SailNet Community - Reply to Topic

   Search Sailnet:

 forums  store  


Quick Menu
Forums           
Articles          
Galleries        
Boat Reviews  
Classifieds     
Search SailNet 
Boat Search (new)

Shop the
SailNet Store
Anchor Locker
Boatbuilding & Repair
Charts
Clothing
Electrical
Electronics
Engine
Hatches and Portlights
Interior And Galley
Maintenance
Marine Electronics
Navigation
Other Items
Plumbing and Pumps
Rigging
Safety
Sailing Hardware
Trailer & Watersports
Clearance Items

Advertise Here






Go Back   SailNet Community > On Board > Gear & Maintenance > Propeller drag test under sail.
 Not a Member? 


Thread: Propeller drag test under sail. Reply to Thread
Title:
  

By choosing to post the reply below you agree to the rules you agreed to when joining Sailnet.
Click Here to view those rules.

Message:
Trackback:
Send Trackbacks to (Separate multiple URLs with spaces) :
Post Icons
You may choose an icon for your message from the following list:
 

Register Now

In order to be able to post messages on the SailNet Community forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
Please note: After entering 3 characters a list of Usernames already in use will appear and the list will disappear once a valid Username is entered.
User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.



Click here to view the posting rules you are bound to when clicking the
'Submit Reply' button below


Additional Options
Miscellaneous Options

Click here to view the posting rules you are bound to when clicking the
'Submit Reply' button below


Topic Review (Newest First)
03-13-2012 05:50 PM
Minnewaska
Re: Propeller drag test under sail.

Quote:
Originally Posted by sailingfool View Post
Whether to leave shifter in neutral or not may depend on the advice of the engine manufacturer. The latest from Yanmar is to leave in neutral.

I used to leave a Westerbeke in reverse, and the MaxProp never seemed to mind.
That's what I would think. The only caveat is that one actually gets it to feather first.
03-13-2012 05:18 PM
sailingfool
Re: Propeller drag test under sail.

Quote:
Originally Posted by Minnewaska View Post
.... Max-prop procedure is..... neutral, engine off, reverse for a few seconds, neutral. ... I'm just curious what happens in real life if the feathering prop is left in reverse.
Whether to leave shifter in neutral or not may depend on the advice of the engine manufacturer. The latest from Yanmar is to leave in neutral.

I used to leave a Westerbeke in reverse, and the MaxProp never seemed to mind.
03-13-2012 04:52 PM
Rockter
Re: Propeller drag test under sail.

Good experiment that one.
I have always locked the gearbox when sailing. It is less noisy that way and it won't make that rumbling noise when it spins.
03-13-2012 04:31 PM
Melrna
Re: Propeller drag test under sail.

Quote:
Originally Posted by Minnewaska View Post
MS, you are a marine mechanical stud. I'm surprised the lady posters here haven't suggested you pose for a calendar..
Who says he hasn't.. Hanging up above my workbench
03-13-2012 04:18 PM
TropicCat
Re: Propeller drag test under sail.

Quote:
Originally Posted by jerryrlitton View Post
I have never done a test in the water like this. I just have practical experience with airplanes.
Which has nothing to do with propellers in the water dragged under a submerged hull.

It's antidotes like this that confuse new sailors and perpetuate the old wives tales.

It doesn't matter if we reference the Sailboat propeller drag article in The Journal of Ocean Engineering - Scotland ... Or The MIT paper.... Or the Practical Sailor propeller test, and finally this test we are speaking about as all of these tests came to the same conclusion.

There is no data published anywhere that disputes any of these tests. It didn't matter if these tests were in tanks or in salt water or fresh water the results are unerringly the same. As a matter of fact, Michigan Wheel Propellers now references the Main Sail test as it's definitive reference source. I know, it's my website.

It's time to stop the wives tales and accept the data. Spinning props under sail have less drag than fixed Propellers.

The only mitigating factor is whether or not you are allowed to free wheel your propeller under sail or whether the engine manual specifies the prop must be locked in reverse. Some diesels use the engine sump for lubricating the transmission and these can not be left to free wheel when the engine is not running. All Yanmars are fine with it.
03-12-2012 10:03 PM
jfdubu
Re: Propeller drag test under sail.

