Would I benefit from a stainless prop?

[madolive3]

first time out today, 16.75 ft boat that the total weight with me and motor and fuel is about 1560 lbs.
1978 Johnny 115, peak hp is@ 5000Rpm. I achieved 43 mph today on a gps running a 13.75x15 prop. Sadly, I did not look at the tach. how much more top end could I get out of this boat/engine with a stainless prop? would it be wroth the try, or could I end up buying a prop and have no or very little gain in top end speed?
Thanks for the help.
Edit: The prop that was installed at the factory on this motor is a 13x19 if that helps.

 

[Texasmark]

Re: Would I benefit from a stainless prop?

The only way that I wouldn't run a SS prop is to boat in tree stumps or rocks. Thinner blades for better efficiency, usually cupped for gripping power in turns/rough water especially on high mounted engines, high rake for bow lift, can absorb mild dings that would bend an alum blade without hurting anything......

My 2c,
Mark

 

[steelespike]

Re: Would I benefit from a stainless prop?

Unfortunately without your rpm we can't evaluate your setup.
Usually a ss prop will improve overall performance.How much would depend on
the results of your present prop.There are a number of al props that produce excellent results.
A ss prop will cost about 3 times that of an al prop.They are rugged but repair is about double that of al.
While the hub should protect the gearcase from damage a ss prop is unforgiving in a really hard contact.
There are those that belive that the weight of the ss prop can cause premature wear of the clutch dog
Personally I believe that with a correct idle speed and shifting deliberately neither dragging it into gear nor
jamming it into gear should not have any measurable difference in wear.

 

[madolive3]

Re: Would I benefit from a stainless prop?

I'll go out on monday again and get those Tach numbers, I should have done that anyway. Thanks.

 

[Randybeall]

Re: Would I benefit from a stainless prop?

Reading what you said brings a question to mind. If the oe prop was a 13 x 19, what were the reasons to change all the way down to a 13.75 x 15? That is a fairly large drop, was it orignally good and changed some time later or over propped from the factory?

 

[steelespike]

Re: Would I benefit from a stainless prop?

Good point.I figure to make 43 with a 15" prop you would have to turn about 6300 rpm.Way too much.

 

[madolive3]

Re: Would I benefit from a stainless prop?

Good job you guys, I went out and tried again today. although the 13.75 x 15 is listed as an alternative prop in the FSM, I am over revving, I was @ about 6200 before I realized it. I am not sure if the Tach is accurate but from your post it sounds pretty close.
So I have to change props. Any opinions as to what the best prop would be for high top end? It came from the factory with a SST 12.75 x 21 and the manual tilt came with an alum 13 x 19. Both are 3 blade. I have to drop 800 to 1000 rpm @ WOT. Can I do that and maintain 40MPH? @ about 1500 pounds total?

 

[steelespike]

Re: Would I benefit from a stainless prop?

Don't know why the pitch would be different on a manual trim. Unless they wanted to force them to pay the difference to up grade.
By our rule of thumb (200 rpm per inch) a 19" pitch should reduce rpm by about 800.
assuming about 6% slip would produce about 46 mph.Would be smart to try to find a dealer that will let you try a number of props for the best performance with the assumption your buying a prop.
Generally a ss prop will give an overall improvement though how much would depend on how good the performance was with the previous prop.

 

[madolive3]

Re: Would I benefit from a stainless prop?

Steel Spike, you nailed it. Man right on the button. I bought a used 13x19 stiletto and topped out @ 46 mph @ 5500 rpm. You can't get more right than that. Thanks.

 

[steelespike]

Re: Would I benefit from a stainless prop?

Congratulations; sometimes you get lucky.