Props spinning out getting on plane
 

Both drives are shifting in and out of gear fine but right before the boat gets up on plane (roughly 3100/3200 rpm's) both engines /props will spin out and rev kinda like its in neutral. When I get off the throttles and slow down it will take off again but do the same thing right before getting on plane. Anyone got some ideas on what to check?

Sounds like they are cavitating. Make sure drives are tucked in, put your tabs all the way down. Also try holding a lower rpm longer to get on plane.

As Pure Energy said, the props are cavitating. Try advancing the throttles very slowly. Keep the rpms as low as possible getting on plane. Let the boat build some speed before you advance the throttles. Depending on the boat, you should be able to get on plane without going much over 2000 rpm. What type of boat and what props?
Eddie

This sounds crazy but try running the tabs all the way up and easying into the throttle. My boat will blow out everytime with the tabs down but rarely with them all the way up. I believe the tabs are lifting the props closer to the surface when you really do not need or want that.
Allen

Thanks guys. My tabs have been up everytime and drives tucked down all the way. I do ease into as slow as possibe everytime. The boat is a 1989 Century Ultra II, 27', twin 454's/330hp with Bravo 1 drives and Elite 1 24P props. Boat weighs appx. 6400lbs dry.
http://i45.photobucket.com/albums/f6...8/watarush.jpg

Did it do this before ? If not maybe you damaged a prop. Drive's in tabs down throttle up slowely bring tabs up as speed increases to sea conditions. Also are you in shallow water when trying to get on plane ? You might be starving the props if they are to close to the bottom of the lake.

Yes it has done it before but seems to be a little worse now. There are a few small dings in the props but not horrible and they were there when I got the boat and they haven't got any worse. Now my tabs could have been down a little before and I just didn't realize it. On this boat I haven't used the tabs much as I only run around for a few minutes then cove out and rarely run at full throttle, just cruise. And no, the water I was in was atlease 20-30' deep, no shallow water.

try a different set of props, some seem to cavitate easier than others.

I thought about that too. Now just to find someone local with some 24's. Now if I can't find them, should I try 23P or 25P props? Right now at WOT I'm running 4900rpm's on my stock 1989 330hp 454's. Thanks everyone for the help!

I would put the 24's back on it, 4900 should be ok but stay with the same setup so you know if it was props, if you change the pitch and it is worse you have not solved anything as you changed the setup. Sounds like props to me.

I would try anything I could get my hands on, just stay with the same # of blades, if the problem is still there, then you know something else is causing the problem, if it goes away, its the props.

Take you props off and have a local prop shop fix the dings and have them add some cupping. If your props are performing overall good there is no reason to buy new ones and go through another learning curve.

When I first got my boat I could not get on plane in anything over 1.5' waves. Took my props to the local shop and they said that over time all of my cupping had been washed out. They reblanced, trued the pitch back up and added cupping. I lost 150 and 1mph but I now can get on plane in any type of water.

Hello I was wondering if the boat has drive showers on it, because I have heard someone say that different drive showers where causing cavitation proplems. That when they take off the water flowing across the bottom would actually suck air from he top causing this. Just something I heard dont know this for a fact.

Do you have drive showers? When I added mine several years ago I had to shorten the pickup tube. The prop would slip or blow out when it was longer.

Thanks again everyone. I'm still looking for someone with a pair of props to try and if I can't in hte next few days I'll send mine off to be redone. And no I do not have drive showers on them.

Something else weird on my boat is both drives/props spin the same direction. Could this have anything to do with it? It sucks as the prop torque get pretty bad when backing off the throttles, wants to make a hard right especially if throttleing down fast. On a good not it gives me a good reason not to let anyone else drive my boat!

Try searching vent holes and diffuser ring ,

maybe a dumb question but what are those?

Vent holes are in the front of some props, at the base where the prop meets the drive. These are plugged with a plastic cap and can be removed to allow the prop to aerate so it can spin a little easier on some boat. The diffuser ring is the flare at the back of the prop, this ring is used to keep exhaust gases out of the blades so you do not cavitate in the exhaust.

You must be running twin Alphas

No, twin Bravo 1's. I'll run up to the storage real quick and take a look at them. Its also straight thru hull exhaust, no captains call etc... so no exhaust runs through the drive/prop what so ever.

Ok, the do have vent holes. 3 on each prop that are not covered with anything. Heres a few pics I just took of the props.
http://i45.photobucket.com/albums/f6.../P10100263.jpg
http://i45.photobucket.com/albums/f6.../P10100272.jpg

Will the vents still aerrate the props any since I don't have any exhaust running through the drive?

They could still bring in some air. You have 2 RH props? you could get a LH prop and just switch the cables on your throttles. A Bravo can spin either way. I thought that you had Alphas because a lot of twin Alpha boats both props spun RH.

Yeah, I knew you could do that, I'm just not sure how to. I figure whenever I have to buy a set of props I'll end up doing that though. Now I guess I gotta get some plugs for the vents also to give that a try. Thanks alot Rookie (and everyone else!) for sticking in there with me on this. Hopefully we get it figured out soon.

That depends on the type of exhaust bellows you have between the lower unit and bellhousing. If you have the open ended bellows or no bellows at all air will get pulled through the passage and down to the prop as you come up on plane. I have thru hull exhaust also and had that problem on my boat when I switched to an "over the hub prop" (Mercury Chopper), so I got a cap plug and capped the exhaust passage in the lower.

Marco

Good call, I never thought about that. I'll check later and see what I have. Thanks!