Yamaha F9.9AM (6G8) propeller size?

[mrmrva]

Hello all,

I own a 1985 4-stroke 9.9HP Yamaha outboard (F9.9AM 6G8) and have broken propeller (one blade damaged) so need to replace it. Current prop is plastic 12 1/4 x 11 3/4, and with it at WOT RPM is 3500 and optimum is 4500. I was looking online stores but could only find props in 9 1/4 diameter which I assume is for "regular" model. Any advice or help would be appreciated.

 

[VicS]

Do you mean 11¾" (diameter) X 12½" (pitch) if so that seems to be listed in the parts lists . ( also 11 x 11¾ and 11¾ x 9¼)

Some models do however seem to use 9¼ or 9¾ diameter props with pitches ranging from 6½ to 10½"

your Yamaha dealer should be able to supply the correct prop

See also THIS LINK to info on Yamaha props

If your WOT revs are only 3500 rpm should you not be using a lower pitched prop in order to increase the rpm and develop the full power of the engine.
Your Yamaha dealer should be able advise you on prop selection

 

[mrmrva]

Do you mean 11¾" (diameter) X 12½" (pitch)/QUOTE]

Yes that is what I meant, made a mistake.

your Yamaha dealer should be able to supply the correct prop

Since my outboard has such a large prop and gear ratio 2.92:1 I've realized that it is a High Thrust model. I've called the only Yamaha dealer over here (Serbia) and they also told me that for this model there are 3 models available just as you wrote: 11¾ X 12½, 11 x 11¾ and 11¾ x 9¼

If your WOT revs are only 3500 rpm should you not be using a lower pitched prop in order to increase the rpm and develop the full power of the engine.

Why do you say this? Wouldn't lower pitch make allow engine to rotate more easily and achieve optimum RPM?
The dealer here isn't of much help and didn't give much thought about my problem. I've told them about my current WOT rpm and they just said "Well you have these three sizes take the 11¾ x 9¼."

My boat is of aluminium 6.5 x 1.5 meters with flat bottom and looks similar to this just smaller and lighter

and with raised stern, like this

If I understand the matter correct, it is sort of semi-planing hull, and we used on river for fishing.
I was thinking of buying 11¾ x 9¼ but would like to hear if you have if any other advices since I can't relly on dealer here.

Regards,
Petar

 

[moonraker 36]

try these's
http://www.piranhapropellers.com/
next time you break a bladed you can just change the bladed and not the full prop.

 

[mrmrva]

I know about piranha but they don't have anything near my current diameter of 11 3/4 for Yamaha 8 spline. It seems my only option is original Yamaha and considering my current WOT rpm I think 11 3/4 x 9 1/4 is the best choice.