Propeller and Speed - 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 > On Board > Gear & Maintenance
 Not a Member? 
  #1  
Old 06-04-2002
Junior Member
 
Join Date: Jun 2002
Posts: 1
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 0
The Journey is on a distinguished road
Propeller and Speed

I have a Universal 25hp that only does 4.5 kts. at 2800rpm in perfect motoring conditions. I have a 3 bladed 12x6 rh prop. Would this be the problem?
Nanci Whitley
"The Journey"
hull #1314
Reply With Quote Share with Facebook
  #2  
Old 06-04-2002
Senior Member
 
Join Date: Dec 2001
Posts: 360
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 13
928frenzy is on a distinguished road
Propeller and Speed

You should find out from Universal what RPM they recommend for normal cruising. If it is less than 2800 RPM (which I think it is), then you may want to install a propeller with a larger pitch, which will provide a bit more speed at lower RPMs.

Check in the library for boat books that cover propellers, HP, and RPM. I seem to recall a few books had tables and charts where if you knew the HP, RPM, pitch and size of the original prop, you could then determine the optimum prop pitch given the same HP, but with a different RPM.

BTW, don''t get too large with the pitch, as the engine may become overloaded, overheat, and ulimately will lose compression, smoke, and wear out sooner.

~ Happy sails to you ~
Reply With Quote Share with Facebook
  #3  
Old 06-04-2002
Jeff_H's Avatar
Moderator
 
Join Date: Feb 2000
Location: Annapolis, Md
Posts: 6,579
Thanks: 5
Thanked 95 Times in 71 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 and Speed

We probably need more info such as: On what kind of boat? Do you have a clean bottom? er....I mean How about the boat''s bottom? Have you had the boat long enough to tell if this has changed any?
Jeff

Reply With Quote Share with Facebook
  #4  
Old 06-18-2002
Member
 
Join Date: Mar 2001
Posts: 49
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 0
harvh is on a distinguished road
Propeller and Speed

I also have a Universal 25. It pushes the boat at 6.5 knots at 1900 rpm. I am using a 3 bladded feathering prop. Two things come to mind, (1) your tack could be off...mine was, (2) you may have to small of a prop on your boat.
Reply With Quote Share with Facebook
  #5  
Old 06-18-2002
Senior Member
 
Join Date: May 2002
Posts: 275
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 0
windship has a little shameless behaviour in the past
Propeller and Speed

It sounds to me like your prop is to small and your pitch isn''t enough.
harvh could be right about the tach.Does the engine smoke excessivly while trying to get to speed? Does it overheat? If not, you just might not have enough prop. Did you just buy the boat? Or is it like this every year.

Dennis
Reply With Quote Share with Facebook
  #6  
Old 06-20-2002
Member
 
Join Date: Jan 2002
Posts: 38
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 0
lecomte38 is on a distinguished road
Propeller and Speed

that is about right. you travel 6" per rpm of the prop. 6 x engine rpm divided by transmission ratio = inches per minute divided by 12= feet per minute x 60=feet per hour divided by feet in a nautical mile = speed in kts

6 x 2500/2.6(? tran ratio) /12 x 60 / 6076 = 4.75 kts per hour

you loose some in in efficiency. (prop slip) My 14 x 14 prop pushes the boat 6 kts at 2000 rpm, 7.3 kts at 2800 rpm
Reply With Quote Share with Facebook
  #7  
Old 06-20-2002
Senior Member
 
Join Date: May 2002
Posts: 275
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 0
windship has a little shameless behaviour in the past
Propeller and Speed

Nanci,
Can you get back to us here and tell us what your trans ratio is,what type of boat you own, the length and is that a diesel or gas engine? At what RPM do you get your max speed? Then we can supply you with more accurate information.

Dennis

lacompe38,
I find it amazing that you came to that conclusion without knowing the trans ratio.
Reply With Quote Share with Facebook
  #8  
Old 06-21-2002
Member
 
Join Date: Jan 2002
Posts: 38
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 0
lecomte38 is on a distinguished road
Propeller and Speed

Dennis
I have no idea what the universal trans ratio is. I used the Yanmar/Kanzaki ratio of 2.6 to 1 for the calc. Most mfgrs aim for about 1000rpm at the prop shaft.
The prop slip/efficiency comes into play a lot more as the boat approaches hull speed. I am slipping/loosing 18% at 1500rpm and 45% at 3000 rpm.
Reply With Quote Share with Facebook
  #9  
Old 06-21-2002
Senior Member
 
Join Date: May 2002
Posts: 275
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 0
windship has a little shameless behaviour in the past
Propeller and Speed

lecompe38,
Yeah, thats cool.
I think nanci is questioning boat speed mainly not prop efficiency.
If we ever hear from her again mabey you and I can offer her more info if she offers us more info.

Dennis
Reply With Quote Share with Facebook
  #10  
Old 09-17-2002
MHRitter's Avatar
Member
 
Join Date: Feb 2001
Location: Northeast Wisconsin
Posts: 30
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 0
MHRitter is on a distinguished road
Propeller and Speed

Here is some data for two and three bladed props on a 36 footer with 30 foot water line and 17000 displacment using 1980 32HP Universal 5432''s with 2.14 reducers. One owner used an optical hand held tach another used a fuel injector sensor type. see http://www.sankaty.homestead.com/speed.html
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
Atomic 4 is 4 lovers agent4change Gear & Maintenance 11 08-07-2011 05:14 PM
2 blade or 3 blade propeller ddilman Boat Review and Purchase Forum 3 11-07-2004 07:27 AM
Propeller performance change - feathering paulmcquillan Gear & Maintenance 2 10-20-2003 07:48 PM
In Gear jimhuggins Seamanship & Navigation 20 06-14-2001 11:09 AM
Feathering Propeller AlWalls Gear & Maintenance 3 12-16-2000 05:26 AM


All times are GMT -4. The time now is 02:23 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.