Quote:
Originally Posted by jerryrlitton View Post
I have never done a test in the water like this. I just have practical experience with airplanes. When we talk fixed pitch prop (non feathering variety) a spinning prop has more drag through the air than a not spinning prop. Example; a single engine airplane. At cruise. Engine failure. Reduce speed to best glide then keep that speed in decent. The engine (recip type) will keep windmilling. As apposed to; cruise, engine failure. Raise nose to slow aircraft. Prop will stop. Lower nose to attain best glide speed. Prop remains stopped (Harder to get a prop/engine spinning then to keep it spinning) glide angle is better with non spinning prop. Both instances at same indicated airspeed. Weird I know. The only variable is the airmass movement which will affect track and speed over the ground. However the IVSI (Instantaneous Vertical Speed Indicator) will show a higher rate of decent with the spinning prop, again with indicated airspeed the same. It is significant. Again I am talking fixed pitch. NOT feathering.
I don't know why air reacts different than water since both are fluids so to speak.
Jerry, Big differance between air and water, one is a compressable gas, the other is a incompressible fluid.

John
03-12-2012 12:16 PM
overbored
Re: Propeller drag test under sail.

on an airplane the free wheeling prop is not fully free wheeling it is attached to an engine that is at idle or still spinning aganst the engine compression. there is no transmission to put in neutral. also a lot higher differencial in speeds between the still fluid and the moving craft. the drag increase with speed is not linear
03-12-2012 11:53 AM
jerryrlitton
Re: Propeller drag test under sail.

I have never done a test in the water like this. I just have practical experience with airplanes. When we talk fixed pitch prop (non feathering variety) a spinning prop has more drag through the air than a not spinning prop. Example; a single engine airplane. At cruise. Engine failure. Reduce speed to best glide then keep that speed in decent. The engine (recip type) will keep windmilling. As apposed to; cruise, engine failure. Raise nose to slow aircraft. Prop will stop. Lower nose to attain best glide speed. Prop remains stopped (Harder to get a prop/engine spinning then to keep it spinning) glide angle is better with non spinning prop. Both instances at same indicated airspeed. Weird I know. The only variable is the airmass movement which will affect track and speed over the ground. However the IVSI (Instantaneous Vertical Speed Indicator) will show a higher rate of decent with the spinning prop, again with indicated airspeed the same. It is significant. Again I am talking fixed pitch. NOT feathering.
I don't know why air reacts different than water since both are fluids so to speak.
03-11-2012 08:45 AM
jfdubu
Re: Propeller drag test under sail.

Gee MS, you could have spend thousands more $ to get the same result. You must not work for the Goverment .

Great test and rig and confrimes the arguement I had last summer.

The bottom line is that if the boat is going thru the water and there's enough energy to spin the prop thats how much energy you loose stopping it from spinning

John
03-10-2012 08:03 PM
CalebD
Re: Propeller drag test under sail.

Thanks MS.
This does make sense:
"1- It is not as hidden as you thought

2- Is taking the path of least resistance"


Quote:
Originally Posted by dabnis View Post
Assuming you have fairly constant wind, course and so on, GPS speed seems pretty accurate?

Paul T
True that ^^ but I'm sailing in a river that has about a 2 knot current in either direction. Still, I can use the GPS to see if there is a slight variation if a) hidden or b) spinning free.
We have to be moving pretty fast (for our boat) to get our prop spinning so I'd bet that in lighter winds it would still be to our advantage to hide the fixed 2 blade prop.
This thread has more than 10 replies. Click here to review the whole thread.

 
Posting Rules
You may post new threads
You may post replies
You may post attachments
You may edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On


All times are GMT -4. The time now is 05:56 PM.

Add to My Yahoo!         
Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
SEO by vBSEO 3.6.1
(c) Marine.com LLC 2000-2012

The SailNet.com store is owned and operated by a company independent of the SailNet.com forum. You are now leaving the SailNet forum. Click OK to continue or Cancel to return to the SailNet forum.