Prop advice to reach 6000RPM - Negative Slip?

[trendsetter240]

I've got two props that I have just got back from testing performance on my newly rebuilt motor. I need to find a new prop that will get me up to 6000RPM at WOT.


Boat:
1969 Slickcraft SS170V, 17ft, 1600lbs to 2000lbs Fully loaded, boat, motor, fuel, passengers and gear. Deep V 17 degrees of deadrise, max 100HP.

Motor:
1995 Evinrude ELEO 70HP. Completely rebuilt and running excellent. 15hrs since rebuild. Recommended WOT range 5000RPM to 6000RPM. Anti-ventilation plate 1 inch above bottom of hull and clearly visible when planing.

Uses:
River and ocean fishing in the pacfic northwest.

Goals:
Maximum fuel economy and correct RPM range for longest engine life.

Props and results with light load setup:

#1 Turning Point Hustler H2-1317 13.25X17 Alum. 3 blade = WOT 5100RPM

#2 OMC 14X17 Alum. 3 blade = WOT 5500RPM (Drops to 5300RPM with increased weight)

The above results are tested with the lightest load that will ever be in that boat. Just myself, 5 gallons of fuel and minimum saftey equipment and tools. Adding an Extra 2 people, extra fishing gear and 18 gallons of fuel brings the RPM down to 5300 at WOT with the OMC prop.

I'd like to find a prop that will put my WOT RPM at about 6000RPM with a light load. That would leave me some breathing room and hopefully keep me between 5700 and 6000 when I load up the boat for long trips.

My first thought was to go with a 15P 4-blade Solas Amita Alum. prop. However I am not certain that I will get the RPMs I need from that prop.

Any advice is much appreciated.

P.S. I don't have speed numbers as a GPS is not available to me at this time.

 

[steelespike]

Re: Prop advice to reach 6000RPM

Re: Prop advice to reach 6000RPM

A rough rule of thumb 1" pitch change nets about 200 rpm,assuming same brand same model prop.Unfortunately without some speed results its difficult to be sure of your performance.You do need to be closer to that 6,000 rpm figure.
A 2" pitch change could net 400 rpm putting you at about 5700 with the same omc prop in a 15".I do see the Solas amita 4 blade being recommended with good results.
Should plane easier and stay on plane with less power.Usually the 4 blade will lower your top end slightly and could dampen the rpm.1600 lb boat is a load for a 70.I think a 13" pitch would be closer to what you need.If it ends up over reving you could throttle back with a light load.Should be a vast improvement over a 17".

 

[trendsetter240]

Re: Prop advice to reach 6000RPM

Re: Prop advice to reach 6000RPM

A rough rule of thumb 1" pitch change nets about 200 rpm,assuming same brand same model prop.Unfortunately without some speed results its difficult to be sure of your performance.You do need to be closer to that 6,000 rpm figure.
A 2" pitch change could net 400 rpm putting you at about 5700 with the same omc prop in a 15".I do see the Solas amita 4 blade being recommended with good results.
Should plane easier and stay on plane with less power.Usually the 4 blade will lower your top end slightly and could dampen the rpm.1600 lb boat is a load for a 70.I think a 13" pitch would be closer to what you need.If it ends up over reving you could throttle back with a light load.Should be a vast improvement over a 17".

Thanks steelespike, I guess what I am worried about is how the change in prop manufacturers and therfore blade design is going to affect me.

For example there is already a 400RPM difference between my two 17p, 3blade alum. props. I read elsewhere from hwsiii that you can calculate the difference in RPM by "Old RPM X (old pitch / new pitch)".

So let's say I picked up a Solas 15p 3 Blade Alum. This could equate to 733 RPM increase from the OMC or 680 RPM increase from the turning point hustler.

So I guess a better question might be anyone out there run a 16.5 to 17 ft deep-v runabout with a 70hp outboard? If so what props have you used and with what results?

Cheers and thanks for any and all replies.

