Noob hacking up props in quest for speed

[Instigator]

Just edited my last post to say add cup instead of pitch.(auto spell!)
Tried to edit it last night and the site wasn’t doing it.

Can be as easy as this:

Yrs ago a friend gave me an ancient 13’ alum boat w/a ‘1956, 30 hpJohnson on it.

Ran 26 mph as delivered.

I bought the (alum) prop I found w/the most pitch and raised the motor and headed for the lake.

The boat was light enough it popped right on plane but the prop slipped bad when trying to speed up.

Went back to the ramp, pulled the prop off and used the top of one of the 4” x 4” posts holding the dock up, as a pitch block.

5 mins later, back on the water.

Slip went down, speed went up!

Did that several more times until the prop was fully locked in.

It now ran 34 mph.

Doesnt sound like much but that’s 8 mph or 31% improvement w/a cheap alum prop and a hammer!

Funniest part was, there was a guy bank fishing right by the ramp and he came up to me when I finished.
Told me when I started hammering the prop he thought I was an idiot but he could tell I was going faster every time.

Said it was one of the coolest things he’d seen!


Case study #2:

My first fast pleasure boat.

A very unique rig w/no previous examples to copy for set up.

Motor was a 235 hp V-6 so good stainless props were available but I had no idea where to start.

So I had the local store order me the largest alum (23”) Prop that Michigan wheel offered and started there.

Boat jumped on plane, ran/handled great but if you touched the up trim button the prop broke loose instantly!

Beat some cup into it (think I used a trailer ball for that one.

Added cup and ran 63.

More cup and ran 65.

Took it home and took a 7” grinder and Sabre saw to it.
Was now scrap as I just bought it to see what size stainless to buy.

I cut the blades to the shape of a Cleaver, thinned the blades and beat as much cup into it as I could.

It now ran 67 mph!

7 mph and 12% for free!

One of most rewarding projects I ever did.

Painted that prop pink, just to screw w/people!

That was back when 65 was fast!

Now we have $5k CNC props!

[LakeFever]

There sure is something special about finding low buck gains. They are not very common. Another thought I’m not sure if this came up or not but be sure to anneal the aluminum each time you work it.

[Captain315]

Looking forward to putting some of these ideas to test! Unfortunately, I am an hour east of the NC mountains that got destroyed by hurricane Helene a couple weeks ago, and debris/muddy water are STILL coming down the river and lake I run. Our lake alone went 10ft over flood stage (13 over normal elevation). Seems pretty trivial, considering some lost homes, lives, even entire towns- literally wiped right off the map.

[Captain315]

Finally got a little tiller time in as the lake debris has nearly cleared up. The two current test props are a 14P with major leading edge mods, sharpened, cone removed, and a 10P with the same and less leading edge mods. Both required heavy cupping to grab the water with plate 2" above transom.
Both props sucked, bad! 4900-5100rpm, 26 and 30mph top speeds. Removed some cup, gained 200rpm and slipped to beat the band.
Dropped motor to 1" above plate, removed almost all cupping- both props slipped but hooked up gradually, 31mph out of the 14 and 29mph out of the 10, the 10 yanked and torque steered so bad it was almost a 2 handed deal, and cruise speeds were down 3-4mph as expected. RPMs back up for both.
Bought a cheap 13P and threw it on stock- 5500rpm and 31mph, efficiency and grip were great.
Best top speed to date was the stock 14P at 33.1mph and motor 1" up- approx 5300-5400rpm.
Seems anybody really hauling azz are running the props half out of the water. Can I expect any significant increases while running submerged, or is a jack plate in order at this point?
Thanks in advance

[OnPad]

It kinda depends on what you want to do with the boat. If you want to move weight, or have some turning ability, deeper is better. The best straight line speeds are usually achieved with the prop shaft above the water. This usually requires significantly larger diameter and more pitch than what would be required to run the prop shaft under water.

[Captain315]

It kinda depends on what you want to do with the boat. If you want to move weight, or have some turning ability, deeper is better. The best straight line speeds are usually achieved with the prop shaft above the water. This usually requires significantly larger diameter and more pitch than what would be required to run the prop shaft under water.

Honestly, its normally used for fishing, but I also load the cooler and hit the sand bars and enjoy ripping down the lake at the same time. Theres no 'best of both worlds' I know that, am assuming at minimum a jack plate and 2 props, low water pickup, etc.... to make it perform decent in both scenarios.
If theres a potential for 5+mph gains count me in, but certainly can not justify that amount of work and expense to gain a couple mph on a 2000.00 tin can HA

End goal is 'only' 40mph, and I havent even spiced the motor up yet. Started at 16mph and have doubled that plus a bit, so in the right direction....

[NZ Sidewinder]

If you have an old expendable prop with some decent rake you can chop the tips off to form a Michigan Wheel cut.
They have a cool cup system.
I've done it to a yamaha drag and made a good prop.
The cup should mimick the MW geometry.