Hi all!! First post here!! I was just wondering if I could get some expert advice. I have an rapid 430s rib with a tohatsu 4 stroke outboard and it's running a 9.9x10 prop. It all seems ok, but will go past the optimal rev range so I have to keep it just under full throttle. My question is.. is it worth changing props to an 9.9x11?
I was just wondering what other people were running of similar sort? Thanks nat
Providing you have found that you are exceeding the WOT rev band with the boat loaded with what it normally carries AND that you don't need rapid acceleration for such things as towing a skier then yes, a prop change would be on the cards.
I don't know what the pitch changes are for yours but I'd suggest going up in twos which may be the way props for yours go - for mine the props are 17, 19, 21, 23, 25.
I'm guessing if the existing prop on that Tohatsu is a 10" it will be about a 20hp?? In that HP range the props are usually in 1" increments. I have both 10" & 11" props for my 20HP Suzuki and the difference is more noticeable in real life than on paper.
We have a largeish crew load in a slightly draggy bottomed SIB and a 10" is perfect for us... the 11" is overgeared.
So I'd consider upping to an 11" or possibly 12" in your case assuming you are running around a 20HP.
With full load it's ok on acceleration but then still gets to speed and will go up to red line when it gets on the plane. So I guess I could get a little more from the engine. Thanks for your quick reply.
i have a suzuki 25 four stroke came with a 10 1/4 x 11 runs at 5650 RPM 22 knots WOT
bought a 10 1/4 x 12 runs at 5250 RPM 21.5 knots WOT
considering a 10 x 10 stainless steel bringing RPM up to 5950 ish theoretically
spy-sea-one
