| Subject: Re: T500 Folding Prop? |
Author:
Brian Henry
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Date Posted: 7/02/04 17:14:18
In reply to:
Brian Henry
's message, "Re: T500 Folding Prop?" on 6/02/04 21:12:11
And a couple more.
From: Victoria Propeller Vancouver Island, British Columbia
http://www.vicprop.com/faq.htm
Subject: Frequently Asked Questions
.
34. Q: On a sailboat under sail, should prop be rotating or locked?
A: There is less drag when prop rotates.
From: MadSci Network: Engineering
http://www.madsci.org/posts/archives/aug2001/996769879.Eg.r.html
Subject: When a yacht is sailing, will it go faster if the propeller can freewheel?
Date: Tue Jun 26 07:30:44 2001
Posted by Jonathan
ID: 993555044.Eg
When racing yachts sailors tend to lock the propeller in gear because they believe that this will be faster than allowing the propeller to freewheel. I myself sail and this has caused many an argument onboard the boat and has now degenerated into a war of emails. We've had views from graduate engineers, physicists and mathematicians, an ex-airline pilot and physics teacher as well as various sailors. We've managed to aquire various theories and even an Excel graph or two but no-one has managed to conclusively answer the question in an easy to understand manner. You're out last hope!!
Date: Mon Jul 30 00:04:06 2001
Posted By: John Metcalfe, Staff, Computing and Information Services, Texas A&M University at Galveston
Area of science: Engineering
ID: 993555044.Eg
Message:
Sorry it's taken me so long to get back to you on this question. I myself have been involved in many arguments on this subject. While I'm sure you've heard both sides of the argument, and opinions either way, hopefully I can give you an answer that will help.
Simply stated, whether the prop freewheels or is locked, you are creating drag. When the propeller is allowed to freewheel some of the force propelling the boat is transferred into the rotational motion of the propeller, thus creating drag at the propeller, and unless you can
disengage the driveshaft at the aftermost shaft seal, at all the bearings between the propeller and the transmission (and for that matter, at the transmission itself).
On the otherhand, if you lock down the propeller, you are creating a vortex behind the propeller caused by the water being forced to follow the blades and continuing in a helical pattern after leaving the blades. Also, because the water will not be flowing past the propeller at an angle of minimum slip, you will be creating a low pressure area aft of the blades, effectively pulling back against the foreward motion of the vessel.
Anyhow, I hope I have answered your question to your satisfaction.
_______________________________
Which, of course, he didn't - answer the question, that is, only huffed and puffed about both fixed and freewheeling both creating drag. Probably, like many, he didn't know.
All the above has now made me consider I should now fix my propellor in reverse when sailing to minimise transmission wear, despite believing that it will create more drag than freewheeling.
Thanks for making me think, Ted.
Best,
Brian.
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