Do stainless steel propellers actually make your bot go faster?

[Cruzieduzie]

Looking to get one for my 9.9hp mercury, wanna be able to put a bit more weight in my inflatable and still be able to plane.

 

[harringtondav]

Opinions differ here. But at 9.9 hp I say not worth the cost. SS is more rigid than aluminum, so it flexes less. This can be a benefit for higher hp. engines/motors. You goals are self cancelling. More weight robs top end speed in most boats. It is a trade off. And propeller pitch and power are the variables, not material so much. Less pitch gets you on top of the water quicker. More pitch gives more wide open throttle (WOT) speed. Your 9.9 OEM prop/pitch is probably the best you can do.

 

[rallyart]

My 11' inflatable with inflated keel would plane with a 4hp 2 stroke and one person. A 9.9 should move most well.
I love stainless props and they have made a speed difference on my boats while on plane. Not much difference getting on plane. However, I don't think I'd put one on a 9.9. It's a heavier prop and quite a bit more money if you are just trying to carry more load. A tab on the transom or foil on the engine will get you planing quicker and at slower speeds than just putting on a SS prop.

 

[Scott Danforth]

other than a lighter wallet, you wont notice anything on a 9.9. now if you had 30 times the amount of power, it may be worth looking at.

 

[Chris1956]

OK, I'll bite..Why would the material the prop is made of make a difference in speed, if they have the same diameter and pitch and overall design?

 

[Scott Danforth]

usually the stainless is stiffer, resulting in less deflection, so the slip numbers are better.

also, the stainless is generally thinner, resulting in less drag.

However its only about a mph or two at the very top end. However in this case with under 10hp, wont make a difference.

 

[Sea Rider]

Instead throwing money into the deep blue buy an induction tach, install it and test the motor at wot as usually loaded on flat calm water cond to check the max wot rpm achieved, will know if the motor runs inside its min-max wot rpm range factory stated, probably running towards the lugging rpm range if not lightly loaded. If wanting to squeeze the max HP out of that motor must run towards it's max wot rpm range. A maximixed 3 blade alum less prop pitch from current installed one if it was the factory delivered with said motor will do the trick...

Important to know :

What's the lenght of that inflatable, is it a Sib or Rib, which current numbers are stamped on the prop body or blade. How many more passengers/load do you plan going boating with as from now ?

Happy Boating

 

[Cruzieduzie]

Length of the boat is 10.5ft

 

[roffey]

Scott is right a SS prop on a 9.9 will not make a difference. In fact a aluminum prop is better as it will bend easier when or if you touch bottom and a SS prop might bend the shaft. I put a SS prop on my boat and other than it looks shiny the juice ain't worth the squeeze...

 

[Cruzieduzie]

searider i plan on having 4 people including myself on the boat, but it only planes when there are 3 or less ppl on the boat. It seems like it’s very close to planing with 4 but it needs an extra something to get it up there it seems

 

[harringtondav]

searider i plan on having 4 people including myself on the boat, but it only planes when there are 3 or less ppl on the boat. It seems like it’s very close to planing with 4 but it needs an extra something to get it up there it seems

Generally that extra something is more power, = larger motor. There is only so much a prop can do. If your boat won't plane under a certain load, that load exceeds your motor's capability.

 

[Grub54891]

Do stainless steel propellers actually make your bot go faster? ​

With that setup, its like putting 3" exhaust on a volkswagon beetle.

 

[jebby]

what motor can you recarb it to get it to 15. a lot of 10 and 15hp motors share the same guts if I remember.

 

[QBhoy]

Ok. So just in I think your last post, you say you want to plane in a 10ft inflatable with 4 people and a 9.9. It’s not going to happen, if you mean 4 adults. No way. Slight chance if it was a little longer with more planing surface. But not as you have. You really need a bigger boat and more engine.

 

[Cruzieduzie]

Thanks everyone. Sounds like I need a bigger motor.. prob should have gotten a 15hp not a 9.9hp. Think I’ll loose much on reselling a “used 3 times” 9.9hp mercury 15”?

 

[mr 88]

Thanks everyone. Sounds like I need a bigger motor.. prob should have gotten a 15hp not a 9.9hp. Think I’ll loose much on reselling a “used 3 times” 9.9hp mercury 15”?

Uhhh , you set the selling price and if you don't get what you think is fair then don't sell it. The number of people that inquire ought to tell you how much of a marketplace there is at this time of the year for that size motor and if your going to " loose " much on reselling it. If you bought it from a dealer they may be willing to take it in on trade so you don't lose much in the upgreade.

 

[Leardriver]

It's not that SS flexes less. It is stronger and can be made thinner, which creates less drag and is more hydrodynamically efficient.

 

[jimmbo]

Thanks everyone. Sounds like I need a bigger motor.. prob should have gotten a 15hp not a 9.9hp. Think I’ll loose much on reselling a “used 3 times” 9.9hp mercury 15”?

If you want more HP, look at the Engine specs very carefully. if there is a 9.9 and 15 hp that share the same displacement, your are not going to gain very much, if anything. The 9.9 very likely underrated(that way they can get under HP Limits and Registration of Boats in some Areas. The 15 would get it's extra power by extending the RPM range and moving the Torque Curve to Higher RPMs, with a corresponding decrease in Low End Torque. On a Very Light hull, that isn't a big Deal, but you are having problems getting on Plane, and you need more Low end Grunt. An engine with More Displacement and Higher HP is what you need.

As for your Original Question...

SS props being stronger can be made thinner which raises their Efficiency,it also allows for better Blade designs that enable changes to Engine Height(really not required until speeds over 45 mph). and higher Trim Angles which lessen wetted Area on a Hull. Some Props can literally lift the Entire Hull Vertically, others are designed to keep the Bow Down and were developed to keep Tunnel Hulls from flipping over backwards at high speed
The much commented 'Blade Flex' was marketing Genius, as it has sold Many SS Props. Get an AL Prop,clamp a blade in a Vice, and you will see how Inflexible(about 1/100" on a 20 " prop) it is, besides, it is pushing a Fluid, and the Fluid will yield long before the Blade does. .