Fixed vs. Free Wheeling Prop - Data !

[darmoose]

I looked at your Michigan Wheel video again, and it appears to me that while the propeller was fixed you achieved a top speed of 3.5 or 3.6. And while the propeller was freewheeling, you achieved a top speed of 4.0.

If this is correct, (and I wish the video showed more of the GPS readings), there was a .4 or .5 differential in the top speed attained between the two tests. This amounts to 10 to 12.5% speed potentiality differential.

I don't know any racing sailor who wouldn't give great sums to get a 10-12.5% increase in speed, or conversley wouldn't throw his crew overboard, who cost him that kind of speed.

This is great evidence, and not unexpected or alone, to what was always true. Where is the evidence of this or any other kind, to support the long believed and erroneous idea that a locked propeller causes less drag (of course it is true that we once believed the earth was flat, perhaps some still do).

Keep up the good work

FWISF

Darrell

[rtbates]

It really doesn't matter to me as YANMAR says, "lock the prop by placing the shift lever in reverse while sailing". I have the 1GM and whatever transmission came in the 25D in 1984..

IF I wanted to reduce drag a tad I could jump overboard and align the two blades with the keel. And IF I wanted to do this on a regular bases I'd mark the drive shaft so I could do this without the swim.

That said I look forward to your test results.

[Boyd]

Hi All:

I propose we keep this information secret. Let John Vigor continue to promote his "Locked Prop" theory and win a lot of races.

Boyd
s/v Tern
CD30 MkII
Fort Lauderdale, Fla.

[darmoose]

It really doesn't matter to me as YANMAR says, "lock the prop by placing the shift lever in reverse while sailing". I have the 1GM and whatever transmission came in the 25D in 1984...

Randy,

I know what you mean, that this whole subject really doesn't matter a whole lot. It is just interesting to solve an age old problem that so many have been so wrong about for so long. Nothing to get too worked up over, surely.

Here's a question for you tho...... your 1984 Yanmar is about to bite the dust, KAPUT. Time to repower, as so many of our brethern have had to do, and more will each year as our treasured boats grow older.

You are looking at two interesting prospects. Both are identicle in every way, including cost, with one and only one exception.

One engine gives you the prospect of 12 to 14% greater performance from your boat. (and we all know how, don't we ) Which one do you choose

Darrell

[Amgine]

That's a false dichotomy, Darmoose.

Whether or not your transmission is lubricated, freewheeling has a cost in wear and tear on the transmission, in steadily reducing the reliability of it in the long term. The case really is: how do you plan to compromise - a decrease in drag or a decrease in transmission life? Everything is a compromise. One could avoid this particular compromise wrinkle by going with a folding or feathering prop.

Let's avoid proselytizing.

[rtbates]

It really doesn't matter to me as YANMAR says, "lock the prop by placing the shift lever in reverse while sailing". I have the 1GM and whatever transmission came in the 25D in 1984...

Randy,

I know what you mean, that this whole subject really doesn't matter a whole lot. It is just interesting to solve an age old problem that so many have been so wrong about for so long. Nothing to get too worked up over, surely.

Here's a question for you tho...... your 1984 Yanmar is about to bite the dust, KAPUT. Time to repower, as so many of our brethern have had to do, and more will each year as our treasured boats grow older.

You are looking at two interesting prospects. Both are identicle in every way, including cost, with one and only one exception.

One engine gives you the prospect of 12 to 14% greater performance from your boat. (and we all know how, don't we ) Which one do you choose

Darrell

Hi Darrell:

I said that only because of Yanmar's advice to lock the prop. Another thing that CDs have that most boats don't is a large keel that keeps the flowing water off the prop while sailing. Align the prop vertically and it's a non-issue. And as Amgine notes any rotating mass is going to wear sooner than a stationary one. I sure hope you're wrong about my 1GM!haha IF I do ever need to replace the 1GM I would go with the one that doesn't require the shaft to rotate while sailing !!!!

