rear wings on boats
 

i was glancing thru a speedboat magazine and saw an article about baja trying to reduce drag and make more aerodynamic boats as opposed to stepped hulls. i thout it was interesting that they said a rear wing reduces drag at teh stern of the boat. does anyone have any experience with rear wings or have any input on the subject?

Re: rear wings on boats
 

I would think that any object like a wing would create drag and slow the boat down :rolleyes:

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I would think a wing at speed could create lift, and possibly reduce draggin the rear of the boat.

Re: rear wings on boats
 

I'm not an aeronautical engineer, but doesn't it depend on the shape of the wing whether it produces lift or downforce? For example Indy Cars, Outlaw sprint cars and of course airplanes. I saw the Baja poker run boat last weekend and it has a carbon fiber wing attached to the rear.

Re: rear wings on boats
 

A wing could produce downforce, as it does on a car, or lift, as it does on an airplane. Depends on which side is "up". The force is applied to the flatter, or higher pressure side.

Fabio Buzzi has had wings on a bunch of his boats. They seem to do pretty well. I would think a wing has to be throughly tested tho, to produce the desired effect, and avoid big problems. Too much lift at the rear...can you say STUFF? A lot more complicated than a 20 year old screwing a carbon-esque wing to the back of his civic.

Re: rear wings on boats
 

Fabio always placed his wings at the exact center of gravity. He also incorporated a ton of dyhedral to help correct any chine walking.

Lifting the whole boat seems safer that just lifting the stern.

Look at any new Skater or MTI, notice the sweeping stern, it's done like that to create stern lift.

Re: rear wings on boats
 

Notice the tiny wings on the bow. Those are anti stuff wings. Once underwater, they help to lift the bow.

http://www.biggerhammer.net/offshorepage/photo/lga.jpg

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Dank368's new Skater has wings incorporated on the rear of the deck,overhanging the hull, which supposedly gives the boat lift.Maybe he can share some pics.

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Fabio did his mostly because of chine walking. You'll get dizzy riding his raceboats. I have had the pleasure of riding multiple race boats witrh him, he's a nut.
The back of skater and MTi do create lift as air accelerates and so creates lift.
Some wings do work but have to be in the perfect place and have to be in the perfect position.

Re: rear wings on boats
 

Certainly, any additional structure and/or lifting device placed anywhere on the boat will incurr its own associated parasite drags, however it's usually not without benefit.

Up lift, down force, doesn't matter what you call it, it is still "lift," -- a product of holding any relatively flat object at an angle of attack in a moving fluid medium. In the case of the Indy car cited above, it's an inverted wing held at a negative angle of attack.

Even a flat sheet of plywood will make lift, just not well...Airfoils aim to make lift with as little drag as possible and have infinite variations on chord to thickness ratio, camber, toe, sweep, dihedral, etc. Some are effective at low velocities and others peek in performance in the compressible subsonic, sonic, and supersonic ranges.

In any event, a small "wing" at the stern of a typical V-bottom with a flat transon could be of good benefit. Held at a positive angle of attack, the lift would reduce the apparent weight of the stern and thus hydrodynamic drag, but the most significant improvement could be achieved by forcing the air from above the boat back down to the water, leaving it as undisturbed as possible...In other words, reducing the low-pressure conical region behind the boat which is responsible for a good amount of drag.

Look at your newer skaters and MTI's...There's a slight bulge about a 1/3 of the way from the stern, which makes a good amount of lift at or near the CG, and then the deck slopes way down towards the water...This helps reduce this low-pressure drag cone.

I've been doing a lot of work and research on marine aerodynamic performance, for example take a look at my models of Miklos's 29 Extreme below. Notice the area of yellow and green directly behind the boat. This is low-pressure air being dragged by the boat which is responsible for a great deal of parasite drag. Forcing air down at the stern could help greatly.

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Yeah that wing looked about as usefull as an Enron stock certificate. :D

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Quite a bit, too!
I once calculated the total lift at about 80 miles per hour to be about 80 pounds...Doesn't sound like a lot, but 80 pounds up at the bow, can reduce the down forces necessary at the prop via positive trim, by approximately 1200#...This translates into less trim, more thrust going aft(not up), and a propshaft centerline more inline with the flow angle, reducing drags and increasing speeds. ;)

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:cool: :cool:

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Found a good pic I took.

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:cool: :cool: :cool:

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This is one of the better looking Baja's that I have seen. I don't know how useful the wing is, and I am not sure about the "roller coaster" seating. It also has Merc 850's and 6's which may be a little a$$ heavy. I didn't ask the price, but this would not be my first choice for that kind of coin :rolleyes:

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My boat came with a wing. I removed it this year and well see if it changes anything.

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so would it be too hard to put a wing on a boat and have it help even the slightest bit without using a windtunnel?

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CigDaze: Nice work, what software are you using? Any comments about what MPH the aerodynamic drag becomes significant. The photo of the spray off the back of the boat showing downward momentum is telling.

