Boat Design Forums  |  Boat Design Directory  |  Boat Design Gallery  |  Boat Design Book Store  |  Thanks to Our Site Sponsors

Go Back   Boat Design Forums > Design > Propulsion > Sterndrives
Register FAQ Members List Calendar Search Today's Posts Mark Forums Read

Reply
 
Thread Tools Search this Thread Display Modes
  #1  
Old 10-03-2009, 11:51 AM
Ambitious Ambitious is offline
Naval Architect
 
Join Date: Jan 2009
Rep: 10 Posts: 23
Location: Serbia, Belgrade
Prop question...

Dear all,

We have just finished testing of our 32 feet mahogany boat.

Lwl=7.7 m
Bwl=2.5 m
D=4.4 t

Engines&propulsion:
2 x yanmar 6byz 260hp@4000 rpm
bravo one diesel X. ratio 1.5
prop: mirage plus 14 3/4" X 21 "

Top speed is 42 kn at 4080 rpm with three persons on board.

I think props might have slightly higher pitch. So we can match 4000 rpm.
What do you think about 4 or 5 blade props maybe?

thanks
Attached Files
File Type: avi Clip_Mazokist-test drive 02.10.2009[(006109)17-42-56].AVI (6.85 MB, 754 views)
Reply With Quote
  #2  
Old 02-02-2010, 06:31 PM
dwwcanada dwwcanada is offline
 
Join Date: Feb 2010
Rep: 24 Posts: 1
Location: Ontario, Canada
Prop /RPM

It seems you have matched your WOT RPM for that engine. Going to a higher pitch will most likely drop you below the recommended 4000 RPM. You can go for the Mercury HighFive Stainless Steel prop, 5-blade designed to replace any Quicksilver/Merc prop pitch for pitch. The 5-blade will reduce vibration at top speed, and great in rough water.
Reply With Quote
  #3  
Old 02-03-2010, 11:17 AM
Jango Jango is offline
Senior Enthusiast
 
Join Date: Aug 2005
Rep: 63 Posts: 519
Location: Mid Atlantic
You are getting about 10% slip with your present 14 3/4 x 21P. PROP which is very good for the speed (42K) and weight of your boat. Increasing Pitch will decrease RPM as previously mentioned and is probably not advised. Going to a 4 blade prop will decrease Slip slightly but will probably drop motor speed by 200 - 300 RPM,s. As long as Hole Shot and Acceleration is adequate, I would stay with your present Prop.

Jango
Reply With Quote
  #4  
Old 02-03-2010, 11:20 AM
gonzo's Avatar
gonzo gonzo is offline
Senior Member
 
Join Date: Aug 2002
Rep: 1397 Posts: 7,215
Location: Milwaukee, WI
You seem to be right on the money. Any modifications would only be to get lower speed and better economy.
__________________
Gonzo
Reply With Quote
  #5  
Old 03-09-2010, 02:56 AM
Ambitious Ambitious is offline
Naval Architect
 
Join Date: Jan 2009
Rep: 10 Posts: 23
Location: Serbia, Belgrade
Thanks for reply.
If I get the point you think that we have a good combination at the moment regarding engine+drive+prop.
I would be happy to get some better acceleration and to keep top speed. Is it doable with 4 or 5 blade prop with same diameter and pitch?

Thanks again
Reply With Quote
  #6  
Old 03-12-2010, 09:43 AM
Jango Jango is offline
Senior Enthusiast
 
Join Date: Aug 2005
Rep: 63 Posts: 519
Location: Mid Atlantic
A 4 or 5 Blade Prop will decrease engine RPM. Max Speed will be reduced, since your current Slip is Low. The Only way to increase Acceleration is to decrease Pitch which will most likely also decrease Top Speed

Jango
Reply With Quote
  #7  
Old 03-12-2010, 10:06 AM
Frosty's Avatar
Frosty Frosty is offline
Senior Member
 
Join Date: May 2002
Rep: 1514 Posts: 5,518
Location: Thailand
That extra 80 RPM will soon be eaten up by the extra weight that you will no doubt put on it now that it is finished.

For instance were you fully fuel'ed and watered.

As said you are spot on there.
Reply With Quote
  #8  
Old 03-12-2010, 10:16 AM
Ambitious Ambitious is offline
Naval Architect
 
Join Date: Jan 2009
Rep: 10 Posts: 23
Location: Serbia, Belgrade
We were fully loaded with four persons on board. But you`re probably right because hull surface was perfect clear. After couple of days in water hull will become dirty.....
Reply With Quote
Reply



Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes


Similar Threads
Thread Thread Starter Forum Replies Last Post
A reverse Prop Question boatmon1955 Props 4 09-01-2009 08:28 AM
Tunnel Prop Question big-boss Boat Design 1 10-17-2008 03:25 PM
New prop question from a newby Quartz Props 4 05-10-2008 05:25 PM
Prop size question jerryniff Sailboats 4 01-11-2006 10:26 AM
New question prop selection simso Propulsion 0 09-01-2005 05:47 AM


All times are GMT -5. The time now is 01:08 AM.


Powered by: vBulletin Copyright ©2000 - 2012, Jelsoft Enterprises Ltd.
Web Site Design and Content Copyright ©1999 - 2012 Boat Design Net