How sailboats sail

[Sea Hunt]

I was (and remain) reluctant to enter this foray. I spent most of my adult life in one battle after the next. Now retired, I take great pains to avoid conflicts and stay out of battles - however important or trivial one might think they are in the grand scheme of things. However, now that such luminaries as "Oswego John" , Carl Thunberg, Stan W., and others have posted I feel somewhat more comfortable doing so.

I would like to address my comments to the originator of this thread, Steve Darwin. I wonder if you have the slightest idea of the war you have managed to reignite I know that you were a seasoned member of the CDSOA board when you posted your comment that has now generated this extensive thread and spawned yet another Darmoose, sir, at long last, have you no shame sir

However, Steve, I am willing to cut you some slack for your lack of foresight and lack of consideration of the consequences. Had you thought about it, I am confident you would have recalled that the locked versus spinning prop war was waged some time ago with mostly the same combatants who shall remain nameless ("JV" who owns a CD 27, an obvious "instigator", and "Boston Gordon" who owns a CD 28, a documented "agitator", among many, many others). The war strategies and tactics then were basically the same as now - indiscriminate shots fired at long range against opposing theories. It was very much like the Hatfields and McCoys, only more bloody. Miraculously, somehow a cease fire was reached and the thread died a merciful death after many weeks of battle. I think everyone on the board was from that day forward cautious that any new post not inadvertently rekindle the prop wars. Once in a while some miscreant would throw a match, hoping to spark a fire. Mercifully, it did not happen. Until you posted.

Unfortunately, apparently unaware of this history or forgetting history, you posted with a reference to an article that can only be described as an "incendiary device", if you will permit, of sailing and sailboat discourse. Had you been aware of the history of the "locked versus spinning prop wars" I am hopeful, as is my gentle and forgiving nature , that you would have resisted the temptation to post your reference.

As would be readily predicted, less than two hours after your post - on a Friday in the middle of a work day no less, the instigator "JV" quickly seized upon your innocent post to launch a surprise strike by the "prop lockers" against the "free wheelers" thus reigniting the Hatfields and McCoys feud yet again.

I have no interest in joining this war and shall remain a passive observer on the sidelines content to sail with my O/B motor and prop lifted up out of water when under sail , although I do worry about those poor bastards in Cape Dory 25s who have an 8-9.9 hp O/B with a large 3 blade prop they cannot even lift out of the water. Imagine what a drag coefficient (Cd ) that must be

I am hopeful a resolution or at least a cease fire can be achieved before this Christmas. I ask only that each of us as CD members search our hearts and souls, as well as our future to-be-posted thoughts, suggestions, comments and observations to make sure there is nothing in them that could possibly be mistaken for an opportunity by the instigator "JV", the agitator "Boston Gordon", (both of whom will quickly grasp at any chance to fire off a round) or others to touch off yet a third round of the Hatfields and McCoys.

Oh, by the way, if you really want to learn which side is right, I would respectfully recommend a thoughtful study of the formula:

Fd = Cd 1/2 pv2A

Of course, as we all know , "Fd" is "drag force"; "p" is fluid density"; "v" is "flow velocity" and "A" is the particular area of the front of the body (measured in sq ft) that is being measured for drag (in this case either 2 or 3 prop blades).

I shall now rest what is left of my small brain with a small sip of Jack Daniels. Thank you, thank you very much.

[darmoose]

Dear Mr. Hunt,

This so called debate is all about correctness for the record, sir, that, and protecting unwitting sailors from falling prey to eroneous theories by so-called authorities. Havent you heard in the news lately of the ponzi schemes, Mr. Mahoff, and such. Fraud runs rampant.

I started another thread with the title "Helicopters and sailboats are the same..." as a direct challenge to the "instigator", hoping to draw him out from his hiding place (he has obviously been avoiding the debate, only firing shots from behind trees then scurrying off).

I relish the attack from him or his minions, having recently put together the complete and irrifutable proof of what i have been saying for two years. It all rests with Sir Izaac Newton's third law, and i must admit that i did not fully understand how to apply same to our struggle until this past couple of days.

There is nothing about the workings of the helicopter as it relates to J.V.'s observation or the drag question relating to sailboats that Newton didnt cover.

