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Prop size. 1985 Thompson 4.3 Alpha one

J

JRemington

New member
Hi Everyone. I just purchased the above named boat with a chipped prop. It says 15 by 17 pitch. Just wondering if this is the correct size. The boat will be used for fishing. The boat is a 21 foot deep V. Thank you in advance. Jeff.
 
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Hi Jeff,..... Prop pitch is perfect when it allows the motor to reach the proper rpms at Wot,..... usually at or near 4800 rpms,....
 
Some folks (like me) run a bit less pitch than is optimal. It provides easier plane off, especially with a load, and doesn't hurt cruising speed that much. Since I do NOT run above half throttle so it doesn't get a chance to over rev.

Jeff
 
I took her out last night with a new 15 by 17 prop. I could have easily gotten it to 5500 RPM’s. After it planed off I backed down to about 3500. Does 5500 seem to much?
 
JRemington said:
What is you guys opinions on 4 blade props? I’m having no luck finding a used 15 by 19 so I guess I’ll have to buy another new one.
Click to expand...

Ayuh,..... Forget about the diameter, 'n look for the Pitch you want,.....

As pitch goes up, diameter goes down,..... our 19" pitch props are more like 14.5 diameter,....
 
In your case, the ideal setup would be the largest diameter prop you can find with a correct, much lower pitch.

Jeff
 
bondo said:
Ayuh,..... Forget about the diameter, 'n look for the Pitch you want,.....

As pitch goes up, diameter goes down,..... our 19" pitch props are more like 14.5 diameter,....
Click to expand...
I was wondering about that. I’ve ran across a couple 14.5 by 19 or 21 I could get for $40.00 dollars.
 
JRemington said:
What is you guys opinions on 4 blade props? I’m having no luck finding a used 15 by 19 so I guess I’ll have to buy another new one.
Click to expand...

I prefer four Blade props because they fit how I use my boat better. Most of my use is loaded down watersports- skiing, wakeboarding, or tubing. I have found I get better hole shot, stern lift, and slower planing speed with a 4 blade. You do loose about 3-4 mph top speed but that is such a small % of my use

I had really hood luck with Michigan vortex aluminum four blades which even new are relatively cheap compared to stainless
 
bondo said:
Ayuh,..... Forget about the diameter, 'n look for the Pitch you want,.....

As pitch goes up, diameter goes down,..... our 19" pitch props are more like 14.5 diameter,....
Click to expand...
I was wondering about that. I’ve ran across a couple 14.5 by 19 or 21 I could get for $40.00 dollars.
 
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