Step hull?

[John Brown]

I saw where Larry got a new boat with a "step hull".

I've heard the term, I think I might know what it means Is it anything like "pad boat" as it pertains to bass boats?

Somebody fill me in, is the function to get more of the hull out of the water when you're up on plane?

If so I would be interested in finding out exactly how the bottom of the hull is shaped, can anybody describe it or show me a picture...Larry??

Thanks, John

 

[jim]

John,

Here is a picture of a step hull, it is nothing like a deep V with a pad:

picture is from an add in the trader

Jim

 

[Larry]

The hull has a step built into the bottom of it, so at speed it acts like a hydrofoil to get the boat out of the water for less drag. The result is a fast and stable ride due to the hull riding on the front and rear, instead of the rear like a flat hull. Here are some pics of step hulls sitting still and in action from the gallery.

Larry

 

[Croc1]

that first picture with the flames was thunders boat I took all of them at the oceola clubs run, these boat do not turn well but go straight real good

 

[John Brown]

Ok,

Thanks guys, I get it, like a hydroplane is the best description.

The post has got me thinking, why couldn't you manipulating the bottom on a conventional flat bottom hull to create a "pad" near the transom for the boat to run on when it gets on step?

It seems to me all it would take is a triangular piece of polymer and some longer screws. Why couldn't you cut a piece and slide it in between the hull and your existing polymer to make a pad for the boat to run on when you're on plane?

My first thought is it may just work like a hook in the hull and slow you down, but at some point if you moved it far enough forward I can't help but think you would get some more of the hull out of the water by doing it. The weight of the extra polymer may be an issue, I don't know. Has anybody ever seen anything like that?

 

[Waterthunder]

Here is the best way to explain a step hull. The drag coefficient is greater between water and a hull than the drag coefficient between air and a hull. Picture that old game of air hockey the puck flies around fast with little effort, then turn off the air and there is a allot more friction between the puck and table so the puck doesn’t slide near as easy or fast. Also for the safety factor if a positive pressure occurs in the bow area when the hull slightly lifts the air escapes out the step this can’t happen in a flat bottom boat because the whole hull must lift to let out the lifting pressure and by then your on the roof. What really makes a step hull fast is the hull rides on a cushion of air instead of contacting the water.

 

[Rich Andrews]

and they are fun as hell to drive.....

 

[SwampMatt]

ccasion5: !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

 

[John Brown]

The danger of getting airborne had occurred to me...not a good thing :shock:

I've got 2 jacks in the center of the boat pushed down as much as I dare right now. When I get up on step it comes out of the water nice and runs good but the boat will fall off left or right kinda like chine walking when I really start running. Its a handful to drive over 40-50 mph or so without getting off the throttle, it's a balancing act, which is why I was thinking about slipping a piece of polymer in between the existing polymer and the hull to stabilize it like this.

It runs ground better and is quicker in the water than it ever was before, right up to the point it falls off to the side, then its a rodeo trying to keep my a$$ behind me.

I think I can pull the jacks up again and go back where I was but it would be nice to find a way to stabilize it and keep the benefits of running less surface area.

It occurs to me the point about a normal boat being stabilized by the rudder in the water is valid. The thrust in an airboat has got to generate some downforce on the bow because the prop is above the hull. If you did get some bow lift while under throttle and backed out of it the down force from thrust would be gone. I can see things going downhill fast from there.

Obviously there is some compromise between going airborne and plowing through the water like a tourist barge. I wish I could find a way to stabilize what I've got happening now.

What do you think? Death wish?

 

[SwampMatt]

-

 

[John Brown]

Yea,

See, that trim tab idea is what I was talking about when I mentioned it possibly acting like a hook in the hull in the earlier post. If the pad doesn't come far enough forward then the boat won't get up and run on it and it would push the nose down like a trim tab or a hook in the hull, right?

My problem is I'm not an engineer and don't know how to calculate the forces acting on the hull to be able to make the thing work right without doing it by trial and error.

Are there any hull designers out there?