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gero1
10-09-2010, 09:11 AM
no step, 1 step, 2 steps? same length boat, what would be the difference in speed and handling

DonZi 26
10-09-2010, 09:25 AM
Im no genius, but from past experiences i believe that stepped hulls would have a smoother ride in rough water and are faster compared to nonstep hulls. But it also depends on the hull lines, and how it is manufactured.

A non stepped hull well built boat may be better than a stepped hull boat built non professionally.....

But if you go for a stepped donzi, fountain, or any major manufacturer it should be a good choice!

Dr. David Fleming
10-09-2010, 02:14 PM
The step has been with boating on the order of 100 years. Garwood and the Miss America boats built in Detroit in the 1920s all ran steps and multiple steps. So did all the competition. The whole idea is to get air under the hull and reduce the water drag. Boats with 4 - 6 steps were used.

Johnson developed a whole line of step outboards that were competatively raced until the 3 point hydro developed - Johnson called them "giant stepper", "big stepper", "baby stepper" - these boat hulls are still available in kit form from Glen L Marine.

Modern step hulls are using the same ideas with advance computor and hydro testing added - but the idea is an old one.

fasttrucker
10-09-2010, 06:25 PM
steps are great,I was just talking to catch-22 about my freinds sonic 31ss(non-stepped) it just goes up and down :dolphin: what a waste of gas..another way to look at the classic 22 vrs the 22zx.If it has the same power the zx with the step is faster.The only downside is spining out with the step hull design(hasnt happened to me yet)Note:Keep the trim-up in the turns.

farmer tx
10-09-2010, 09:24 PM
Isn't the 22zx a 19* hull and the 22-c 24*. That would factor in to the speed equation also.

fasttrucker
10-10-2010, 07:31 AM
Isn't the 22zx a 19* hull and the 22-c 24*. That would factor in to the speed equation also.
I did think about that,just the 22 part.

VetteLT193
10-11-2010, 10:40 AM
no step, 1 step, 2 steps? same length boat, what would be the difference in speed and handling

Depends on the boat length. The 27 Fountain runs with one step and seems just as efficient as the 28 ZX with two. The 28 seems to run flatter.

On longer hulls more steps can help. Also, it is a combo of the whole bottom that makes the boat. The 28 Donzi has a flat spot on the bottom and an interesting combo of strakes. The deadrise is 22 Vs. others @ 24. I think everything is a compromise of speed, handling, and ride.

here is a link to my 28's bottom: http://www.donzi.net/forums/attachment.php?attachmentid=56617&d=1275929061

The Hedgehog
10-11-2010, 04:41 PM
I would say that these guys have it summed up.

You have to drive them a little differently. You can't trim the drive in and do a hard turn or the back will out run the front and it will spin. Basically as long as you drive it accordingly it is no big deal.

The advantage increases as speed increases.


I did not know the Garwood thing. That is pretty cool. They also used them a good bit on float planes.

Greg Guimond
10-12-2010, 08:31 AM
Interesting topic. I always thought that "steps" occupied the entire cross section of the hull but then I ran across this in the pic. I'm not sure what the actual terminology would be......is it still considered a step? It looks more like a keel notch given how small. The hull it is on is 21'10" long.

VetteLT193
10-12-2010, 09:29 AM
That is really a notch with an aft flat pad.

If you look at my link in the post above you'll see the forward part kind of looks like that. A true V from the bow until you reach the middle part of the hull. then it goes flat. Of course it is a true step Vs. just a notch but the ZX hull seems to combine a bunch of different hull technologies.

Greg Guimond
10-12-2010, 09:47 AM
Thanks. Very informative pic. I guess on smaller boats the term would/should be "keel notch"? With the Surface Tension project we opted to fair the pad right into the keel with smooth transition lines.

Dr. David Fleming
10-12-2010, 11:35 AM
The "off shore" hull which is what you guys are talking about was a historical development of the 1950's. This means the "Deep V - offshore hull." First one was called "Brave Mopsy" and represented a re-thinking of hull design to run in something besides perfectly smooth water.

Before this development boat hulls was confined to three designs of hydroplanes,

1 - "displacement hulls" that did not run on the surface of the water
2 - "hydroplane hulls" that were flat in the back designed to rise
3 - "step hull hydroplanes" designed to run with air under a step
4 - "3 point hydroplanes" - designed to to run on sponsons and a prop
5 - "deep V offshore hydroplanes" - modern go fast boats - wave breakers

Catamaran - a narrow log raft or float propelled by sails or paddles. A boatwith two parallel hulls, built in the style of such a float.

Dr. David Fleming
10-12-2010, 12:31 PM
Got off the track on the last post, as I am interested in the 22ZX bottom one of which I have.

Front v section - is a "deep v" with 4 strakes running the full length. The only unusual section is on the bottom of the keel which is quite rounded. Possibly to keep the keel from acting as a pivot for the boat to spin around.

Aft section - behind the step is a shallower v section with a couple of hull tricks - 4 flat strakes that act like hydroplane sections to lift - one each on the chine and mid v. 2 strakes mid v with a half round cross section and vertical outer edge.

Hidden rocker - The aft v is flat except for two triangular section adjustments that form a kind of hidden "trim tabs" these are at the "quarter beam buttock" on each side.

There is a lot of lift in the back hull v section and a lot of deep v in the front section.

End result - a cadillac for rough water running

1 - a very fast hull in rough water
2 - lift decreases depending on how much is elevated
3 - rough water running improved at speed and elevation
4 - very high speed you are riding on a point bouncing on the chines

Greg Guimond
10-14-2010, 08:44 PM
"Aft section - behind the step is a shallower v section with a couple of hull tricks - 4 flat strakes that act like hydroplane sections to lift - one each on the chine and mid v. 2 strakes mid v with a half round cross section and vertical outer edge."

Do you have any pics of this aft section?