Z21 porpoise

[suprtrkr1974]

Okay so got a new z21 with a new V8 250 on it. I finally got enough time on my motor that I can start really opening it up and running it, and from what I'm seeing I'm not really impressed with the ride. The motor runs great outstanding good power good torque all the way through boat jumps up on plane no problem. The ride turns to crap once I get up to about 71 72 it starts porpoising really bad. At first I thought it may be chine walking and thought maybe it was feeling a little bit different where Nitro head redesign these hulls. The only thing that tells me that it's not Chine walk is the front end of the boat is more bouncing up and down. Just curious if anybody else has ran into this porpoising deal, I know I had seen something somewhere but I think that was on the z19 models. just trying to figure it out before I throw in the towel and sell it.

[jasonG]

Getting it at those speeds I’d say motor may be to high or your overtrimming.

[Jimmycast]

How far do you have the motor trimmed up? My '17 Z21 is smooth as silk in the lower 70's with the motor trimmed half way on the trim gauge. It will porpoise a little when slowing down rapidly with the motor still trimmed up. Sorry to hear that. That sucks. I could have a different hull. I don't know.

[Sun Fish]

I can chine walk some approaching 70+ with a 2 Stroke 250 Pro XS but that's to be expected.

[Teadow1972]

Cant compare the 250 ProXs 2 stroke to the new v8 4.6 liter 250. Completely different rpm range different prop pitch. Nothing the same. I have read that some guys are pitching up to 24p. All the ones I have seen have caome with 23p, seems small but that 4 stroke turns 6200 rpm not 5800. Anyway my 2 cents.

[suprtrkr1974]

How far do you have the motor trimmed up? My '17 Z21 is smooth as silk in the lower 70's with the motor trimmed half way on the trim gauge. It will porpoise a little when slowing down rapidly with the motor still trimmed up. Sorry to hear that. That sucks. I could have a different hull. I don't know.

According to my little cheap generic trim gauge on the dash I'm trimming halfway needle in the middle is straight up and down

[suprtrkr1974]

Cant compare the 250 ProXs 2 stroke to the new v8 4.6 liter 250. Completely different rpm range different prop pitch. Nothing the same. I have read that some guys are pitching up to 24p. All the ones I have seen have caome with 23p, seems small but that 4 stroke turns 6200 rpm not 5800. Anyway my 2 cents.

I'm currently running a 23 pitch fury on mine haven't stepped up to a 24 although considering it to see if it will take the porpoising out of it

[BMCD]

My 2017 would do this. I think adjusting the motor might be your first option. My 19 has been very easy to drive at speeds.

[suprtrkr1974]

My 2017 would do this. I think adjusting the motor might be your first option. My 19 has been very easy to drive at speeds.

Are you running the new 4 stroke? If so could you get me a prop to pad measurement, so I will at least have something to compare mine to.

[texasfisher]

Suprtrkr, I noticed porpoising as you described it in my 2017 Z21 above 73. Replaced the 24p Fury with 26p Bravo 4 blade and raised the engine about 3/4 inch and it the stopped the porpoising. .

[BMCD]

Ill try to get that tonight. Yes my 19 is the new v8.

[KCLOST]

A little general info in Porpoise.....

What Causes Porpoising?
Porpoising is the result of the motor’s outdrive pushing the boat upwards, essentially boosting it out of the water – albeit for a short period of time. Once the boat comes back down, the outdrive will once again push it back out of the water. This cycle will continue to repeat until either the boat’s speed is reduced or the trim is fixed.
Allowing a boat to porpoise is a serious hazard that can leave both the captain and his or her passengers at risk for injury. There have been countless injuries reported due to severe porpoising, so don’t overlook this element with your boat.
Stopping The Porpoising Effect
So, what’s the best approach to fixing a boat’s porpoising effect? Unless you want to reduce your speed, you must adjust the trim to prevent this effect from occurring. Access the trim controls on your boat and gradually lower it until the boat is no longer bouncing out of the water. It’s important to note that lowering your trim too low will result in a loss of speed, which is something most people want to avoid; therefore, you should lower it just slightly until you find a happy medium in which you maintain your speed but no longer experience the porpoising effect.
Not All Boats Porpoise Equally
While porpoising may occur with any powered watercraft, it’s far more common in boats with inboard/outboard or propeller-driven outboard motors. If your boat falls under one of these two categories, be prepared to adjust the trim when operating at high speeds.
It’s also worth mentioning that there’s no such thing as a universal trim setting. The appropriate trim varies depending on the boat’s hull design, size and weight. If you recently unloaded a large amount of heavy gear off your boat, chances are you’ll need to adjust the trim once more. The lighter load will directly affect how much “bounce” your boat has. In order to stop this bounce, the trim must be adjusted to fit your boat’s new weight.

What this info does not cover are a few other factors....

Motor height (or prop to pad) in addition to trim angle
Prop type and pitch
A desirable affect to most of us is to have the boat lift be maintained at high speed, so poor prop bite, boat load, and trim angle also prevent us from getting there as well. In other words we want the boat to be up in the air rather than trim down to stay flat on the water.

With all that said, I believe the Fury prop is not a good high runner.
Let's see what Bryan has to say about his set-up and then go from there. Loads can also make a huge difference on a prop/boat ability to overcome drop-off/porpoise. The old Tempests weren't as affected by motor height, but they don't have the power with heavier loads like the Fury does.

[BMCD]

Im 4inches below pad.

[suprtrkr1974]

Im 4inches below pad.

Ok thanks I'll check mine when I get home and see where we're at. Maybe one of those things I have to throw a little bit more weight up front

[Fishysam]

im guessing you motor is to high for that prop or you have to much up front to lift with that prop, maybe over trimmed

[KLSU]

Stopping The Porpoising Effect
So, what’s the best approach to fixing a boat’s porpoising effect? Unless you want to reduce your speed, you must adjust the trim to prevent this effect from occurring. Access the trim controls on your boat and gradually lower it until the boat is no longer bouncing out of the water. It’s important to note that lowering your trim too low will result in a loss of speed, which is something most people want to avoid; therefore, you should lower it just slightly until you find a happy medium in which you maintain your speed but no longer experience the porpoising effect.

Wait, I have always done the opposite of this.

If boat is porpoising I either trim down or go FASTER not slower..

[Fishysam]

if your wide open throttle you cant go faster, thats where his issue is at

[Wisfarmer]

It's not a porpoise really or a Chinese walk it acts as if the boats starting to gallop is my guess in what your description is several z21 have done this play with the motor height

[BMCD]

Reality is its a setup issue. Possibly u need to raise or lower. Possibly u need more cup on ur prop. Mine did when she was running plus 70. It almost like the prop cant keep the bow up.

[framer]

is it the norm tohave to play with multiple props ad engine heights when buying a nitro, from a nitro dealer, brand new, factory rigged.?