 

[steelespike]

Re: Prop advice to reach 6000RPM

Re: Prop advice to reach 6000RPM

The Turning point is a very aggressive prop.I think that could account for the different rpm with the same pitch.Checking the 75 hp 3 cylinder etec on boats about 800 lbs they run 15" and 17" props.Running about 5,400 rpm.thats a 3 cylinder with a 2.00:1 gear ratio.rated 4500 to 5500 rpm.Not exactly the same animal but I think
its signifigant running a 15 or 17" pitch on about a 800lb boat.

 

[trendsetter240]

Re: Prop advice to reach 6000RPM

Re: Prop advice to reach 6000RPM

The Turning point is a very aggressive prop.I think that could account for the different rpm with the same pitch.Checking the 75 hp 3 cylinder etec on boats about 800 lbs they run 15" and 17" props.Running about 5,400 rpm.thats a 3 cylinder with a 2.00:1 gear ratio.rated 4500 to 5500 rpm.Not exactly the same animal but I think
its signifigant running a 15 or 17" pitch on about a 800lb boat.

That's a good point, they are very similar in that they are putting out about the same HP. Mine is lighter though at 237lbs and my gear ratio is 2.65:1.

I think I will give a 15P prop a try as I think the 13P might take too much off the top end for my setup. I had a Solas 3blade 13P on a 25HP motor I used to own and it was great. So I'm thinking a 15P solas will be a good start.

Thanks for your help.

EDIT: Correction, my gear ratio is 2.41:1 (12/29). oops.

 

[steelespike]

Re: Prop advice to reach 6000RPM

Re: Prop advice to reach 6000RPM

Yes yours is a lot lighter and smaller displacement probably accounts for the different ratio.
The 15 should surely improve your hole shot and add some rpm, will be interesting to see.Going with a different brand does introduce another variable that may affect results.May be plus or minus.Lets us know what you find.

 

[trendsetter240]

Re: Prop advice to reach 6000RPM

Re: Prop advice to reach 6000RPM

Well, I bought a new prop today from my local evinrude dealer. It's a BRP 13.5 X 15P 3 blade alum. I decided to go this route it was relatively cheap and I'm impatient

I ran test runs today and the new prop will just barely turn 5700RPM fully trimmed out. I guess this makes sense because the new BRP design is closer to the TP Hustler prop than the older OMC prop I have. So about 600RPM gain.

The biggest difference I noticed was the power the engine had between 4000RPM and WOT. I was out in the ocean with some decent rolling waves and this prop felt like it would bite right into the water and gave great control in that range. Hole shot and low speed handling were also improved.

With regards to speed, I still have no GPS so I can only speculate. It felt about the same, maybe a tad slower than the 17p props. Not much difference at all. That could be attributed to significantly less slip with the BRP 15P. Have to wait for GPS to see.

Once I have a GPS again I will run proper test with all 3 props to see exactly what's going on.

 

[kenmyfam]

Re: Prop advice to reach 6000RPM

Re: Prop advice to reach 6000RPM

Any of these props in question "cupped"

 

[trendsetter240]

Re: Prop advice to reach 6000RPM

Re: Prop advice to reach 6000RPM

Any of these props in question "cupped"

Yes all the props had some degree of cupping. The most being on the older OMC 14x17P and the least on the new 15p BRP.

 

[bob johnson]

Re: Prop advice to reach 6000RPM

Re: Prop advice to reach 6000RPM

I dont know if this info will result in anythign for your application...but..

I have that 14 X17 OMC aluminum prop as well..it came on my 1997 90 hp evinrude

but I tried it on my 1995 115 hp johnson on a 2070 low mod V with a 12 degree dead rise, weighing about 1100lbs.

that prop was only giving me 5300 RPMs at WOT and 38 MPH...unladened

I also had a SS 13.75 X 15 prop and tried that....it gave me 6200 RPMS !! at 39 MPH!!!!

my point is to try a SS prop..might pick up RPMs with out the drop in speed...


bob

 

[trendsetter240]

Re: Prop advice to reach 6000RPM

Re: Prop advice to reach 6000RPM

I dont know if this info will result in anythign for your application...but..

