Spectacular Blow Over at Key West Worlds!

[Jimboat]

I was asked some time ago, about "the forces that cause 2 tunnel hulls to flip simultaneously when the are too close together?"

Here's the explanation that I wrote up...

In general, if 2 tunnel boats are side by side, then they each start out on the edge of dynamic stability. If they get close enough together, their decks start to act as one large wide wing, instead of two smaller wings, with both boats experiencing an instantaneous increase in aerodynamic lift. This is because the higher aspect ratio wider wing is more efficient (larger Lift coefficient, CLa) than a low aspect ratio wing. This small add'l lift is enough to cause an instability of the boat. Even if the experienced increase in lift is relatively small, this added aerodynamic lift is applied forward of the boat's dynamic CG, causing a slight increase in angle of attack... which causes an increase in Lift... which causes an increase in angle of attack...which causes an increase in Lift... etc, and ultimately.... blowover. Also, if one boat following another then the following boat can see increased airflow also causing blow over.

Also, here's an article on blowover that explains some of the engineering behind it.

[Northlakeguy]

Jim
That all makes perfect sense...until the next race when the same class boat did the excat same flip. Only by itself. No boat near

[Jimboat]

Jim
That all makes perfect sense...until the next race when the same class boat did the excat same flip. Only by itself. No boat near

NLG - oh yes, for sure! a boat by itself can most certainly blow over and do it regularly! there are several ways that a boat can blow over. 2 side-by-side is a good way, though. more lift when flying on the edge of stability usually spells a problem coming.

[check out an article on blowover]

[CUDA]

Jim
That all makes perfect sense...until the next race when the same class boat did the excat same flip. Only by itself. No boat near

So what were the details of that, any video? was that the Victory, doing a individual flip?


Watching the video of the Allen drivers I see the throttles close upon lifting, being tail lift racing props, does this not compound the rotational effect?



It's truly a engineering accomplishment that these 32 ft boats run over 100 mph with only 600 HP , Just don't see the need to add HP, the newer motors will have

to go on bigger boats, Very efficient designs true airplane wings and thank God for the enclosed cockpits

[David]

The article is informative

[AZMIDLYF]

I quess the Victory hulls are pretty stout. They are planning to race in Englewood.

[Li'l Toy]

1975 OPC Closed Course Nationals at Miami Marine stadium. Right at the start three of the biggest single engine tunnels of the day--Mod U?--blew over together right in front of the stands. Some incredible photos of it, I bet there are some in the Racing History forum. Looked just like the video that started this thread, but three boats. No touching, just the influence of air entrapment boats running so close together.

[CUDA]

Beautiful boat

If they ever allow 450 hp motors they will need 40 ft boats

Who would have ever thought Outboards could be where they are

Power to weight ratio, funny they don't even sell these antique motors anymore

Wing boats that can sustain 100 mph crashes with drivers protected

The transition to the new motors will be interesting...

[JPEROG]

This is just the start of what I have been preaching about "no room for drinking and stupid B.S. that guys do". These new motors are going to put another 10 to 15 mph in the picture and the pleasure boats don't have the enclosure. This happened at 107 and there are guys out there approaching the mid 130s and having another 300+ pounds on the transom. It doesn't take a physics engineer to figure out having this along with passengers in the rear seat to add even more offset to the C.G. is a recipe for disaster in the wrong hands. Please wear your jackets and use your head.

Glad to have seen all of these guys out and about with us for dinner after this all happened.

Joe

[mr fun]

Wow, imagine a "tunnel hull" blowing over,,, where have I been.

[JPEROG]

Wow, imagine a "tunnel hull" blowing over,,, where have I been.

This was a first ever Keith. The only Super Stock boat to blow over was Nick when he came into the freighter rollers (practice session in St. Clair two years ago). Other then that there were none until this weekend so you haven't missed anything "this was a first". My point being that if people are not careful this has the potential to become common with all of the new "ultra fast" outboard cats being added to our hobby.

Joe

[Northlakeguy]

This is the first flip of these boats? That makes these crashes that much more of a mystery. Conditions were calm with little wind. Perhaps these current hulls have tunnels that are just to wide...thoughts?

[JPEROG]

This is the first flip of these boats? That makes these crashes that much more of a mystery. Conditions were calm with little wind. Perhaps these current hulls have tunnels that are just to wide...thoughts?

Its no mystery (read post #46)--when you run that close, you are "feeding your neighbor". This is to be considered operator error and was a good learning lesson for everyone to have witnessed "lucky for no major injuries to the guys involved". I now feel fortunate to have never experienced this in route to the first turn bouy "its been a tight pack several times". I have been displaced many times by having larger boats running up next to me in small boats-its like passing a semi truck with your car.

There was a head wind, there is current, and the boats are going faster in this class then they ever have--again, guys that are going to run light cats need to use their heads as pleasure versions are capable of much higher speeds and often contain passengers.


Below is a quote from Steve David about this incident Via Eric Colby's interview;

I figured it was a question plenty of other people who watched the crash had and I knew who to call. I’ve been friends with Steve David since he started racing Unlimited hydroplanes in 1988 because that was the year that I started covering powerboat racing. He’s one of the few guys to have raced Unlimiteds and offshore and he’s a pilot so he’s unwillingly flown boats and willingly flies his private plane regularly.
“Those two boats were so close to each other that it was air turbulence flowing off the decks,” David said when we spoke last evening. “When air flows over a surface it’s not laminar, and what you get are vortices that roll to the side and back. They’re each spilling the air to each other and all of sudden, the lifting force is significantly greater than the down-force created by the deck.”
So everyone who thinks it’s cool to see boats so close together might not want to wish for that in the future.



Joe

[Northlakeguy]

I am not so sure.. The single boat flip looked excatly the same. I saw both in person fairly close

[Northlakeguy]

And the fact is nobody really knows for sure