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Prop Help-'69 sport
Chris in MD	#1  Posted on 06/21/09 - 5:26 PM
Member Posts: 29 Comments: 0 Joined: 06/04/08	I have a 1969 13' Sport and just put a 2007 (new Factory Clarance) 2 Stroke 25 HP Yamaha on it. Right now I am getting 27 MPH out it with just my 200 # on board, but don't have a tachometer on to be sure of the RPM range. The motor came with a 9 7/8" Dia X 9" Pitch propellar on it. In looking in catalogs I can't even find a propellar that small. Everything I see starts at 10 1/4" Diameter and about a 10 pitch. What have you guys and gals found to be a good propeller for the 13' Sport with a 25 HP 2 Stroke. Thanks Chris
Tom W Clark	#2  Posted on 06/22/09 - 8:21 AM
Member Personal Page Posts: 4280 Comments: 7 Joined: 09/30/05	Chris, Not all 25 HP outboards are the same and as such they may use different propellers to achieve the same performance on one boat. We need to now the gear ratio of your outboard as well as the WOT RPM range the manufacturer recommends. Both these bits of information are in your owner's manual and are always the starting point for figuring out what propeller to use.
Chris in MD	#3  Posted on 06/23/09 - 4:12 AM
Member Posts: 29 Comments: 0 Joined: 06/04/08	Tom Max RPM Range from the manual is 5000-6000. As I said I don't have a tach on the boat right now. Gear ratio is 2.08 Chris
Tom W Clark	#4  Posted on 06/23/09 - 8:09 AM
Member Personal Page Posts: 4280 Comments: 7 Joined: 09/30/05	OK, we know your Sport 13 with 25 HP is able to do about 27 MPH. With a 2.08:1 gear ratio, at that speed with a 9" pitch prop and a reasonable 5 percent propeller slip, your engine is spinning way over the redline, almost 7000 RPM. Not good. You should increase pitch. There are lots of propellers out there for this motor. Yamaha offers both aluminum and stainless steel and there are numerous aftermarket props to try as well. Looking at Yamaha's offerings: http://www.yamaha-motor.com/outboard/...%20F25.pdf I suspect you have their 9-7/8" x 9" aluminum prop, part # 664-45941-01-EL A better propeller to try would be their 9-7/8" x 10-1/2", part #664-45945-00-EL The much better choice would be a stainless steel propeller. I recommend their 10-1/8" x 10" Performance stainless steel propeller, part # MAR-GYT3B-02-10 which happens to be the same thing as a Turbo Hotshot and Stiletto Triad 3.0 of the same size (they are all made by Precision Propeller Industries, which is owned by Yamaha). Edited by Tom W Clark on 06/23/09 - 8:12 AM
Chris in MD	#5  Posted on 06/23/09 - 4:31 PM
Member Posts: 29 Comments: 0 Joined: 06/04/08	Thanks Tom. Yes it's the 9 7/8"x 9" prop. I was way afraid I was up in the red zone. Any thoughts of a 10 1/4" DIA X 10" Pitch? That seems to be a readily available aftermarket without having to buy a YAMAHA prop. If not I'll go with one of the 2 you recommended. I am betting I can get 32 or so out of her. Chris Edited by Chris in MD on 06/23/09 - 4:33 PM
Tom W Clark	#6  Posted on 06/23/09 - 9:57 PM
Member Personal Page Posts: 4280 Comments: 7 Joined: 09/30/05	Chris, It depends on exactly which 10-1/4" x 10" prop you are referring to. There is a lot more to propeller design than just diameter and pitch. What do you have against Yamaha props? You *might* see 30 MPH, which would be very, very good for a 25. I doubt you will see 32.