Notices
The Boating Forum

Prop question for Twins

Old 10-11-2008, 03:11 PM
  #1  
MemberCaptains Club Member
Thread Starter
 
Join Date: Nov 2003
Location:
Posts: 41
Likes: 0
Received 0 Likes on 0 Posts
Default Prop question for Twins

Hi there:
I currently have a twins outboards on my boat and I have been told by machanics that I need to change the pitch from 21 to 18.5 to get the right RPMs.
Stupid question but are there props specially made for port engine and one for starboard engine?
Thanks for your time in advance.
Old 10-11-2008, 03:16 PM
  #2  
Senior MemberCaptains Club MemberPLEDGER
 
Join Date: Oct 2002
Location: mass/Point Judith, RI dockage
Posts: 11,909
Received 470 Likes on 275 Posts
Default Re: Prop question for Twins

If your engines are "counter-rotating", then yes, you need a different prop on each engine. One engine will be turning clockise (looking at the stern) and one will be rotating the other way (counter-clockwise).

To make matter worse, I don't know of many aluminum prop makers that make the counterclockwise blade - you may have to buy stainle$$ $teel.

Old 10-11-2008, 08:34 PM
  #3  
MemberCaptains Club Member
Thread Starter
 
Join Date: Nov 2003
Location:
Posts: 41
Likes: 0
Received 0 Likes on 0 Posts
Default Re: Prop question for Twins

Thanks for the info, someone told me that you can actually have a shop change the pitch on an existing prop, is that possible on a stainless prop?
Thanks
Old 10-11-2008, 08:51 PM
  #4  
Senior MemberCaptains Club MemberPLEDGER
 
Join Date: Oct 2002
Location: mass/Point Judith, RI dockage
Posts: 11,909
Received 470 Likes on 275 Posts
Default Re: Prop question for Twins

Sure, they can make minor adjustments, but it's costly. It will probably be cheaper in the end to buy two new ones and sell the ones you have.

It sounds like that is a big change, so it may not even be possible,.

Just a guess though. It's best to ask a prop shop....
Old 10-11-2008, 11:37 PM
  #5  
Senior MemberCaptains Club Member
 
Join Date: Dec 2007
Location: PBG, FL
Posts: 8,938
Likes: 0
Received 12 Likes on 12 Posts
Default Re: Prop question for Twins

when i talked to the prop shop they said they could go up or down 2. so if you had a 17 you could get 19 or 15. but that was with aluminum not sure about stainless blades. assuming you have a large enough boat that you need twin engines i would stick with stainless for performance. what are your wot rpm?
Old 10-12-2008, 12:59 AM
  #6  
Admirals ClubCaptains Club Member Admiral's Club Member
 
Join Date: Apr 2005
Location: Fort Walton Beach, FL
Posts: 957
Likes: 0
Received 11 Likes on 5 Posts
Default Re: Prop question for Twins

Here's my two cents... Yes you need counter rotating props... to offset the torque created by the engines... Next, They do make aluminum props for counter rotating... I got mine from Tacoma Propellor in Washington state... I have twin Honda 150's... I bought four blade props for my motors to try them out and i am pleased with them... think they are 15' dia by 16 pitch... i had stainless props on my boat till they got ganked from me... so, that's another story... I would not recommend Repitching your props.. if they are casted stainless steel, they were designed to be a certain pitch.. they can be repaired and "true'd" out, but to repitch them, i'd just get a different set... I found out that my props were a 17 pitch on the port engine and a 19 pitch on starboard... they shaved down the pitching on the 19 to tone it down a bit, but after i looked at the serial numbers when polishing them one day, i was like, "what the F(#@" ... so, i took off the stainless props, got two matching aluminum and been eyeing the POWERTECH Props like crazy... best props, hands down i think....

also, you engines have max RPM range... WOT (wide open throttle) should be "blank" on your motors... my hondas are 6,000 rpms, but i'd be happy with 5800 RPMS, just to prevent over reving when the boat launches out of the water in a wave... but right now i'm getting close to 5300 with aluminum props...

my two cents...
Old 10-12-2008, 04:31 AM
  #7  
Senior Member
 
Join Date: Jul 2004
Location: Gulf of Mexico,Louisiana
Posts: 6,289
Likes: 0
Received 13 Likes on 7 Posts
Default Re: Prop question for Twins

I had ss wheels repitched in the past with no problem.Around here it cost around $100 each.I would check into that first.Used wheels sell around half of what new ones sell for.
Old 10-12-2008, 09:46 AM
  #8  
Senior MemberCaptains Club MemberPLEDGER
 
Join Date: Oct 2002
Location: mass/Point Judith, RI dockage
Posts: 11,909
Received 470 Likes on 275 Posts
Default Re: Prop question for Twins

Hmm, new stainless wheels are about$400 each, and you can sell the ones you have for about $200 each. Or you can spend $100 each and try to get them reduced (leaving them with little real value to a third party). The risk is that they won't be able to get the props tuned for your boat, in which case you have spent the retuning cost, won't be able to sell your old props, and will still have to buy new ones.

