My Nitro Cavitates

[zewski]

just bought a 2000 nitro nx 882 DC and it is really great, but one problem I have is understanding the trim, I put it all the way down when I start and as soon as im on place im supposed to trim it up a little, but when I do so the boat starts to bouce around like im into big waves, but the water is flat lol. I look like a rapper into a 65 impala with hydraulics.

 

What im i doing wrong?? Is it a propeller problem?

 

Thank you guys!

 

 

[Hi Salenity]

Are you trimming the motor or jack plate?

[zewski]

I don't have a jack plate

[Hi Salenity]

Are you just trimming it up to far? How's it run if you don't trim it up?

[zewski]

I trim it all the way for kick-off then as soon as i trim it up a little thing it starts to cavitate, I cant even put it straight with the boat. 

[martintheduck]

Length of the boat? What HP motor are you running?At what speed does it start bouncing? Take a picture of your motor and how it's mounted to the hull (so we can see what holes it's mounted in). 

 

 

EDITED: Your description went clear over my head and I was convinced you were chine walking... not porpoising. ANYHOW ---- get us the above information.

Edited October 23, 2013 by martintheduck

[Fishing Rhino]

Cavitation (ventilation), porpoising, or walking (chine)?  They are three different things.  You say cavitation, but you describe porpoising, while someone else talks about walking. 

 

Did you buy the rig from a dealer, or was it a private sale?  Either way, I'd talk to the seller, and see what they have to say. 

[Sam]

It's a Nitro.

You get what you buy.

Fishing Rhino is correct. What you describe is porpoising.

You can check with your BPS Power Pros but don't be disappointed when they tell you the have no idea. That's Power Pro for you.

Do what Martintheduck suggests and send photos for us to see.

I would venture to guess it has to do with the motor mount and your trimming.

[martintheduck]

Cavitation (ventilation), porpoising, or walking (chine)?  They are three different things.  You say cavitation, but you describe porpoising, while someone else talks about walking. 

 

 

His description of the problem went clear over my head. I read the title and figured he meant the boat is walking.

 

I will also throw in my only experience with the porpoising -----

 

My boat did it (18ft w/ 150hp) and it turns out I was driving the boat wrong. I learned a few things actually....

 

1) My boat is not meant to drive at less than 25 -> 30mph. It will STILL start porpoising even despite adjustments I've made... such is the nature of the game.

 

2) Learned to get up on pad you're supposed to jam to WOT trimmed all the way down, then back off the throttle a bit. My boat will porpoise if I just ease into the throttle and don't give it enough power.

 

3) I wasn't trimming enough. Based on boats I've driven before, they're setup has usually been "get going and trim just a little." - In my boat, it's "get going and trim up a LOT." Like I trim for a solid 4 seconds before the motor gets to it's proper position. So here's how I get the boat going and avoid porpoising - jam to WOT (trimmed down), back off a little from WOT, start trimming up. Trim up till motor is parallel to the boat (then I continue in smaller increments till I get to my max RPM's or top speed).

 

 

Now that I've actually read your description, I'm almost convinced you're driving the boat wrong.

[Glenn]

Hmm....no jackplate?  Meaning the motor is mounted directly to the transom?  That could be the issue right there.  Without an offset of 4-10", you will have all sorts of handling issues - porpoising and chine walking the most notable.   At the very least, raise your motor, meaning mount it higher (not trim it up). I'd fathom a bet it's too low right now.

[Walleye2Bass]

Sounds like porpoising to me.  Is it the original motor or did someone replace it recently?  I would hate to think the factory rigged it incorrectly, then again anything is possible.  I believe that the proper height is with the motor trimmed down and level the cavitation plate ought to sit level or to within and inch above the bottom of the hull (I read that somewhere so don't quote me on it).  Another issue might be weight distribution or you may be a tad under powered (could be prop, could be HP) for your load...       

[zewski]

I will put some pictures soon guys thank you all for your help... I have no experience with bass boats, maybe the problem is seating behind the wheel lol....

[martintheduck]

I will put some pictures soon guys thank you all for your help... I have no experience with bass boats, maybe the problem is seating behind the wheel lol....

 

 

So what horsepower is it? How fast are you going when it's porpoising?

