Right ss prop for 40hp/16ft. Have testing data

[FishingMotor]

Hello and thank you for reading

I have a 1990 mariner (yamaha built) 2 cyl 40hp, mounted on a light 16ft mod v flat bottom. The engine has been moved up on the transom so the caltivation plate skims the top of the water over 4000rpm light load, *and runs 1/4" below under heavy loads. Max engine rpm 5700. I have tested 3 aluminum props and now I want to switch to a SS prop

Oem prop 12p 51kph@5750rpm light load 48kph@5500 heavy load

Prop has no cupping, slips more than the other two did. Hard time raising the bow as much. Over 5300rpm I think slip is greatly increased. However it made the most out of the engine

Quicksilver 11p over revs at 3/4 power
Holds the bow up nice

Quicksilver 15p 46kph@5000rpm light load, 42kph@4800rpm



So in review I am getting the right engine speed with my 12p but I don't think I am transferring all the power to the water. The engine comes on very strong between 5200-5700rpm and I think the 12p is slipping I don't know where it start for the right pitch in a SS prop. I have no clue if a 12,13,14p would give me what I am looking for.

I would be happy with 55kph@5700 light , 50kph@5500 heavy.

Thank you for your help

 

[TX-17]

Re: Right ss prop for 40hp/16ft. Have testing data

I am a novice, but it sounds like a SST 12 Pitch would be the right answer on a couple of levels.
Going with a Stainless Steel 12 pitch should drop your RPM's between 2 and 400 RPM, which would put you in the sweet spot.
Being a shiny new prop, you would have the advantage of great hole shots on the bottom end and max MPH at the higher end.

You would not be bogging the engine at WOT and your would not have pistons tripping over themselves as they try to reach beyond your red line. You could load your boat to the max and still get on plane very quickly..

Although I am not a strong proponent for stainless steel props on smaller engines, I feel you will be making a wise choice for your application.

Let's wait for the experts on here to voice their opinion, but if it were me I would make the SST decision and jump out on the water.
Cupping along with the thinner blades will make a noticeable difference.

Or, I would stay put with the OEM... Perhaps a new aluminum one won't slip as much and it sounds like you are within a few KPH of a near perfect match...

 

[FishingMotor]

Re: Right ss prop for 40hp/16ft. Have testing data

Thanks tx-17

I am now thinking about buying a Stiletto triad II in a 12p. Looking over the props for sale on Iboats, I was thinking it looked good, but what do I know

Any further feedback?? Does anyone else think I may need another pitch??

Thank you!!!

 

[MARV1]

Re: Right ss prop for 40hp/16ft. Have testing data

Go with a 13 or 14 SS, my experience is they gain RPM over aluminum...

 

[steelespike]

Re: Right ss prop for 40hp/16ft. Have testing data

If your gear ratio is 1.85 your slip is about 10% at 5750 and 31.69 mph.A respectable number.
I also think a 13" ss prop should improve things.

 

[Sea Rider]

Re: Right ss prop for 40hp/16ft. Have testing data

According to Iboats Prop Finder : Stainless steel boat props are ideal for large or heavy boats and those running in saltwater. Although more expensive than aluminum, stainless steel is more durable and will last longer. When running at speeds over 50 mph, stainless props will perform better than aluminum.

It's just a 40 HP achieving 48-51 K/H not M/H or knots...You decide.

Happy Boating

 

[FishingMotor]

Re: Right ss prop for 40hp/16ft. Have testing data

I have ordered a 13p SS prop..... couple weeks to get to Canada and I will post my new numbers. fingers crossed for 55 kph!

 

[TX-17]

Re: Right ss prop for 40hp/16ft. Have testing data

Double post

 

[TX-17]

Re: Right ss prop for 40hp/16ft. Have testing data

I, for one, will be very interested in your success!
Although I still believe going with a Stainless Steel 12 pitch would have dropped your RPM's between 200 and 400 RPM, which would put you in the sweet spot, I also agree your engine should easily pull the 13 pitch which should bring your RMP's down another couple of hundred.
If you trim the engine right, you may very well be looking at 5,300 RPM. If you can pull 5,300 RPM you could be at 54 kph (perhaps even higher due to the cupping and the thinner blades that do not slip as much), but now you will not be over revving. I agree that the 13" Stainless Steel Pitch will be your best choice for your highest kph..
Your hole shots are going to be noticeably better and your engine will thank you..
Give us a real good run down on your impressions.. 55kph would be a really nice surprise and I believe is in the realm of possible, if trimmed just right, the load is light, the gas tank is on its last two gallons and the water is cooperative. 55 kph (GPS) both ways will impress us all..

Now you have me looking at my aluminum prop and thinking SST... If you hit 55 I will probably be ordering one too..

If it works for a big engine, it should work for the smaller ones (Just not as rewarding)

Now, if all you get is 51 kph, you will still have made a very wise decision for the long haul..

 

[dazk14]

Re: Right ss prop for 40hp/16ft. Have testing data

Which brand/model/size (incl diameter) did you purchase?

With a progressive pitch, cupped prop, I think you'll be very pleased compared to the stock prop.

Turning point and Stiletto make pretty good ones in that size range.

 

[FishingMotor]

Re: Right ss prop for 40hp/16ft. Have testing data

Thanks to everyone for all the great input.

I have ordered a 13p Stiletto triad II, 10.25" diameter (same as others tested)

I have been testing with a GPS and digital tach attached to #1 cylinder

the new prop will be tested the weekend of August 3 and I will post lots of feedback. Speed is not the only issue I am looking to correct. My OEM prop can blow out at high speeds, it doesn't hold the bow up nicely like the wrong pitch more aggressive quicksilver props I have tested.

fingers crossed, and come on UPS bring me my Prop!