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Stepped hull design in cats?

Posted By: dave mosley

Stepped hull design in cats? - 07/01/15 02:27 PM

Anyone tinkered with or have reasons that a stepped hull design would or wouldn't work with our type of cats?
Sea Hunt and Glassmaster are claiming doubling of fuel efficiency and increase in speed with their stepped hull designs.
If that's true, then what would it do for us?
ps patent pending....!
Posted By: jkkartz1

Re: Stepped hull design in cats? - 07/01/15 03:15 PM

Look for the ORMA cat, Region Aquitaine.

It was not very successful.
Posted By: rehmbo

Re: Stepped hull design in cats? - 07/01/15 04:42 PM

Steps would be hugely draggy at less than planing speed = 95% of the time. Those big power boats can do it as they have 7 kazillion horsepower on the back that can quickly get them up on the step.
Posted By: Jake

Re: Stepped hull design in cats? - 07/01/15 07:20 PM

Originally Posted by rehmbo
Steps would be hugely draggy at less than planing speed = 95% of the time. Those big power boats can do it as they have 7 kazillion horsepower on the back that can quickly get them up on the step.


agreed...that's a high speed planing hull shape. We don't go fast enough to take advantage of that.
Posted By: dave mosley

Re: Stepped hull design in cats? - 07/01/15 07:30 PM

you do Jake!
Posted By: Anonymous

Re: Stepped hull design in cats? - 07/02/15 05:32 AM

Mattia back in 2003. Lets just say they only built one.

[Linked Image]

[Linked Image]

There are two issues stopping it working.
1. As stated above speed.
2. Venting. for the steps to make a difference you have to be able to get air to them. a normal cat (non foiling) would require vent cutouts to go almost up to the gunwales to achieve this. If you can't get air in the step actually sucks you down onto the water and adds drag.

Attached picture bella,alzata sailing.jpg
Attached picture Mattia beach.jpg
Posted By: Bille

Re: Stepped hull design in cats? - 07/03/15 06:58 AM

That Tri , l'Hydroptere ; they use stepped hulls.

Here is a good shot of them ; it turtled after a 60K
run.

http://yachtpals.com/hydroptere-4036

Bille
Posted By: rehmbo

Re: Stepped hull design in cats? - 07/03/15 11:36 AM

I think Hydroptère is one of those corner-case boats. Huge amount of sail power allows it to work in windy conditions.

You could probably do this on an 18' boat too, but would only be "fast" and up on the step when its blowing over ~20kts. In all lesser conditions I'm quite certain that normal style hulls would be faster.
Posted By: Bille

Re: Stepped hull design in cats? - 07/03/15 06:21 PM

Originally Posted by rehmbo
I think Hydroptère is one of those corner-case boats. Huge amount of sail power allows it to work in windy conditions.

You could probably do this on an 18' boat too, but would only be "fast" and up on the step when its blowing over ~20kts. In all lesser conditions I'm quite certain that normal style hulls would be faster.


I Totally agree !
To make a stepped hull work ; you'd need Copious amounts
of power, to drive it.

The thing that impressed me most about Hydroptère ; is
the speed they'd get out of conventional sails !!

Bille
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