drive height x-dim question
 

31 cig bullet new style bravo 1 drivwes 24 degree dead rise notch transom (pad) 8900 dry weight
with the cavitation plate paralle to the botton how far below (or above) the hull should the centerline of the prop shaft be
I would like to get some more speed (80) with out more hp I am running in the high 70 range now spinning 26 bravo props at 5300-5400 rpm

Re: drive height x-dim question
 

WOW! Is that ever a heavy dry weight 31'! Which means it probably weighs in at over 10,000 pounds with fuel. No water. No passengers. Cigarette is known for their conservative X-demensions, which is probably best in your application. The only way to overcome this, would be with sheer horsepower. The latest offshore powerboats, built in the recent few years since the low water pick-up Bravo's(non cresent) & 4-blade Bravo One propellers have been introduced, have been rigged in the 18 to 19" X-demension range. But this is only possible on hulls that can be hydrodynamically and/or aerodynamically lifted at speed. A Bravo One drive, on a vee-hull such as yours would need to be installed at a much more conservative X,...Especially if you are using a standard, non-low-water pick-up Bravo Drive. A standard drive X demension on your boat would be in the 16" demension range. If you are using a low water pick-up drive, say in the 17" to 18" range. Much higher, with your weight, and you will be plagued with planing difficulties. You can raise these demensions a bit if you will always run 4-blades & never use 3-blades(Mirage Plus's, etc...) By the way, these basic X-demensions apply to single engine packages as well as twins. There are a few other variables that would need to be considered on a given hull, such as whether or not there are thru-hulls in front of the drives, transom water pick-ups in front of the drives or not, where the bottom strakes are in relation to the drives, if you are cooling the engines via remote water pick-ups, rotation of drives, etc...Hope this helps. Ed

Re: drive height x-dim question
 

Ed
thanks a lot for the info
I will get a acurate x-dim before I out it away fro the winter
I have over come the HP issue I am running 1 x 500hp that have been reworked to 565 dyno hp each
I am almost touching the 80 mph number and thgink by raising the drives 1 inch I should gain 2-3 moh I have no difficult plaining at the present time and know of a bullet that actually raised the drives 2 inches and claimed no difficulty with the drive at that height.
I guess the best solution is shorten the drives 2 inches and then if need be use spacers to drop them back down

Re: drive height x-dim question
 

Yes, that would be one good solution. Ed

Re: drive height x-dim question
 

Good Info!
Thanks!

Re: drive height x-dim question
 

I rode in a 92 bullet with 2" shorties & the boat had no problems planing or carrying the
bow. that boat had bravo 4 blades with remote pickups at the keel. we ran the boat with the stock intakes on the imco's without a problem. we switched to the remote pickups
when the boat was repowered with supercharged motors.

Re: drive height x-dim question
 

I re-rigged a 31' and during this process we raised the x from exactly what you just specified, 3 inches. The boat picked up almost 11 mph, and ran about 84. Cigarette put those x's in the basement for what ever reason, and the boat is a a lil slow because of it. But from my experience on this particular boat raise it up man, raise it. Cheapest mph for the buck on your boat. Good Luck!

Re: drive height x-dim question
 

Not familiar with the 31, but, the 38 top guns with SSM 3's on them have the prop shafts between 6-7 inches below the bottom of the boats. Checked 5 different guns this summer, all the same. That's REAL deep !!! :rolleyes: but I guess it works. :eek: