Turning point vs omc stainless

[9758JB]

Hello. I have a 70 hp johnson. When I got it it had a stainless steel omc 17 pitch prop. It had a few dings in the blades but nothing too serious. I bent and filed them out. With a full load about 2000 lbs, it would pushes me 31.5 mph at 5400 rpms.
I got this turning point hustler, 17 pitch prob. I'd figured it would be about the same but it's not. Rpms are 4600 to 4800 and speeds at 30.5 mph. It's a heck of a lot smoother now, feels really nice to drive.

2 questions, would those dings cause it to slip enough for ke to get those rpms. Someone mentioned those rmps where high for the size of boat.

Also. Is it safe and okay to run it at these rpms. Omc manual says 4500 to 5500, alot of people act like 5000 is bogging the engine, but it is a much heavier load. Not like its light.
Any help would be appreciated

 

[9758JB]

Its a 1981. Am thinking about getting a 15 pitch

 

[Scott Danforth]

Take your prop to a prop shop to have it repaired

 

[jimmbo]

Your engine, being small for the Horsepower it produces, will perform better and last longer if it propped to run as close to 5500 as possible

My math shows at 5400 rpm a 17" prop.would yield, with 10% slip a speed of about 32.5 mph
At 4600 rpm a 17 would provide 27.5 mph with 10% slip. 30.5 mph with 0% slip, which is Impossible

 

[9758JB]

Jimmbo, at that speed it was 4800 rpm. Around 29 mph at 4700 as so forth . It was just a range depending on winds

 

[9758JB]

https://forums.iboats.com/forum/gene...75-hp-evinrude

This guy kinda looks like he got something similar. Look at post #7. He lost a bunch of rpm but nowhere for then to really go... I lost about 600 to 800 rpm and have the same pitch prop. The stainless seemed to have low slip... I'm confused where my rpms are going

In this same thread it is stated that since this is a cupped prop. You add 1 pitch for wot. So making it an 18 giving 10% slip at 30.5 mph, rpm at 4800

 

[dingbat]

This guy kinda looks like he got something similar. Look at post #7. He lost a bunch of rpm but nowhere for then to really go... I lost about 600 to 800 rpm and have the same pitch prop. The stainless seemed to have low slip... I'm confused where my rpms are going

If what you say is true, the stainless prop has significantly more slip than the aluminum. The slip is masking what I suspect is the need to drop another couple of inches of pitch if you stay with the aluminum prop.

Always prop to the top end of the WOT range if possible. Your motor will thank you for it

 

[9758JB]

If what you say is true, the stainless prop has significantly more slip than the aluminum. The slip is masking what I suspect is the need to drop another couple of inches of pitch if you stay with the aluminum prop.

right, that was my thoughts. This prop isn't to terribly bad, atkeast I thought, but it was deffinently off balance and I can feel that now. Out of the hole shot with the stainless was scary fast... maybe that's why bc it slipped so much and got rpms up.

I was always told stainless acts like its 2 pitches up vs an aluminum. Idk how true that is. If it works that way, the stainless would be slipping 22% maybe that's where some of my rpms are going? I lost about 800 max. 600 for normal operation

I could get the stainless repaired, and wouldnt mind fixing it, but wouldnt it drop rpms in that case?

Thanks for the replys guys. Ik I ask alot of questions on here but you guys ate great

 

[dingbat]

I could get the stainless repaired, and wouldnt mind fixing it, but wouldnt it drop rpms in that case?

In theory, yes it would.

The only way to "increase" RPM without an increase in speed is slip.

Not sure what you mean by "normal operation". You prop for max. rpm and everything else falls in place.

What is WOT of both props?

 

[mstotler8]

etht

 

[9758JB]

In theory, yes it would.

The only way to "increase" RPM without an increase in speed is slip.

Not sure what you mean by "normal operation". You prop for max. rpm and everything else falls in place.

What is WOT of both props?

I mean normal operation as wind snd load size. Normally will drop about 100 to 200 rpm if winds are up and I have a few extra ppl on board

With the stainless 17. Wide open is 5300 to 5400.
aluminum 17 is 4700 to 4800

Someone mentioned the stainless may of had a pitch change.. but tbh the casting looks unchanged. I feel like I'd be able to tell. But maybe not

 

[Stinnett21]

Just to confirm, you are talking about a 3 blade Hustler correct? The Hustler comes in a 4 blade also which would explain some of your results.

 

[dingbat]

I mean normal operation as wind snd load size. Normally will drop about 100 to 200 rpm if winds are up and I have a few extra ppl on board

With the stainless 17. Wide open is 5300 to 5400.
aluminum 17 is 4700 to 4800

Someone mentioned the stainless may of had a pitch change.. but tbh the casting looks unchanged. I feel like I'd be able to tell. But maybe not

I looked around but nowhere do you say what boat this motor is on.

In an earlier post you said something about a 13-3/8" diameter. Is this aluminum 13-3/8" x 17" or 14.25" x 17?

An inch increase is diameter is a lot given the HP of your motor

 

[9758JB]

Both are 3 blade
The stainless is 1/8 inches LARGER. The aluminum is 13.25 inches. So stainless is 13. 3/8

Boat is older trihaul. Can be about 2000lbs full load(boat motors people ect.) But never and rarely over.
Thanks

 

[Texasmark]

"Artificial slip", a term I just coined, is due to "porting"....holes under the leading edge of the blade. In the hole shot you usually are thrust limited due to the load placed on the engine by the resistance of the hull attempting to get out of the water. Porting, adds compressible air/exhaust to the medium in which the blades turn allowing for faster acceleration of the rpms which are one element of determining HP and HP on the Prop shaft is what gets you the thrust to get out of the hole.

I have 4 Turning Point Hustler props. All are ported, have rake, and are cupped in 3 and 4 blades for about a hundred bucks a prop....iboats sells them. TP props advertise the attributes of stainless with the economy of aluminum. Only thing they are missing is matching the thin blade that stainless can give you....rake, cupping, porting are all there. Unless you are running a hot mill running 65 mph, thin blades aren't all that big of a treat (opinion). On what does what, go to the top of this page and look under the tutorial on prop performance.

 

[9758JB]

Just wanted to give anyone who was curious an update. I ordered a new turning point prop from here at iboats. This one was 13.75 ×15

I noticed the blade geometry instantly was quite different then the one I got at the marina. not sure if that's bc it's a pitch change or they changed there mold. One from marina was a H2. This one from iboats was an LE. Although that's just if anyone was curious.

This new 15 brought my rpms up to 5300. And this was over some rough waters I do say. About 31 mph top speed. Handled really good. I noticed it had a similar speed to rpm ratio as the stainless but the turning point stayed on plane way better. Went on plane about the same time as the stainless too. Not sure if the stainless was modified to a 15. Regardless out of the two the turning point handled way better in all factors. Steering, low speed acceleration ect.