I just had a nose cone installed on my B-Max drive on my Carrera 257 Effect and now I get a lot of cavitation when getting on plane. It seems to happen just after the bow reaches max rise and is just starting to drop. I have the trim at full down (or in) and the throttle around 2,500 rpm. It pulls good until the bow starts to drop, then the rpm jumps up to around 3,000 and I can feel it slow down. I have to back off the throttle to try and get it to hook up and bite. Once I do that and it bites, it will start accelerating normally. I guess I won't be pulling any big skiers anymore unless I can correct this (although it's worth the trade off).
The good news is that it seems to have eliminated my porpoise from 75 to 105 and the max mph has increased from 116 to somewhere past 120 (my GPS speedo stops there). More testing to follow this weekend with a hand held GPS.
Congrats on your speed run. Sounds like you got that thing dialed in on the top end. I assume you did that 120+ mph run recently in the heat of summer. Just wait until you get some good cool air. She will be flying. Tell me about the conditions and trim settings. Later.
SVO, Thanks for the congrats. I think that slowly but surely it is getting there. The prop slippage numbers are much better with the addition of the nose cone, but still seem excessive to me (18%)unless I was going quite a bit faster than 120 and the recall only recorded the maximum the speedo was capable of. I had the trim set on #8 on the Blue Water indicator which is about 6.5 degrees out. During the next test, I think I will try bumping the trim down some to see if I can get less prop slippage. I was spinning the motor 6,200 RPM with the lab 32 through the 1.3 gears in the B-Max. The conditions were 3700' of corrected air density. There was hardly any wind but the water was pretty choppy due to small boat and jet ski wakes. I think the speed was still climbing when I had to get out of it because of some boats that I was coming up on faster than I felt it was safe to do so. Each fuel tank was about 1/2 full for a total of about 40 gallons of fuel on board. I had about 600 lbs. of passenger weight on board at the time of the run. I had the motor set on the 12 psi boost mode running 110 octane 76 race gas. Any other suggestions? Thanks again.
How long have you had the drive on the boat? Are you happy with it? I am having a hard time choosing between the B-max and IMCO extreme advantage SC. I don't have a drive on the boat. Waiting for cash!! Let me know if you have any thoughts on drives. I am very impressed with your performace!!!
Congrats Keith. You're doing much better out of the hole than I am. I just have to let it spin away to at least 4000 rpm until the bow sits down. I'm thinking of getting a 16.5" diameter Hoss Offshore prop to see if I cure that a bit with a bigger diameter. I find that if I trim up beyond 2 degress above level the engine gets unloaded and revs away. It does seem to carry the whole boat there well. Need to get more GPS number to see what it's doing these days.
Wally
Hey Keith, thats awesome, great jump in mph, now throw the extension box on. Hope you make it next weekend. Saw pics of the AO, in 3 sections of course. Am told it will be together by monday and will have pics. My motors at the builder, we are dicussing it. I may have some questions for ya later. Should have got the 140 gps LOL later Ken
Thanks for the comments guys. M&D to answer your question, I have had pretty good luck with the B-Max. I currently have about 105 hours on it and the only problem was at around 90 hours when I broke a prop shaft (right behind the lower gear). I thought the Bravo Shop should have replaced under warranty but they would not. They said their warranty only covers motors up to 850 hp and I have 1160. I was thinking of possibly switching to the IMCO Extreme Advantage but I have also heard that they have had some breakage problems. I have run it hard for the last 15 hours with the new prop shaft and so far, no more problems with it.
Wally, I don't feel so bad about my cavitation now after I compare it with yours. I did a little more experimentation last week and tried a cupped 30 pitch prop and my lab 30 as opposed to my lab 32. My lab 30 seems to cavitate just a little less than the lab 32 but still quite a bit. I found that if I hit it harder from the start, it will pick up a little more speed before it starts cavitating at max bow rise and then it will roll over a little better. Also, the cupped prop worked a lot better to reduce launch cavitation. But, I noticed that my old problem with porpoise at 75 mph came back when using that prop. I still need to do some more testing though this week because the water was pretty flat with that test where it was choppy with the other props. That may be the reason the porpoise came back. More info to follow.
Ken, that's great news that the AO is coming along on schedule. I will look forward to seeing you at Tower Park this weekend to see the pictures and to find out what happened with your motor. Keith
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