I have that 14 X17 OMC aluminum prop as well..it came on my 1997 90 hp evinrude

but I tried it on my 1995 115 hp johnson on a 2070 low mod V with a 12 degree dead rise, weighing about 1100lbs.

that prop was only giving me 5300 RPMs at WOT and 38 MPH...unladened

I also had a SS 13.75 X 15 prop and tried that....it gave me 6200 RPMS !! at 39 MPH!!!!

my point is to try a SS prop..might pick up RPMs with out the drop in speed...


bob

Hey bob, thanks for your reply.

Yes I've been thinking about trying a SS prop but it's a little expensive to experiment at 300+ per shot. Couldn't find a local shop that had any SS props that I could try out without buying. They didn't have return option either.

What brand SS did you use? Also how many blades?

I was considering the Solas HR Titan 4-blade SS prop from iboats.com.

 

[bob johnson]

Re: Prop advice to reach 6000RPM

Re: Prop advice to reach 6000RPM

I dont know the brand...it actually came off a 1988 evinrude 70 hp i had bought, but took apart to rebuild. it is three blade.

it is a broad leaf design , much different than the pointy type blades on the 14 X17 aluminum prop..

bob

 

[trendsetter240]

Re: Prop advice to reach 6000RPM

Re: Prop advice to reach 6000RPM

Just got back from another few hours on the water. I have to say I am impressed with this 15p BRP prop. Performance is good, hole shot, handling and top end..everything is good enough that I can't complain.

So I will keep this as my main prop even though it will only reach 5700RPM. I don't believe I would see enough of a benefit from a SS at this point to justify the expense.

One thing I will try however is raising the motor another hole. Right now it does not vent even under full throttle turns until after the apex of the turn. that will put the anti-vent plate at 2" above.

Thanks all for your advice and happy boating

 

[kenmyfam]

Re: Prop advice to reach 6000RPM

Re: Prop advice to reach 6000RPM

Just got back from another few hours on the water. I have to say I am impressed with this 15p BRP prop. Performance is good, hole shot, handling and top end..everything is good enough that I can't complain.

So I will keep this as my main prop even though it will only reach 5700RPM. I don't believe I would see enough of a benefit from a SS at this point to justify the expense.

One thing I will try however is raising the motor another hole. Right now it does not vent even under full throttle turns until after the apex of the turn. that will put the anti-vent plate at 2" above.

Thanks all for your advice and happy boating

Make certain you are still getting enough cooling water if you raise the motor. I have "de-cupped" a couple of props to increase WOT RPM with good results. You could experiment with one of yours.

 

[trendsetter240]

Re: Prop advice to reach 6000RPM - Negative Slip?

Well I got a new GPS and went and tested the props out again. The new BRP prop comes up with a negative slip number? Could this be from the cupping on the prop? I read somewhere to add 1" pitch for a cupped prop. When I add the 1" my slip is still only 4%....

Any thoughts?


DATA for the BRP 13.5X15P prop. I added the second set of data to see what the numbers would be if the cupping made the prop 16p.

 

[trendsetter240]

Re: Prop advice to reach 6000RPM - Negative Slip?

And here are the numbers for the 14X17 OMC prop. I also included the numbers if the cupping on this prop were to add 1" pitch.

 

[kenmyfam]

Re: Prop advice to reach 6000RPM - Negative Slip?

Add approx 1 inch for cupping.

 

[v12mac]

Re: Prop advice to reach 6000RPM - Negative Slip?

I thought BRP had an "Orange" Loaner or trial prop program?

 

[trendsetter240]

Re: Prop advice to reach 6000RPM - Negative Slip?

Add approx 1 inch for cupping.

Thanks. So that means my 13.5X15P BRP prop has approx 4% slip at WOT. This is very good

 

[trendsetter240]

Re: Prop advice to reach 6000RPM - Negative Slip?

I thought BRP had an "Orange" Loaner or trial prop program?

Not at my local Evinrude Dealer. They had some used props that I could have bought and returned if they didn't work out. Unfortunately they didn't have any in the size and pitch I wanted.