Catamarans High Speed Blow Over - Causes & Solutions

I recall reading that side-slip associated with roll was a factor in causing aircraft wings with positive dihedral to have a restoring moment. As the aircraft rolls the lift vector is tilted which causes a velocity component normal to the original direction of travel. That component of velocity has different effects on the angle of attack of wings when they are at a dihedral angle, and results in a restoring moment if the dihedral angle is positive.

 

That concept is well proven for boat roll control, it never actually went away. Was slightly modified, incorporated into a cutting edge hull design [the B28], race proven, APBA outlawed, later reinstated, further modified to become retractable, patented in 2009, and most recently fitted to 140+ mph 40ft V-bottom cruisers.



Makes me wonder what control surfaces on the trailing edge could add to the game, if attached to a flight control computer? Take note of that little vertical stabilizer stashed in there on the race boat also... Did it all work?

--
B28 by Ocke Mannerfelt.

The B28 won the Popular Mechanics Design and Engineering Award in 1995, and backed that up with the 4-Litre UIM World Championship in offshore racing in 1996.

The B28 became the new icon for efficiency and performance, and was actually banned for five years in APBA offshore racing because it was too fast and gave the rest of the fleet no competition. This ban was due to an over 5-minute lead on its competitors in each race
--

I know someone who still races one of those hulls today. I always called it a yard dart, but that short little .... jumps waves like a dolphin.

Here is where to find the latest renditions.

http://www.google.com/patents/US8453591

http://www.vectorpowerboats.com



But that's on a V-bottom and we are talking catamarans..

So I'd still like to see a control surface canard, or better yet split canards, tucked between a pair of these pointed forks just to see how nasty it looks.


Works in H1, and it's old school, manually controlled.

 

Kidturbo,

You are not looking for something that works.

You are looking for something that fits your ideal 'look.' That is art, for art's sake.

 

That is true, though it is related to the transverse velocity component induced by the side-slip. The moment created by the wings with a dihedral is indeed a restoring moment in case of an aircraft. It makes the plane get back into a level flight, but decreases the flight altitude during the process.

In the case of a boat the level is nearly-fixed, as there is the water surface below. But if the hull yaws, then the situation becomes similar to the side-slip of an airplane and the dihedral starts doing its job again, countering the yaw.

So, in effect, the wing with a dihedral (like the one on Buzzi's Cesa 1882) has a double stabilizing effect - against yaw and against the roll. And it also unloads the hull bottom at high speeds, thus decreasing the drag. It is imo a finest example of how an interdisciplinary approach to the design can create a winning solution (and also a so cool-looking one).

Cheers

 

It would look very nasty and cool, imo:

 

I read your previous explanations closely, a couple times actually, and still chose ?

B. You understand a little about a canard and think this would be a great place to experiment.



Not that I feel your theory is incorrect, but when asking $1,000,000 for a piece of "high speed" art, looks do count...



This doesn't mean form, fit, and function can't co-exist in something beautiful. Daiquiri demonstrates artist vision is also in his skills tool box.

Pay close attention at 1:50 below. The type of technology I'm speaking of, and one should expect in any million dollar thrill ride.

Cause that's what your ultimately buying, a thrill. Whether on wheels or props...

 

That canard, with active computer control, would have to be pretty darned effective at maintaining running trim within a safe envelope...hull airborne or not.

The drawback....what might happen if such a canard ever gets plowed in below the water surface.

 

Which might actually happen in offshore sea conditions. However, the canard shouldn't necessarily break, imo. A torque limiter could be mounted on the canard stock (shaft), which would let it slip and align with the flow if the lift force becomes too high (such as when it hits the water). That, plus a generously scantled mounting structure could be sufficient to avoid structural failure in case of plunging the bow into a wave.

I would be even more worried about the canard getting hit by the rooster tail of another boat (in case of race boats). That would be a strongly destabilizing situation. In that case, imo, only a powerful and rapid actuator with a wide motion range and a robust automatic control system could save the day (and perhaps even a pilot's life).

