Hot Boat

Yes. Not an XR but a stock bravo with the 600 hp motor I had before.

I'm not sure what if at all any speed gains I got with the 2" shorty but the over all ride of the boat was 100% better. My wife insisted that I keep the 2" shorter drive on the boat.

If running the 2" shorter drive is my problem I would rather keep it on the hull for the gains in rough water handling. It’s a mater of keeping the wife happy. But I would like to try a drive spacer and see if it helps just for piece of mind.

Here is a copy of the post that got me thinking if my drive is off center. I haven’t checked yet but I'll bet $$$ it’s off.



Pantera 28-650,

I have a friend of mine, of which he has a 28 foot boat (UK phantom now called Chaudron) powered with 600 hp. This boat wouldn't run more then 67/68 mph with 22% slip. We tried diffrent props like 3 and 4 bladed, but still no luck. Then we turned on the gear ratio and went from 1.36 to 1.50, changed and tried diffrent props still the same. So our last goal was to try a spacer. Got the spacer 1 1/2" and still we had high slip numbers with no extra mph.
One day, we were going to the other Island to spend the weekend and from my boat I noticed that his boat was leaning to starboard. When he took up the boat I told him to check if the drive was fixed in the center of the boat and he found it 3/4" to 1" off the center line to the starboard side.
We arranged the drive to center ( easier said then done) and now the boat runs 76 mph with 12% slip.
I don't know if you have the same sort of problem but there are alot of similarities.

Just my 02cent.
Good Luck in finding the problem.

monstaaa

possibly the ride quality increased because of the stability inherent with the design of the shorty. maybe you can try a standard length imco to see if it helps.
the set up seems o.k. i might say that the stern jack is addind extra pressure to the gimbal helmut and gimbal over all.

maybe you can test a standard length imco, and stock xr with out the stern jack v.s with and see if you notice handlind and speed increase or decrease.

raising the x may have lost your ability to carry the bow without too agresive of trim.

Hot Boat

I'll give it a try. Its not as easy as prop testing, frankly it’s a pain in the ass, but it what has to be done.

Could I get the same effect if I try a drive space??? I know the stern jack increased the speed and handling of the boat. If I could I would rather start with spacer first and go from there.

Thanks for all the help.

Hang Time 27

Seems like no one really answered the drive center issue - I've never heard of putting a driveline off center to counter engine torque.....I would think it would make "off throttle" lean the other way - towards the weighted side. If yours is indeed off center, that could be an issue. I would think that with the drive off center and perfectly straight, in theory the boat would then want to turn slightly, requiring that the drive be turned slightly to counter-act that, which would then scrub some speed????

I did see a 29 Warlock that had it's cabin stripped out, a bulkhead added, and was setup for F-1 racing(not an F1 boat from the factory) that actually had "free weights" from the gym mounted to the stringer at the rear of the boat on one side to optimize the boats balance against prop torque - kept them from having to use a tab to level boat, and to add weight to the rear for less trim angle needed for bow lift. Boat did run 82 GPS with a stock Merc 500HP, so I'd say the setup worked pretty good for that particular boat.

I do remember racing side by side against a 26 Scarab CV (same bottom/hull as your boat, just without the swim platform and tall deck) at 80 mph and it was standing on it's tail with only the last foot or two of the pad touching the water - he had no problem with bow lift, thats for sure - but that boat is a bit lighter.....

Hot Boat

Thanks Hang Time.

I had a chance to try a 32P Bravo 1. I was able to get some better #'s this time out.

The boat was full of fuel 2 people. We ran 86 @ 5200. I found out I was trimming to high and that’s where the high slip #'s were from.

It seems that I have 16 % slip. I don’t think that’s bad for a 20 year old hull that needs work to the bottom and full of fuel.

My engine builder says I need to be up around 5700 to be at peek HP and I could also go one pulley size smaller on the blower if I wanted.

If I was to send the prop out to get labed and increased boost by 1 psi, smoothed the bottom of the hull and was lighter on fuel, I would hope I should hit my goal of 90 mph

Elite Marine

Sounds like you're getting there. I'm sure you'll hit your goal.

Then come and fix mine!