Why does my prop keep spinning? - Page 2 - SailNet Community
Seamanship & Navigation Forum devoted to seamanship and navigation topics, including paper and electronic charting tools.

Reply
 
LinkBack Thread Tools
post #11 of 56 Old 05-12-2006
Senior Member
 
Join Date: Jun 2004
Location: Malaysia
Posts: 314
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 12
 
he Borg Warner boxes needs oil pressure from the input shaft, engine on. to engage the clutches. I guess your engine is not of the newest model, so has it been spinning this long, let it spin but keep the box in neutral position. It was not recomended by the older Borg Warner to let the propeller spin but a shaft lock to be innstaled, but as I said has it been spinning for the last 20+ years (?) I would keep on unless You plan a circum navigation.
haffiman37 is offline  
Quote Quick Reply Share with Facebook
Sponsored Links
Advertisement
 
post #12 of 56 Old 05-12-2006
Just another Moderator
 
Faster's Avatar
 
Join Date: Sep 2005
Location: New Westminster, BC
Posts: 16,534
Thanks: 104
Thanked 314 Times in 301 Posts
Rep Power: 10
     
Folding props can keep freewheeling, especially of you start sailing at speed before taking the engine out of forward gear. The resistance of the gearbox (generally in reverse) forces the prop to fold due to drag. Once folded, you can go to neutral again, but in most boats there's no need.
We have a Hurth gearbox, the recommendation is to put into reverse while sailing, and further not to let the prop drive the gearbox if the gear is in forward without the engine running. (I believe the input shaft must be powered to provide lubrication for the gearbox)
Faster is offline  
Quote Quick Reply Share with Facebook
post #13 of 56 Old 05-12-2006
Senior Member
 
Join Date: Jun 2004
Location: Malaysia
Posts: 314
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 12
 
The locking of the clutch systems are different on the Borg Warner and Hurth. The hurt is purely mechanical, but the cluch neds the resistanse given by the propeller to lock. That gives that is has to be put in reverse to lock the clutc pack. This goes for all boxes with multiple disk clutch pack, Hurth, most Yanmar, ZF.
The lubrication is performed by the lower shaft splashing the oil around, no pressure, and the upper only rotates with the engine. The output shaft and bearings are not in oil and letting the prop shaft rotate means the bearing runs dry!
haffiman37 is offline  
Quote Quick Reply Share with Facebook
post #14 of 56 Old 05-12-2006
gc
Member
 
Join Date: Feb 2003
Posts: 63
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 13
 
Quote:
Originally Posted by WanderingC's
A free spinning prop is not good. If for no other reason, it will slow the boat. Either put the transmission in gear or if hydraulic install a shaft break.
This has been argued many times over the years, always without facts as far as I have seen. If anyone knows of any experiments or measurements I would love to know of them.

My belief is that a spinning prop offers the least resistance. If it offered more resistance, it would stop spinning. But that is just a belief, not even a theory.

But I can definitely recommend you not install a "shaft break". A shaft brake would be more appropriate.
gc is offline  
Quote Quick Reply Share with Facebook
post #15 of 56 Old 05-14-2006
N30II
 
bradleyjdonaldson's Avatar
 
Join Date: Jan 2006
Location: seattle
Posts: 5
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 0
 
A free spinning propeller will have the same drag as a solid disc of the same diameter. DO NOT LET THE PROP SPIN FREE. Shut down the engine in gear and this should be enough to stop the prop from spinning. If you are in gear and the prop still spins, youu need a shaft brake.

