Anyone know what causes this??

[mrcool]

I have a Evinrude 90 VRO on a 15.5 foot Glastron bowrider. When I nail the throddle and go for the "hole shot" the ole Evinrude takes right off and gets it up on plane quickly, but then the RPMs rev way up (I haven't checked the tach, to see how high it revs) when I hit the top of the water, I normally back off on the gas right away, and let it settle on the water before opening her up once she's leveled off. It's almost like the prop comes out of the water for a few seconds, The trim is all the way down. Any one know what causes this? and what can be done? I've never expeiranced this with any of my other boats. Thank you for your help!!

 

[wavrider]

Re: Anyone know what causes this??

Sounds like you may need to lower the engine one hole in the mounting bracket.

I believe you answered your question saying the prop comes out of the water once you get on plane.

Does the engine still continue to "REV" once you back off the throttle and then settle in for a run?

Possibility of a spun prop does not seem likely due to the hole shot being fine.

 

[Joe Reeves]

Re: Anyone know what causes this??

If this boat/engine combination has functioned properly in the past, suspect a slipping hub in the propeller, otherwise I'm in agreement with wavrider.

 

[F_R]

Re: Anyone know what causes this??

Call it cavitation, ventilation, sucking air or whatever you want to call it, it is caused by a high motor mounting. People do that to get the last ounce of speed out of it. Ever hear a race boat take off? Some of them have a terrible time getting on plane, for all the air sucking.

If it bugs you too much, lower the motor a notch.

 

[mrcool]

Re: Anyone know what causes this??

If this boat/engine combination has functioned properly in the past, suspect a slipping hub in the propeller, otherwise I'm in agreement with wavrider.

Thanks for the answers, I just bought this boat in August and has always done this since I've had it, though I've only had it out about 8 times.
It makes great sense that lowering the motor, would work, however I do love the fact that I can take this little boat in pretty shallow water without hitting bottom. The previous owner did a lot of water sking with it and may have raised the engine one notch for a higher top end speed. This boat with just my wife and I tops out at 44mph...does that seem right?? I don't really trust it's speedometer

 

[NelsonQ]

Re: Anyone know what causes this??

It makes great sense that lowering the motor, would work, however I do love the fact that I can take this little boat in pretty shallow water without hitting bottom.

Yup, most likely up too high

The previous owner did a lot of water sking with it and may have raised the engine one notch for a higher top end speed. This boat with just my wife and I tops out at 44mph...does that seem right?? I don't really trust it's speedometer

You should get a GPS to test it out for a more accurate reading if you don't trust or believe the tach.

 

[emdsapmgr]

Re: Anyone know what causes this??

Are you running an aluminum propeller right now? If it is an aluminum, that would explain your problem. Running an engine high on the transom is a good performance trick. You will find it works best with a high-rake, cupped stainless prop. These tend to bite more and don't ventilate the way the aluminum ones do. Perhaps the person you bought it from set it up to run a stainless, then changed props before he sold it..

 

[mrcool]

Re: Anyone know what causes this??

Are you running an aluminum propeller right now? If it is an aluminum, that would explain your problem. Running an engine high on the transom is a good performance trick. You will find it works best with a high-rake, cupped stainless prop. These tend to bite more and don't ventilate the way the aluminum ones do. Perhaps the person you bought it from set it up to run a stainless, then changed props before he sold it..

Nope, it has s stainless prop on it, I just went out and looked, the only markings I could find on the prop say : Raker J2 595
Does that help??
As far as GPS, I'd love to get one, I'll start a thread about them or do a search in the proper area.

 

[emdsapmgr]

Re: Anyone know what causes this??

The raker is a great stainless prop. Normally, it should provide minimun ventilation and max bite. It does have vent holes in front of each blade. These vent holes bleed a small amount of exhaust air over each blade to help accelleration. This limited ventilation "slippage" is normal-increases rpms a little and helps get the torque up quicker and out of the hole faster. They quit bleeding air once you get on plane. The fact that the prop is made to "slip" somewhat on takeoff, may combine with your high engine mounting to cause your ventilation problem. You can run it the way it is, lower the engine, or consider plugging the three vent holes. If you decide to run it at the current engine height, you might want to add a water pressure guage to insure that you are getting proper water flow through the lower unit, especially at high trim angles.

 

[d.boat]

Re: Anyone know what causes this??

Thanks for the answers, I just bought this boat in August and has always done this since I've had it, though I've only had it out about 8 times.
It makes great sense that lowering the motor, would work, however I do love the fact that I can take this little boat in pretty shallow water without hitting bottom. The previous owner did a lot of water sking with it and may have raised the engine one notch for a higher top end speed. This boat with just my wife and I tops out at 44mph...does that seem right?? I don't really trust it's speedometer

How is the weight distributed in the boat when it does this? People, gear, position in the boat?

 

[mrcool]

Re: Anyone know what causes this??

How is the weight distributed in the boat when it does this? People, gear, position in the boat?

Mostly, Me in the drivers seat and my wife in the bow seat on the passenger side. a few times she has been in passenger (middle) seat, next to me, in that position she won't plane as quickly, I'll go a fare distance with the bow high in the air before it planes off. Gas tanks, battery, and a small cooler is all we normally have with us, all kept in the back, behind the rear seats.Once we're up and flying she runs great!!