Prop barrel slightly smaller than the gearcase

Joshto

Petty Officer 2nd Class
Joined
Jul 29, 2019
Messages
103
This is interesting, as my boat planes quickly with the current aluminum 4-blade 14.25 x 21P (4-3/8 barrel), and stays on top at ~3200 rpm. I guess I don't pay too much attention to performance or top speed, as it's mainly a family boat.
To clarify, my aluminum prop is 4-3/8 inches at the base (milled barrel), otherwise it is approximately 4-9/16 inches.

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Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
28,467
How about a temp fix? Clean up the edge of the gearcase hub, and the recessed part of the prop. Wipe them with some solvent.

Now rub some wax, candle etc. on the edges of the gearcase hub. Install the prop. Now run a precise bead of silicone caulk where the gearcase meets the prop. Let it dry, and then run a single edge razor to make sure the silicone doesn't stick to the gearcase. I would think that will seal it well enough, not add any drag and not add anything that could damage the hub or gearcase.
 

jlh3rd

Master Chief Petty Officer
Joined
Jul 10, 2017
Messages
817
I wanna clarify my "hub ring" statement.
The '05 Merc. 60, 4stroke I had was missing that ring. There was a lot I didn't know with the boat purchase in 2017.
My new re-power, 2021 Merc. 115 hp, I think (ass-u-me d) that it has that ring. I bought it brand new so I never looked, I don't know.
However, the gear case diameter is 4 3/4". If a prop hub is 4 1/4" , that prop will not work, as evidenced by the 2 props sitting on my shelf. Another lesson learned concerning propping a boat.
I have no idea about a merc stern drive, but thought worth mentioning.
 
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Texasmark

Supreme Mariner
Joined
Dec 20, 2005
Messages
14,844
That was the Mercury 'Chopper'
View attachment 411901
I think the physics behind this is similar to ported props. As soon as you reach a certain speed, water pressure from new water forces the exhaust to hug the hub, rather than being spread out over the blades like is the case at lower speeds where slip is significant.
 

Joshto

Petty Officer 2nd Class
Joined
Jul 29, 2019
Messages
103
How about a temp fix? Clean up the edge of the gearcase hub, and the recessed part of the prop. Wipe them with some solvent.

Now rub some wax, candle etc. on the edges of the gearcase hub. Install the prop. Now run a precise bead of silicone caulk where the gearcase meets the prop. Let it dry, and then run a single edge razor to make sure the silicone doesn't stick to the gearcase. I would think that will seal it well enough, not add any drag and not add anything that could damage the hub or gearcase.
That's some McGiver Sh@t haha. I'll keep searching for a gearcase-mounted ring (aka weed ring), if I can't find any....I'll give this idea a shot. I don't want to keep the prop if it affects min-acceptable performance.
 

Joshto

Petty Officer 2nd Class
Joined
Jul 29, 2019
Messages
103
It appears the part number 350626 might work; it's a weed ring (exhaust ring) for Renegade Bass props on Evinrude V6 (which seems to share the same diameter as the Alpha One gearcase).

Only 15 bucks, so I ordered one to see if it fits.

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