TMI - 4 or 5 Blade - 575 SCi
 

Ok - read a bunch of threads and now I am really confused.


I have a 2001 single step, 29 Ft Fountain with a 575 SCi ----- 1.5 XR Drive -- stock 30" Bravo 1 prop. --- I just freshened the engine.

It runs over 80 mph (on GPS) any time I want to, runs 82 most any time I want, and 84 in just the right conditions after long WOT time getting there.

(I increased the boost from a stock 4-1/2 psi to ~ 6 psi to do this, with No intercooler)

Last year I was pushing the rev limiter (tach reads 5400 rpm), but now after freshen job, with a full tank of fuel (100 gals), on fairly calm, cold (48 degrees) fresh water, I an right into the rev limit, and only running 80 - 81 mph on GPS.

I am assuming I increased power with the freshening --- I also assume the full load of fuel, plus the cold water is creating some extra drag and slip (i think) therefore the lower speeds.

I believe the peak hp (where i want to run at) is at 5100 to 5200 rpm ------- so I think I need to re-prop to get the rpm's down, the prop slip down, and my speed back up.

I was thinking a lab'd 32" B1 would be the ticket but the Hydro P-5 is being talked about a lot -- NEED HELP !!!

Re: TMI - 4 or 5 Blade - 575 SCi
 

We have found that the P5X works very well on the 29 Fountain. We worked with the Xtreme F1 Fountain and found the stock P5X ran the same top end as the lab Hydro Quad IV which was used for racing. The Quad IV was used to set 2 kilo records in Factory 1 on the same boat.

Your slip is higher than it should be. The 5 blade may bring it a little closer to where it should be. I think you are still going to need a spacer to lower the prop shaft a little deeper. You should be able to run the speeds you are running now with a 28 Bravo 1.

Matt

Re: TMI - 4 or 5 Blade - 575 SCi
 

But shouldn't I be expecting higher speeds out of a prop change if I am over-rev'ing now, and slipping too much ?

Re: TMI - 4 or 5 Blade - 575 SCi
 

You will get your best top end speed when the prop slip is at it's most efficient. Too much or too little prop slip is either over or under loading the blades on the prop resulting in lost efficiency.

In your case, with excessive prop slip, the boat will go slower with a higher pitch prop with a lot of slip verses a lower pitch prop with less slip. By lowering the drive, in your case, you may find additional speed, both top end and cruise.

Matt

Re: TMI - 4 or 5 Blade - 575 SCi
 

I understand what you are saying now -- that kinda sucks that my drive may be too high -- it is in it's stock location right from the Fountain factory -- i can't believe they would be that aggressive with the x-dimension on a production boat -

I just loaded my boat to take testing at another lake tomorrow - friend of mine has a pair of stock 32" B1's on his 42' -- I am going to try them for the hell of it to just see what happens --

When i went to load it, it ran right up to 5400 rpm at 82 mph without any effort at all -- on flat water too --

i could hear the engine running against the rev limiter -- wasn't even WOT yet - i noticed i was at 7 psi boost too - that is where i am getting the extra power verses last year a 6+

If the weather holds off and i get some testing in, i will let you know the results.

Re: TMI - 4 or 5 Blade - 575 SCi
 

It's not unusual for a boat to have the drive mounted too high. Better too high than too deep. Putting a spacer in is no big deal and doesn't take long. If you run into the rev limiter that easily at 80-81 then a spacer is almost needed for sure.

Matt

Re: TMI - 4 or 5 Blade - 575 SCi
 

Ok Matt -- here is a little bit of data from testing today ---

55 degree ambient temp ---- 12" + chop --- full (110 gals) fuel

1. Baseline run with my stock 30" B1 RH prop.= 5450 rpm 82.0 mph -- rev limiter kicking in (all GPS readings - all trim the same on all runs)

2. stock 32" RH B1 prop. = 5150 rpm -- 80.2 mph

3. stock 32" LH B1 prop. = 5150 rpm -- 79.8 mph

4. back to stock 30" B1 RH = 5450 81.9 mph -- rev limiter kicking in

Re: TMI - 4 or 5 Blade - 575 SCi
 

Your slip numbers are high, too high. I would work on reducing the slip before working with props. When you can run the 30 Bravo 1 at 82@5100 rpm, or so, then the drive height is right. Then it would be time to work props.

I would expect an increase of top end speed when the drive is lowered and the slip reduced. I would recommend a spacer of 1" to start with and see what your numbers are.

How does the boat get on plane? Is there a rooster tail at top speed? How much trim do you have to put into the drive to get top speed?

Matt

Re: TMI - 4 or 5 Blade - 575 SCi
 

Fountain has continued to raise their drive heights over the past half dozen years. Always looking for more top end.

I agree with everything Matt has been telling you. Your slip is too high. You're better off lowering the drive first to decrease the slip%, then work with the props.

Going to 5 blade props right now would be a band aid for the actual set up issue.

Re: TMI - 4 or 5 Blade - 575 SCi
 

Ok -- to answer the questions ---

How does the boat get on plane? ------ it requires 3/4 throttle - full "in" on the trim - No tabs needed - Zero blowout 95% of the time, or cavitation or whatever the real term is - not real fast coming up but I don't use full throttle either unless 6 people in boat.

Is there a rooster tail at top speed? ------- No rooster tail -- i can make one but when i get it fine tuned to get max speed, there is only about a 12" high max rooster tail, which shoots off toward the starboard direction a little.

How much trim do you have to put into the drive to get top speed? --------- well my indicator is reading about 3-3/4 when i seem to get max speed - my spacer in the slot in the drive, where the through-shaft goes for the rams, in located on the inside (towards the transom) so the drive is pre-positioned in verses out - and i can run the drive out to 5 without loosing a lot of speed.

so --- what do the two of you think now ?? does it sound like the drive is still to high ???

Re: TMI - 4 or 5 Blade - 575 SCi
 

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.

Re: TMI - 4 or 5 Blade - 575 SCi
 

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" ??

Re: TMI - 4 or 5 Blade - 575 SCi
 

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

Re: TMI - 4 or 5 Blade - 575 SCi
 

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

Re: TMI - 4 or 5 Blade - 575 SCi
 

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.

Re: TMI - 4 or 5 Blade - 575 SCi
 

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 ???

Re: TMI - 4 or 5 Blade - 575 SCi
 

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

Re: TMI - 4 or 5 Blade - 575 SCi
 

Ok guys -- thanks for the info.

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

Re: TMI - 4 or 5 Blade - 575 SCi
 

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???

Re: TMI - 4 or 5 Blade - 575 SCi
 

Spacers should be available next week for testing.

Matt