snave8

I started a thread a while back about some of the issues I was experiencing with my new boat. This thread deals with a specific issue so I thought I'd start a new thread. I've also posted this to the Donzi Forum.

I recently purchased 22 Classic Anniversary Edition with a 496 Mag/Bravo One.
Compared to where I started out, I'm much more comfortable with the boat now. I switched the Bravo One prop that came with the boat for a Turbo One 25P.
The boat seems too handle better overall and I picked up a couple more MPH with the new prop but.........Here's the problem: I'm getting an extreme intermittent porpoise that starts at 63MPH.
I'll take the boat out with 4 adults in light chop and she'll do 67mph the whole length of the lake. I'll take the same people out the next day in the same conditions, and can't get over 63 before the boat starts to develop a severe porpoise.
I know this is a drivers boat, and believe me...I'm drivin it. I'm a commercial seaplane pilot, so I'm used to operating complex machinery, that requires constant control inputs on the water.
Here's what I'm doing, and what happens:
I typically run the boat with an eighth up trim and tabs halfway down for normal cruising (25-40 mph). Any less tab than that and the boat porpoises. When I want to go wide open, I open the throttle, raise the tabs all the way up, then trim to max speed. This configuration puts the bow WAAAAY up in the air, leaving just a few inches of the transom in the water. Some days everything goes well (although it's a scary ride when I encounter boat wakes) and some times at 63 MPH the boat develops a NASTY violent porpoise, with each cycle getting progressively worse, with the bow going increasingly lower, to the point where I'm sure, if let go, it would stuff. The only way to stop it is reduce power and aggressively down tab.
The only way I can go anywhere near top speed consistently, is to leave the tabs down slightly, but this knocks 3-4 mph off my top speed, and even then, I have to drive with my hand on the trim tab control, so I can immediately drop the tabs at the first sign of porpoising
Fuel level effects this also. with full fuel, the porpoise is less likely to develop, and when it does is less severe.
When I first got the boat, I ran it out of gas (When the gauge reads 1/4, there's about 1 gallon left in the tank). In any case, I put 5 gallons in it to get me home. I figured I'd see what she'd do with just me and 5 gallons aboard. Couldn't even go 60 before it would porpoise uncontrollably.
I've owned high performance boats all my life and have NEVER experienced anything like this. Obviously they're not all like this, so I'm wondering.......Do I have a bad hull possibly? could the drive height be wrong when it was installed. Should I try a different prop? The bravo one caused the boat to chine walk and porpoise some, but nothing like it's doing now,.........Help!!
Mark

thirdchildhood

iTrader: (6)

I don't have any porpoise issues at all. I mean I can induce it at low speeds but if I trim down it stops. Never an issue at higher speeds. A few boats left the factory with the drive slightly off center. 1/4" can cause problems. Start by checking that.

Cevert

Have you tried using a straight edge on the hull to determine if you've got a rocker issue?

snave8

Not yet, but I'm going to this weekend.
just curious, if that's the problem, what's involved in fixing it?

Cevert

Depends on what you find; could be as simple as a little grinding or as much as reworking the entire hull (the "blueprinting" you may have read about). Have you posted in the Fiberglass forum here on OSO?

Have you posted over at http://www.donzi.net/forums/index.php ? There are some experienced 22C owners there too.

I see you are a seaplane pilot. What do you fly? 208s or Twin Otter floatplanes? Or maybe oldie Grummans?
Sorting out your hull isn't that much different than getting the ac weight and balance right, there just isn't an app for it, yet!

snave8

Yes, posted the same thread over at the Donzi Forum.
I fly a Lake Turbo 270 Seafury.

Mark

thirdchildhood

iTrader: (6)

The shorty advice probably won't cure your issue but you will probably be happy with one anyway. A lot of us run those. At least one of the "problem" boats mentioned had the drive installed off center.

93viperboy

Following

SB

iTrader: (1)

Is the Turbo prop what others with your boat are running ?

My only experience with a Turbo prop was on a light weight 20ft boat and wholly schit did it provide bow lift. Way too much for this boat. When you would use the trim, the outdrive would not move in relation to the water, the boat would just lift....like the whole damn boat. Scary actually.

Props can make or break how a boat drives.

thirdchildhood

iTrader: (6)

Yes it can but the 22 Classic hull should not have any bad handling characteristics at speed with any prop. I'm running a BBlades 30p Bravo 1. The Bravo 1, Turbo and Mirage plus are all common on these boats and will not induce porpoising or chinewalking. I'd say the M+ is the most common prop and is what they come with from the factory, or at least they used to.