Reply
 
Thread Tools Search this Thread
 
Old 09 September 2014, 05:32   #1
Member
 
JohnnyMW's Avatar
 
Country: UK - England
Town: Chester
Boat name: Black Hawk
Make: Osprey Vipermax 6.8
Length: 6m +
Engine: Etec 200 HO
MMSI: 235114488
Join Date: Aug 2014
Posts: 85
Propellor Pitch 23 vs 21 degrees

As you know I have bought an Osprey Vipermax 5.8 with a Suzuki DF140 on the back. I have two props one with 23 pitch (currently fitted) and a spare with 21 degrees if pitch both same diameter.

The boat was previously a dive boat but have just added 4 x pod seats to carry the family. Any thoughts on which prop I should use? Pro's/ Con's of each?

Thanks again
__________________

__________________
JohnnyMW is offline   Reply With Quote
Old 09 September 2014, 06:15   #2
RIBnet supporter
 
Pikey Dave's Avatar
 
Country: UK - England
Town: South Yorks
Boat name: Black Pig
Make: Ribcraft
Length: 5m +
Engine: DF140a
MMSI: 235111389
Join Date: Feb 2008
Posts: 7,595
RIBase
Try 'em. We can sit & speculate all day, but there's no substitute for sticking them on & having a go. Load the boat up with your "normal" load & go WOT. You should be able to get close to your engines max RPM at WOT. The difference between the 2 props will be around 400rpm. i.e. the smaller prop will run around 400rpm faster than the biggun.

PS Pitch is measured in inches not degrees.
__________________
Rule#2: Never argue with an idiot. He'll drag you down to his level & then beat you with experience.
Rule#3: Tha' can't educate pork.
Rule#4: See rule#5
Pikey Dave is offline   Reply With Quote
Old 09 September 2014, 07:40   #3
Member
 
JohnnyMW's Avatar
 
Country: UK - England
Town: Chester
Boat name: Black Hawk
Make: Osprey Vipermax 6.8
Length: 6m +
Engine: Etec 200 HO
MMSI: 235114488
Join Date: Aug 2014
Posts: 85
Quote:
Originally Posted by Pikey Dave View Post
Try 'em. We can sit & speculate all day, but there's no substitute for sticking them on & having a go. Load the boat up with your "normal" load & go WOT. You should be able to get close to your engines max RPM at WOT. The difference between the 2 props will be around 400rpm. i.e. the smaller prop will run around 400rpm faster than the biggun.

PS Pitch is measured in inches not degrees.

Thanks for your thoughts! And clarification on inches! I'm still learning! I'll try both and see how I get on. I've heard a lower pitch will give better fuel economy too!!
__________________
JohnnyMW is offline   Reply With Quote
Old 09 September 2014, 07:49   #4
RIBnet supporter
 
Pikey Dave's Avatar
 
Country: UK - England
Town: South Yorks
Boat name: Black Pig
Make: Ribcraft
Length: 5m +
Engine: DF140a
MMSI: 235111389
Join Date: Feb 2008
Posts: 7,595
RIBase
Quote:
Originally Posted by JohnnyMW View Post
........ I've heard a lower pitch will give better fuel economy too!!
Could go either way, propping is a black art & there are no hard & fast rules. That's why you need to experiment. If the engine can spin it, the higher pitch will give you more top speed, but lower "holeshot" (acceleration) & vice-versa for the smaller prop. If you cruised all day at a constant-ish speed, the taller prop could in theory give better economy, but would use more fuel accelerating, so like I said, trial & error.

If you're going out lightly loaded for a jolly on a calm day, stick the bigger prop on. Fully loaded, rough seas, towing toys, skiing etc. then the smaller prop will probably be the better option IF you can achieve WOT (Wide Open Throttle) RPM i.e. full beans, pedal to the metal etc.
__________________
Rule#2: Never argue with an idiot. He'll drag you down to his level & then beat you with experience.
Rule#3: Tha' can't educate pork.
Rule#4: See rule#5
Pikey Dave is offline   Reply With Quote
Old 09 September 2014, 13:17   #5
Member
 
JohnnyMW's Avatar
 
Country: UK - England
Town: Chester
Boat name: Black Hawk
Make: Osprey Vipermax 6.8
Length: 6m +
Engine: Etec 200 HO
MMSI: 235114488
Join Date: Aug 2014
Posts: 85
Quote:
Originally Posted by Pikey Dave View Post
Could go either way, propping is a black art & there are no hard & fast rules. That's why you need to experiment. If the engine can spin it, the higher pitch will give you more top speed, but lower "holeshot" (acceleration) & vice-versa for the smaller prop. If you cruised all day at a constant-ish speed, the taller prop could in theory give better economy, but would use more fuel accelerating, so like I said, trial & error.

If you're going out lightly loaded for a jolly on a calm day, stick the bigger prop on. Fully loaded, rough seas, towing toys, skiing etc. then the smaller prop will probably be the better option IF you can achieve WOT (Wide Open Throttle) RPM i.e. full beans, pedal to the metal etc.

Thanks I'll give that a try and let you know how I get on. I hasn't realised there was so much to learn.......!!!!! Much appreciate your time. Cheers
__________________
JohnnyMW is offline   Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search

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





Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -5. The time now is 15:10.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.