Air Cushion Drag Reduction

-- Last Updated: Dec-15-10 12:43 PM EST --

The U of Michigan, in connection with Dutch Naval Architects at MARIN and shipbuilders at Damen Shipyards Group are making available an air lubrication system to significantly reduce drag and reduce fuel use.

Air bubbles are injected near the bow and combine to form an air cavity along the ship hull. As air has a much lower Reynolds number than water, friction is reduced between 5 and 20% depending on hull shape.

Canoes with forward air tank flotation can easily be converted to use air lubrication to reduce drag. Using the front tank as a plenum, paddlers drill a series of holes through the hull to release air bubbles. The tank stopper is replaced with a barb and length of flexible tube fitted to a snorkel mouthpiece.

I originally conceived this conversion as useful to solo canoeists, as they continually bloviate, OP included, about how cool their boats are and how others might improve their technique.

Upon reflection, it is obvious the concept extends to tandem canoes. The poor bow paddler is continually shouting into the wind, completely unheard by the stern paddler. The stern paddler continually shouts advice and instructions forward, completely unheeded by the bow. It would be a shame to continue wasting all that hot air when it can be harnessed to reduce hull friction.

Costs more than double as two tubes, two barbs and a $1. T fitting are needed, but air lubrication systems may be the next silver bullet to increase efficiency in canoes. The technology is extendable to kayaks with front bulkheads and sealable hatches. Kayaks will need the longer hose of the stern paddler unit.

must be…

cabin fever gotcha Charles?



air supply
powered by beans?

Maybe a really rotten polyester resin
might put out a useful number of bubbles through hydrolysis.

Maybe I should just attach
a tube to the the bailer and then blow air through it.

Surely it will work even better riding on a air cushion under the hull.

jack L

Been Thaar… Done dat…

– Last Updated: Dec-15-10 2:22 PM EST –

in me Pamilco XXL expeermental contraption of a couple years ago...

Beanee Weenie by-products under pressure.

Yes, if truth be told. The temp started out at 9dgF this morning and has been descending all day while I wait for a 'Fridge repair guy and freight delivery.

And there, in the 11 Dec Economist, pg 10 of the Technology Quarterly, was an article on air cushioning hulls!


taint cabin fever nor fiction

Think hydrofoils too.

FE will make millions if he follows up on conversion of Beenie Weenies.

Don’t show the photo’s of…

– Last Updated: Dec-15-10 4:17 PM EST –

when you ate all that spam topped with beenie weenies, then stuck a tube up your a** and then put the other end of the tube in the water behind you and achieved jet propulsion.

I have the video.

Air under the canoe . . .
I believe Bill Mason tried paddling with air under his canoe in “The Rise and Fall of the Great Lakes”. The effect was similar to Wile E. Coyote’s attempts. Paul Mason seems to get more air under his canoe, but he finds water that is naturally foamy.

What was the name
of the scoop on the front of the USS Enterprise NCC-1701 that picked up hydrogen atoms from space as the ship flew forward?

I’m thinkin a CF scoop that would channel low pressure air into an ever-decreasing diameter tube that is attached to the front flotation tank. Just remember to keep paddling!


It was called a ram scoop
See the science fiction of Larry Niven for more scientific details. Also read stories cowritten by Niven and Jerry Pournelle. Pournelle’s full time job was at the Jet Propulsion Labs, I wonder where the hydrogen ram scoop drive concept came from…

Bussard Ramjet

All great books by the way (Niven and Pournelle)

Shazam! A’nudder Larry Niven fan…
Jus’ half way through Ringworld’s Children…


Russian Torpedoes
It sticks in my mind that the Russians were using the exhaust bubbles from their torpedoes to form a friction reducing layer along the torpedo that gave it great speed. Problem seemed to be the need to put the propeller out front so it was in clean water.


‘Cavitating’ propeller
The Hickman Sea Sled, a high-speed cat from way back (20s or 30s) used a surface-piercing propeller. It was called a cavitating propeller, but it’s really ventilating - bringing air from the surface down the backside of the propeller to reduce pressure on the back surface of the blades, thereby reducing drag. The blades were huge, high-pitch and I think very noisy…

what keeps it from sinking?
I’m sure these guys have an answer for this, and perhaps someone here does, too – what keeps the boat/canoe/hull from sinking? As we inject air about the hull, there is less weight being displaced by the hull (air weighs less than water). So I would think the hull needs to sink deeper in the aerated water to displace the weight of the hull and its load, creating more drag, which means you need to inject more air. Carry this far enough, you sink the boat. I’ve read proposals that boat sinkings in the Bermuda triangle are due to sudden destabilization of methane hydrates creating methane-“aerated” water incapable of floating the boat. Yeah, the boat goes fast all right – right to the bottom. What am I missing or not understanding about this?

High pressure
In order to be injected from the hull, the air has to be at a higher pressure than the water it displaces. So the air layer around the hull is able to support the hull due to its higher-than-atmospheric pressure (it’s not quite a displacement hull any more, I guess). The lower viscosity of the air gives the drag reduction. It takes work to produce the high-pressure air, of course, which will partly or wholly offsets the propulsion power saved due to drag reduction.

The tube and mouthpiece for solo canoeists!

Also of interest, Google USS Independence LCS. A different concept. Air injection reduces skin friction. The Indy reduces wave making resistance.

Tangentially related…
But probably as to the point as the starship Enterprise…

Used to make flying model airplanes. I liked rubber powered because it was a challenge to get anything to fly at all on so little power and they had such a strange torque curve.

Anyhow, I once considered a rubber version of the Supermarine S5. (1927 Schnider cup winner and Spitfire predecessor) While reading up on rubber powered scale float planes, I saw an article about inserting a small straw into the floats to allow air passage from the top of the floats to be released as fine bubbles just aft of the “step” on the underside. It was supposed to draw air by pressure differential created by movement, rather like drain plugs on a sailboat.

It wasn’t really for drag reduction though… the idea was to break the surface tension that tended to take a lot of power to overcome in order to allow take-off. It wasn’t so much a problem in full-sized aircraft because they had the horses to overcome it (almost 900 in the case of the S5, if I’m recalling correctly) and there is a proportionality (like a Reynolds factor but applying to surface tension) that “glues” a smaller objects to the water more strongly than larger ones. Very hard to get a rubber powered model to take off from water and still have enough ooomph left for a decent flight. So the air injection… much like you’re describing.

Never built that one though… decided the nose wasn’t really long enough to make for an ideal flying rubber model. Plus, any model sea plane would have to be so well sealed against moisture to prevent tissue sags and balsa warpage that it would be overly heavy.

I’m surprised this wasn’t tried long ago by the Navy. I wonder if on a canoe this would reduce drag enough to be noticeable by a paddler. In one of Winter’s articles he mentions in passing the frustration of designers knocking themselves out to get, say, a 5% drag reduction and not having it be noticed by paddlers who are suddenly more aware of the handling problems that result from designing solely for drag reduction.