Julie,

What kind of improvement in slip do you see on average when you add a 1" drive spacer on a package that is experiencing the 17% slip that you mention as the decision point for such an addition?

I take it that when you say that the "496HO is the question" for a 5B that you are refering to the 425HP for that unit? What HP is needed to make a 5B work well on a Rage versus staying with a 4B?

What is driving me here is that a 2002 Power Boat test of an identical open bow Rage to mine with a labbed 26P Bravo1 recorded 75.6 mph at 5000 rpm radar for an efficiency of 7.9% with full tanks and two men on Lake Havasu. I realize that LH is ~sea level and I am running at 916 feet but 5000 rpms is 5000 rpms. With just myself and half tanks with excellent atmospherics I can just hit 69.5mph at 5000 rpms for about 15% slip with a labbed 27P Bravo1 from the same prop shop that supplied the boat test prop. Also the mercury slip calculation WEB site describes 10-12% slip as typical for a "heavy" V bottom" and 8-9% slip for a "fast V bottom". I do not consider a 3700# dry weight Rage as a heavy boat. Under the same conditions and prop with full gas plus a modest HP increase I can hit 71 @5150-5100 for a similar 15% slip. What in your opinion is the potential top end of my Rage given its current history at 916 elevation. What other mods would you suggest that I try. At this point I have no complaints with hole shot and mid range acceleration is very good.

Sorry for the question bombardment.

Thanks!

Julie,

I discovered that my slip numbers were worse than I thought. I was inadvertently using 26P theoretical speeds to calc my 27P slip numbers. Computer spreadsheets are nice but can cause complacency which = errors.

The stock 26P Bravo1 slip was still 17% at WOT, 5000 rpms.

The lab finished 27P Bravo1 was in fact ~19% slip. The actual labbed 27P numbers are:

@4060# test wt: 5000rpm/85.2mphTheo/70mphAct=18.5%
@4230# test wt: 5150rpm/87.8mphTheo/71mphAct=18.8%

What thickness drive spacer would you recommend for overall improvement in top end?

Thanks!

Your slip will depend upon the pitch of the 27P props, without scanning them there is no way of knowing the true pitch. Bravo I's are not true to pitch. They are actually 1 inch less than is marked on the propeller. So a 28P Bravo i propeller is really a 27P. Now you have to know what services were performed on the propeller to have had them remarked the propeller to a 27P. They probably did not change the pitch, but adjusted the RPM to that of a 27P (This is usually the case). So it is difficult to know without scanning the propellers. Baseling with stock props is always the way to go.

So with 14% slip on your 26P Stock propeller running at 5000 RPM at WOT at 68MPH you are basically there. With no need for a drive spacer. Keep in mind that when calculating slip you need to decrease one inch of pitch from a Bravo I, so your 26P is really a 25P. This is the number you need to use.

Julie

Julie,

The Bravo 1 pitch marking policy is a key piece of information that I was definitely not aware of. It sure clears up a lot regarding the 26P stock Bravo1 and drive spacer question. Once more thanks a lot!

Conversely the issue with my labbed 27P is still the same i.e. ~19% slip if in fact it is a Bravo1 28P with a true 27P thinned down to turn the same rpms as a 27P stock Bravo 1 if there was such a prop. Am I wrong here?

Thanks!

[SIZE=5]Julie,

Attached is a PDF file comparison of slip numbers from two different tests of a Nordic rage with a 496HO + Bravo1 drive and the numbers from my boat. My numbers have been repeated on several occasions under different water conditions that were from good to excellent so they should be an accurate representation.

Based on these numbers what do you think is the problem with my boat setup and possible corrective actions that I can take to achieve the performance of the other two Nordic Rage boats shown?

Thanks!