Cheers

 

That's proven to be a primary cause of many high speed blow overs, in several tunnel classes. I'd like to read all of Jimboat's latest article on the subject, if he would send me one. "hint hint" There is plenty of videos out there of these roost assisted departure situations. Found where BMcF posted a link of the top 10 H1 crashes under another related blow over topic awhile back. Couple good ones in there.

Kinda the reason I feel a control canard or movable slat is "part" of the solution. Need an option that could either deflect the spray, or possibly create some down force on the bow at this time. Aerodynamic values are out the window anyways by the introduction of spray, so we want ZERO lift right now.. Yeah canard is best used to increase bow lift or improve stability , but it could also become a "Bow Plane" in when hydrodynamic forces are introduced. On these big cats your not likely to ever dip the sponson tips at higher speeds 120mph+, COG is so far to the back, and if ya do, that canards the least of your problems.

If ya look at most of the H1 blow overs, they are trimmed up and using the canard to lift the bow even higher for faster speed. Once the boats angle of attack reaches design limit, the canard becomes useless for aiding to recovery. However a computer based stability system could sense this lift or pitch up way before any human, and take faster actions to correct it. In a bow down "stuff" situation, it would probably shine at recovery speed.

Main thing I've noted in the documented blow overs of larger high speed cats, it usually happens lightning fast.. H1 boats look graceful compared to the 40' pleasure cats taking flight. Unlimited hydro's are always flown on the edge for speed, so the pilot is constantly anticipating angle changes and controls bow lift with pedals connected to his canard. Off shore boats, not to much about flying. Jumping small wakes or large waves, it's about throttles, drive trim and pointing the bow where ya want it go. If all is well, they will skip over 4 footers for hours that would total an H1 boat in under 30 seconds. So much different concepts or usage.

Unless outside force causes a bow pitch up, the big cats usually perform as designed. When those outside forces do come into play, the pilot has no options to correct this. That's how I see it. These guys would blow the deck panels off it for some better odds of surviving these situations. Cause there is typically not much left of the boat if you do happen to make it out alive...

So lets say anything is acceptable that could be autonomous, fast acting, aerodynamic or hydrodynamic surfaces to halt this departure before it goes critical. But it can't involve drastically changing the shape of the boat, or degrading it's current performance. Wanta blow some hatches open, fine. Wanta add a huge tail wing that's primary use is to control flight pitch, probably not gonna be a hot seller, unless it drastically improves performance and looks..

So off to Photoshop or the sketch pad if ya prefer. Let's see the crazy ideas too, I know they're caged up out there waiting to break free.

 

Look at the Sukhoi SU27 cobra maneouver. Although it is using vectored thrust, it is amazing how it can recover from more than 90 degree "blow over" at zero speed. Amazing!

http://www.youtube.com/watch?v=vvCCSU4F0qs

 

A slat would add nothing to the lift of the tunnel at a given angle of attack. Slats serve to increase the stall AoA of a wing, which you don't need here because you have to reason in terms of "how to increase the downforce at the bow at a given AoA".
So, a canard - yes (if fully movable, with a wide range of deflection angles), a slat - no.

I think that you still need to make your goals more clear. I mean, your personal goal in this story - the one which made you start this thread.

 

To get the best out of the canard you more or less have to make it work with the rest of the structure, the one in the C01 pic is a full flying canard with the pivot at around 30% of the root chord, and theoretically is capable of bring the nose down from around 38 deg up.

The rest of the pics are a comparison against an existing F1 hydro so you can see the differences in pressures and flows paths compared to something designed for canards specifically.

 

I like very much the position of that canard in the first pic. The vortices from the canard tips go over the dorsal part of the tunnel hull, and in case of an unwanted high angle of attack situation will delay the stall of the lifting body of the hull (which is very nicely shaped). In that situation it means a smaller travel of the center of pressure towards the bow, hence smaller pitch-up moment, and hence less effort required to bring the boat down to level attitude.
Very neat.

 

"Blow Over" article available here.

 

Jim,
How fo I download the complete article. Everytime I try to download, I am prompted that the mail clent list is not installed or I am directed towards the "elephant" download manager. Thanks.