Catamarans High Speed Blow Over - Causes & Solutions

rxcomposite - just send (PM or email) me your email address, i will send you the article.

/jim

 

Thanks Jim.

 

Two fold.

First as the owner of an offshore style catamaran. I've found purchasing insurance for these boats is like being diagnosed with a terminal disease, then shopping for a life insurance policy. Actually was recently turned down on a small V-bottom boat simply because the manufacture also produced catamarans. Was once told "we don't insure tunnel hulls, and your boats manufacture is listed in our DB as a tunnel hull builder. Have a nice day"...

The larger cat I recently purchased is in full restoration mode, would be the perfect time to incorporate some safety and stability features. Though I don't plan on running above 120 mph, I do plan on operating in off shore conditions where suddenly getting pitched up is highly possible. Calculating the boats COG on the trailer can prove much different than real world operations. Things like ballast tanks are always an option, but I'd prefer to keep it light and use that weight savings for added fuel capacity. Which burns off and changes COG.

Second.

Looking to improve the overall safety of the class. At least for now, present a retro-fit option to current owners. Have personally witnessed a couple blow over events. Most recently saw the aftermath of one at a large poker run here in the states. The video of this is listed in my second post. Two lives were lost in that crash. Although I didn't see it happen, I did roll up on the boat being towed in after. A beautifully laid out craft from one of the worlds oldest racing cat manufactures, utterly destroyed by the forces of water impact. Watching the video I quickly noted the cause, same as so many before.

My engineering background tells me this event is avoidable. We can launch a space probe to another planet moving at thousands of miles per hour, slow it down enough to survive a landing, but we can't solve a well know problem with a simple boat design.. Just the lack of trying to fix it by the industry troubles me. On the boat racing side, surviving a crash has always been the primary focus. In modern pleasure craft these safety components like a canopy are often traded for napa leather seats and stylish design. All good if we maybe used a little technology to avoid needing that canopy. There is no fair competition rules stopping us, so why not explore the options.

The crash this month sparked a heated debate on another popular site over the cause. Too hot to even get involved in, never the less find a solution. I see this as a design flaw that exists in hundreds of boats. Insurance companies view it the same way. So lets determine the causes, develop a solution and move on. Air bags weren't developed because seat belts don't work. My original solution when presented this question several years ago, jet aircraft ejection seats, problem solved...

There ya have it. Not personally looking to fix the design, leaving that to those who should be working that angle. Just trying to understand the forces involved here and possibly develop a solution that can be deployed to avoid the outcome. Basically an air bag for a boat approach to the solution..

Cheers

 

Thanks Jim, nice read. I'm guessing the math scales up comparable to size?

R.R; sweet analyst illustrations. Is that raised canard concept a new addition to F1?

Has anyone ran hull dynamics that replicated taking roostertail induced turbulence? Just curious how far moves the numbers.

Tks

 

I dont see a hydro in any of these photos?
what is an F1 hydro?

 

well a car has an issue of going sideways at 200 so Nascar has to keep them under that, flawed design, un solvable ???

 

Flawed or better yet out dated. Bound by rules stating they must look and measure within specs of a production car. Jack Roush invented roof flaps so when one gets sideways at 200, they don't catch air, flip over, and fly thru a crowded grand stand. Back in the 70's they used a wedge nose and tail wing to run that fast, rem the Super Bee?

Now check look at a Bugatti Veyron, wouldn't even be a fair race vs anything from NASCAR. Which would you buy?

 

i'll bet the Veyron gets airborne if its going sideways at 200
which would you rather crash in...

 

I think you are on the right track. One thing that occurred to me was the use of the "jet fins" on the side, as large vortex generators . These devices have very little area and have small effect at low angles of attack, so they will not affect much when the boat is in ground effects in normal operation. but when pitched up to 15-25 degrees or more angle of attack, where a normal foil would stall, it generates a large vortex that generates very large amounts of lift far aft on the hull, and large amount of drag too. Both of these far back on the hull would serve to move the aerodynamic center aft. this will create large amounts of nose down pitching moments. once the angle of attack is back under about 4-5 deg, they stop generating that much lift, and presumably you will be back within ground effects.

No moving parts are necessary. Just careful sizing, shape and placement. The only "trick" here is to size and angle them to develop the correct amount of lift where and when needed, before departure occurs. reliably determining vortex lift is tricky because so much depends on the shape of the leading edge, the sweep angle and the angle of attack. But it can be done, that is how they managed to land the first delta wing fighters. they could maintain stable low speed flight with as much as 45 degrees angle of attack (considering that conventional straight wings stall at about 15 degrees, this was a major breakthrough in being able to land high speed fighter aircraft). Now all modern fighters depend on vortex lift for landing and high angle of attack flight maneuvers.

of course they had the big government bucks to solve the problem, but a lot is now known about vortex lift that was not some 40 years ago. You just have to find it, and than build some trial and error models to try it out.

 

As far as I'm aware nobody has run a canard in F1.
Its not possible to model spray/roostertail in CFD at this time

 

try looking at the 2nd pic or go to here

 

Not with RANS or some other techniques, but it should be do-able with SPH.

 

Vortex Generators

Great thinking Petros, apologies for missing this in your first post on page 10. But google didn't. lol

Vortex Generators sometimes referred to as Strakes. Have noticed them on many planes but never really understood the usage. Quick google search shows they are highly effective and also becoming popular on cars, subi guys are big on em.

Detailed Explanation


Thanks for your updates RR . You guys ever explore these vortex generators in F1?

I could swear I've seen them on a big tunnels leading edge somewhere, but searching under boats, basically nothing... Some mentions as Hydrodynamics enhancement, but nothing aero. One of those sites being Jimboats tunnel software, so please indulge us a bit.. Can it calculate these vortex generators effect as aerodynamic inputs?

Here is one example of them on a laminate leading edge, wind turbine blades.



Thinking if placed strategically on a hull with help of some software and a smoke wand, they could possibly be a game changer to any existing design. Worth exploring further I'd say, unless I'm missing something??

 

Hi Leo, I 'd love to see how good tunnel designs react when hydro blasted from a prop"S" wash near peak lifting specs. Shouldn't be real hard to replicate with some basic data, and feel it falls under "related causes" most can agree upon.

 

they are tunnel boats not hydros
2 completely different things