Reply With QuoteYour going to have to fix the trim issue, so repair it and see if your problem goes away before dealing with the prop.
Wondering what anybody's ideas might be on this. Running a 26 ft Wellcraft Nova with a Bravo I, mildly blown 454, and a 23 pitch 3-blade. When I hammer it out of the hole, it goes for a short period and then feels like I have a cavitation issue. If I baby it up until it's on plane, no problems. My trim must have slight leak as the outdrive requires fairly regular adjustments and the trim will "sag" if it sits on the trailer for a few days.
My question, is this a cavitation issue with the prop or is my trim pump not strong enough to keep the outdrive down in the water? I think it's the latter because when this "blow-out" occurs, I've noticed a little rooster tail from the prop angling upward.
Has anyone experienced something like this? Would a new trim pump fix it? Thanks in advance.
SM
Your going to have to fix the trim issue, so repair it and see if your problem goes away before dealing with the prop.
I really don't think it's the prop and I'd just as soon narrow it down before I start throwing new parts at it. I've read those pumps can get debris in them that prevents the valves from sealing completely. Would that explain both the sag and problems when we launch?
Normally if you have a problem with the trim pump or cylinders you can spot them by trying to move the outdrive by hand when the boat is on the trailer. Trim the o/d down and then try to move the o/d, try hard.........If you can't then probably the trim system is okay.
On the other hand if the o/d sags on the trailer or the boat constantly needs to be retrimed while under way then you may have a leaky check valve in the pump.
My question, is this a cavitation issue with the prop or is my trim pump not strong enough to keep the outdrive down in the water? I think it's the latter because when this "blow-out" occurs, I've noticed a little rooster tail from the prop angling upward.
In forward, the force of the prop will push the outdrive down, not up. Usually, the drive tucked in will give you a better holeshot...so I'm not sure that's it.
I agree- get the trim fixed, so you can try different trim angles when coming out of the hole.
If it's not leaking anywhere (check for sheen in the water when sitting), then fluid is getting past the valves in the pump or seals in the cylinders.
I've looked several times for a sheen on the water, but have never noticed anything. I don't seem to be losing fluid, either. Guess I hadn't thought of the prop pushing itself down during take-off.
I'll give the deadlift-the-outdrive-test a shot tonight. This should be interesting...
Thanks for the ideas, guys. Anything else I should consider?
It could be leaking down and you still will not be able to move it by hand! The stall pressure in these pumps is a terrific amount. BEFORE you start buying trim pumps you better have the system pressure checked, it could be the checkvalves in the pump or it could be o-rings in the cylinders letting it bleed past. Pumps are not cheap but o-ring kit are inexpensive and easy to install. Just my .02
Hey after going back over your original post... blown 454 i'm assuming thruhull exhaust??? Make sure that the exhaust bellows is removed! If that bellows is there with thruhull exhaust you will create a massive vaccum inside the drive and prop untill the boat breaks over on plane this could be causing your "blowout" Just a thought cause this was the case on my Eliminator.
Hey after going back over your original post... blown 454 i'm assuming thruhull exhaust??? Make sure that the exhaust bellows is removed! If that bellows is there with thruhull exhaust you will create a massive vaccum inside the drive and prop untill the boat breaks over on plane this could be causing your "blowout" Just a thought cause this was the case on my Eliminator.
This sounds exactly like what is happening to me. I'll get a nice hole-shot and just as soon as the bow starts to bow down, the "blowout" occurs. I do have thru-hull exhaust.
Dumb question, but what exactly are the exhaust bellows? Those butterfly-looking valves that redirect the exhaust on my captain's call? We might be getting somewhere here....Thanks for the idea'rs, guys...
I don't think that the trim has anything to do with your cavitation. HH is right, when you are going forward, the force in pushing the drive down and down is where you should be getting the best hole shot. Cavitation usually has to do with the prop itself. Try another prop and see if it does it. If it doesn't, you have found your problem.
I really don't think that you could have gotten debris into your system unless you poured it into the trim pump and only then could small particles get into the pump. It really wouldn't cause a problem. I think that it could be more of the "O" rings that are in the trim cylinders or pump. If the O rings have any slight problem with them, they would be letting fluid pass and causing the trim to drop. Same with the valve. If the trim valve doesn't close fully it could cause that problem as well. Good luck.
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