Author Topic: Props  (Read 509 times)


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« on: August 01, 2022, 09:51:36 PM »
After a few years of dormancy (or at least, using it 'as is') I'm upgrading the minimax I built with my kids 8 years ago or so.

Adding steering and remote control (we are all too big and old now to reach behind for the tiller).

I know that this will improve weight distribution too - running a minimax with a tiller pretty much guarantees too much weight in the back. So I'm expecting it to go a bit faster.

BUT... My recollection is that with my 1986 Evinrude 8, I'm pretty much over-revving the engine already.

Does anyone know where to get more aggressive props for this era motor?

58 Johnson

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Re: Props
« Reply #1 on: August 02, 2022, 01:52:44 AM »
I have no idea myself… this reminds of questions asked here in the past about motors small enough to barely plane a sea flea, and how to get more performance from them.  I’m not sure it’s possible but I, too, would be interested in knowing.

My thought is to go to a major source like Michigan Wheel Propellers and see if they have a “hot line” of sorts.  We also had a member of the site who was going to contact a “cocktail racer” club (where max horsepower is only 6)… but we lost contact with him… not sure if he ever received information on how and why those little boats perform so well.  That might be a good avenue to pursue.
Ross Jewiss, Huntsville, Ontario


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Re: Props
« Reply #2 on: August 05, 2022, 01:13:58 PM »
It may be an easier / less expensive option to selll your 8hp and move up to a larger motor.  The 9.9 / 15hp OMC's only weigh approx 10-15lbs more than your 8hp and are far more common when you need parts down the road.  A boost in horsepower will give you way more bang for your buck than a prop.     

They are out there if you keep checking the classifieds and don't mind a road trip.  ( Johnson 15hp $600! *see link below* )

seattle smitty

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Re: Props
« Reply #3 on: December 15, 2022, 08:37:58 AM »
veeDub, you might be right that a slightly bigger motor would be better for him (I don't know, never had one of those boats), BUT, he still will be over-revving the engine and getting sluggish performance if he's using the factory-original prop.
    Boat motors come propped for what the manufacturer believes will be the most likely usage  .  .  .  which is NOT powering a seaflea.  Your factory prop is selected to push a 200+ pounds fishing boat with a couple of fat Americans with all their tackle, food and beer cooler and what-not. In automotive terms, you have a one-speed transmission in Low or "granny-low" gear. Plus, the blades are shaped to shed weeds and fishing line, and aren't optimized for a ninety-pound planing hull with only the driver as the load. The factory also understands that many owners buy these motors as "kickers" and emergency "get-me-home", for cabin cruisers;  again, "granny-Low" gear. Since we don't have outboards with 5-speed overdrive trannies, we need to select props for the task at hand.                                                                                                                       
   If I were propping a flea, I might first explain my problem to the local dealer for the engine, asking what prop he can get for my engine that has the most pitch. This might even come from a more powerful model if that still uses the same size propshaft.  I might also write a letter detailing my needs to Michigan Wheel.  Be sure to include the propshaft dims, the lower unit gear ratio, the top engine rpm, the weight and maybe a photo of the boat. Don't specify a 3-blade just because your engine came with one;  the best props for your use might well be 2-blades, might be bronze or steel, might even have less diameter than your fishing prop.                                                                                                                                               
    Actually, having done that homework, what I would probably do is go to and talk to the site originator/host/admin, Ron Hill. Ron has been a top-rank racer AND prop-man since the early Sixties, has built, modified, and sold props for many varieties of powerboat racing, and whose word is gold on this subject. If you end up buying a prop from Ron and are less than impressed, send it back and he will rework it until you like it.                                             
    What racers call "set-up" is very important in getting the most out of your new, high-pitch prop. Motor height and kick-out angle is determined by testing at the lake, with the aid of a speedometer and tach. If you had a non-shifting racing lower unit, you would be using a "surfacing" propellor (invented in the late Forties or early Fifties by Hy Johnson in California, IIRC), which is generally set with the top edge of the propshaft about even with the bottom of the boat. With a normal outboard lower unit and non-surfacing prop, you won't set up that high.  But if I was helping set you up, with a prop that we guessed would be somewhere in the ballpark, my initial set-up would be to shim up the motor on the transom to where the bottom surface of the so-called cavitation plate was even with the bottom edge of the boat (assuming the engine would still get good water intake at that setting), and I'd adjust the tilt so that the cavitation plate was parallel (checked with a straightedge) with the bottom, neither "kicked-out" nor "kicked under."  Then send the driver out to first make sure that the boat is not too squirrely or inclined to blow over (in which case kick-under by one notch). Warn the driver that, first, the boat will be a lot slower to get on plane than it was with the Low-gear prop. He'll need to get forward in the cockpit until the boat gets over the hump.                                                                                                                                           
    Second, warn him that once over the hump he will quickly be going a good 15 mph faster than he's ever gone in that boat, which will feel a lot lighter and livelier and less tame than he's expecting  .  .  .  .


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Re: Props
« Reply #4 on: January 26, 2023, 12:13:12 AM »
I raced hydro's for 13 years with Mercury KG-4H's and  30H's. All the race guys now have many of these 9/16" prop shaft, shear pin props, available at resonable prices. If you run a Vintage Merc on your sea flea, by all means, contact me and I can help. I have 15  - 2 cylinder powerheads from 7 1/2 Hp up to 20 Hp on a choice of three lower unit styles- gear shift, forward only and racing "quickie" lower units.
Mercury "Sea Flea" Engines available-KG-4H, KG-7H, Mark 15H, KG-4 and KG-7 standard lower unit rebuilt engines-all for hydro's and runabouts!