Locked Prop vs. Freewheel vs. Boat Speed

[Roger Long]

Many also used narrow blade props especially for racing that were pretty inefficient under power.

That reminds me. Does anyone here remember something in the racing rules about the prop actually having to be capable of driving the boat? I have a vague memory of some joker or jokers having props built with about 65 feet of pitch. They could just barely get the boat back and forth to the starting line but they were practically feathered full time while giving the time allowance of a fixed wheel.

 

[RichH]

Roger -
If there is a loophole in the racing rules someone WILL find it, take advantage of it, until everybody is imitating it. Just remember the grotesque hull forms that have evolved as 'rule beaters'.

 

[RichH]

Until something better comes along, which could happen in a subject this complex, I'll go with this paper. However, my transmission is one of those that says to put it in reverse for sailing and I not going to ask it to change its habits at its ripe old age

You must remember that both papers are 'hypothesis' which means in geek-speak: Ive found something contrary to accepted thoughts and practices, heres my data to support ... Tear it apart, etc. Blindly following a hypothesis is like following a 'populist' politician ... you wont know how 'right' you were until its over and the historians are remembering.
There is NO publication date on the MacKenzie paper - submitted but is accompanied by NO publish date ... pretty important in scientific circles. One must surely know or remember that after 100+ years since man first flew, the general population still is under the false impression that flying has something to do with Bernoulli and the speed of the air on top of the wind somehow going faster than that of the bottom flow ... totally wrong, still accepted and still being taught.

 

[Roger Long]

Blindly following a hypothesis is like following a 'populist' politician ... you wont know how 'right' you were until its over and the historians are remembering.

No blind following here. On an arcane subject like this, on which even experts disagree, the best I can make is a prediction as to what will be found true after either definitive research or careful measurements in an individual case.

The paper I read years ago left me with the belief that the most likely outcome of careful resistance measurements on any individual vessel would be greater resistance for a free wheeling prop. The McKenzie paper tips the probabilities and the predictions I would make in the other direction but it's still just calling odds.

It's more a question in my mind of whether the majority of vessels will benifit from freewheeling. Whatever is found in theory, I expect there will always be exceptions in practice.

 

[Don S/V ILLusion]

Like many things, this is largely an academic issue. Many have folding or feathering props making it a moot point; others lock their props in reverse for a myriad of reasons unrelated to boat speed and still others are too busy enjoying themselves to be concerned about a fraction of a knot in boat speed. It must be winter...

 

[newly anonymous]

predictability

It must be winter...

Ah yes, the type of conversations we have on this site are indeed predictable.

Spring: "Has anyone had luck with polymegavarnish?"
Summer: "What does it mean when black smoke comes out of my engine?"
Fall: "I'm going to circumnavigate. Is a HunBeneLina really a bluewater boat?"
Winter: "Is it better to freewheel your tranny or lock it in reverse with a..."

 

[Maine Sail]

yes winter indeed! It does give me a lot of time to get work done though.. My cracked bell housing is turning into a HUGE engine project based on the old "while you're in there" mentality!!


I am working on the experiment Rich H. described and finishing the drag apparatus I started on back in 2007 when this same subject came up. Once my dinghy is melted out of the three feet of ice on the beach I'll put it to the test and make a video of drag resistance at freewheeling & locked as measured by GPS speed as a constants. The drag load difference will be measured with a digital hanging scale. It should be fairly cool and as far as I know it's never actually been done. I will use the actual prop off my own boat and hopefully I will have a new prop to compare to by then as well.

 

[Ross]

Mainesail if you can borrow a variety of props for this, particularly two blade versus three blade and pitch greater than diameter and less than diameter it will answer most of the variables. Good idea.

 

[kloudie1]

I lock mine but I do know that the loads are so low when freewheeling that there won't be a problem in the Kanzaki (?) The only way to damage it is to leave it in forward gear and let it freewheel there.. That will eat up the forward clutch.

Outstanding, Main Sail !! That is going to be an interesting test! Ya probably want to look at the "EAR" (expanded area ratio) for the props .. This is kind of the ratio of open area versus blanked area for a disk of the propeller diameter.. as well as the # of blades ..

 

[tsmwebb]

yes winter indeed! It does give me a lot of time to get work done though..
I am working on the experiment Rich H. described and building the drag apparatus in my garage (winter).

Hmmm, yes, I put on a long sleeve t-shirt today. I feel your pain .

Since it is winter where you are you might want to look at High Performance Sailing by Frank Bethwaite. As I recall he goes into detail on how he ran full scale drag comparison tests on skiffs. Might save you some re-inventing and it's a good read anyway.

--Tom.

 

[DougM]

I alway lock my prop in reverse. That's what the dealer recommended. Further, if left unlocked, the freewheeling prop causes a "hum" that's annoying.

I've heard about as many conflicting theories as there are owners in our marina on this topic. My take on it is that the prop turns the transmission from the wrong end. I don't think its turning ast enough to cause any serious overheating unless one is sailing for days on end.

 

[novelman17130]

When I owned my Catalina 30' with an inboard I always left it in forward gear when sailing with the motor off.Now that I have a boat with an outboard I tilt the engine to put the prop out of the water. If am sailing with the prop in the water and the motor off (getting ready to douse the sails) I always leave the motor in neutral, failure to do so can result in the prop turning which in turn makes the pistons go up and down and can result in flooding the motor with gas. When this happens the motor is difficult to start.
Novelman

 

[okawbow]

Another reason for sailing a long keel with attached rudder. My Bristol has a 2 blade prop that will position it'self straight up and down behind the keel. I can usually leave the transmisson in neutral and the prop won't spin when sailing. That tells me the keel is blocking the water flow to the prop, and I'm not getting much drag. If we are really sailing fast in high wind; I sometimes lock it in reverse, straight up and down.

 

[hillman100]

MacKenzie Paper

RichH said:

"There is NO publication date on the MacKenzie paper - submitted but is accompanied by NO publish date ... pretty important in scientific circles."

The Strathprint pdf has been made available free of charge under arrangements recently made by many universities with most of the scientific publishing companies. It is one edit short of the very pricey publisher version. The watermark states clearly that the manuscript has been accepted (i.e., peer reviewed and, if necessary, amended to the satisfaction of the reviewers and the scientific editor).

A fairly obvious link from:-

http://strathprints.strath.ac.uk/5670/ takes you to:-

http://dx.doi.org/10.1016/j.oceaneng.2007.07.004

which is the relevant section in the research journal, Ocean Engineering, fully dated (2007)etc., and to the final printed version of the paper.

The front page of the Strathprint pdf states:

"This is an author-produced version of a paper published in Ocean Engineering, 35 (1). pp. 28-40. ISSN 0029-8018. This version has been peer-reviewed, but does not include the final publisher proof corrections, published layout, or pagination."

The second page of the pdf gives comprehensive information regarding publisher dates, journal pages, etc.

Compared to the Strathprint version, the publisher version has had no alterations of any substance. The final publisher version is available online and in print to subscribers only, and should be available in all good university libraries.

Almost all this information was present in the document but perhaps this will clear up any confusion.

 

[Bill Coxe]

My manual says put the transmission in reverse while sailing with the engine secured due to a lack of lubricating oil. Book says, I do, no problems in the four years we have had the boat.
Bill Coxe, O40 Kukulcan, New Bern, NC

 

[higgs]

Seems to me if one is worried about speed one should get a folding/feathering prop.

It also seems to me that anything moving is going to cause friction. Friction = wear.

A prop not moving may slow you down, but how can it have any effect on anything otherwise?