Speed Amplification Techniques

[jibes138]

One of the large sources of drag on a hull, other than the drag from your dinghy and the drag on your psyche from listening to your wife complaining all day about how much money you spend on your boat, is turbulent flow on hull appendages. I am proposing using an air injection device to force the flow across your keel and rudder to be laminar. My idea is based on the technique they use on turbine blades to keep them cool in turbine engines for aircraft. If we hollow out the rudder and keel and the drill millions of little holes angled in the direction opposite the flow and then put an air pump in the boat to blow air into these appendages and let the air flow out it will create a low drag region immediately above the surface of the keel and rudder. The water will no longer be attached to the keel and rudder and will slide across the air boundary layer with far less drag.
I am proposing that Hermit the inventor create a model for tank testing in Maine Sails dinghy using his propeller drag set up so we can see what percent drag reduction we can expect.
Comments?

 

[Rick D]

I remember about 20 years ago, an Australian guy brought his power boat over to the west coast using a similar principal. In his case, he exhausted the engine via a zillion small ports in the hull to reduce drag. There were some numbers thrown about the increase of efficiency and they were pretty impressive. Some west coast power boat designs subsequently advertised the design on their hulls and then it dropped off the map.

 

[All U Get]

Hi Jibes,
Wouldn't the bubbles cause the boat to sink lower in the water. I seem to remember it being more difficult to swim in aerated water.
All U Get

 

[Tim R.]

I would think this would cause cavitation along the surface of the rudder and keel limiting their ability to create lift.

 

[Moody Buccaneer]

One of the large sources of drag on a hull, other than the drag from your dinghy and the drag on your psyche from listening to your wife complaining all day about how much money you spend on your boat, is turbulent flow on hull appendages. I am proposing using an air injection device to force the flow across your keel and rudder to be laminar. My idea is based on the technique they use on turbine blades to keep them cool in turbine engines for aircraft. If we hollow out the rudder and keel and the drill millions of little holes angled in the direction opposite the flow and then put an air pump in the boat to blow air into these appendages and let the air flow out it will create a low drag region immediately above the surface of the keel and rudder. The water will no longer be attached to the keel and rudder and will slide across the air boundary layer with far less drag.
I am proposing that Hermit the inventor create a model for tank testing in Maine Sails dinghy using his propeller drag set up so we can see what percent drag reduction we can expect.
Comments?

The "tiny bubbles" theory of drag reduction has been proved worthless. It comes up as new "great idea" about every 3 months ... more often in winter.

Randy

PS: on the other hand, a neoprene version of flexible bottom paint to mimic porpoise skin ... with golf ball dimples ... and shark skin "riblets" ... now we're talking drag reduction!

Have a beer, long board the bottom to 1600 grit and go sailing ...

R

 

[Hermit Scott]

Unfortunately I am not that creative when it comes to fluid dynamics. But a million tiny holes in Texas waters would be filled with barnacles in about an hour.
If you want to go faster install some hydro foils to lift your boat out of the water.
I have thought of a foam V for the bottom of my dinghy to make it plane, one that straps on so it will maintain it's ability to roll up and be stowed easily.

 

[jibes138]

Hey, I read about your dinghy a while back. What size,is it an inflatable keel? What size motor? I used to be able to plane my 10'2" achilles with wood floor and inflatable keel with a 2.2 mercury motor. The trick is to perfectly distribute and minimize the weight in the dinghy. You do this by laying down in the dinghy and steering with your foot. No other stuff in it (the 2.2 has an internal gas tank with about a quart of fuel). It would get up on plane and move pretty good like that. If you are rowing it you will never plane :>). Unfortunately after 20 years the achilles is finally shot. It is in the back of my kids pickup waiting to go to the dump. All the seams are starting to fail along with the material. Multiple patches to fix leaks, at 50 bucks a year it was a great investment. Cost me about a grand and lasted 20 years. Only the last couple years did it start to leak.
Try this trick distribute the weight then find a boat wake and max your motor speed and start surfing on a wave, this will get it up on a plane and should allow you to keep it planing. For two people and some stuff you willl need probably 6 HP to plane. I have a 4 horse Johnson and that won't plane the achilles with 2 people in it.
My next dinghy will probably be another Achilles but a bigger motor, Defender is selling an 8 HP Yamaha 2 stroke that is only 60 pounds. All new motors are four strokes and very heavy.

 

[jibes138]

How about injecting omega 3 fish oil through the little holes? You could use a cast net to catch menhaden, grind them up in a food processor, extract the oil and coat the hull with it and then release some every time you needed to race.

