One Man’s Quest for a Fully Aerated Hull

High performance stepped hullRoger Mutimer (all)

Australian boatbuilder Roger Mutimer is developing an alternative to a high-performance stepped hull: a completely aerated hull.

Recently we heard from a fellow in Australia who has been experimenting with a somewhat radical hull surface. A welder by trade, Roger Mutimer says he has been designing and building aluminum boats for many years; they range in size from 13′ to 75′ (4m to 23m). Here’s what he had to say:
I just subscribed to Professional BoatBuilder and wanted to let you know what I have been trying to do in Australia. My passion is designing and building aluminum boats. My latest project is a new hull design for powerboat racing. This aluminum hull is fully aerated and can be used on any powerboat design. My concept is not to try to get the hull out of the water, where you have no control, but to keep the hull on the water and use its movement over the water to draw air in so as to create a completely aerated hull.

The problem I find with the stepped-chine racing hull is that everything stops at the step. So when it comes down and hits the water, the water hydraulics up into the step, forcing the hull to go in the opposite direction.

My theory is to have a lot of small steps over the hull to overcome that problem. All trailing edges plus planning strakes are sharp enough to cut your finger on.

Hull surface with numerous mini-steps

Looking a lot like a cheese grater, the surface of Mutimer’s aluminum hull has numerous mini-steps.

I have tested the hull with a Mercury 300XS racing outboard on the back; with 35 gal [132 l] of fuel she came in at 2,646 lbs [1,199 kg]. On the water we managed to get 70.1 mph, but we could only get 5,700 rpm out of the motor. So we did a run at 70.1 mph and then released the throttle, and the boat stopped as though you had put your foot on the brake.

My next test was doing a vacuum test because I came to realize that I wasn’t getting enough air under the hull.

I have been working on this hull concept since 1990, but it has only been in the last four years that I have decided to do something about it.

Vacuum test illustrationThe drawings explain how I did the test. As you can see, 3,516.48 lbs vacuum is a fair bit of drag on the hull.


Vacuum test illustration

Mutimer performed a vacuum test to determine drag, which he concedes is “a fair bit.”

Mutimer is interested in hearing what PBB readers think of this concept, and how he can improve on it. Please share your thoughts with editor-at-large Dan Spurr at

About the Author: Dan Spurr is Profes­sional BoatBuilder’s editor at large.

One Comment

paul w

Hello I’ve been tig welding for 38 yrs . Certified 6g aluminum 5/8ths thick titanium and all else. I work on off shore racing boats, and have lived on the water my whole life. I have friends that have built the hull design that I consider artists.I’m not going to spew about my accomplishment s . But looking at it seems that your over,thinking the goal. Sometimes less is more. If you would like to talk or just call me crazy, I believe that my friend might be able to help.I’ll take some pictures of what he has done and send.them to you. Text me at 419 283 name is Paul I really don’t know computer s , I’m old school.if we can Skype or gmail great good luck! Some of the boats race around the world,best I’ve been in was 127 mph

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