Yamaha F25 propping

junkyardwarrior

Seaman Apprentice
Joined
Sep 28, 2008
Messages
40
I'm working with a customer's War Eagle 548 (15' length, 48" width). Hull weight around 340 lbs, plus the 140 lb motor, plus 40 lb battery , 3 gal fuel and gear. Probably around 600-650 lb total (he runs light most of the time).

Currently has a factory Yamaha 2 stroke prop on the motor. 9 7/8 x 11 1/4 Aluminum. Max RPM at normal load is 5910 RPM (tinytach). I do not have any speed data. I'm assuming 28-29 mph based on RPM and slip. I've run this thing and I'm more or less satisfied with it's performance, however, the customer wants stainless prop. I can get him just about any brand, but trying to get him into a Turbo brand, probably a Hot Shot. It planes fairly easily and runs smooth. Motor is raised on the transom 1 1/2" with a spacer. We are going to install a CMC PT35 sooner or later, and at that time we'll probably have to raise the outboard up a little more.

My question is, do I need to get him into an 11" pitch or go up to a 12"? Only want to have to do this once....and I want him to be satisfied 100% as he has been a good customer. But picky.

or should I be looking at, say, a Powertech SRA or something else? He just wants stainless thinking that it might pick him up a MPH or two. All his friends own 2 stroke twin cyl twin carb 25 Yamaha's and they are right at 29 or 30 mph, except the guys who are modded (they are up around 35-40 depending on the mods), and I think he'd like to run right with them.

Current prop is not dinged or anything...he ruined one last year, at which time we replaced it with a new one, which is still on the motor. Hull looks good (no hook or anything).

Any of ya'll got any experience with these little motors? the smallest I've messed with in any detail were 90HP and up. I can get him close on that stuff, but not on these little 25's.
 

steelespike

Supreme Mariner
Joined
Apr 26, 2002
Messages
19,069
Re: Yamaha F25 propping

I think if you're trying to do a real good job for this guy a gps for the speed is important. Obviously it will tell you what your speed is but more importantly will help tell if the setup seems to work.
Others may be along with more technical suggestions.
 

steelespike

Supreme Mariner
Joined
Apr 26, 2002
Messages
19,069
Re: Yamaha F25 propping

My calculations indicate that 29 at 5910 is about 4% slip possible but not likely.
Usually a ss prop is rated an inch higher than it numbers. a 11" calculated as a "12"prop at 5800 is 28.5 mph. at 10% slip and 30.1 @ 5%.
I would think it would be hard for a boat with 5 keels to be fast.
 
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