[RyneB]

I have an 18 footer with a 150 (Ranger). I have only noticed it porpoise when I let off the throttle to slow speed to let a barge pass and what not. I have never had it porpoise coming out of the hole or when im running wide open. I have no jack plate either. It doesn't happen often, so I don't really pay attention when it does happen. All I do on my hole shot is trim the motor all the way down, hammer the throttle all the way and gradually trim up to the sweet spot on my gauge. Have never had a problem doing it that way.

[Koofy Smacker]

I have an 18 footer with a 150 (Ranger). I have only noticed it porpoise when I let off the throttle to slow speed to let a barge pass and what not. I have never had it porpoise coming out of the hole or when im running wide open. I have no jack plate either. It doesn't happen often, so I don't really pay attention when it does happen. All I do on my hole shot is trim the motor all the way down, hammer the throttle all the way and gradually trim up to the sweet spot on my gauge. Have never had a problem doing it that way.

If you keep trimming it it will start to bounce. I do it with my G3 tin boat. Same as everything you said, except once it gets on plane I trim it up until I start to bounce and then just tap the trim down until it flattens. I noticed keeping it right on that limit can get you an extra mph or even two (depends on wind direction)

[jly]

you might not be carrying enough speed to have it trimmed up very high...the slower you are going the less u will be able to trim it up....but I am shooting in the dark until more info surfaces

[marinetech]

you might not be carrying enough speed to have it trimmed up very high...the slower you are going the less u will be able to trim it up....but I am shooting in the dark until more info surfaces

My thoughts exactly.

[ksboy]

Simply put, I think as you try different approaches to running your boat, you will learn how to stop it porpoising. I think this happens to most guys with a boat they are just beginning to drive.

My boat (92 Champ 168 w/100 Evinrude) will porpoise if I trim or tilt it too high no matter the speed I'm going. I have to be sure I get the motor all the way down to start.

Be aware that your hydraulic Trim/tilt is named that because there are two different stages: Trim=the motor is ALL THE WAY down and can be lifted hydraulically to the Tilt, where the sound of the hydraulic lifting will change and the lift (tilt) becomes a more rapid movement toward the "up" position.

One way to discover the difference is while the boat is on the trailer. Run the hydraulic all the way down till it bottoms out or almost reaches the ground, whichever is the furthest. Then run the hydraulics up till you hear a different sound. Notice the position of the motor (it will probably be about level with the ground) this is where trim stops and tilt begins. (At least this is all true with my boat).

I hope this doesn't confuse the issue but I doubt the porpoising is caused by the boat as much as your inexperience at operating it. Relax and have fun with the learning process.

[tomustang]

I trim it all the way for kick-off then as soon as i trim it up a little thing it starts to cavitate, I cant even put it straight with the boat.

Are you getting up to the max speed of it trimmed down before you start to trim up?

[salmicropterus]

My experience is that porpoising is caused by too little speed combined with too much trim. Some to maybe all of your issue will be solved by some seat time. The comment about the jackplate is a good one though. Offset from a jackplate can help this out and as suggested, without a JP, you may have to adjust motor height.

[zewski]

Ok here is what the motor setup looks like... is this a jack plate?

 

Is it ok?

 

[South FLA]

Ok here is what the motor setup looks like... is this a jack plate?

 

Is it ok?

 

 

No its not a adjustable jack-plate, but it does give you an offset from the transom, so all appears fine from the picture.  Most people never setup their boat to perform at the optimum, so the previous owner most likely used what was given to him and never tweaked it.  Also, you really can't trust most marina or dealers to know what they are doing or take the time to do it right.

 

Therefore, spend time reading this

 

 

http://www.kencook.net/Setupart.html

 

and surfing the internet for information on your specific boat and engine configuration.

 

Lastly be willing to spend some money on trying different props or borrow some that fit your needs.  Powertech propellers does an excellent job of providing setup advice here is their website

 

http://www.ptprop.com/

 

We can speculate all we want, but unless we know gear ratio of engine, prop pitch, prop height relative to planing surface, weight distribution, etc. we may lead you astray.

[slonezp]

I would definitely ditch the aluminum prop.

[indianabasshunter]

I would definitely ditch the aluminum prop.

Ignorant question here but why would you ditch the aluminum prop?

[JCOX2011]

Ignorant question here but why would you ditch the aluminum prop?

The reason being is that a stainless steel prop is much stronger.  Here is a quick link that might help with more information. 

http://www.mercurymarine.com/propellers/about/how-to-choose/stainless-vs-aluminum  I think a lot depends on the size motor you run.