supermx96

I have broke the lower gear for the second time in std Bravo 1 lower drive. Now I am loocking to install a imco -2 or -3 or equivalent Sport Master for my Scarab 29 single engine strait V hull, I am runing now 80 mph with std height Bravo 1 drive, I am loocking to gain more speed, witch one is the best to go with strait V hull single engine config?

Black Baja

iTrader: (2)

I would probably say whichever one you can get I better deal on. I was told by a boat builder that the sport master on his boats had a little more trouble getting on plane. Could be the other way around with yours or make no difference at all. If you go with a -3 you will need a custom cavitation plate.

fysis

I would think twice before choosing the -3 IMCO shortie on a straight single v hull. Myself and friends have tried it without success. on single v:s . The -2 on the other hand seems to work great for the most. If someone here hit the spot with the -3 on a single v i I will be glad to hear about it. I donīt think there is anything wrong with the -3 just curious. .I think that to many out there seems to think that a high drive height is the straight way to high speed and therefore seems to overemphasize on it. . Yes there is less drag with less propp and drive in the water to a certain degree but with a heavy Powerboat you also need the prop leverage to get as little wet surface of your hull as possible when trimmed out( thatīs where the true speed is).If the prop does not have enough water to work in it will all end up in high slip figures.

BLUEMAGIC

+1 on that, more speed usually and more times than not go hand in hand with more power

supermx96

I know that the hard part is chosing the right combo for the hull. You are right probably a -3 was too much on a V single. But my prop shaft is at 7,375'' below the hull that is prety deep i think, cavitation plate is 1'' over the bottom of the hull.

I have never play with drive height before so any input before doing that will be appreciated.

fysis

I have a Donzi 22 Classic. .The stock propshaft center under the keel was the same as you have 7.4" (x dimension =14.5" thatīs the crankshaft center to Keel) Center of crankshaft is the same height as the trim stop and trim sender center. In 2011 I put the -3 Imco on the boat thinking high speed gain. I could not get the boat on plane at all untill a put a 5 blade Maximus on and had the trimtabs all the way down. then it just planed. . At that point the prop was 4.4 under keel wich for many boats are no problem at al. But al boats are different. Then i tried with a one inch spacer but still no good results. The way the -3 is designed itīs not supposed to be deeper than about 4.8 under keel because anything more that the wider part of the drive gets in to the water and troubles the water going to the prop.. Last year i put a - 2 on and that one works just fine . Some boats are more sensitive to drive height than others.

drivrswntd

Do you have a notched transom or not? What is your current prop shaft height? I have an AT 28 stock prop height with a standard lower and notched transom is 1.5" below the bottom. With a 4 blade couldnt trim the drive up at all without loosing speed. I'm now running a 1" spacer at 2.5" below, I can trim the drive up positive now, but with a B1 4 blade prop it's just not deep enough in the water and I'm still getting too much slip. Going to switch to a 5 blade and see what that does next, as I need more blade in the water. I know now i'm running the B1 prop partially surfaced as trimmed 1 click past neutral I throw a 2-3' tail. Found so far that was when the boat was fastest, any more trim than that and the slip goes up.

supermx96

For me no notched transom and shaft height at 7,375'' below the edge of the V of the hull and cavitation plate is 1 inch over the edge of the V.

Is cavitation plate height afect the efectiveness of the prop height?

louisfever

I have a scarab 29
i raised my engine and drive 2.75 inches
had a 502 in it then and picked up a solid 2.5mph
Now I built a 588ci motor and xr drive with a sports master lower ...
With 28 and 30 bravo props im seeing really high slup numbers and doing a rooster tail at a little past neutral trim !!!!!
Im thinking of installing an extention box to put the drive in cleaner water and get mote trim leverage to lift the bow up and at the same time it puts the prop about an inch deeper since the setback will be 12 inches ..... !!!!
Feel free to msg me on FB
my name there is Louis Scarab Portelli

Griff

Try a 1" drive spacer first.