trying to find the correct prop

[deester]

Iboats Boat and Motor Info

1. Year, make and model of boat

2001 MCKEE CRAFT BACKWATER 172

2. Length, width and base weight of boat, look for boat decal on back of boat

17'2" 80" 1250LBS

2a.What is the maximum recommended HP for your boat

115 MAX HP---I HAVE A 90HP JOHNSON (2001) OCEAN PRO

3. Number of people and gallons of gas normally on boat

2 ADULTS 25 GALLONS GAS

4. What do you use the boat for

CRUISING--FISHING---JUST RIDING AROUND

5. Is it a Deep Vee and if so how many degrees of Deadrise

VEE HULL---16.95742 DEADRISE

6. Year, manufacturer and model of motor

2001 JOHNSON 90HP OCEAN PRO--J90VLSIF

7. HP and gear ratio of outdrive IMPORTANT
If you don?t know the gear ratio, you need to pull the plugs out of the motor and put a piece of tape across the prop and the lower unit and then cut it between the prop and the housing then do the same thing on the flywheel and turn the motor until the tape lines up with each other on the prop, it is easier if two people do this, so one can watch the prop while the other counts the revolutions of the motor

90HP--13:26 (I BELIEVE THIS IS 2.1 RATIO)

8. Manufacturer?s recommended Wide Open Throttle (WOT) range

5800--REV LIMITER IS SET AT 6400

9. Anti-ventilation Plate height above the bottom of the transom of boat if it is an outboard in inches, use a straight edge or a board under the keel and sticking out to the anti ventilation plate for a reference, and take about 4 pictures for us to see.

2 3/4" ABOVE THE KEEL

Is it a bass boat or does it have a pad bottom and is it on a bracket, if so how far does the bracket extend from the stern.

NO---NONE OF THE ABOVE

11. Does it have a hydrafoil, dolefin, whale tail or trim tabs and is the motor on a bracket, and if so how far back from the stern is the bracket

NO---NONE OF THE ABOVE

12. Manufacturer, model, diameter, pitch, number of blades and whether SS or aluminum props.
IMPORTANT


1.MAKE: STILETTO- MODEL: ADVANTAGE I,- 13 1/4X17,- 3 BLADES,- STAINLESS STEEL
2.
3.

13. WOT RPM and speed from your current prop and how much gas and how many people were in the boat for the test data and is the speed by GPS. Make sure you trim the prop up until it starts ventilating and then just trim in until it quits ventilating. If you do not have a tach you can buy a Tiny Tach for less than $ 50
RPM 5100-- Speed (GPS) 42 MPH--No. of people 2 ADULTS Gal. Gas 20 GALS

14. Are you at sea level or a higher elevation, give us the elevation in feet SEA LEVEL

15. Has your motor been tuned up lately and have you checked that the carburetor butterfly is opening all the way by only using the control on the console, checked compression, looked at the plugs and checked spark, is the bottom of the boat clean and barnacle free, and have you checked the Tachometer against a mechanics tach, all of the foregoing could be the reason your prop is not attaining full RPM.

JUST BOUGHT BOAT AND MOTOR--SO NOT TUNED UP LATELY THAT I KNOW OF--BUTTERFLY ON ALL CARBURETORS OPEN ALL THE WAY WITH CONTROL ON CONSOLE--NO TO COMPRESSION CHECK--NO TO SPARK CHECK--BOTTOM VERY CLEAN---NO TO CHECKING AGAINST MECHANICS TACH BUT I USED THE TACH THAT CAME ON BOAT AND A BRAND NEW FARIA TACH AND GOT IDENTICAL READINGS.

16. How long has this prop been on the boat and why, at this time, do you think it is the wrong prop.

JUST PUT ON FOR THE TEST RUN---NOT SURE IF IT IS THE RIGHT ONE OR NOT. I JUST REMEMBER HEARING SOMEWHERE THAT THE RPMS SHOULD BE CLOSER TO THE WOT RATE OF 5800.

17. Does the prop show any damage that you can see

NONE---IT IS A BRAND NEW ONE AND IS PERFECT.

18. What problems are you trying to cure or what are you looking for the boat to do that it is not doing the way you think it should or to your expectations

I AM HAPPY WITH EVERYTHING BUT I AM WORRIED ABOUT NOT ATTAINING A HIGH ENOUGH RPM AS I WANT THE MOTOR TO RUN AT ITS MAXIMUM EFFICIENCY FOR THE MAXIMUM LIFE AND HEALTH OF IT IN THE LONG TERM.

19. If you are trying to attain a better cruising speed and fuel savings or trying to attain a faster speed I will want you to take your boat and run it with 1 or 2 people and give me the RPM and speed readings starting at 3,000 RPM in 500 RPM increments all the way to WOT.
1. 3000 RPM
2. 3500 RPM
3. 4000 RPM
4. 4500 RPM
5. 5000 RPM
6. 5500 RPM
7. 6000 RPM

REMEMBER, The prop I recommend will be NO better than the information you give me.


THANK YOU IN ADVANCE FOR YOUR HELP!!!

 

[steelespike]

Re: trying to find the correct prop

I'm not one of the real pros but from my research and your info:
I believe your rpm range is 4,500 to 5,500.Your on the high side I don't see any problem unless you typically run with a full load.A 17 in the same model would give you a real hole shot boost but may knock a little out of the top end.

