Prop slip concerns
 

I was not getting any response over in the prop forum, so I decided to post here as well.

I am now worried about the durability of my IMCO SC drive.

I have an 09 Nordic Heat with a 600sci that I have been doing prop and spacer testing for the last 6 months. Below is the table of my results. These are real slip numbers. Tach has been verified with a digital tach, and speeds with my analog GPS, my digital GPS and a radar gun.

The current best prop is a Hering 26 pitch, 5 blade bravo style prop. Slip is coming in at 5.2%

Mine is not the only Nordic Heat to post such low slip numbers. The Illmore 700 Heat regularly posts numbers between 6%-8% with the same drive and hull.

For you doubters:
Prop= 26 pitch Hering 5 blade bravo style prop
Speed= 83.8 mph
RPM= 5400rpm -- On the rev limiter

I am about to upgrade my 600hp motor to aproximately 750+hp using some upgrades offered by Whipple for my motor.

What I am worried about is that 750+hp and 5.2% slip on a 28 foot boat, sounds like a recipe for a broken drive.

What do you think??
Should I switch back to a 4 blade prop for reliability sake?
How much horsepower is safe in front of the IMCO SC drive?

I would like to hear some opinions.

Chris

I'm far from an expert, so I won't comment on what you need. But I think it would be intresting to try the 26 Herring and no spacer. Let the extra blades help carry the bow instead of a deeper drive.

Agreed you should loosen her up a bit.

What motor is it that you have now...or can you tell me at what RPM the peak HP is produced and at what RPM the peak torque is produced?
This may help the longevity of your drive as well.

Julie

Julie,

The motor is a Mercury 600sci. I do not know at what rpm peak torque is at. Dustin Whipple did tell me that peak hp is at 5400, which is where the rev limiter is set. On my digital tach, the rev limiter kicks in at 5420.

I am thinking that I will try the 27 Hering with less spacer in order to gain some more rpm, and increase slip on that prop. I am already just barely hitting the rev limiter with the 26, so increasing the slip would not do me any good on this prop because I can not spin it any higher in the rpm range.

What slip do you think I should aim for?

Chris

You should PM EWB or Steve Zuckerman. There are several Nordics here around Nashville with similar power running mid to upper 90's. They have all the specs for what they are doing with props and spacers. You might even post in the Nordic Section and see what they have to say but those Nashville Nordics run really well.