://www.amazon.com/exec/obidos/tg/de ... ver-std-20

Thank Carter for finding the Amazon link!

By the way, as a special this week, Amazon is also including for free a six volume set of this thread.

Carter,

I presume your point is that when you are free-wheelin while stoned, you are actually going slower but you're having a much better time? I think Blowin in the Wind was also featured on that fabulous album. It never occurred to me that Dylan was an accomplished sailor. I should have known better.

Dick

[M. R. Bober]

in her search for another 1000 views.

Mitchell Bober
Sunny Annapolis (where you can lead a horse to water, but before you push him in. Think about how a wet horse smells), MD

[darmoose]

Fellow Cape Dorians,

since my last post on this subject four days ago, when i wondered out loud if folks had had enough of this debate, and when i laid out what is the obvious truth about this question, there have been several thousand views added to the count. at the same time, the folks of the opposite persuasion have not seen fit to defend their weakened position, nor challenge the logic of our final argument.

i think it is fair to conclude that the many views registered, bodes well for a high interest level, while the deafening silence from the "proplockers" when called to battle, portends a successful conclusion to our debate.

simply stated: a screw (propeller), when unemcumbered by drive train friction, will take the path of least resistance when being pulled through the water. if it is a folding prop, it will fold: if it is a feathering prop, it will feather: and if it is a non-adjustable prop, it will spin.

it will spin at a rate that matches the speed that it is being pulled, and can only increase the drag on the boat if frictional resistance is applied just like the falling helicopter (see previous post). the propeller has no ability to do otherwise. and as you increase any applied friction, (whether deliberately or accidentally) you increase drag, until ultimately, you stop the propeller, creating the ultimate drag.

i want to thank all those who shared their experiences of slower sailing speeds with locked propellers with us (sometimes in the face of ridicule), and those others, who could see instinctively the fallacy of the argument of locking ones propeller to sail faster.

the upside of finally getting to the bottom of this question is that whenever any of us CDers are confronted by this query, perhaps by a less informed sailer, we can claim that our illustreous board solved this problem for good. be proud fellow CDers.

we may even be able to read in future books that locking ones propeller is a sure fired way to lose the race.

...and i"m sure Mitch didnt mean what he said about anybodys mother.

freewheeling to all
darrell

[Dick Barthel]

I finally got the response I asked for from Michigan Wheel. First my email to them and then the response:

I purchased one of your propellers last season when I put a new Beta Marine engine in my Cape Dory.

On our Cape Dory board we are currently embroiled in a debate of whether from a drag standpoint it is better to lock your prop when sailing v. letting it freewheel. The "thread" has over 4,000 hits. I told my friends I would ask for an opinion from an engineer from Michigan Wheel.

There are many that think that a freewheeling propeller on a sailboat sailing at or near hull speed would actually produce more drag or resistance than a fixed blade. Could you shed some light on this question?

I have mentioned you Company any number of times and will credit you again if you respond. A lot of the original Cape Dorys came with Michigans.

Thanks,

Dick Barthel
Dear Mr. Barthel:

Sorry for the delay in responding to your recent inquiry. I just received the following reply from our engineer and thought it would simplify matters if I just forwarded it on to you. Hope it helps with the debate, and thanks again for your inquiry.

Sincerely,
Greg Verseput
MWC Inboard Cusotmer Service

Greg,

I honestly cannot say for certain, one way or the other. I seem to recall seeing a magazine article that tried to answer that question, as do these links found via Google:

http://www.shaftlok.com/FreewheelStoryShaftLok.htm

http://www.boatdesign.net/forums/showth ... p?p=112414

http://www.setsail.com/c_central/faqs/f ... nship.html

Hull form certainly has an effect; it will definitely be better to lock a two blade propeller behind a full keel than to let it freewheel, for example.

If I had to, I'd vote for locking the propeller in place.

Kevin

___________________________________________________

I suggest we ask Michigan Wheel to design a propeller where one blade can lock and one can freewheel! I for one am not going to the links but I assume they must conclude it is an open question. Maybe we should give them Darmoose's number so they can be enlightened.

Let's go for 10,000 hits!

[Oswego John]

[DARMOOSE WROTE]
[i think it is fair to conclude that the many views registered, bodes well for a high interest level, while the deafening silence from the "proplockers" when called to battle, portends a successful conclusion to our debate.]

A successful conclusion...yes, yes,...a successful CONCLUSION. Yup, that's what it is. The conclusion, the end, finis.

Us prop lockers know when we've been beat. Uncle,...uncle. Please don't keep bringing up the subject, it's so embarassing to us. It's like rubbing salt in the wounds of our egos.

We concede victory to the freewheelers if that's all it takes to arrive at a permanent conclusion. A huge, resounding UNCLE.

Amen, RIP
Ever moving forward, our next important topic,
Tillers or Wheels? (Excelsior)
O J

[John Vigor]

Fellow Cape Dorians,

since my last post on this subject four days ago i think it is fair to conclude that the many views registered, bodes well for the "proplockers".

the upside of finally getting to the bottom of this question is that whenever any of us CDers are confronted by this query, perhaps by a less informed sailer, we can claim that our illustreous board solved this problem for good. be proud fellow CDers.

darrell

Darrell: I have taken the liberty of editing your last post a little. But as you see, I have retained the guts of it, the bit that makes sense. I have used nothing but your exact words.

I commend you for reaffirming your epiphany and seeing the light at last.

However, as O.J. put it so eloquently, can we move on now, please? Enough already.

Cheers,

John V.