The proplockers are very much on the run

Darrell

[wingreen]

... it helps me to imagine that I'm wearing a hat with a little helicopter blade on top of it. The prop slows down the thinking process just enough so that this all starts making perfect sense...

[Duncan]

I was (and remain) reluctant to enter this foray. I spent most of my adult life in one battle after the next. Now retired, I take great pains to avoid conflicts and stay out of battles -

Wise words, as usual, sir. I am bowing out of this as well, since I didn't realize the emotional content (locked thread). It has been interesting for me, but now I realize it may be wiser to leave well enough alone.

I will make a general point, though, in parting from this discussion. I think that analogies work well when they simplify, and when they relate to things we already understand.



The helicopter analogy is horrible from either viewpoint. It is far more complicated, and most of us have very little understanding of rotary wing aircraft in the first place.

As an example of a good analogy, I recall teaching my son how to throw a fly line when he was five years old. I said "It's just like a stick with a string tied to the end. Make the string go straight backwards, then make it go straight forwards". It was a gross oversimplification, but it was all he really needed to get started. Three tries later, he threw a beauty of a 50 foot cast straight out into the current.

Sometimes you just have to keep it simple, and stick to what you know. Most of the time, actually, for me, anyway.

[Neil Gordon]

>>It is far more complicated, and most of us have very little understanding of rotary wing aircraft in the first place. <<

That's why I tried replacing the helicopter with a maple seed. No moving parts, no adjustable whatevers, no pilot, no flare, no etc.

BTW, Stan, as you know, they come in parts, left and right wings, and they only "helicopter" if they're broken apart. One side spins one way and one spins the other, but I have no idea which goes which way.

[Sea Hunt]

For those of you engaged in the "prop wars", whether wearing the insignia of the "freewheelers" or that of the "prop lockers", I commend to your reading the book authored by "the instigator" JV entitled The Seaworthy Offshore Sailboat, ISBN13: 9780071376167. In Chapter 7, Engine and Propeller, he devotes three full paragraphs to this issue. I believe you will find his comments, suggestions and rationales "interesting" if not incendiary, especially a rationale for locking or not locking the prop that I do not believe has been presented before in this forum by either group of combatants.

[M. R. Bober]

http://www.capedory.org/board/viewtopic ... t&start=30


"PostPosted: Wed 12/27/06 9:15 pm Post subject: We can't all be wrong.

In an effort to provide some light to accompany the heat, I descended deep into the bilge to retrieve the October 1, 1993 issue of "Practical Sailor" (way back when that publication was still worth its salt; before...[Ed. note: rant withheld at this time.]).

An article entitled "M.I.T. Prop Test" presented propeller research by--then--graduate students Beth Horwich & Todd Taylor, which included the following:

"... Also, Taylor and Horwich tackled the age old question of whether it's better to allow a fixed-blade prop to free wheel or to lock it in place.
Their conclusion is that '...a substantial reduction in drag, and thus gains in boat speed, can be realized from a fixed pitch propeller by allowing the propeller to free wheel. The decision to free wheel or not, though, must also take into account the factors of noise and wear-and-tear on the transmission and bearings.'
Despite some claims that freewheeling works best at higher speeds, Taylor and Horwich found there were 'savings across the whole range of speeds.'"


The thrust of the article (good one, eh?) was a quantification of fixed, feathering and folding propellers' characterists.

Alas, John Vigor, in answer to your question "Am I right or am I right?" The answer appears to me, to be, neither. The discussion that your thread provoked seems to prove Zymurgy's First Law of Evolving System Dynamics, to wit: Once you open a can of worms, the only way to recan them is to use a larger can.

Every best wish,
Mitchell Bober
Sunny Annapolis (where we discuss propulsion, prop-erly), MD"
_________________
CDSOA Founding Member"


Like fine old wine it keeps getting better, or is it sour old milk. They are alike as are sailboats and helicopters. I am still going with the MIT tank tests.

Mitchell Bober
Sunny Lancaster (if you want tolerance, get a micrometer), VA

[Neil Gordon]

>>The decision to free wheel or not, though, must also take into account the factors of noise and wear-and-tear on the transmission and bearings.<<

You're suggesting that the loss of speed by free-wheeling is due to the helmsperson being distracted by the noise?'

