Why Does Lge Hub Prop Fit Small Gearcase?

[keeper]

Hi Guys!

Here's The Story!

Wen't To Buy A New Prop Because It Was The Last Thing I Figured My Problem Was, Very Slow Plane, Major Cavitation Getting On Plane, Too High Pitch, No Lift, Only 4900 Rpms. Specs Are 1977 Merc 1750, 3 Blade Hooter Sst 24 Pitch.
Anyway, I Accidentally Bought A 21 Pitch Large Hub Hi Five Thinking It Was Small Hub. The Hooter That Came Off Measured 3.9 Across Hub. My Gearcase Measures 4.375, Leaving Almost A 1/4 Inch Gap On The Sides Of The Prop. I'm Thinking Thats Why My Prop Was Breaking Loose To 6000 Getting On Plane. So I'm Thinking I Will Have To Sell This Hi Five And Buy A Small Hub Until I Get The Hi Five And It Measures 4.34 Across Hub And Fits In My Case Like A Glove. What Gives? Is This A Small Or Lge Case. It Is A 2:1 Ratio. And Measures 4.375. Did They Make A Mid Size Case?

Thanks For The Help!

Mark

[Techno]

I think its ventilation, not cavitation. If your prop is near the water its loaded so much that its sucking air into it.
Anyway short of lowering it, doing what your doing and getting a lower pitch prop. I solved my problem by getting a land&sea variable pitch prop. That solved my problems. BUT you can't surface it or revv it past some set RPM. I think this is a much better solution. Low fixed pitch means no high speeds.
High fixed pitch means a PITA to get on plane.
Low pitch on launch and high at top speed means cake.:) This means you can rip a skiers arms off and drag them at top speed.:eek:
They are expensive but since most think they are junk might be able to find one comparable to the prop you getting.
It sounds like your boat don't need a surfacing prop but thats a guess?
Whats your top speed and how many RPMs with the 24"?

[keeper]

47 mph at 4900 rpms with 24 pitch prop

[moparbarn]

had a hooter prop on a bass boat a while back. came with a plastic ring to fill the gap to the ghear case. mine disappeared/blew off one day at the lake, and acted exactly like you describe. too much exauhst(air) over the prop. i made a ring out of pvc pipe. couldn't find an exact fit, just cut it and squeezed it down. then i cut three sections and left gaps in it in the same positions that the holes are in on omc hubs to help ventilate the prop for hole shots. had to play with the size/length of the open areas to get the results i wanted, worked out pretty good. used pop rivets to hold them on while tuning, then counter sunk the holes in the pvc and used ss screws and the thinnest nuts i could find inside the hub. should help with rpm up top also. be careful with that hooter, they are known to throw blades-mine did! that and that has to be an old prop, had mine about 10 or 11 years ago, and they were out of business then.

AIRWALK