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09-26-2024, 10:27 AM #1
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Noob hacking up props in quest for speed
Got hooked up with a crazy Aussie dinghy racer online and hes been walking me through some prop shaping. Trying to get some more speed out of this 1436 Jon which peaks about 5300-5400rpm and 33mph. (Stock Suzi 30hp 2 stroke triple)
I raised the motor to where the stock solas 14p had no chance and ended with cav plate 2.5" up and went to work. First work netted me a 1mph loss and 400-500rpm drop, if I knocked any cup out id gain 100-200rpm back and slip bad.
Second prop I cut up was a cheap 10p which required a heavy, tight radius cup. Went 300rpm down and 7mph loss, thing was an absolute turd!
Plan to build a zero setback jack plate over the winter and can try getting a bunch of prop above the water, but until then I dropped the motor back to where a stock prop will run (1.5 up) and want to continue playing at submerged height where a ton of cup shouldnt be required.
In completely unchartered territory here, so would love some additional advice, ideas, education! Stainless props are out of the question as I run some skinny areas with a lot of rocks and submerged log mines. Thanks in advance!
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09-26-2024, 01:05 PM #2
Put cup in some of my race boat props years ago at the races. A trailer hitch ball and a ball peen hammer and you're good to go.
2005 APR FORMULA 2 ROOKIE OF THE YEAR
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09-26-2024, 01:18 PM #3
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09-26-2024, 03:17 PM #4
Stainless props will survive the rocks and logs better than an aluminum prop will.
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09-26-2024, 05:16 PM #5
Coat the blades in lipstick and take it out for a hard run. Wherever the lipstick remains? Cut off those parts. Then cup and shape etc.
Hydrostream dreamin
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09-26-2024, 06:33 PM #6
I like aluminum..
The good is, aluminum props are easy to work and stainless are not.
Largecars post it spot on.
Yrs ago I did a 13’ Whaler w/a 50 hp OMC on it.
Bought every stainless prop ever offered for that motor and was fastest w/an aluminum wheel I beat cup into w/a hammer.Last edited by Instigator; 10-01-2024 at 06:17 PM.
I'd rather be competitive w/junk I built in my garage than win w/stuff I bought.
I refuse to allow common sense to interfere w/my boat buying decisions.
Checkmate 16' 140 Johnson
Hydrostream 17' Vector FrankenRude I
Laser 480 (?) 21' w/GT 200
Glastron Carlson Conquest w/XP 2.6
Glastron Carlson CVX 20 w/XP 2.6
24' Sonic w/twin 250 Johnsons
24' Sonic w/twin 250 HO Johnsons
19' STV River Rocket w/FrankenRude II
Allison XR 2002 w/Frankenrude II
Hydrostream 18' V-King w/Frankenrude II
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09-27-2024, 12:14 PM #7
6000 RPM
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10-01-2024, 07:01 AM #8
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Appreciate the info fellas. We got hit HARD by hurricane Helene and my testing/fishing lake is a mess, so things will be delayed a bit. Lake is fed by a river which starts in the mountains 1-2 hours away and there are entire towns wiped off the map up there and a lot of folks still missing, so I am not complaining.
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10-01-2024, 07:05 AM #9
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Im pretty new to this, but that appears to be the case with real power, not so much with little 20-30hp tillers. The dinghy racing boys are doing some crazy stuff with aluminum props. Really rather not wipe out a gearcase, lot of parts for these 90s Suzuki's are made out of unobtanium.
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10-01-2024, 09:14 AM #10
I guess it depends how fragile the gearcases are... we've seen rocks split in half and 4" logs chopped into foot-long sticks by stainless props.
Aluminum are easier to fix and easier to wreck.
The thicker aluminum blades are just not "efficient" though... and you thin them they flex and flatten out.
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10-01-2024, 09:25 AM #11
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These Suzi gearcases appear to be pretty tough as I dont see too many things on the webs about them exploding. Stainless MAY be an option one day, but certainly more cost effective to cut up and potentially (likely) ruin a handful of 50.00 aluminum props vs 250+ stainless. Least til I learn what the hell I'm doing HA.
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10-01-2024, 02:14 PM #12
I like Kirchner's wood hack. I use a large round of wood as a backer, and a 2lb brass hammer. Start with a larger diameter blade than what you need, but near the pitch you desire. Do as much work as possible on the back side of the blade, minimize grinding on the face of the blade. Square the trailing edge. Leave a 220-400 grit finish. Lakefever's lipstick trick is a good idea that will give you a idea of where you can cut (backcut, or detongue) without losing effiecenty. There's alot of info about shaping model boat propellers on the web, much of this will cross over to a full size propeller.
I would get your engine mounting height, and water pickup sorted before going too crazy building props. The higher the engine requires more diameter, pitch or blade count
I don't know if this is who the OP has been talking to, but this is a good video of a extreme prop rework.
https://youtu.be/wCCUClvZhEA?si=-ciy-IWU4l-RdK0c
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10-01-2024, 06:25 PM #13
Sorry, my earlier post was fubarred.
Clamp a pc of a wood 2” x 4”, vertical in a vice.
Use a corner of the 2 x 4 as your pitch block.
Hold/position the prop, on the block while using the hammer in your other hand while you beat it.
Move the prop as you add cup.
Add more cup as you go and rotate between blades until you get them to match.
Cool thing is, tin props are cheap so if you screw one up…., so what?
Have fun!Last edited by Instigator; 10-03-2024 at 05:44 AM.
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10-02-2024, 06:36 AM #14
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Appreciate all the advice! The lipstick idea is awesome, reminds me of the old 'paint the header collector extension and cut where it burns off' trick. Had no idea RC boat prop shaping can apply to bigger props. Hopefully be able to get back on the lake soon and put some of this stuff to the test!
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10-02-2024, 07:08 AM #15
Wow paint the collector trick! That’s old school stock car stuff I haven’t heard about that in more years than I care to admit. I suppose you are correct though the lipstick trick is a similar trick. Fun thread hope you get some great gains. That aussie guy with his little motors sure impressed me
another thought worth mentioning is the front face of the prop blade is all that matters. The backside of the blades only job is to support the load from the front side of the blade. That’s what I learned from one of the seasoned pros on here along the wayHydrostream dreamin
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