[darmoose]

Hi Darrell:

I said that only because of Yanmar's advice to lock the prop. Another thing that CDs have that most boats don't is a large keel that keeps the flowing water off the prop while sailing. Align the prop vertically and it's a non-issue. And as Amgine notes any rotating mass is going to wear sooner than a stationary one. I sure hope you're wrong about my 1GM!haha IF I do ever need to replace the 1GM I would go with the one that doesn't require the shaft to rotate while sailing !!!!

Hi Randy,

I too hope your 1GM runs for another 25 years, truly, I do. But, hopefully without straying too much further from the point of Mainsails thread, let me point out two things you've said that may lead to some confusion.

Most people interested in this question aren't sailing with a two bladed propeller, thus the concern for performance, and secondly, I know of no engine/transmission that "requires" the shaft to rotate while sailing.

As for Amgine's ascertion that I would ever offer you a false dichotomy.....I think not.

I think anyone given the choice I offered to you, all else being equal, would be somewhat foolish to choose an engine that limited your performance by 12 to 14%. I recognize that we CDer's are practical sailors valueing longevity, durability,and comfort over pure speed at any cost.

However, inasmuch as with any engine I know of that allows you to "freewheel", it also allow you to lock your propeller in reverse gear (during your more "compromising" moods), I simply don't see the reason to not opt for the increased performance option.

You and Amgine should think of it like having an overdrive or a supercharger available to you when you find yourself in one of those races where the other guy doesn't know he is in a race (you know, John Vigor wrote about those), and you can secretly reach down and shift that gearshift lever from reverse into neutral, and WHOOSH!!

And Amgine, really, have you priced one of those folding or feathering propellers lately. I assure you one can buy a new tranny for the same or less. That is truly a false choice.

Darrell

[Joe Myerson]

Thanks Randy,

I thought that's what the manufacturer suggested.

Unfortunately I've got a three-blade prop, so the drag is even worse. Still, I wouldn't want to damage my faithful thumper. (I might replace the prop some day though.)

--Joe

[Matt Cawthorne]

Very nice job on the test. There are a number of variables, like the area of the deadwood etc that can affect results, but there is nothing like a little data to clear things up. One point that was of interest to me was the speed at which your prop begins to freewheel. If you ever get your rig back in the water, I would be interested in the drag as a function of the speed at which the prop breaks free. If you could crank up the torque somewhat and do a repeat it would be appreciated.

Matt Cawthorne

[Amgine]

When you say Randy can either buy engine A, or engine B with a 10-12% performance boost, you're offering a false dichotomy (only two choices) since he might choose to sail without, or any of a dozen other options than solely engine with or without freewheeling. This is pretty much the definition of a false dichotomy.

All this being irrelevant to whether, *if* he needed to repower, he still might not need to replace his transmission.

I'm personally torn regarding the question of performance. It would be great to have less drag from the prop. But then, it'd be great to have less drag from the full-length keel, the heavier displacement, and the rudder configuration. It'd also be great to have a taller mast, longer waterline, and a lot of other things I can't actually change on my boat. So it really comes down to whether I'm willing to sacrifice longevity of my transmission to additional wear and tear, or a fraction of the force developed by my sail area to drag. I think it will come down to wind speed: in light air where I can't get hull speed I might freewheel, and in moderate or higher when I'm more worried about reefing I probably won't.

[Parfait's Provider]

I think the video shows a difference of 0.5 knots, from 3.5 locked to 4.0 freewheeling.

[Dean Abramson]

Does this constitute "torture," or merely "enhanced discussion techniques?"

:-)

[mattlydon]

The manual doesn't say either way. Lock it or not?

Matt

[Joe CD MS 300]

Contact the manufacturer of the engine / trans? Until you find out lock? In general is the recommendation (from the manufactures, not John or Darrell) to lock?

[darmoose]

Ken,

I agree with your assessment, looks like about a 12% speed differential to me.

Dean,

Torture, NOOO. This is just quantitating the results. A great service by Mainsail.

and .....Joe,

Just to clarify the point, I do not, and never did, recommend that someone freewheel to the detriment of their transmission. Those that do not have a lubricated transmission under sail will just have to sail a little slower.

FWISF

Darrell