Which prop; 80 HP / 19' Aluminum?

[Alan]

The one I have is not listed as an option in my factory parts list, and the dang thing’s been slipping! One more mystery solved. Now that I look back I think it’s been misbehaving for a while, but pretty much let go today. it’s a 10X9 1/4.
Parts list says I can choose from 10 1/4 x 10, (which someone has penned in, “stan” by; for standard, I assume), 10×12, 10X11, and 9 1/2x 10. I’ve found the pretty 10X12 I got is too big. Dag nab it. Which of the listed ones would be best for my hull? I’m not skiing, and am looking for highest top speed, I guess. Fuel efficiency, maybe.
This is for a 19′ Lund Aluminum, closed bow runabout. hull is about 980 lbs; motor is 80 HP, something like 230 lbs. The hull has a nice sharp bow, but flattens out completely for the last 8′.
Any other info I can provide; let me know.
Many thanks;
Alan

• This topic was modified 4 years, 9 months ago by Alan.
• This topic was modified 4 years, 9 months ago by Mumbles.

[dave-bernard]

use 48- XXXXXXX to look up prop
x is your # in the book.
Or have it rehubed.

• This reply was modified 4 years, 9 months ago by dave-bernard.

[fleetwin]

I would go with the “standard” prop: 378040/10.25X10″. That 9″ pitch prop in your picture looks pretty beat up, not worth rehubbing….I am assuming the 12″ pitch prop causes the engine to lug, that is a big boat, so the 10″ pitch prop will allow the engine to wind up/breath and provide good performance in most all loads…

[Alan]

Thanks Fleetwin! Yep, the pretty 10×12 I got would not let the motor get up to full speed. Too bad, as I say, since it was NOS, with a matching prop nut.
I will go with the “Stan” 10 1/4 X 10. It seems to have been used with a lot of other motors as well.
Appreciation to you, and happy motoring to all.
Alan

[frankr]

10 x 9-1/4 is listed on the parts list you posted as a propeller kit.

[frankr]

Does your current prop look like it is wrong for the motor? In other words, is the hub smaller than the gearcase? I believe that is the propeller kit. It was a very good prop for most cases. The other props look more like a proper fit with a flow from the gearcase, over the larger prop hub. Nevertheless, the small hub prop with the funky look works well on most boats.

[fleetwin]

Keep the 12″ prop as a spare, that way you will never need it!

[Alan]

Wow, and yes. The prop is exactly as Frank R described. It does look small compared to the gearcase. “Wow” in that I hadn’t spotted it on my parts list. What makes it a, “kit”?
I always keep every part that’s even close to useable, (and some that aren’t very close). I carry the bigger prop as a spare, and will hang onto the one pictured. It’s not as ugly as the closeup pic implies.
This motor has been quite the challenge. When I bought it, the guy told me an engineer had given it to him for free, and wished him, “good luck”. He helped me load it, and said, “good luck w/ that”. I’m not really superstitious, but that’s generally a bad omen when buying an old machine. The wiring was fried from his jump starts, and it looked like it sat outside for a decade or two.
I just finished my 6th less than successful lake trial. A new record for me; I’ve never needed more than two. One thing that didn’t help was my vintage factory service manual said the low speed needles should be backed out 3/4 of a turn as the initial setting. Even though the newer Clymer manual said 1.5 turns out. Gosh, I sure spent a lot of time chasing a lean sneeze at idle til I re-adjusted. That, and I learned one must twist spark wires when testing them. They tested fine, until I moved them a little. Car spark wires don’t twist, but outboard wires do. Live and learn.
Many thanks and happy motoring to all.
Alan

[dave-bernard]

MY guess is that there is parts missing and exhaust is going in to the prop and causing the slippage.

[frankr]

It is a “kit” because it comes with a smaller / shorter prop nut, drive pin, and cotter pin. That because the stock parts are way bigger in order to conform to the larger stock prop hub’s diameters. I agree that the small hub prop looks for all the world like it would cavitate like crazy, but it doesn’t.

[Author]

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