what's the name of these ?

look at the photo.
high speed boat usually come with that, i know what it used for, but I don't know the name .

 

vent !!!

 

They are called steps.

http://www.fastelectrics.net/monohulls.php
http://www.ittcwiki.org/doku.php/structured_dictionary:shipgeometry#step

They are common on ultra high speed monohulls to reduce WSA:

 

They also make the boat run in trim with less sensitivity to fore and aft loads.

 

So the vents allow air to come in from the side of the hull to reduce skin friction and airate the surface between the hull and the water and yes they are used with STEPS
But there is a popular brand of boat that has 2 VENTS eachside to let air in the down turned chined edge of there DYNA hull !!and the hull dosent have steps !!

 

Not really. What they do is make the water touch only the aft end of the steps, with a reduction in wetted surface. They are not vents. You can maybe visualize them as a series of trim tabs. The original design in the 20s was called a "shingle bottom" and was promptly banned from racing.

 

ITS A VENT !!!

 

Actually they are ventilated steps. You can have steps without vents, though vents make them more effective. Shape, size and location can be (usually is) critical. The dynamics of their application are pretty easy to see, if you look at high speed tank test video.

 

You hit the nail right on the head! Here is what Sorensen's guide to Powerboat has to say.

 

LOL!

Yeah, but actually both vents and steps can be seen in the pic. So you all guys are right.

 

I suppose it would be possible to install some kind of endplates to prevent the steps from venting. I think that there is a lot of confusion, mainly caused by advertising, about "air lubrication" and other related claims.

 

Why would one want to do that??

 

I think he's saying most steps are small vents because they're cut up into the hull. That makes an opening at the chine. To not be a vent some kind of end plate would have to block off the opening.

Some steps have bigger vent openings than others:

Active Thunder's "Patented DDC Ventilated Step (#36879)"
http://www.activethunderboats.com/37.html

 

Here's an outerlimits 40 with a much larger vent opening on the step

 

Cool boats