Propeller Question - SailNet Community

   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 > General Interest > General Discussion (sailing related)
 Not a Member? 


Reply
 
LinkBack Thread Tools
  #1  
Old 02-18-2003
Junior Member
 
Join Date: Oct 2002
Posts: 6
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 0
Scurvy_Dog is on a distinguished road
Propeller Question

I am new to sailing. I am an ex cooperate jet pilot and flight instructor. I understand the dynamics of a propeller in the air. Just wondering if when sailing does a free wheeling prop (eng in neutral) create more drag than a stopped prop? If so how much difference? In a propeller aircraft a stopped prop can offer considerably less drag. Talking to the mechanic who works on my engine he claims it will do no harm placing the engine in gear after shutdown.

Thx
Reply With Quote Share with Facebook
  #2  
Old 02-18-2003
paulk's Avatar
Senior Member
 
Join Date: Jun 2000
Location: CT/ Long Island Sound
Posts: 2,533
Thanks: 4
Thanked 20 Times in 19 Posts
Rep Power: 15
paulk is on a distinguished road
Propeller Question

This question comes up often enough to generate considerable discussion on occasion, with various anecdotes, but the upshot is what you know applies in the air also applies in the water. The trick is to mark your propshaft when the blades (of a two -bladed prop) are vertical and thus not projecting beyond the "shadow" of the keel. Then you engage the clutch when the mark shows, and you''re done until you need the engine.
Reply With Quote Share with Facebook
  #3  
Old 02-18-2003
Member
 
Join Date: Dec 2002
Posts: 43
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 0
peterpan2k is on a distinguished road
Propeller Question

Hi Scurvy
You bet it works the same. as far as puting it in gear. Depends a whole lot what type of trans you have. Trans that are fluid coupled putting it in gear does nothing. there are several folding props both two and three blade for that purpose. As to effectiveness. What? You going for the world cup. You would never know the differance on a Sunday cruise around the bay.
Jim
Reply With Quote Share with Facebook
  #4  
Old 02-19-2003
Member
 
Join Date: Mar 2001
Posts: 30
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 0
loki is on a distinguished road
Propeller Question

Free wheeling will create less drag than a stopped prop. One of the problems with this is that this can generate heat in the transmission. If the transmission is water cooled, there is no water circulating with the engine off-ergo a potentially damaged transmission. Best check with the engine people first.
Reply With Quote Share with Facebook
  #5  
Old 02-19-2003
Jeff_H's Avatar
Moderator
 
Join Date: Feb 2000
Location: Annapolis, Md
Posts: 6,564
Thanks: 5
Thanked 93 Times in 70 Posts
Rep Power: 10
Jeff_H has a spectacular aura about Jeff_H has a spectacular aura about Jeff_H has a spectacular aura about
Propeller Question

Actually the correct answer depends on the propellor and the transmission. There was a lot of research done on this a few years back.

The pretty widely reported results came up that a two blade prop fixed in the vertical position has less drag than a two blade prop either freewheeling or fixed in any other position.

A three or more blade prop with minimal resistance on the shaft will have less drag free wheeling, BUT if there is much friction on the shaft, the turbulence of the semi-free wheeling propellor is greater than that of a fixed prop in the ''Mickey Mouse'' position, which is the lowest drag position for a fixed three bladed prop.

Then there is the issue of transmission wear. In all cases freewheeling causes more transmission wear than being fixed. On most small marine transmissions there is no problem with lubrication or heat build up. That said some larger transmissions have shaft driven lube and cooling pumps which are not being turned when freewheeling.

Jeff
Reply With Quote Share with Facebook
Reply


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools

 
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


Similar Threads
Thread Thread Starter Forum Replies Last Post
2 blade or 3 blade propeller ddilman General Discussion (sailing related) 3 02-12-2006 12:45 PM
2 blade or 3 blade propeller ddilman Boat Review and Purchase Forum 3 11-07-2004 07:27 AM
Embarrasing Question, what in definition is a charter? KainX General Discussion (sailing related) 4 07-21-2003 03:43 PM
Glassing Question pirateofcapeann Gear & Maintenance 6 05-29-2003 02:58 AM
Keelboat Certification Question... 808state Learning to Sail 3 07-10-2002 03:18 AM


All times are GMT -4. The time now is 09:08 AM.

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.