Drive Spacer for Nordic Rage????
 

Anyone have experience with drive spacers on a Nordic Rage?
Currently running 496HO, 425hp with lab finished 27P and experiencing from ~15% slip for best conditions light load to ~17 % slip for poor conditions heavy load. I understand that 10-12% slip is ideal.

Also considering future 525hp upgrade.

All insight and suggestions welcome!

Re: Drive Spacer for Nordic Rage????
 

Post your performance data so we can take a look.

What drive and gear ratio?
Make and Model of propeller?
WOT RPM?
WOT MPH vis GPS?

Julie

Re: Drive Spacer for Nordic Rage????
 

Julie,

BravoX, 1.5:1
@~4550#, 26P stock Bravo1, 5000rpm=68mph, Lt chop
@~4060#, 27P lab finish Bravo1, 4900-5000 rpm=69mph, Mod chop (just about perfect conditions)
@~4230#, 27P lab finish Bravo1, 5150 rpm=71mph, Mod chop (just about perfect conditions)

Re: Drive Spacer for Nordic Rage????
 

With the 496 HO you need to run at 5000 RPM at WOT, as this is were the peak HP is produced. This is were the peak top end will be found. I have calculated 14% slip with the numbers that you posted. Unfortunately I don't know what the pitch of your 27P Bravo I propellers are. The Bravo I propellers are only available in the even numbers pitches so a 27P is obviously a modified 26P or 28P. How did they come to be 27P propellers is the question.

Julie

Re: Drive Spacer for Nordic Rage????
 

The 27P lab is a converted 28P stock Bravo1's. All the propeller lab re finishers I contacted including Mecury Racing said that based upon my numbers with the 26P stock Bravo1 that the increased rpms to be obtained from the thinner lab finish blades should be offset with about a one inch increase in pitch.

I have now also have a modest increase in top end horsepower that I did not have before along with optimum weather conditions and light load generated the 5150 rpm's noted. This will be the exception rather than the rule which will be in the 5000 rpm WOT with the current labed 27P.

Re: Drive Spacer for Nordic Rage????
 

This is why the props are running similar RPMs. I would suspect that the 27P that ran at 71 MPH has a little more cup removed and may be a little thinnner lab. You are basically there and should maybe consider some adjustments that may improve slip.

Julie

Re: Drive Spacer for Nordic Rage????
 

Julie:
How does the P5-X work on the Rage? We know it works well on the Heat :D !
Regards,
Steve

Re: Drive Spacer for Nordic Rage????
 

Julie,

Thanks!

Actually both sets of data on the 27P lab that I showed are the same prop just from different days run. I apologize for not pointing out that fact. The 27P lab @69mph did not have the advantage of the modest increase in motor hp I mentioned. The 69mph was run a year ago with 25 hours on the motor and the 71mph was run this Sunday with 80 hours on the motor on the same lake (916 elevation) and ~ same near perfect atmospheric and water conditions. The hp improvement was in the form of reduced exhaust restriction that provides the increased hp at the top rpms. I suspect this is why I could turn 5150 rpms at WOT with the same prop this week and only 5000 rpm a year ago.

My calculations for % slip with the stock 26P is ~17%+ and with the 27P lab is ~15%+ for both runs noted.

Actually it is the 'adjustments' in the form of a drive spacer to improve % slip by 2-3% that I am inquiring about i.e. what is the experience out there with adding a drive spacer to the stock Rage setup with the 496HO?

Are there other adjustments that you are referring to to accomplish the same result of improving % slip? If so please elaborate.

Thanks again for your help!

Re: Drive Spacer for Nordic Rage????
 

Julie,

Please let me know what options are available to improve slip and top end.

Thanks!

Re: Drive Spacer for Nordic Rage????
 

I typically recommend that you install a drive spacer with 17% slip and above. If you have 17% or greater then I will recommend a 1" spacer to get a little more prop in the water increasing propeller efficiency. I think in your case then I would recommend a 1/2 inch spacer. Again I have not had great luck with the 5B propellers acheiving the goals of top end & cruise speeds. Hole shot seems a little quicker with the extra blade and of course accleration. The 5B works well on the Rage but the 496 HO is the question.

Julie

Re: Drive Spacer for Nordic Rage????
 

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!

Re: Drive Spacer for Nordic Rage????
 

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!

Re: Drive Spacer for Nordic Rage????
 

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

Re: Drive Spacer for Nordic Rage????
 

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!

Re: Drive Spacer for Nordic Rage????
 

[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!