Last edited by bradleyjdonaldson; 05-14-2006 at 01:23 AM.
bradleyjdonaldson is offline  
Quote Quick Reply Share with Facebook
post #16 of 56 Old 05-14-2006
N30II
 
bradleyjdonaldson's Avatar
 
Join Date: Jan 2006
Location: seattle
Posts: 5
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 0
 
This is base on Aerodynamics, but it is essentially the same in Hydrodynamics. The point is "The propeller produces much more drag as it windmills than it would if it simply stopped turning."

http://selair.selkirk.bc.ca/aerodyna...lti/Page2.html

http://avstop.com/AC/FlightTraingHan...eathering.html
bradleyjdonaldson is offline  
Quote Quick Reply Share with Facebook
post #17 of 56 Old 05-14-2006
Member
 
Join Date: May 2006
Posts: 30
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 0
 
i still think the example there doesn't fit the problem here.

for starters, the propellers on aircraft don't spin free. because they are usually atached directly to the crankshaft of the engine, a windmilling propeller has to overcome the engine's internal friction and compression. the power needed to do this produces drag.
as solution the blades are turned so they don't produce spinning force at all, reducing drag to the minimum.
it doesn't address the problem of a nonfeathered propeller spinning with no friction, or almost no friction, as only the friction of the bearings has to get overcome. and neither does it address the drag of a nonfeathered propeller stopped by a brake.

Last edited by Tea-Rex; 05-14-2006 at 08:26 AM.
Tea-Rex is offline  
Quote Quick Reply Share with Facebook
post #18 of 56 Old 05-19-2006
N30II
 
bradleyjdonaldson's Avatar
 
Join Date: Jan 2006
Location: seattle
Posts: 5
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 0
 
Actually there is NO FRICTION in a free spinning propeller on a turbine powered aircraft. There is no mechanical linkage between the propeller and the power turbine. If you watch a pre-flight on a turbo prop aircraft, you can free spin the prop like a windmill with no resistance what so ever. It is still detrimental to fully feather the prop as soon as you loose power to keep the dead windmilling engine from dragging the aircraft down. In fact if it is an air transport category aircraft it must have a AUTOFEATHER system to make the climb requirement after an engine failure on takeoff. ANYWAY..... Try this...Get a small prop from the toy store. Hold it out the window of your car while somebody else drives. Look at the difference in force aginst you with a spinning prop and a stopped one. You will be amazed how much drag a spinning prop makes!

Last edited by bradleyjdonaldson; 05-19-2006 at 02:53 PM.
bradleyjdonaldson is offline  
Quote Quick Reply Share with Facebook
post #19 of 56 Old 05-20-2006
Member
 
Join Date: May 2006
Posts: 30
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 0
 
still the only conclusion those articles offer is that a feathered propeller has less drag than a nonfeathered propeller, either stopped or windmilling.
don't get me wrong here, i'm not saying that you're wrong, just that those articles don't support your statement.

however i googled around a bit and found this:

http://www.goshen.edu/physics/PropellerDrag/thesis.htm

the test involved severall propellers with different pitch. some of them had less drag windmilling than stopped, some had more.

i guess it depends too much on the individual propeller to make a general statement.
Tea-Rex is offline  
Quote Quick Reply Share with Facebook
post #20 of 56 Old 05-20-2006
Senior Member
 
Join Date: Jun 2004
Location: Malaysia
Posts: 314
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 12
 
You seem to have lost contact with the 'sea' in the above discussion! The question is not what creates the less drag, the question is what the gear box may handle and tolerate. Most marine gearboxes can not tolerate free spinning due to lubrication problem!!!!!!!!!!!!!!!!!!
haffiman37 is offline  
Quote Quick Reply Share with Facebook
Reply

Quick Reply
Message:
Options

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

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:
OR

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.




Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page



Similar Threads
Thread Thread Starter Forum Replies Last Post
Prop walk with a Max Prop ikent Gear & Maintenance 19 06-05-2011 08:32 PM
proposing to paint prop tappers Gear & Maintenance 16 04-06-2008 11:40 AM
Zincs for Sail Prop feathering prop jrbarn Gear & Maintenance 4 09-20-2006 10:40 AM
Max prop on a saildrive levenezia Gear & Maintenance 16 09-20-2006 12:07 AM
Prop for Pearson 35 gbeardmore Gear & Maintenance 0 04-24-2001 12:49 PM

Posting Rules  
You may post new threads
You may 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 On
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome