SS prop vs. Aluminum prop

[1080tommy1]

So thanks to all the input and feedback from you guys, I think I have the right prop on my boat for a heavy loaded situation. I have dialed in the rpms with a 3X10 5/8X12 aluminum prop. I say heavy load because I am still under propped slightly with the tiny tach readin 5720 WOT and my spec is 4500-5500. I would like to get another prop and would like to go with SS. I have heard that a 13 pitch SS prop is more like a 12 pitch aluminum, just wondering if this is true should I go with a 14 pitch SS prop instead of a 13 pitch. I just need to drop the rpms 200 or so and I know from reading here that would be about a degree of pitch but if a SS prop runs smaller I may go to a 14. In 13 pitch props here on Iboats, they only have a 10 1/2 or an 11 1/8 for diameter so I am thinking I could go with the 10 1/2 because if you increase pitch the diameter should decrease but the 10 5/8 prop already looks small for this motor so can I go to an 11 1/8th.

I know this comes across as sort of confusing but I am just trying to figure out which SS prop to put on the boat. I know that the prop performs really well now and it was really thanks to the feedback gained here in these forums. Just looking for some opinions on the SS prop and if a 13 pitch SS is more like a 12 aluminum?????

Thanks a lot for all the help you guys have given already and I think this will conclude the re-propping saga for me!!!!

 

[steelespike]

Re: SS prop vs. Aluminum prop

What is the speed at 5720?ss will likely lower slip,should load the motor more,finer blades should turn easier,ss may lift better allowing
more speed and rpm. final results depend on how well the al prop works and how good the ss does its thing.
Hows that for a tap dance? Depending on the present speed I think I would go 1" bigger to a ss prop.

 

[1080tommy1]

Re: SS prop vs. Aluminum prop

I kindof thought that would be the answer. I just don't entirely trust myself yet although I feel as if I have learned a great deal about getting the right prop on a particular hull and motor combo. I am going to go with the 3X11 1/8X13 SS I believe it will be a solas saturn. The other one I was looking at was the Michigan Wheel Apollo in a 3X10 1/8X13. I am not really interested in more speed at this point because when I was out this weekend, I got 34.2 MPH with two guys in the boat. I do not think the tiny tach is 100 percent accurate because I saw 5400 to 5950 rpms and it sounded to me like the rpms were definitely on the high not low side. When I tested last week with just me in the boat I was getting 5720 at 34 or 35.43 mph on two gps. The one in my phone and the one in my sonar. I do know that this is the more reliable number because I think the rpms were slightly erratic. I read the tiny tach directions and mounted exactly but the rpms seem to jump around quite a bit. At idle I am getting 850 to 900 which is just above spec which is 800+- 50. The motor is running great and the gas mileage was great as well. I think this will be the final prop and then I will keep the aluminum prop for hunting season when the boat is loaded and the SS for fishing season when the boat will be considerably lighter.

Can't say enough how much I appreciate all the feedback and advice you have provided from this site. Thanks again!!!!!!!!!!

 

[1080tommy1]

Re: SS prop vs. Aluminum prop

Well just pulled the trigger, went with the Solas New Saturn 3X11 1/8X13. I will keep you posted on performance. Thanks a lot!!!!!!!!

 

[Star]

Re: SS prop vs. Aluminum prop

The techs I have talked to say that a SS prop will increase your rpm from 200 to 250 rpm given the same dia. and pitch. I put a Solas Saturn SS 9 1/4 x 11 on my silly Mercury 15hp just to get over the hump when loaded. It did the job I wanted, but in my heart I know that it is slightly over proped. It is a very nicely made unit.

 

[1080tommy1]

Re: SS prop vs. Aluminum prop

That is awesome! I hope that my slightly higher diameter will allow for the rpms to come down slightly. With the aluminum I am only slightly underpropped with the 12 so worst case scenario I think will be rpms will not drop a full 200 and I will still be slightly underpropped. Good news is I will probably get on plane faster and get more efficiency from the increased lift and reduced throttle to stay on plane. I will post results when I get it tomorrow.

 

[Texasmark]

Re: SS prop vs. Aluminum prop

One thing no one mentioned is that the SS is usually cupped and most alum are not. That adds effective pitch to the ss that is not accounted for in the "pitch" number. The reason for the cupping is to reduce ventilation and help props hold in rough water and turns when turbulence are present. But it also increases the load hence drops rpms and reduces some of the gain you get from thin blades and bow lifting which comes with a lot of ss props.

Like Steel and others say, you never know till you try it. There are so many variables to consider there is just no way that you can say for sure this will do this and that will do that. Good luck on your purchase. And on your rpm's I run my mercs (2 cycle) 500 to 800 rpm's over the upper limit and have for 30 years. They just love it. I guess an overhead cam 4 cycle wouldn't care either. Formula 1 engines run way up there and stay together; indy engines run way up there and stay together and I suppose they are push rod engines; probably solid lifters which OB's don't have.

My 2c,

Mark