What is this on the boat ?

Hello everyone,what is the area inside circle ? What does is do ? I dont understand...Attachment 156417

They are steps, they increase the effective angle of attack of the hull thereby reducing it's wetted area and increasing its efficiency at speed, without the increased likelihood of blowovers that comes from running an unstepped hull at a higher AoA, or moving the CoG back to reduce the wetted area. Shaped right they can also reduce a mono's tendency to chine walk.

Thank you,i have one more questions.this steps,what characteristics are the crafts made or designed?

That question is hard to interpret, but if I am reading it right, the steps are designed to make the boat faster for a given power and/or, use less power for a given speed.

Some believe that steps aerate the water behind the step, and that this is reduces drag, while some believe that any aeration of the water decreases the efficiency of the lifting surface or surfaces and prop behind it. While the benefits in my first post are long proven I have not seen conclusive proof either way on this, indeed in order to prove it to myself I designed and built a cat specifically to test aeration with air tunnels through the sponsons, fed ram air from lipped naca ducts on high pressure areas of the deck, I got no noticeable performance differences with the ducts in use or taped up. It was a single drive cat, so the prop would not have been in aerated water. The steps were large enough to prevent a vacuum forming in them that lifts the water up behind them creating a lot of drag which is a problem that can happen with poorly designed steps, even some that are scaled proportionately from well designed full size boats, as boundary layers don't scale.

Thanks your answer,sorry for my english :) this is not very well...you are testing a cat,how do you do design ? Is there a specific rules ? Or is it random? For example,the steps would be build on the balance point of boat, is more effective ? As a result of, what is the steps rules ? According to what criteria they are built ? Is there a formul ? This is my boat, i do step has been done according to balance point of boat and this is female mold .

I am not testing, I tested, that cat has long since retired. Generally my design was based on trial and error, a bunch of boats with variations on a theme and seeing if it improves or gets worse with each change, if it works trying to exagerate what worked and see if that works better, movable elements like taped on ride pads etc can speed the proccess up a lot.

The step, or front step if there is more than one has to be in front of the CoG, about 10-20% in front like the sponson of a sport hydro seems to work, if there are more than one steps the CoG will be between the front 2 steps. For the racing I do with a 60m straight, 5m radius turns and boats with around 500W/Kg a medium height single step is optimal, bigger single steps give the best efficiency but worst handling, smaller multi steps give better handling but worst efficiency, unstepped gives best handling but worst efficiency.

Hopf did some monos very much like that one, which I would call 1.5 steps, with a high AoA middle step, well forward of the middle and slightly higher than a line between the front step and transom, I never understood the concept and haven't tried it myself, they didnt last long, Hopf's later boats had single steps.

Some time ago, maybe 6 or 7 years, I saw a canard with steps on the front. Unfortunately, I was unable to connect to or converse with the designer because of the language difference. It was the same timeframe when I built my own canard, only to have it smash into pieces at high speed while testing. The canard I saw had evenly spaced steps, about the same depth in the water, so their purpose had nothing to do with getting on plane or keeping the canard on plane while turning. I don't know that I have a picture anymore to share.