My preference would be to get the new props and recover whatever you can by selling the old ones. Ground and trued outboard props can't be as efficient as new ones (that may not be true for the big wheels used on inboards though).
Old 10-12-2008, 10:44 AM
  #9  
MemberCaptains Club Member
 
Join Date: Apr 2007
Location: Pompano Beach
Posts: 64
Likes: 0
Received 0 Likes on 0 Posts
Default Re: Prop question for Twins

Try contacting the engine manufacturer for guidance. When I was dissatisfied with the props that came with my boat, I contacted Mercury. An engineer called me back within hours and, by the next day, made a recommendation. The props were fabulous. Why not tap into the expertise of the company that made the engines in the first place.
Old 10-12-2008, 12:46 PM
  #10  
MemberCaptains Club Member
Thread Starter
 
Join Date: Nov 2003
Location:
Posts: 41
Likes: 0
Received 0 Likes on 0 Posts
Default Re: Prop question for Twins

Thanks for all the info, I think I am going to go buy new set of props and try to resell my old ones on ebay. I understand that when you move from 21 to say 18 pitch, you gain more RPMs and get better fuel efficiency. Is it true that I will also lose top end speed?
THanks
Old 10-12-2008, 01:10 PM
  #11  
Senior MemberCaptains Club Member
 
Join Date: Nov 2006
Location: boynton beach fl
Posts: 4,742
Received 146 Likes on 109 Posts
Default RE: Prop question for Twins

That depends on how over propped you were.You won't lose anything that was good unless you end up with the wrong props.Better ask someone with the experience to set you up perfectly,....THE FIRST TIME, Props ain't cheap and you only need two sets in case of emergency, not 3 or 4!!Prop gods, should be your first step and probably your last.
Old 10-12-2008, 08:41 PM
  #12  
Senior MemberCaptains Club MemberPLEDGER
 
Join Date: Oct 2002
Location: mass/Point Judith, RI dockage
Posts: 11,909
Received 470 Likes on 275 Posts
Default Re: Prop question for Twins

Just don't mix them up and put them on the wrong side or you will surprised how fast reverse can be.....
Old 10-12-2008, 09:49 PM
  #13  
Senior Member
 
Join Date: Jan 2008
Location:
Posts: 1,562
Likes: 0
Received 2 Likes on 2 Posts
Default Re: Prop question for Twins

I would try 19's first
Old 10-13-2008, 08:45 AM
  #14  
Senior MemberCaptains Club Member
 
Join Date: Sep 2002
Location: Hattiesburg, Mississippi
Posts: 2,067
Received 37 Likes on 21 Posts
Default RE: Prop question for Twins

Talk to the pros about this. Ken is a sponsor on this board.

http://www.propgods.com/content/index.aspx
Old 10-13-2008, 05:28 PM
  #15  
Admirals Club Admiral's Club Member
 
Join Date: Feb 2005
Location: Central Florida
Posts: 1,337
Received 188 Likes on 102 Posts
Default RE: Prop question for Twins

Like said above talk to the pro's. A good prop shop should let you test out a couple type of prop's. Of course it is understood if you damage a set you own them and you will purchase your prop's from them in the end.

That being said, what is your WOT RPM's now? With every 1" drop of pitch you should gain around 200 RPM's. When I first bought my H/S with twin Yamaha F250's I had 21" Stainless props on them. The boat ran great, until I filled the fuel tank and added all my electronics and gear. Then the hole shot suffered and Max RPM's were only around 55 to 5600.

I dropped to 19" props and the Hole Shot came right back along with the Max RPM's of 59 to 6000. I didn't lose top end (50mph) because what I lost in pitch I made up in RPM. The fuel mileage actually went up and I didn't have to play with the throttles while running in sea's. The engine was lugging along with the larger prop's. Kind of like running uphill or pulling a load all the time. With the engines not working as hard they use less fuel and should last longer.
Old 10-13-2008, 05:32 PM
  #16  
Senior Member
 
Join Date: Jul 2004
Location: S Fla
Posts: 23,411
Likes: 0
Received 31 Likes on 27 Posts
Default Re: Prop question for Twins

I wrote this with Ken's help and proofreading - complete with pics, it gives you a good start on the subject:

http://www.veradoclub.com/smf/index.php?topic=137.0
Old 10-14-2008, 09:39 PM
  #17  
MemberCaptains Club Member
Thread Starter
 
Join Date: Nov 2003
Location:
Posts: 41
Likes: 0
Received 0 Likes on 0 Posts
Default Re: Prop question for Twins

ReelDreams1: I am only getting 5200 RPMs right now. It should be hear 6200 RPMs I believe. Your thoughts are greatly appreciated.

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 On
Refbacks are Off


Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information -

Copyright © 2021 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.