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i read that "areo dynamics" come into play at around 60 mph and become a major factor in design and performance :eek:

Re: rear wings on boats
 

same one

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Is Baja not testing their new boats in a wind tunnel? I would assume that is why the wing is there, but I could be wrong.

Re: rear wings on boats
 

http://www.bajamarine.com/index.asp?...dtunnel&tab=1&

i still doubt a wing of that size on a tank like a 40 outlaw that runs sub 100 would do anything more than being a fancy place to catch your lines on when docking... :rolleyes:

Re: rear wings on boats
 

the buzzi boats would be the exception... those boats were desinged with the wings in place and count on their performance for the boat to "fly" correctly...

the rest are tacked on ornaments...

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:rolleyes:

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the wing thing was done some in the 80s and early ninties i would guess they abandoned the idea when they realized they could not control the angle of attack... think of the apache vid and ad a wing :eek:

steamlining and reducing drag ie most supercats and the race fountans seems easier and more rewarding

Re: rear wings on boats
 

There is little or no "Quality" airflow within a couple of feet (vertically) of the deck, especially aft of the cockpit. We did some air work at Cougar 20+ years ago. We even set the UIM Class 1 straightaway record with Ted Toleman's 38' aluminum Cat with a 12' wide NACA 33 slotted flap wing raised 6 FEET! Turns out, that wasn't high enough! Sonny Levi said that the only benefit we got, was the fact that the wing raised the vertical drag center, and held the nose up. When Howard Arneson rigged his first 38' wooden Cougar, he wanted to ram some air into the engine rooms. He ended up with the air inlets about 7 or 8 feet above the deck (wouldn't stay together, but it worked). The fast cat boys are on the right track with the 'full body' treatment, turning the whole body into a wing. In short, a wing on the aft deck of an open cockpit boat is lipstick....

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I don't doubt it at all. But a wing is all about downforce and is in fact an "anti-aerodynamic" device.

false

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Aerodynamics refers to punching a hole through the air with minimal resistance

false

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The kind of wings we're discussing here are devices that, in principle, try to keep you connected to the surface

false

three strikes your out :eek:

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from nasa

aerodynamics

The science that deals with the motion of air and other gaseous fluids and the forces acting on objects as a result of the relative motion between the air and the object

Re: rear wings on boats
 

While we're on the subject. I've always wondered why cat makers have not added an adjustable wing between the front of the sponsons. With speeds in excess of 100mph, it would seem to be an effective way to control trim.
Anyone know of any attempts at this?
Gary

Re: rear wings on boats
 

some use a tunnel tab at the rear

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Formula, Betty Cook and John Connor built a pretty advanced composite 38' cat in the 80's. It had a had a non-slotted nose flap that extended down and forward like a dc9. Didn't work. On a dc9, it modifies the wing shape, makes it larger and gives more lift and drag. On the boat, it only stopped up the tunnel and slowed it down.

Re: rear wings on boats
 

Yep. A friend did some design consulting for the unlimited hydro boys on adjustable front wings between the sponsons to kill the lift at take-off and try to help prevent blow overs. I don't remember which team. Trick I think was no one could dedicate enough attention to how the boat was flying to be able to kick the wing fast enough if it started to get away.

-Greg

Re: rear wings on boats
 

you would spend all your time trying to adjust the angle of attack on that wing and unable to throttle or drive, the main problem with adj wings on boats is that boats never have the same attitude... they are always pitching and rolling, just like a tunnel tab that is used incorrectly, a front wing like that could be deadly in a high speed cat...

Re: rear wings on boats
 

The water surface for a cat acts just like the ground on formula cars, and creates a much different set of aero than a wing in nice free space on an airplane (it's also a much more complicated analytic model). Rolling tires are even harder to model correctly.

The height/spacing is very critical, on formula cars a 1/4" or less change makes a big difference. On a cat running height over the waves is continuously varying, making it nearly impossible to optimize as a single solution. In "very" general terms the height of the gap as a function of the wing/tunnel length as a % is what drives the effects, so on a 40' cat the senestivity is less, but still a few inches matters.

-Greg

Re: rear wings on boats
 

Randy Scism built a victoryTeam cat in the early nineties, with a big stabilizer wing on the back and also an adjustable front tunnel flap. I can't seem to find photos of it.
They called it the bat boat. was weird looking, but fast.
It had a huge wreck with Polli and Curtis, who were in the BILBOA boat, I think it was in St. Tropez.

Re: rear wings on boats
 

Wings produce lift (more accurately a normal force) and drag (axial force). If the camber/angle-of-attack is "up" it make lift ala an airpalne. If it is down it creates downforce ala race cars. If you put it vertically it creates side force (like in direct sideforce generators for advanced fighter aircraft). It's the same wing, same physics. Just point the force the direction that you want it.

Oh, and if you rotate it "just right" it produces thrust for a propeller or lift again for a helicopter rotor.

"Streamlining" is the coloqial term for minimumizing drag or disturbance to the airflow. Now days it's just called drag reduction.

I won't get into boundary layers and viscous -vs- induced drag as it's time for lunch.

-Greg

Re: rear wings on boats