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Forced air ventilated stepped hull?

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Old 11-15-2005, 09:28 PM
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Default Forced air ventilated stepped hull?

Anyone know the story behind this boat? photo gallery



In this pic it appears to have some sort of forced air hull ventilation
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Old 12-02-2005, 03:24 PM
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Default Re: Forced air ventilated stepped hull?

I have been considering an air pressure system under a stepped hull myself. Theoretically, it should decrease wet area, reducing friction, and increasing performance. I know it will work. But, how much pressure, where the openings should be, their size and shape would have to be engineered. With 65 OSO views and only my reply since the 16th, it doesn't look like too many people know much about air under hulls, or they just have'nt seen your thread. Hovercrafts have been doing it forever.

If you've learned anything new since your post, please let me know. There must be knowlegeable people out there on the subject. Tony [email protected]
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Old 12-02-2005, 03:36 PM
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Default Re: Forced air ventilated stepped hull?

Firt off I know jack sh!t about this boat or anything to do with forced air hulls. That said it looks like a cool concept but will it be faster or not is the question. You need to build 2 hulls identicaly and test.

It looks to me like the intakes on the bow are connected to a system of ducts layed up in the mold. The air is then forced through the ducts simply by the speed of the boat. Just my guess. Air pumps would add huge weight.
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Old 12-02-2005, 03:48 PM
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Default Re: Forced air ventilated stepped hull?

Hallett has already been doing this on some of their stepped boats. The way I understand it it is not really forced air as much as a venturi effect of the suction behind the step drawing the air through the tubes layed up in the hull. The intakes can be on the sides above the steps. This also breaks of the vacuum sucking the hull down. This is possible more of a problem on single engine boats that have high prop torque and tend to lean to the torque side already. My understanding is the ventilated steps are faster than the nonventilated. I've seen this in person at the lake and it really is a pretty simple concept to incorporate while laying up in the mold.

Last edited by zahndok; 12-02-2005 at 03:52 PM.
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Old 12-02-2005, 03:52 PM
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Default Re: Forced air ventilated stepped hull?

We talked about this back in the early nineties when we were racing offshore. We raced an open cockpit conventional vee hull. I was the tallest member of the team and buffeted the hardest by the wind. My thought was to induct air from the deck at the base of the fairing, route down thru the forward cockpit bulkhead and out the bottom at the deepest part of the vee (keel). Our thinking was this would help reduce turbulence (resistance) in the cockpit and aerate the bottom of the hull. Unfortunately we destroyed the boat in Key West before we were able to test our theory.
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Old 12-02-2005, 04:00 PM
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Default Re: Forced air ventilated stepped hull?

Ask Tim Sharkey on this forum for information. He knows the boat and it's builder.
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Old 12-02-2005, 04:08 PM
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Default Re: Forced air ventilated stepped hull?

Outerlimits has been doing it for a few years now.
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Old 12-02-2005, 04:29 PM
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Default Re: Forced air ventilated stepped hull?

I saw a 50' Delta conic hull, made in europe. Looked kind of like an canopied infinity deck on a delta conic sigle step hull.At the single step it had large ventialated holes in the vertical section of the step.
Forced air was introduced fromj the exhaust of the 3 turbo diesels that powered it. My understanding is that it was not too sucessful since the bare hull was offered to me for under $10K.
Gary
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Old 12-02-2005, 04:45 PM
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Default Re: Forced air ventilated stepped hull?

Originally Posted by Gary Anderson
I saw a 50' Delta conic hull, made in europe. Looked kind of like an canopied infinity deck on a delta conic sigle step hull.At the single step it had large ventialated holes in the vertical section of the step.
Forced air was introduced fromj the exhaust of the 3 turbo diesels that powered it. My understanding is that it was not too sucessful since the bare hull was offered to me for under $10K.
Gary
If seen a few diesel powered boats where they designed a venturi for the exhaust. The the boat is underway the exhaust is being sucked out of the motor. On the boat that I saw tested it picked up a couple MPH in a 40 ft Trawler.
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Old 12-02-2005, 05:10 PM
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Default Re: Forced air ventilated stepped hull?

Diesel soot pumped under the hull. That should be nice looking after a long run.
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