Porpoising problem

[Bronzer]

I have a 2004 19 foot Skeeter with a Yamaha 150 4 stroke and I have a lot of trouble with porpoising. I can get it to run smoothly as long as I have it trimmed up on the pad and I run at 4000 rpm or higher. Once I drop below 4000, it starts porpoising. I can trim it down and it doesn't stop. Once it is completely trimmed down, it is better, but not entirely gone. Doesn't matter if the water is rough or smooth. If it drops below 4000, it's going to porpoise regardless of where the trim is. I can't move weight forward, batteries, etc., because there is nowhere to put it. The boat uses 4 batteries and has a 32 gallon tank. I've even let the gas get down to a quarter of a tank to eliminate fuel weight and it didn't help at all. I've thought about getting a fin to mount on the cavitation plate. Any ideas would be greatly appreciated.

 

[JASinIL2006]

SmartTabs.

 

[harleyman1975]

You are running a heavy boat with not enough engine. I bet max hp on that is 225 or 250?

 

[Stumpalump]

That boat is made to run on the pad.

 

[Bronzer]

Actually, the boat is rated for a 150 hp max.

 

[Texasmark]

Got a jack plate? Up it a notch. No, just bolted to the transom? Unbolt it and up an notch. Your running the gas low helped to solve the "is there too much weight in the stern" question. Porpoising is thrust angle vs amount. Too much of one and not enough of the other is a problem. On raising the engine, you get the AV plate out of the action and let the hull design and thrust angle work for you....BTDT on more than one boat. Avatar is an 18' alum bass boat with a stock 90 Merc, right at 50 GPS, one of the boats that responded.

 

[Bronzer]

It has a jack plate. I'll up it a notch and see if that helps. Thanks.

 

[Old Ironmaker]

Is this a new problem for you or a new to you boat?

 

[Texasmark]

It has a jack plate. I'll up it a notch and see if that helps. Thanks.

Let us know the result. If better move it up it more till it gets worse then back it down a notch.

 

[Bronzer]

Old Ironmaker, I bought the boat in November and it has had this problem ever since I got it. I'll post the result. Thanks.

 

[Texasmark]

I wonder how this is going......no word yet.

 

[Old Ironmaker]

On many forums the OP is new and posts but never returns. Not just here, many forums. I as well am guilty of it. Forgot where I posted the original query or the 21 digit password.

 

[Lowlysubaruguy]

On plane watch the outdrive its upper plate should be planing and not below the water line. I assume it does not have a jack plate which means shimming the outboard on the transom. You might get a good idea how much it needs moved by watching it first then rip a few pieces of 2x4s in 1/4" increments ( thinner and thicker than what you think the outdrive needs raised meaning you can cover a width of about 1 to 1 1/2") head to the water and try a few different thicknesses until you get it right. From there you can decide if you want to leave the 2x4 in it or make something out of aluminum or plastic that will withstand time in the water.

 

[Bronzer]

Okay,
I raised the jack plate about 1 1/2 inches. Didn't seem to make a difference. I've often heard that the AV plate should be a few inches above the bottom of the transom. Mine is quite a bit higher than this. Is it possible that the motor is too high? Should I continue raising it up an inch at the time or try lowering it? Thanks for all the input.

 

[QBhoy]

I'm thinking it's a combination of a big heavy 4stroke and too many batteries in the back.
Can you cut down on the batteries ?

 

[Texasmark]

How about a few pictures:

1. Side view 4' from nearest side of boat, even with engine AV plate. Strait edge (yardstick will do) extending from the keel area with it extending back to the AV plate. Engine vertical respect to hull (90 degrees) aka zero trim. Include the prop in this picture and if you can't, move the camera from the same location but slightly aft till you can pick up the prop too, including the prop's blade tips.....2 pictures if necessary.

2. Rear view of transom, 4' aft of engine , height of AV plate looking straight forward. Would expect the prop to be visible in this pic and if not, from the same position just tilt the camera down till you can and shoot #2.

3. Interior of boat showing from transom to 3' forward. If you have to lift a hatch or remove seat cushions you need to do it and expose what's below them.

4. From up at the bow, get down to where the camera can just see the top of the LU gearbox while looking all the way down the keel area. Try to focus on the hull midsection (half way between fore and aft of the hull). You're looking for a hook in the hull.

Let's work with the results of that.

 

[Bronzer]

Not really. I have 2 for the trolling motor, one for cranking and one to run the electronics, lights, live wells, etc. The boat actually came with 4 battery trays installed, so I would think that it was built to handle 4 batteries.

 

[Bronzer]

I believe I'll have to take the boat off the boat lift and put it on the trailer to take the pictures. I'll do that and post them as soon as I can.

 

[joe833a]

I recall when a boat had this problem, it may have a hook in the keel. Check to see if the keel is flat, front to rear.