6 hp kicker prop suggestions

james__12345

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Jun 26, 2012
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196
I have a 1976 Johnson 6hp as a kicker on my 1648 lowe flat bottom. The current prop is a two blade 8x7 1/4. I currently am only getting 4200 rpm at wot. The prop isn't in great shape so I feel like just replacing with a new one just like it may get me closer to the 4500 which is the lower end of the range. I see here on iboats that there is a 7 pitch available, but it is a 8 1/4 diameter three blade. I get the basics of changes in prop on rpm, but between these two changing diameter, pitch, and blade count I'm at a complete loss for what the better choice would be. I'm currently getting around 6 mph from the kicker best I can remember if that makes any difference.

Also, the 4200 rpm was with 2 people which will be my usual load. But with some additions I'll be making soon (front and rear decks and a generator) the typical load will more like 4 people weight wise. How much difference does a couple hundred pounds generally make on rpm for a flat bottom with a motor that won't get on ever get on plane. Will it change things enough that I should wait on picking the new prop?
 

james__12345

Petty Officer 2nd Class
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Jun 26, 2012
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196
Boat is basically finished and I'm getting 4300 rpm from the kicker. I've kept looking for props and I can't find anything that seems like what I need. Seems that I need to drop at least 3 inches to get to the middle of the operating range and from what I've read I need to drop a bit more going from a 2 blade to a 3, so call it 4, that puts me at a 8x3.25 to hit 4900, doubt finding that prop is going to happen, so next is dropping the diameter

One inch drop is 500 rpm increase so the 1 inch pitch drop for the extra blade becomes .5 inch of diameter drop, then another 1.5 inch drop puts me at 5050 rpm with a 6x7.25 or split the difference and go something like 7x5.25 for around 5050. Of course all those numbers are rough approximations but should get me in the ballpark I think . Does anyone know of a three blade 6x7.25 or 7x5.25 that will fit this motor?
 

Bondo

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I have a 1976 Johnson 6hp

Ayuh,...... 1st thing I'd do is see what is available for props for that motor, then buy the smallest you can find, 'n try it,.....
 

james__12345

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Jun 26, 2012
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196
Al I can find officially listed for this motor is 8x7 1/4 2 blade, 8 1/4x9 3 blade, 8 1/4x7 three blade, 8 1/4x7 1/4 3 blade, 8 1/4x8 3 blalde, 8 1/4x8 1/2 3 blade, none of which are anywhere close to what I need. That's why I asked here hoping someone would know of a prop that's technically for a different motor but would still fit the pin drive of this motor. All the lower hp motors I've looked at around this year use a completely different style of prop that's plastic.
 
Last edited:

Bondo

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8 1/4x7 three blade

Ayuh,..... This one is the lowest pitch,..... A prop shop can beat the blades down at least 1" of pitch, possibly alittle more,......
 

Sea Rider

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Sep 20, 2008
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12,345
Some prop shops can beat down your current prop up to -2" which will be ideal....

Happy Boating
 

Faztbullet

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Mar 2, 2008
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15,589
Got to e careful as most shops now cannot repitch aluminum props due to manufacturing process of prop.The new press diecast props break where the old cast one bend and ding.
 

jimmbo

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May 24, 2004
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12,944
At 4300 you are within the WOT RPM range, which is 4000 - 5000 for your engine.

OMC did make a 3 blade 8 1/4 X 5" Plastic prop for that engine OMC part #386587
 

james__12345

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Jun 26, 2012
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196
How sure are you that the rpm range is 4000-5000 I had heard somewhere it was 4500 to 5500. I know that's the case for the 1986 and on 6 hp Johnsons but I'm having trouble finding anything to verify it for the 76.
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
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Jul 23, 2011
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I have a 1976 Johnson 6hp as a kicker on my 1648 lowe flat bottom. The current prop is a two blade 8x7 1/4. I currently am only getting 4200 rpm at wot. The prop isn't in great shape so I feel like just replacing with a new one just like it may get me closer to the 4500 which is the lower end of the range. I see here on iboats that there is a 7 pitch available, but it is a 8 1/4 diameter three blade. I get the basics of changes in prop on rpm, but between these two changing diameter, pitch, and blade count I'm at a complete loss for what the better choice would be. I'm currently getting around 6 mph from the kicker best I can remember if that makes any difference.

Also, the 4200 rpm was with 2 people which will be my usual load. But with some additions I'll be making soon (front and rear decks and a generator) the typical load will more like 4 people weight wise. How much difference does a couple hundred pounds generally make on rpm for a flat bottom with a motor that won't get on ever get on plane. Will it change things enough that I should wait on picking the new prop?

there is a weight capacity tag on the boat. that is 1014# total weight of motor, fuel, gear, people and stuff.

adding front and rear decks will subtract from that load capacity, not to mention make it harder for that little 6hp to do anything but putt along. adding decks and you need to subtract 1 person. adding decks will also make the boat tippy as you will be raising the CG significantly by standing

most 1648's are rated at 35hp. so you may want to step up to a real motor to push it with the added weight. generally nothing less than 50% rating (usually 75%)
 

james__12345

Petty Officer 2nd Class
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Jun 26, 2012
Messages
196
most 1648's are rated at 35hp. so you may want to step up to a real motor to push it with the added weight. generally nothing less than 50% rating (usually 75%)

I have a "real motor" The boat has a 35 on it. The 6 is a kicker motor. I know it will be slow, that's what it's for, but it still needs to operate in the proper RPM range.
 

JimS123

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Jul 27, 2007
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I used to own that very motor, so I dug out the old owner's manual.

CBHP = 6.0 @ 4500 rpm
Operating range - 4000-5000
Smallest Accessory prop = 3 blade, 8 1/4" x 5"

All of which has already been stated.
 
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