Bryan Little

Need Help - Have 03 38' Fountain Lightning Staggered - Merc 575's w/Chillers, AZ Speed ECU's (rev limiter set at 5650-5700), Aeromotive fuel pump, Imco lower (1.50 ratio) - standard length - I have tried 3 different props: I am thinking about trying 5 blades - Hydromotive P5 or Merc Maximus - or getting 34 Bravo labbed.

My 2 ?'s are which 5 Blades and how much harder on lower units are 5 blades over 4 blade Bravo

My friend runs identical boat & power less shore power (AC, Battery charger), -1 Imco Lowers (1.36 gears), Hydromotive P5 stock 5Blade - 30' pitch - 97 mph - 1 person - 1/2 tank, spring time (70' temp)

GPS Speeds are mid July - 90+ degrees, 2 people 3/4+ tank of fuel

34 Bravo - stock w/ring cut off - 92 mph - 5100-5200 rpms
32 Bravo - stock - 89 mph- 5400 rmps
32 Bravo - Labbed - 92 mph - 5600+ - all over rev limiter
-32's just seem to run out of momentum around 87-88 mph

The 34 Bravo handles 10x better in midrange - I am either going to lab 34 Bravos -to get rpms and top speed up or get 5 blades. My friends boat seems to ride much looser w/-1 Imco lowers and P5's than my boat. Why is this?

Per conversation w/Hydromotive - thought I should get P5 30 pitch to get my rpms up close to 5600 -

Any suggestion's on P5 vs. Maximus and what pitch - Should I have Lab or leave stock?

I know if I went with -1 or -2 Imco lower I would pick up speed but with my stock Imco lower what will be best setup and not damage lower unit.

I feel this boat is capable of high 95+ - anybody with same setup or close?


Bryan

bbladesprops

First, decide your ultimate goal!! Is it speed or cruise or over all handling, etc.

Current drive set up dictates a custom recipe Lab with the 34's to get the 95 you are looking for or very close to it. Working with the 5 blade propellers "may" give you top end speed at the X dimention you have. I should say that 95 is a little bit of a stretch but within reach. Shortening the drive depth and working with 5 blade propellers, specifically the Maximus might give the best top end, but testing with the 5 blade propellers would be my first choice. Get a base line and it will tell us alot. Then a better decision can be made.

Standard Lab 34 B1 propellers won't do the trick.

Your friend has a prop creating more stern lift at a higher X dimention. It only proves to ride looser.

Call us if we can help.

Brett

Bryan Little

thanks for the response - I am 2 hrs from where my boat is stored for winter, but when I get a chance I will drive down and measure x dimension or could I call Fountain with boat serial # to see what original x dimension was with xr drive's.

James

Brett,

What is the relationship to wear and tear on the drives with a 4 blade that slips Vs a 5 blade that hooks up on a boat like above - 10,000 + lbs 600 + hp - A props that slips "sounds" like it might be easier on the drive but in this case the drive has to rotate 15% more to go the same distance as a lower slip value 5 blade. I have read many times where people do not want a five blade becuase they are more likely to break a drive and would rather settle for high slip values of 20%. For sure good driving habits such as coming out of the hole with massive drag and 700 ft lbs torque will not help - I'm really thinking about everyday cruising and moderate throttle input is a five blade that is "hooked up" harder on a bravo drive ?

bbladesprops

No it is not harder on the drive as long as the things you mentioned are adhered to.

I have had this dicussion many times in the past and have researched and written about it over and over. The first big issue is whether or not the boat owner is putting the recomended HP through a drive designed to handle it. This is key! If it is a matched set, fear not, the drive should handle it. If the drive does fail, it may not be related to 5 blade propeller.

Concider the fact that 5 blade propeller induce a more constant load on the drive line since the pulses of load and unload (distance between blades for lack of better description) are smalller.

All this being said, logic tells us a non slipping propeller will load and wear the drive harder and faster than a propeller that is waiting for the boat to catch up to it. Therefore remind yourself of the capacities your powerboat has, and try your best to help it live. This is another good argument for the possitive sides of slip %. Sometimes slip is good for other reasons too such as top speed (but that is another thread).

Driving style and 850 hp through a Bravo X drive ruin more drives than 5 blade propellers. Be nice to your eqipment or hammer down and call your drive guy every Monday morning.

Answer ; yes and no, but in your case James, you should be fine.