TMI - 4 or 5 Blade - 575 SCi

[bbladesprops]

No, some of what you are saying is contradictory to the drive being to high. No blow out, no rooster tail.

Can you get an actual reading of the prop shaft in relation to the lowest point of the boats hull? In other words, how many inches below or above the bottom is the prop shaft?

Are the Bravo 1 30's in great condition or have they seen some sand and/or gravel? Just curious.

[VP]

OK Brett - here are the answers to your questions -- by the way this is a single engine

Can you get an actual reading of the prop shaft in relation to the lowest point of the boats hull ? ------------- the prop shaft measures 1" below the lowest part of the Vee hull - it measures 7-3/8" below the notch -- the notched transom runs 10" forward from the transom

Are the Bravo 1 30's in great condition or have they seen some sand and/or gravel? Just curious. ------------ the Bravo prop is in very good condition - there were a few nicks that I removed with a small high speed sanding drum (ie: I basically sharpened the leading edges of each blade)

Now one more bit of info and a question -- I am assuming my tach reads 100 rpm high -- I have been giving you tach readings because that is how i am recording my data - I assume it is reading high because Mercury says my Rev Limiter is 5350 and i can hear it kick in when my tach is reading 5450 ------

Now a question for you guys -- for a B1 prop, do you enter the advertised pitch in the calculator, or subtract 1-1/2" ??

[throttleup]

Since you have not mentioned an extension box I assume you don't have one. If you don't have an extension box the drive is on the high side. Fountains don't usually have a problem getting on plane.

As far as the pitch for slip purposes we use 1" less than what a Bravo 1 is marked. With Hydro's use the pitch it is marked.

At what number is your drive at neutral trim? What happens if you run the boat at neutral or slightly positive trim? I would go with a drive spacer.

In a couple weeks, if all goes as planned, we will have drive spacers available for testing purposes.

Matt

[VP]

Matt,

my drive looks neutral (ie: parallel with the bottom of the vee hull) at about 3-1/2 -- I trim to almost 4 to to get max speed

oh -- no extension box on boat either

[bbladesprops]

Your drives are slightly on the high side. Try the spacer, it will help you.

I use 29.3" when calculating slip on 30P Bravo 1's. 29-29.5 will be close. They all vary slightly.




Water is an inaccurate medium. Perfectly pitched propellers are not always the fastest..................hmmmmmmmmmmm.

[VP]

OK Brett and Matt -- I will test a spacer

But - how much spacer ???

and --- will my prop size have to be reduced to say - 28 ???

[throttleup]

You will eventually have to run a lower pitch prop but for testing purposes the 30 will work fine. After a run with the spacer then it would be time to calculate the slip and go from there.

I would start with a 1" or 1.5" spacer and see what that does. It should put you close.

Matt

[VP]

Ok guys -- thanks for the info.

Matt, please let me know when you get spacers for testing

[VP]

Hey guys,

just tested another prop last nite and thought i would let you know the results

1. i ran a baseline run with my 30" std. B1
- engine ran 5450 rpm again (my tach reading) banging against rev limiter but 84.2 mph GPS - only 50 gals of fuel - 1 person - flat water- trim was at 3-3/4 to get max speed

2. then tested a 32" lab'd B1 - ran 5300 rpm (my tach) and 86.5 mph GPS - same conditions - trim went to 4-1/2 to get max speed - much bigger rooster tail - maybe 2-3 ft way back

any new time estimate on drive spacers for testing???

[throttleup]

Spacers should be available next week for testing.

Matt