Alum or SS?

[dellsboater]

Have a 21 foot Liberator, 350 has beat up 14 1/2 x 21 pitch alum prop, does 52 MPH at 4700 RPMs.

Looking at a 23 pitch alum or 21 pitch SS...
Looking for top end speed increase...

Do not water ski, pull tubes, just cruise....

 

[armone]

Re: Alum or SS?

First: FIX THE ALMUMINUM.. beat up props beat up performance and drive trains. Second: spring for the SS, but get exchange agreement with dealer or hit the water with 3-4 props on a trial basis (expect to put down a healthy deposit to do this) keep the aluminum for a spare

 

[dellsboater]

Re: Alum or SS?

Do you think the 21 pitch SS will be faster then a 23 Alum?

 

[cribber]

Re: Alum or SS?

To help you out there are a few things that need to be known before the experts can help.

Gear Ratio:
Max Recommended engine RPM:
HP of you motor:
Boat weight:
Boat length:
GPS Speed at WOT:
Prop Pitch:

Once you have all of this information handy then you can tweak any of the prop calculators out there to get a sense of what any changes you make would do for you. Going to 23" SS or aluminum will drop your WOT RPMs by about 400. What you want to strive for is the least slip, maintain recommended WOT RPMs. Speed and hole shot are dependent on all the above.

http://www.hillpropellers.com/propcalc.html is a decent prop calculator.

 

[dellsboater]

Re: Alum or SS?

How do I get the gear ratio? Its a 1988 Cobra behind a 350 gm at 270 hp

 

[cribber]

Re: Alum or SS?

If it is an I/O it is usually stamped somewhere on the lower unit or in an owner's manual if you have one handy.

If it was direct drive then it would be one for one as in 1:1 unless that is geared as well.

 

[dellsboater]

Re: Alum or SS?

I will have to clean up drive and see if I can see any numbers, will it say "gear ratio"?

 

[robjen1019]

Re: Alum or SS?

Here is my humble opinion. Skip the SS prop. Your not going to gain much of anything with a ss prop on that boat. Fix or buy your aluminum prop. Or buy another one with higher pitch for speed. Ive played this game with my boat, 20 ft cuddy. Nothing made it go faster. 4 blade increased hole shot and decreased top speed, but ss and aluminum both netted within 1 or 2 mph gps of each other.
biggest difference is if you hit something. Aluminum breaks or bends. SS breaks gear case. If you boat in areas where you come in contact with the bottom occasionally, keep the aluminum.

 

[Robbabob]

Re: Alum or SS?

Have a 21 foot Liberator, 350 has beat up 14 1/2 x 21 pitch alum prop, does 52 MPH at 4700 RPMs.

Looking at a 23 pitch alum or 21 pitch SS...
Looking for top end speed increase...

Do not water ski, pull tubes, just cruise....

Many already suggested great ideas.

How about a picture to show your description of the "beat up prop"? You are getting pretty good numbers, but should be higher in RPM at WOT with a bad prop. We also have to assume you are well able to level your trim for optimum planing.

Post some pics and more good ideas will come.

Good Luck!

 

[steelespike]

Re: Alum or SS?

How do I get the gear ratio? Its a 1988 Cobra behind a 350 gm at 270 hp

My info indicates 88,270hp is 1.41 gear ratio, rpm 4,800.
A 21 ft boat that makes 52 mph factory equipped w a beat up prop,
you could spend a lot on a ss prop and not see much increase.
When your allready over 50 imo feel pretty good if you can get 2 or 3 mph.

 

[dellsboater]

Re: Alum or SS?

I have a 20 inch SS prop that came with the boat, just needs a ding taken out, was wondering if I should have it repitched from a 20 to a 21.
The alum prop on the boat now is a 21 pitch....

 

[steelespike]

Re: Alum or SS?

I wouldn't make any pitch changes until you see how ss runs first with the ding taken out.
It also would be nice to have a base line with your 21 al repaired.

 

[boat1010]

Re: Alum or SS?

Props are hard to get dialed in on a boat. Different manufactured props do different things. Are you close to somewhere that you can try out some props? If so that is the way to go. I'm not sure your 350 will push a 23 pitch prop. The SS will give you a little more speed but not very much. As said here before once you get over 50MPH it is starting to take some pretty big $$ to get more speed out of your boat. Different gears more HP and things like that. Good luck.