 

[Randybeall]

Re: trying to find the correct prop

You have done a fine job of filling in all the information, however, as you pointed out, the engine has not had a tune up. I would make sure the engine is in its best possible tune and a fresh tank of fuel to make a test run. If your still down on rpm, then drop to a 15" prop.

 

[trendsetter240]

Re: trying to find the correct prop

From your numbers it seems you have a very good prop already for that setup. I would feel fine about running that motor at 5100RPM, as steelspike said you are in the high range of the recommended.

If you are shopping for a spare prop, and you should always have a spare prop on board, then I would try out the 3-blade 17p BRP alum. You can pick one up right from your local Evinrude dealer. Choice number 2 would be the 4blade 15p solas amita.

Maybe hwsiii will be along to give you a better estimate.


Cheers~!

 

[deester]

Re: trying to find the correct prop

Thanks guys, I appreciate your input and I will get a good tune-up and try it again.

 

[ezeke]

Re: trying to find the correct prop

If 5100 is your maximum RPM at WOT with an average load you are over-propped and lugging the engine, shortening the life of the engine.

 

[trendsetter240]

Re: trying to find the correct prop

If 5100 is your maximum RPM at WOT with an average load you are over-propped and lugging the engine, shortening the life of the engine.

Ezeke are you certain that is the case? I've had this discussion with a number of Johnson/Evinrude mechanics and they all said that if you can turn more than the RPM where the HP is rated you are setup correctly.

I.e. recommended range is 4500 to 5500 RPM and HP rated at 5000RPM should be propped for between 5000 - 5500 RPM at WOT with an average load.

Please let me know if i'm wrong and your reasoning as my own setup is propped to turn 5700RPM with an avg load and my range is 5000 to 6000. I would like to know if I need to switch props again to push out another 300RPM.

 

[ezeke]

Re: trying to find the correct prop

Ask anyone who rebuilds motors. With fuel as it is today, you should prop for maximum of slightly over the listed full throttle range at average load to prevent lugging the engine and coking the engine.

In the instant case, he has a motor set up with maximum of 5100 RPM with a rev limit of 6400.

 

[deester]

Re: trying to find the correct prop

Does this mean I need to go with a smaller prop?

 

[deester]

Re: trying to find the correct prop

I have also talked with the previous owner and he told me that he had the motor tuned-up at the end of the summer so the motor ought to be running right. I don't know if this helps as I was told earlier to have it tuned-up and try again. any suggestions as to where to go now. Thanks.

 

[trendsetter240]

Re: trying to find the correct prop

Hi deester, I still have the same recomendation for either the 17p 3 blade BRP aluminium prop or the 15p 4 blade solas amita aluminium prop.

I can't tell you exactly what RPM you will see with these props but either will be more than your current 5100RPM. If I were to guess I'd say 5300RPM for the BRP and 5500 RPM for the solas.

I have a 3 blade 15p BRP alum. prop that performs very well with my 70hp evinrude & 17"boat.

Good luck and please post back with your results when you try a new prop.

 

[deester]

Re: trying to find the correct prop

Trendsetter, Thanks for the input and both props sound great but I was hoping to stay with the stainless steel. Would a 15 in the same prop,(stiletto advantage I) give me the rpms that I need? D

 

[trendsetter240]

Re: trying to find the correct prop

Trendsetter, Thanks for the input and both props sound great but I was hoping to stay with the stainless steel. Would a 15 in the same prop,(stiletto advantage I) give me the rpms that I need? D

Sure. That's even easier. If you buy the exact same model prop in stainless and same number of blades then a 15p should put you right at about 5800 RPM WOT.

Old RPM X (old pitch / new pitch) = new RPM. So 5100 x (17/15) = 5780

 

[deester]

Re: trying to find the correct prop

If I go to a 15 pitch and the rpms go to 5700+ won't I be above the 4500-5500 rpm level as stated by steelspike. I may have been wrong in my original post as to the 5800 rpm max at WOT. I took this level from someone that answered an earlier post as to what my motors rpms were supposed to be. What will this do to the motor? Is this a problem or will it be ok? Sorry for so many questions but I am new at this and want everything to be just right. D

 

[trendsetter240]

Re: trying to find the correct prop

If I go to a 15 pitch and the rpms go to 5700+ won't I be above the 4500-5500 rpm level as stated by steelspike. I may have been wrong in my original post as to the 5800 rpm max at WOT. I took this level from someone that answered an earlier post as to what my motors rpms were supposed to be. What will this do to the motor? Is this a problem or will it be ok? Sorry for so many questions but I am new at this and want everything to be just right. D

From what I've seen online your recommended range is 4500 - 5500. Now, it seems that the majority on this site will tell you to prop for the top of your RPM range or slightly higher.

I doubt it will cause the engine any issues and it's certainly better to prop slightly over the range than slightly under.

I like the RPM your original prop spins (5100) for the reasons I stated in prior posts.

If the new prop spins too may RPM for your liking you could always take it into a prop shop and have them add cupping which would reduce RPM.

EDIT: Also you could just ease off on the throttle a bit and run it at 5500RPM.