Anyone Tried a Hull Like This

I found this when I was looking for some ideas on boat plans.

http://www.youtube.com/watch?v=UB1X2gNFI_Q

 

Air intake to the step was try'd before, Beneteau perfected it and claims measurable improvements, patented their system and put it in production. Dont think its a good one for homebuild.

 

It's impressive, but not so feasible to construct I'm sure. Many hundreds of hours of testing probably go into a hull like this. Coming from an aeronautical background I am always curious to design and look at improving drag coefficients, etc.

Of course, standard hulls offer the stability and predictable handling that most users want and require.

I cut my teeth on fast cars and fighter jets, so I am always looking for performance gains and unique mods and designs....

 

Of course, my first pressing issue is to get the family fun/fishing/everything 17 footer to change from a shell to daily user for the Summers here in Greece. After that, we'll move on to bigger projects...

 

Yes, it was tried before: http://www.sassdesign.net/InterceptorpresentationengJGK JS.pdf

 

Pretty cool design. This is a lightweight example of the project though. I wonder how this design would function on a mid-range sport boat. Let's say a 18 - 20 footer.

 

When you look at the sales brochures and data, they are usually consistent in showing gains at top speed or "ease to start planing" or similar claims. The overall performance, for specialized designs is often poor. For example, a hydroplane can get a very high top speed for the available power. It will be a bad boat to go fishing with the family or any other than the designed use. For most owners, a multi-purpose boat is necessary.

 

Air injection step designs have been around for a very long time. Saw my first one in the 1950s'. There was one on this forum a few years ago that used ram air from the topsides like the one in the youtube. Any information on how they work and why they offer improvement seems to die out after a brief splash. Whether it is "riding on air" or "reduction in wetted surface" seems to be the issue. Like many others, I have thought about it and even drew a couple up but the complication and the belief that it would only offer advantage in higher speed stopped the venture.

 

Gonzo,

I think you are right. When it involves the family, it also involves spending the CA$H--safety, multi-purpose, functionality, etc. The performance factors have to be put on the shelf sometimes....

 

There is a correct term for this type of thing,its called a Sales Gimic.
It dont work and very easy to see why it dont actually work.
for a ram air system to work, the air going through a passage needs to be under more pressure than where it exits to be allowed to escape.
Now with a stepped hull the void created by the step does not break away like you might think, if it does just simply break away then the step itself is not working.
this area is a trapped void of air that aids the boat to lift higher,if the air escapes, the boat falls back down.

Many people have tried tio do this and only realy seen a gainl when compressed air was introduced to help the flow of air under the boat causing the boat to ride as if lighter built.
Ram air under the boat by benetau is nothing new and the size of air ducts for it to be any good would need to be enormous.
Look at the size of air vents on cars to help cool brakes, the vents are as big as possible and yet still only a small amount of air gets to the brakes via ducting.
this is on high performance cars that are travelling at 150mph with the front air dam helping the vents as well.
Now does anyone realy think that a tiny airvent can help lift a 2 ton boat ??????

What happens when the boat sits in the water for 2 months and the air ducts are full of creepy crawlies ? will the air blow out the barnacles from the pipes as well.

I wonder how much the new extra large pipe cleaners from bennetau cost ?


phill

 

phill,

You definitely have a point. I am a NASCAR fan and observe the significance of brake cooling during races; however, these cars are traveling at high rates of speed. The "creepy crawlies" I had not even thought of at all yet. As I said, I happened across this when searching for hull designs and had not really thought of it before.

My purpose for anything like this would be trailering, so the creepy crawlies have to be able to live out of the sea in very dry Greek air. I'm addressing small performance boats that don't stay in the water for long periods.

And also being the fighter jet world, RAM Air is a huge factor. It cools the engine and provides flow to the environmental system (HVAC, if you will). You are correct about the speeds. All of the above uses are traveling at high rates of speed which make RAM Air a successful tool as it is applied.

 

Previous thread discussing this concept: http://www.boatdesign.net/forums/boat-design/air-ventilated-planing-hull-design-38431.html

 

As Phill said, unless the intake is pressurized, how can it work? Steps normally are ventilated from the chine and the air there must be lower pressure than ambient or it would not be "sucked" in.

There have been some that did that. There was one called CAT (Controlled Air Technique) from Australia some years ago in BoatBuilder Magazine. I think it had chine fences to contain the introduced air that was pressurized by a fan.

Several kinds of boats do use air under pressure to reduce drag though, like the Sea Sled and Inverted V. As was also mentioned, these have huge intake cross sections and the outlet at the stern is small. Aero lift is common in racing hydroplanes.

 

Around 1906-1908 William Fauber obtained a US Patent for multi-step planing hull with steps ventilating air ducts, some water-based airplanes (round 1930-40) incorporated such ducts.
K.

 

Get a tunnel and solve all your problems in one !!

Dont have to guess make a tunnel hulled boat the faster you go the better it performs !! your a air person so its in surface effect and rides on a cushion of air between the two hulls !!
No its not a catamaran !!!
its a tunnel hull !! cats are just two hulls end of story !!