9.9 prop questions

[12guns]

Ok, so this 77' 9.9 now has 15 hp carb, open air intake and no exhaust baffle. It runs rather well and doesn't have many hours on it. I was told it came w/ a 9 x 10 prop from the factory, at some point my grand pa put a 9 1/4 x 8, I assume for a bit of extra "off the line" power?? So what do I need? I duck hunt and generally don't haul much weight. I would rather take a bit longer to plane out and have more top end speed. The motor w/ a 14' duracraft tops out w/ only me at 24 mph, and that w/ a tail wind!
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So if the 10" pitch moves the boat forward 2 more inches per revolution, but your overall rpm's decrease, what good is it? I'm confused. Also, should I consider SS Props? or are they too heavy and overkill for such a small motor? Some advice would be great!

 

[steelespike]

Re: 9.9 prop questions

You shouldn't make any changes without checking present rpm.You can maybe beg or borrow a shop tach or get your self a tinytach.
A stock 9.9 would be good for about 21 mph.a 15 about 25 under ideal conditions.If your 24 is accurate your pretty close.
A 9.9 is rated at 5,000 to 6,000 rpm.A 15 5,500 to 7,000.
As far as increasing pitch the "basic" idea for speed is as much pitch as possible and still reach max rated rpm.Your 8 may be ok.Establish your present rpm and make your decision from there.Let us know what you find.