Is a SS prop worth it?

[HeadnSouth]

Re: Is a SS prop worth it?

Ok I had the boat out yesterday and WOT @ 44MPH @ about 4500 RPM.

Are those outdrive fins worth it? I can fabricate one out of either SS or aluminum.

 

[jestor68]

Re: Is a SS prop worth it?

How are measuring speed, as those numbers equal a really high (28%) slip factor if that speed/rpm is accurate.

I would guess that either your speed or rpm numbers are off. You should be producing slip factor in the 10-13% range.

For example; using a 1.47 gear ratio(normal), 21 pitch and 11% slip works out to a theoretical 49 mph using your reported 44 actual mph. This works out to only 3622 rpm.

If your rpm is accurate, using a 11% slip factor, you should going 10 mph faster than indicated.

Bottom line; your numbers don't add up. Do you have something other than the "standard" 1.47 gear ratio normally used with a 5.7L ? Using a "normal" slip factor would indicate a 1.81 gear ratio.

 

[HeadnSouth]

Re: Is a SS prop worth it?

I measured my speed with a gps. Next time out I'll use 2 GPS and hook up a tach to the engine.
Thanks for your reply.

How are measuring speed, as those numbers equal a really high (28%) slip factor if that speed/rpm is accurate.

I would guess that either your speed or rpm numbers are off. You should be producing slip factor in the 10-13% range.

For example; using a 1.47 gear ratio(normal), 21 pitch and 11% slip works out to a theoretical 49 mph using your reported 44 actual mph. This works out to only 3622 rpm.

If your rpm is accurate, using a 11% slip factor, you should going 10 mph faster than indicated.

Bottom line; your numbers don't add up.

Don't buy a prop until you determine why the numbers don't make sense.

 

[jimmbo]

Re: Is a SS prop worth it?

A neat thing about Stainless props, unlike Aluminium props which break blades off in hard impacts, the SS blades just bend a bit and keep hammering until you have a ball of metal on a now bent propshaft. If you boat in shallow water, unless the bottom is only sand or mud, Aluninium will be much less expensive.
Someone will pipe up saying the rubber hub protects the prop on impacts. Not really, it was there to cushion the shock on the drive train during shifting, when 20 lbs of prop are instantly accelerated from standstill to propshaft speed in 1/6 to 1/2 of a revolution. Most props today have non flexing hubs that shatter on impact.

 

[MikDee]

Re: Is a SS prop worth it?

How are measuring speed, as those numbers equal a really high (28%) slip factor if that speed/rpm is accurate.

I would guess that either your speed or rpm numbers are off. You should be producing slip factor in the 10-13% range.

For example; using a 1.47 gear ratio(normal), 21 pitch and 11% slip works out to a theoretical 49 mph using your reported 44 actual mph. This works out to only 3622 rpm.

If your rpm is accurate, using a 11% slip factor, you should going 10 mph faster than indicated.

Bottom line; your numbers don't add up. Do you have something other than the "standard" 1.47 gear ratio normally used with a 5.7L ? Using a "normal" slip factor would indicate a 1.81 gear ratio.

I agree with jestor, I think you should be going faster, you need to get your WOT RPM, and post it? It should be at least 4500rpm. I wouldn't go buying a new prop, until your engine can do this rpm with the prop you've got now.

 

[HeadnSouth]

Re: Is a SS prop worth it?

I did post my WOT RPM. 4500

I agree with jestor, I think you should be going faster, you need to get your WOT RPM, and post it? It should be at least 4500rpm. I wouldn't go buying a new prop, until your engine can do this rpm with the prop you've got now.

 

[jestor68]

Re: Is a SS prop worth it?

As far as I know Lake Lanier is pretty stainless friendly.

So the main factor to consider is cost versus performance improvement.

 

[HeadnSouth]

Re: Is a SS prop worth it?

Ok out on the boat at the moment. 5600 RPM @ 48MPH.
I've got another question. Why is my dash tach off so much and can I adjust it? It reads fine at low RPM (idle)

 

[dan02gt]

Re: Is a SS prop worth it?

Ok out on the boat at the moment. 5600 RPM @ 48MPH.
I've got another question. Why is my dash tach off so much and can I adjust it? It reads fine at low RPM (idle)

There should be a switch on the back off it you can rotate for what type of engine you have. You didn't say what type of 5.7 you have (MPI, EFI, or carb) but the settings are different for them. When I got my boat the tach was about as far off as yours. I found it was set for a V6 which is fine for a carb V6 but mine is a MPI and there was a different setting for that. To top it all off the MPI vs carb settings sticker were on the side of the tach not the back like the cylinder number settings sticker.

 

[HeadnSouth]

Re: Is a SS prop worth it?

It's got a carb. Can't post a picture from my phone for some reason. But it says C=cyl and the pointer is at 8. It also says P= pulses?

 

[jestor68]

Re: Is a SS prop worth it?

If your tach is like mine(with a one piece plastic connector with three pins), I need to pull the connector off once in a while and clean the pins. When they get dirty it causes the tach to bounce around and read too high.

Cleaning the pins returns the readings back to normal.

 

[HeadnSouth]

Re: Is a SS prop worth it?

Thanks, I tried a quicky cleanup with no improvement. I'll pull the tach and give it a good cleaning.

If your tach is like mine(with a one piece plastic connector with three pins), I need to pull the connector off once in a while and clean the pins. When they get dirty it causes the tach to bounce around and read too high.

Cleaning the pins returns the readings back to normal.

 

[H20Rat]

Re: Is a SS prop worth it?

A neat thing about Stainless props, unlike Aluminium props which break blades off in hard impacts, the SS blades just bend a bit and keep hammering until you have a ball of metal on a now bent propshaft. If you boat in shallow water, unless the bottom is only sand or mud, Aluninium will be much less expensive.
Someone will pipe up saying the rubber hub protects the prop on impacts. Not really, it was there to cushion the shock on the drive train during shifting, when 20 lbs of prop are instantly accelerated from standstill to propshaft speed in 1/6 to 1/2 of a revolution. Most props today have non flexing hubs that shatter on impact.

+1 on that... I boat on a river that has frequent sandbars that will sneak up on you. The guys with aluminum props carry a spare and have them repaired every so often. The guys with stainless steel rarely have to have prop work done. They get their lower unit redone at an alarming rate though. Replacing a prop shaft is expensive!

 

[HeadnSouth]

Re: Is a SS prop worth it?

What do you guys think of my new WOT RPM's and speed? Do they add up?