Reply
 
Thread Tools Display Modes
 
Old 12-06-2013, 11:54 AM   #1
Guru
 
Edelweiss's Avatar
 
City: PNW
Country: USA
Vessel Model: 1976 Californian Tricabin LRC
Join Date: May 2011
Posts: 1,834
Propeller Drag

Here is a study on propeller drag that I found on Michigan Wheel's website. It's written to answer the question of locking the prop verses allowing the propeller to free wheel while under sail. If accurate, it answers the question of free wheeling the prop for those with twins, with a transmission that can be free wheeled, who occasionally run on one engine. It also alludes to a MIT study that came to the same conclusion? I would like to see that!!

http://www.catamaransite.com/propeller_drag_test.html


Propeller Drag Test Results

Jig Drag = 12 pounds with no prop mounted. Measured at WOT. (wide open throttle)

Locked Prop Drag: 45-50 pounds: 50 -12 = 38 pounds of actual propeller drag when locking the propeller in reverse under sail.

Freewheeling Prop Drag: 20-25 pounds: 25 - 12 = 13 pounds of actual propeller drag when freewheeling the propeller under sail.

The locked propeller drag is 2.92 times more drag or a 292% increase in drag over a freewheeling propeller when you remove the test jig from the equation!!!!

As I said earlier, the test results are not even close. There's no need to worry about the .001's or a few pounds of drag here or there or even the rather "unscientific" method I used in this test. If a sailor cares to find an additional knot of boat speed in light winds, he must free wheel his propeller under sail. (note: I picked an average wind day with flat water and tried my props both locked and free wheeling while under sail. I have two props on my catamaran, and Main Sail's test was verified on my boat (it wasn't even close) --Rick)

Despite the Yamar advisory, which voids their warrantee if you lock their transmissions while sailing and despite Volvo's recommendation that you sail while their transmission are in neutral and despite the MIT study, the University of Strathclyde Ocean Engineering white paper, the Yachting Monthly data and this webapge, which all basically show the same thing, that a fixed prop caused more drag, there are still a few die hard types arguing the helicopter blade theory.


I have never seen as much misinformation on a sailing subject as we get on this one. I recommend you read this page carefully and that we all get this right. Unless a transmission manual specifically says to shift into reverse, all sailboat owners should be free wheeling their propellers while sailing. On second thought, if they ignore this webpage, it will be great for our economy as the diehards will have to buy new transmissions!
__________________
Advertisement

__________________
Larry B
Careful . . .I Have a Generator and I'm not afraid to use it !
Edelweiss is offline   Reply With Quote
Old 12-06-2013, 12:29 PM   #2
Senior Member
 
yachtbrokerguy's Avatar


 
City: Fort Lauderdale, FL
Country: USA
Vessel Model: I have keys to lots of boats...
Join Date: Jan 2011
Posts: 469
Most newer boats have water injected stuffing boxes with water injected from the engine cooling water. If you have a turning shaft without injected water you might burn the shaft seals which will be a lot more expensive than saving some fuel cost.
__________________

__________________
Tucker Fallon CPYB
www.yachtbrokerguy.com
yachtbrokerguy is offline   Reply With Quote
Old 12-06-2013, 01:26 PM   #3
Guru
 
koliver's Avatar
 
City: Saltspring Island
Country: BC, canada
Vessel Name: Retreat
Vessel Model: C&L 44
Join Date: Nov 2007
Posts: 2,174
"If you have a turning shaft without injected water you might burn the shaft seals which will be a lot more expensive than saving some fuel cost. "

After several hours of free wheeling, I checked the temperature of my stuffing box and found it was warmer than the outside water, but far cooler than the ambient engine room temp (one engine working, one off). I couldn't get more than 6 knots of boat speed, so at what became my maximum speed, I don't see any concern that I might burn something by failing to lubricate the stuffing box from the engine cooling water (off at the time). My fuel savings came from going 6 knots instead of 8. I don't believe pushing my boat from one corner is as efficient as from both corners, especially when you add prop drag from the free-wheeling prop.When hauled out, I have tried to turn the props, trans in neutral, and have never been able to do so without extreme exertion. While traveling at 6 knots, the prop is turning, so there is more energy used to get that prop turning and thus more fuel consumption.
YMMV
koliver is offline   Reply With Quote
Old 12-06-2013, 02:00 PM   #4
Guru
 
Edelweiss's Avatar
 
City: PNW
Country: USA
Vessel Model: 1976 Californian Tricabin LRC
Join Date: May 2011
Posts: 1,834
Quote:
Originally Posted by koliver View Post
"When hauled out, I have tried to turn the props, trans in neutral, and have never been able to do so without extreme exertion.
YMMV
I wonder why all the resistance on you shafts?? Mine turn easily, I mean two fingers easy. Borg Warner Velvet Drives, 1 3/8" shafts, wet shaft glands with Teflon graphite packing.

I don't do it for fuel savings, only for fishing, slow cruising or running with a slower boat. 7.5 kts @ 2400 and 8.5 kts @ 2800 WOT on one engine.
__________________
Larry B
Careful . . .I Have a Generator and I'm not afraid to use it !
Edelweiss is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off





All times are GMT -5. The time now is 06:05 AM.


Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2006 - 2012