Prop damage and small motor - effects?

Here is the just of it.

Basstender 10.2 - 10' Plastic semi tri-hull boat
'73 Evinrude 6hp

worked on it for a month but could not get RPM's above 2K (if that fast) Did everything in reason to motor. Some things 2 times.

On Recommendation from here - Changed Prop to 8x5p
Motor runs up quick, rpm good and boat moves 2x faster (8mph)

Now: The original 2 blade 8x8p prop looked really bad. Pitted, hammered, cracked on one blade and possibly twisted or bent.

What I am wondering is if the prop itself was the cause of all the issues? The boat mfg. recommends 7hp Max so the basic 6hp should perform @ under 50% max load.

My Question now is.......... Was it the Boat/Prop pitch causing low rpm and no speed(4mph max) or was it possible the Prop damage causing loss of power?

Can a 2 blade prop cause enough turbulence as to kill RPM and forward movement?

I am happy that it is running better than when I began but I would love to be able to get more speed out of it without killing the RPMs again.
My only alternatives to the prop I now have are a 8x7.25p or 8x8p prop?

Any recommendations, theories, thoughts?

Re: Prop damage and small motor - effects?

If your prop was all messed up it sure could cause problems for a small motor.
Have you double checked that both cylinders are actually working.Try running the motor with plug wires alternately unhooked and grounded?
Your motor should be able to plane with a 180 pounder driving.12 or 13 mph.
Perhaps the boat shape is not condusive tp planing.
You may need a tiller extension so you can sit in the middle seat.
You might consider a Jon boat I don't like them but they do get up on the water easily. We had a 12' steel flat bottom with 5hp Bucaneer and a tiller extension it would pop on plane with a 180 pounder.

Re: Prop damage and small motor - effects?

I had to put an 8 HP on mine to get it plane, but it planed great with that motor even with 2 people and a bunch of gear, inlcuding a battery and a trolling motor on the bow. Total weight of people and gear about 625 pounds.

H

Re: Prop damage and small motor - effects?

Interesting........ Maybe it would be worth investing in another prop to see if it improves or not. Guess I can always sell it if things don't work out.

Yes, firing on both cylinders and 80psi compression on both with rope pull. Been using it most weekends this summer.

Re: Prop damage and small motor - effects?

Cr, since you don't have a tach we have no ideas how many RPM you were turning with the 8 x 8" prop but lets guess at 4,000 RPM.
When you changed to a 8 x5" the RPM would have increased by right at 2,400 RPM if the 8 x 8" was in good shape.
Changing from the 8 x 5" to a 8 x 7.25 lets guess they are at 5,500 RPM now will lower your RPM to right at 3,800 RPM. But all this is just guessing because we have no Base RPM to go by, that is why it is good to have a tach, it gives you a basis to judge how your engine is doing.
A Tiny Tach only cost about $ 50. Without one it is only supposition not reality.


H

Re: Prop damage and small motor - effects?

hwsiii........ you just answered my question. I've raced 2stroke motorcycles for years and gotten a good feel for what the motors are doing.

Right now the 6hp is running about right around 4800. I guess the hull design is the killer. It is not a planing hull.

I'll stick with what I have for now.

Thank you

Re: Prop damage and small motor - effects?

How do you know its running at around 4,800 RPM?

Re: Prop damage and small motor - effects?

ondarvr said:

How do you know its running at around 4,800 RPM?

Click to expand...

A borrowed timing Snap-on light/tach.

Re: Prop damage and small motor - effects?

That's about the best answer I can think of.