Prototype on a Bravo XZ drive

[BDMar]

Prop testing a boat without exhaust bellow and a prop with big vent holes the prop slipped so much the boat wouldn't get on plane. Would almost make it though. Making holes smaller let boat get on plane but prop slipped some at speed. Totally closing vent holes prop had no issues other than being too big for application.
My little experience 02 on this is that without bellows and vented prop (try different vent hole sizes) would be much better way to do what your trying to do. But ya' never know if it hasn't been tried before.
This is good info. The only thing I would suggest is to try the Bravo I 26 first. Then if you still have issues start venting the prop starting very small and working your way up. In general 5 blades are much happier on high X dim. cats than Vee bottoms.
Back to basics. Hardly ever and I mean ever does the correct propeller hook up so much that you can't get the boat on plane unless you are running a cat with huge props and high X dim. In your applicaton I believe you will find that the correct prop will solve your problems, and from what you have stated, again, try the 26 4 blade. The 24 ran too many rpm's so try the next size up....

[Cat-n- Around]

This is good info. The only thing I would suggest is to try the Bravo I 26 first. Then if you still have issues start venting the prop starting very small and working your way up. In general 5 blades are much happier on high X dim. cats than Vee bottoms.
Back to basics. Hardly ever and I mean ever does the correct propeller hook up so much that you can't get the boat on plane unless you are running a cat with huge props and high X dim. In your applicaton I believe you will find that the correct prop will solve your problems, and from what you have stated, again, try the 26 4 blade. The 24 ran too many rpm's so try the next size up....
One thing I did during the summer while the Bravo 3 was on was I changed the Ignition to an MSD, maybe the quicker rev's and the RPM's coming on faster might make a differance. I'm putting the XZ drive on tomorow. I will start with the 5 blade and then try the 26 pitch 4 blade, the 4 blade isn't drilled, but I don't think that will make any differance any way. Thanks again, I'll let you know what the outcome is. Jim

[BDMar]

One thing I did during the summer while the Bravo 3 was on was I changed the Ignition to an MSD, maybe the quicker rev's and the RPM's coming on faster might make a differance. I'm putting the XZ drive on tomorow. I will start with the 5 blade and then try the 26 pitch 4 blade, the 4 blade isn't drilled, but I don't think that will make any differance any way. Thanks again, I'll let you know what the outcome is. Jim
Now I'm confused. I thought the XZ was on the boat with the 5 blade and you already ran it and it wouln't get on plane unless you turned the wheel back and forth???

[Cat-n- Around]

Now I'm confused. I thought the XZ was on the boat with the 5 blade and you already ran it and it wouln't get on plane unless you turned the wheel back and forth???
BDMar, No, the XZ drive was put on when I put in the HP500 motor last year. At that time it wouldn't bring the boat on plan, so I reinstalled the Bravo 3. The Bravo 3 has been on all summer while I have been trying too figure out how to make the XZ perform. I will let you know tonight if it is any different. Jim

[Cat-n- Around]

Results were. I removed the gaget that I made, thinking it would create more drag. People that say that drilling the prop hub will only work on through hub exhaust are wrong. Took the boat out, as soon as it reach 2000 rpm the prop blew out and and the boat didn't do shit. Took it back to my dock, pulled the prop and pluged 3 of the five holes in the hub. Went out and the boat came up OK but the prop was cavitating a little, so I pluged one more hole, this time it came up good and gained speed like it should,but the motor toped out @ 4500 rpm and 65 mph. Tomorow I'll put on the 26 pitch Bravo one. It is not drilled. Could the MSD ingnition have made any differance? Jim

[BDMar]

What size holes did you start with?

[Cat-n- Around]

What size holes did you start with?
There are 5 1/2 inchs holes. I pluged all but one. How could one 1/2 inch hole make that kind of differance on getting the boat on plan. Now I have to deal with getting the other 1000 rpm's out of the motor. Like I said I have a 26 pitch Bravo-1 with no holes, when I put it on last year it did the same thing that the 5- blade did on getting the boat to plan. I didn't have time to run it today. I'll ask again, do you think the MSD made any differance?
What is the formula to comput boat speed. I've seen it on the boards before
Thanks again Jim

[DMOORE]

I'll ask again, do you think the MSD made any differance?
What is the formula to comput boat speed. I've seen it on the boards before
Thanks again Jim
Unless the old ignition was having problems, the MSD shouldn't make that big of a difference. As far as boat speed, a GPS is only way to get an accurate reading.
Darrell.

[spectras only]

Jim , this 550 HP engine is in your deckboat , right ? I think what you need is
more HP to get your tub on plane .We have a B1 24P prop , 1.5 d/r behind 620 HP on a 33' V boat that weighs 6000 lbs . Doesn't blow out , just takes a little time to get on full plane because we have to nurse the throttle to keep the Bravo X drive from grenading . We had no issues with the drive for nearly 100 hrs since new , until my buddy forgot to fill his drive full, before some testing this summer and blown the drive in 10 minutes .His drive is at a merc shop who told him gears/parts are on backorder [ he blew the drive in august ] , so much for quick service . .

[spectras only]

Here's a simle prop slip calculator >
http://www.go-fast.com/Prop_Slip_Calculator.htm
A more elaborate one . Go to the bottom of the page and hit 'Download Program Now' >
http://www.castlemarine.co.uk/pitch.htm