Freewheeling propellers: the chopper theory

[Neil Gordon]

It's really too bad John couldn't have gotten a nice radio controlled sailboat, without a motor.

By the way, do radio controlled sailboats with tillers sail faster than radio controlled sailboats with wheels?

[Parfait's Provider]

As the water hits that fixed prop it is trying to turn the boat over which will result in heeling and since the prop and hull are unlikely to be in a symmetrical relationship, the forces will be such to cause yawing as well. Now then, if the affect is to heel the boat to windward and the boat is not at hull speed, there is likely to be an increase in speed. Further, if the yawing is to windward, the rudder won't need to be used quite so much to keep headed up, adding another fractional increase in speed.

Further, if the boat is sailing with the current, then a fixed prop would help push, whereas a freewheeling prop would add nothing.

Now then, if a fixed prop helps push better than a free-wheeling prop, does it not follow that a free-wheeling prop drags less than a fixed prop? Uh huh.

I'll bet we can make this the longest thread yet.

[Neil Gordon]

Which creates more drag in,lets say, 60% humidity 75 degrees?

Varnish creates significantly less drag, but if you use Cetol, you get to leave sooner. The head start is either worth it or not, depending on whether you lock your prop or let it spin free and/or steer with a tiller or a wheel.

[John Vigor]

Never mind the darned barnacles. I would like to dismiss a scurrilous rumor being bruited abroad by the Freewheeling Sect that clamping your shaft grows hair on your hands.

The fact that I shave my palms every second day is due to an inherited genetic disorder and has nothing to do with my penchant for stalled propellers.

John V.

[Parfait's Provider]

We all know that boats with blades sail faster than boats with wheels and the tiller has nothing to do with it.

Which I guess brings up the question of whether a boat that doesn't float is really a boat at all.

No wonder ice boats were invented.

[Dale W. Bridges]

Prop noise IS a drag! My tranny is in reverse to accentuate the sweet sound of sailing...the numbers be damned![/url][/code][/quote]

[bill2]

Though we may be locked in this infernal debate I should like to freewheel for just a moment to wish everyone

Happy New Year !

[darmoose]

well...

here we are in 2007, i hope everyone made it trough ok. HAPPY NEW YEAR to all.

J.V.... that was a beautiful attempt to try to cut off the debate. your eloquence is something to behold. but then, thats when you are in your element, isnt it. as i said before, you do have a way with words, you silver tongued devil, you.

it appears people are very interested in the outcome of this "debate" as there are over 2600 veiwings now, so alot of folks are tuning in. thats fun, aint it.

the only thing i have to ad this morning is this:

went out sailing yesterday, and guess what i did....

under sail, when i engaged the transmission in reverse (locked that baby up) there was a definite measurable reduction in VMG.
anywhere from a couple of tenths to a lil over a half a knot (did it numerous times (your not surprised, i can tell)

also, in the intercoastal waterway, i did several checks by killing the engine at 2500 rpms and timing how long it took the boat to stop ( did this in both directions to eliminate the wind and current)

with the prop freewheeling, the boat would take on average about 20-25 seconds longer to stop, than when i locked up the propellar. naw, this aint no laboratory, but..........

meanwhile, its been 26 hours since TS and his sidekick Lew offered up his scientific diatribe. and 23 hours since i challenged either of dem boys to elaborate and answer a few simple questions

i am still waiting. anybody seen the guy with the kilty all in a bunch?
oh well... maybe silence speaks louder than words.

gotta go out and lay some mulch with the admiral now, so long for now.

waiting.... in so fla
darrell

[Didereaux]

As the old year drags to an end, and this overlong thread likely with it, I’d like to thank all of you who took part in the Great Fixed vs. Spinning Prop Discussion.

The result was evident from the very beginning, of course, but this polite and civilized board gave us all the opportunity to air our views; that is, to expose to the public glare our individual prejudices, our deep and thorough lack of grasp of the principles involved, and our ingrained resistance to new ideas that might upset our preconceived notions. And we managed to do all that without swearing. (Except under our breath, because, as you know, there are always those #@^$! idiots out there who know it all and who ... well, never mind.)

It was an act of foolhardiness by some to try to disprove the exhaustive conclusions of such luminaries as the great F. S. Kinney, of Skene’s Elements of Yacht Design; the renowned engineering firm of P. Newall Petticrow; the legendary Eric Hiscock, et al – yet I have to admire Darmoose, Didereaux and their cohorts for being such wonderful losers. Their charm, politeness, and finely tuned talents of persuasion almost won me over to their side. Fortunately my brain did not cease to function completely and I needed only a small portion of it to understand that a fixed propeller creates less drag than one free to spin.

John V.

High praise indeed (?) from one who's ego is seemingly so fragile as to approach disintegration by the mere dint of questioning a single statement. I further accept the acknowledgement that previous to this we, at any rate I, refrained from molesting the messenger overmuch. Rest easy, your infallibility is safe...but from what?
heh

Happy New Year from the charmingly polite, but Vigor declared braindead sector!
....and you're still wrong about the helicopter analogy nyaaa, nyaa LOL

[ray b]

if you hook up a alternator to the spinning shaft
if will slow the boat a little but gives free energy
and no need to run the noisy stinkie motor at anchor
to keep the batterys up

[M. R. Bober]

That freewheeling shaft would need to be turning VIGORously to produce adequate output. I think Matt Cawthorn has written on the pulley sizing problem.

OBTW: The only way to stop this thread is to lock down the prop.

Mitchell Bober
Sunny Annapolis (where we are charging currently ), MD

[Neil Gordon]

... The only way to stop this thread is to lock down the prop.

Or would that accelerate the thread?

[M. R. Bober]

It would, as a certainty, slowly bring this thread to a stop. Although the local breezes might delay the process.

Mitchell Bober
Sunny Annapolis (Where all's well that ends), MD

[Neil Gordon]

It would, as a certainty, slowly bring this thread to a stop. Although the local breezes might delay the process.

The local breezes are the reason this thread isn't ending. Perhaps if we all agreed to lock our props, we'd be on equal footing and we could move along to more important matters such as Cetol or Cetol light.

[s-dupuis]

Buy a folding prop!

Before anyone replies that they are not as efficient (true) as fixed props, remember that these are sailboats we are talking about.

I had a folding, Martek, two bladed prop on a 26' boat with a Yanmar GM10. It was 14" in diameter when deployed by centrifugal force but only an elliptical 4" X 2" when folded. The prop shaft still needed to be marked to indicate the prop position otherwise one of the blades may droop down or fluctuate while under way making an annoying noise as it opened and closed. Also, the prop would not foul on lobster pots when it was inactive.

If you race or cruise and are justifiably concerned about drag, regardless of this debates topic, a folding prop may be worth the investment. It may add anywhere from 1/2 to 1 knot to your speed - a significant amount on a long passage. When you arrive at your destination (hours earlier than if you have a fixed prop under the same conditions) You can start your engine and motor into port, although a bit less efficiently than with the fixed prop.

Yes - They are expensive. Whether they are worth the extra cost can only be determined by the individual and the type of sailing/motoring conditions.

Now, I keep my outboard motor in neutral, tipped up out of the water.

Steve