[M. R. Bober]

>>The decision to free wheel or not, though, must also take into account the factors of noise and wear-and-tear on the transmission and bearings.<<

You're suggesting that the loss of speed by free-wheeling is due to the helmsperson being distracted by the noise?'

Not at all, the conclusion was that of the crew at MIT, who were probably never distracted.

Mitchell Bober
Sunny Lancaster (where the weather is here; wish you were beautiful), VA

[Neil Gordon]

Not at all, the conclusion was that of the crew at MIT, who were probably never distracted.

You mean Beth and Todd? Maybe MIT is different, but at Penn State, they would have been distracted by each other.

[Dalton]

I'm going to replace my cutlass bearing and engine mounts this year. I think I'll buy a Max Prop. Ouch, $$$$$ but I can ignore this thread then, or can I?

[darmoose]

Neil,

When i apply friction to the driveshaft of our sailing boat in my example......

you would argue that the boat speeds up while i say it slows down.

Answer me this.....when i let go the the driveshaft, does the shaft stay at the same speed, slow down, or speed up

Darrell

[Neil Gordon]

Answer me this.....when i let go the the driveshaft, does the shaft stay at the same speed, slow down, or speed up

Overall, the shaft moves at the same speed as the boat. If the boat moved faster, the shaft would go out the hole in the back which would most definitely slow you down.

If you're talking about rotation, on the other hand:

If the prop is locked, RPM on the shaft is zero. Unlock it and it will turn; the less friction the faster it will go until it's maxed out. Since the prop starts in the fixed, locked position and then starts spinning, where does the energy that makes it turn come from?

[darmoose]

Answer me this.....when i let go the the driveshaft, does the shaft stay at the same speed, slow down, or speed up

Overall, the shaft moves at the same speed as the boat. If the boat moved faster, the shaft would go out the hole in the back which would most definitely slow you down.

Neil,

Very CUTE......actually though, I am sure if the shaft leaves out the hole in the back of the boat, the first reaction from the boat will be to speed up, as drag has been reduced. Depending on how fast the boat is traveling (keeping the water from entering), it wont slow down.




>>If you're talking about rotation, on the other hand:


If the prop is locked, RPM on the shaft is zero. Unlock it and it will turn; the less friction the faster it will go until it's maxed out. Since
the prop starts in the fixed, locked position and then starts
spinning, where does the energy that makes it turn come from?

Neil,

If you aint a politition, you oughta be. You didnt answer my

question, but I will answer yours.

The energy that makes the propeller turn comes from the force of the water pushing against it, it always has, currently does, and always will. No "Freewheeler" would deny this.

What "Proplockers" fail to see or understand, is that if this energy is not allowed to spin the propeller (THEREBY RELEASING THE BOAT TO MOVE FORWARD FASTER), this energy simply goes into pushing directly against an "IMMOVABLE" object (your locked propeller) like a brick wall, thereby slowing the boat.

Now, you may try once again to answer my earlier question, if you wish. I would appreciate it.

Darrell

[Neil Gordon]

Darrell,

>>If you aint a politition, you oughta be.<<

I was thinking about buying a high legislative office, but after losing a bundle in a ponzi scheme, it wasn't practical. (That would be poetic for the IL governor, by the way... take a bribe, invest with a slime ball, go to jail and also lose all the money.

>>The energy that makes the propeller turn comes from the force of the water pushing against it, it always has, currently does, and always will. No "Freewheeler" would deny this.<<

"Lockers" don't deny that, either, so there's a point of agreement.

>>... if this energy is not allowed to spin the propeller (THEREBY RELEASING THE BOAT TO MOVE FORWARD FASTER), this energy simply goes into pushing directly against an "IMMOVABLE" object (your locked propeller) like a brick wall, thereby slowing the boat.<<

No. The water doesn't simply push endlessly against the locked prop. It flows around it. Since the water needs to change direction to do that, there's an energy cost that slows the boat. So there's an energy cost to keeping the prop locked and an energy cost to letting it spin. (Each as compared to not having the prop at all.) The question is which costs more.

As for immovable objects... if I lift a rock from the floor to table height, I add potential enegy to the rock. Putting the rock on the table, it's forced downward by gravity and the table exerts an opposing force that keeps the rock in place. There's no energy gain or loss there, though. Neither the table nor the rock gets tired exerting force against the other.