Can anyone tell me what this is for?

[Evildwarf]

saw this feature on a wakeboard boat hull and wondered what it is for?
it is midships at the water line on both port and starboard sides, obviously a beneficial feature for handling or wakes but I cant figure out what it does?

 

[Ajax]

A lot of boats manufacturers are adding these to the hull. I can't remember the technical name. I think I first saw one on a Regal. I believe they aid in tracking and possibly getting on plane easier. Not sure about it affecting the wake. Pretty sure it's all about handling.

 

[Murf'n'surf]

Typically you will see these vents on boats with stepped hulls. The boat might have 3 steps; one for slow speeds(entire hull), one for mid range(mid hull) and one for top end(aft portion of hull). The second and sometimes third steps have these vents to allow air to be sucked in and under the boat to aide in faster speed. Without the vent there is a brief period that the boat sticks to the water as it tries to rise. This vent can also allow air to mix under the hull and reduce drag.

 

[Woodchuck]

Like Murf said, it is to prevent the suction or vacuum that the water can create on the hull.

 

[Julian]

Yup...this is one area that jetboats are at a disadvantage....you don't want to inject air to reduce drag as it will get sucked into the pump.

 

[Englewoodcowboy]

That is also where a jet boat has its performance advantages as well. Jet boat time to plane is significantly less due to the nature of the thrust, air vents are not needed on them to improve that.

 

[Glassman]

Typically you will see these vents on boats with stepped hulls. The boat might have 3 steps; one for slow speeds(entire hull), one for mid range(mid hull) and one for top end(aft portion of hull). The second and sometimes third steps have these vents to allow air to be sucked in and under the boat to aide in faster speed. Without the vent there is a brief period that the boat sticks to the water as it tries to rise. This vent can also allow air to mix under the hull and reduce drag.

As usual, Murf is spot on. Here's a picture for those of us who need to visualize things....

 

[txav8r]

y'all are spot on...except that in my view it isn't generating lift, it is reducing drag. And drag is a byproduct of lift. A stepped hull simply separates the hull from the water behind each of the steps, which reduces the amount of hull in the water when at speed. @Glassman , those pics make it easy to see on the lateral view, the underside view is a little washed out for me (pun intended). I also see it as the step adds a layer of air between the hull and the water, that decreases drag, friction if you will. Kind of like a hydroplane or a hovercraft uses air to decrease drag to let an otherwise large surface pass over an area with less resistance. There is a great deal of adhesion that is created between the hull and the water, breaking up that adhesion really decreases the amount of force required to get the boat on step, as well as reducing fuel consumption and possibly letting a manufacturer either get more speed or use less HP to get the same speed as a non stepped hull. But like @Julian said, it would be a feat to design a stepped hull that works well with a jet boat that has to have a totally undisturbed water intake into the pumps. It is probably very possible on larger vessels.

 

[Glassman]

I'm going straight to hydrofoil for my next mod!

 

[Murf'n'surf]

When air is mixed into the water it makes whatever is above it more buoyant. The mixing of water and air generates lift to the aft most part of the hull and the initial air that breaks the hull to water seal is reducing drag.

At any rate, this technology works well! When you get going fast (65-70 mph in my experience) the small amount of hull that's left in the water can give you the major pucker factor. Your steering becomes ultra sensitive and the feeling of un-stability overcomes your senses ---- but man are you trucking fast!

 

[GTBRMC]

All of the above are accurate.

In fluid dynamics terms, the hull step(s) trip the boundary layer and change the flow of hull against water from a laminar (higher drag) to turbulent (lower drag) flow.

Brief reference (note, it is Wikipedia, some of the article appears incorrect, but it might be interesting to some).
http://en.wikipedia.org/wiki/Boundary_layer
http://en.wikipedia.org/wiki/Fluid_dynamics

 

[BoaterGuy]

This video does a good job explaining...

 

[Julian]

This video does a good job explaining...

Not only explaining it...you can actually see the air being pulled in under the boat! @Englewoodcowboy it doesn't only help with getting to planing speed, but also while on plane it reduces drag/adds lift. Makes one wonder if there is a way to quickly remove air from a stream of water? That would be an interesting patent to own!