 

[MoonSailer]

Flaps??? airplanes chhange their wing structure by using flaps. More curvature more drag more lift when landing or some takeoffs. Then a flatter wing when flying faster. Maybe have flat thin rudder and keel most of the time and then inflatable sections that are used when added lift is needed as when beating to windward. Or more simply design the appendages for minimum drag at hull speed and accept less control more sideslip at lesser speeds.

 

[All U Get]

Would this help? http://www.oregonjetsprint.com/Pics.html click on videos.
All U Get

 

[KandD]

amusing column to read... as I'm sitting in the lab working on my thesis. I'm integrating fluid dynamics and behavior with predator foraging techniques in snails.

I like the flap Idea, I thought it could be used on racing boats to keep the boat more upright... it wouldn't be useful at lower speeds though.

 

[Sandy Stone]

Flaps - back in the late 60's, early 70's, quite a few boats were built with 'trim tabs' on the trailing edge of the fin keel. For whatever reason, you don't see them any more.

 

[Tim C350 April IV]

What are you guys smoking this winter?

Laminar flow is real, and in the '80's, America's Cup boats installed some sort 3M tape on their hulls and appendages with grooves in it in order to try to add additional attachement of water to the surface - reducing turbulent drag.

Drill as many holes in your boat as your feel comfortable with. Guarantee at least one thing, each hole reduces weight in the hull. Do you feel lucky?

Good Luck, and keep smokin this winter!

Tim Brogan
April IV C350 #68
Seattle

 

[Moody Buccaneer]

What are you guys smoking this winter?

Laminar flow is real, and in the '80's, America's Cup boats installed some sort 3M tape on their hulls and appendages with grooves in it in order to try to add additional attachement of water to the surface - reducing turbulent drag.

Drill as many holes in your boat as your feel comfortable with. Guarantee at least one thing, each hole reduces weight in the hull. Do you feel lucky?

Good Luck, and keep smokin this winter!

Tim Brogan
April IV C350 #68
Seattle

The 3M covering was "riblets" ... designed to reduce friction inside pipes ...

Laminar boundary layer flow does not exist over much a sailboat hull or over much of a sail.

The film was used not for "laminar flow" but to reduce the thickness of the turbulent boundary layer.

This is mostly junk science. In the case of a golf ball for instance, it has been proved that the dimpled surface reduces drag ... the balls fly farther than if they were smooth. That is not because the flow in the boundary later is laminar, it is because the laminar flow over the part of the ball that has a positive pressure gradient gets tripped to turbulent and the flow does not detach ... decreasing the wake (and drag) of the ball. It works for golf balls at that range of Reynolds Number. Doing the same thing to a boat hull will not have the same effect.

What has been proved to work for sailboat hulls is a polished surface ... if you want to reduce drag, fair the hull and sand the bottom paint to 1200 grit or finer. This delays the transition from laminar boundary layer flow to turbulent boundary layer flow.

If the flow has NOT gone turbulent before the pressure gradient goes negative, you might have increased drag to to boundary layer separation if the flow does not re-attach to the surface of the sail or hull. This rarely happens on sails or hulls at the speed that we see on sailboats.

This does not keep people from coming up with new patents for crap that does not work.

There is a group of people that think that the riblets that DC used in 1987 were mostly a psyche job. Stars & Stripes was the faster boat all along.

Randy

(who has wasted more than his share of time and money trying magic drag reducing methods)

 

[jibes138]

Tiplets

Ok you convinced me not to drill millions of holes in my boat to test and air injection system. So how about this instead? Airplane wings are now being built with large tiplets at the outer end. This stops the mixing of high and low pressure air at the wing tip that creates a large vortex that causes a lot of drag. If we were to add tiplets to our keel and rudder we would reduce the vortex caused from the same effect. Another approach I have seen tested successfully is to corrugate the underwater surfaces to also reduce the vortices of the underwater appendages. Instead of a perfectly smooth sanded hull it would be far better to have it look like the corrugations on the inner layer of a piece of cardboard.
So get out your portable milling machines and lets start cutting some grooves.

 

[Cayennita]

You should concentrate more on reducing drag on the hull than on the appendages. A well built rudder with a nice narrow trailing edge cut square will do that. Same for the keel. Many, many years ago, I believe in the 6 meters, polymers were ejected though holes at the sides of the hull at the separation of laminar and turbulent flow. The book of racing rules has (had?) a paragraph prohibiting this. Some mine sweepers also carried this modification together with oil filled engine mounts to make them more silent and hopefully not attract a mine.