Keel lift
 

In books about sailing, I have read that the keel, going through water,
produces lift in a similar way to a sail. Given that water is a
non-compressible medium, I wonder how this can be so. Has it ever been
documented?


--
Michael Hobbs
Minneapolis, Minnesota

Keel lift
 

Many, many ways and times.

There is a book about sailing physics by C.A. Marchaj. (I hope I got the
author's name right.) It will have enough information about sailing
physics to satisfy even a graduate level physics person.
good luck and have fun sailing.

Mike wrote:
In books about sailing, I have read that the keel, going through water,
produces lift in a similar way to a sail. Given that water is a
non-compressible medium, I wonder how this can be so. Has it ever been
documented?


--
Michael Hobbs
Minneapolis, Minnesota

Keel lift
 

What Marty said is correct most books will have some reference to this lift.
The boats underbody is mainly used to create lateral resistance and helps
push the boat forward when beating and reaching.

But remember the keel/fin/centerboard are symmetrical in shape so you get
equal lift on both tacks. So the keel's lift is negated. There are boats
which have been designed with asymmetrical underbodies which are great for
one tack. I remember a speed record was set using this method. Others have
designed asymmetrical bilge boards and catamaran hulls to give greater lift.

Do not sweat it - just sail and enjoy
stu



"Mike" wrote in message
...
In books about sailing, I have read that the keel, going through water,
produces lift in a similar way to a sail. Given that water is a
non-compressible medium, I wonder how this can be so. Has it ever been
documented?


--
Michael Hobbs
Minneapolis, Minnesota

Keel lift
 

In article ,
"Mike" wrote:

In books about sailing, I have read that the keel, going through water,
produces lift in a similar way to a sail. Given that water is a
non-compressible medium, I wonder how this can be so. Has it ever been
documented?

What makes you think that lift depends on compressibility?

As has been pointed out before, lift really depends on changing the
momentum of the fluid through which the foil is moving, and you can
certainly do that regardless of whether or not the fluid is compressible.

--
Alan Baker
Vancouver, British Columbia
"If you raise the ceiling 4 feet, move the fireplace from that wall
to that wall, you'll still only get the full stereophonic effect
if you sit in the bottom of that cupboard."

Keel lift
 

In article ,
wrote:

What Marty said is correct most books will have some reference to this lift.
The boats underbody is mainly used to create lateral resistance and helps
push the boat forward when beating and reaching.

But remember the keel/fin/centerboard are symmetrical in shape so you get
equal lift on both tacks. So the keel's lift is negated. There are boats
which have been designed with asymmetrical underbodies which are great for
one tack. I remember a speed record was set using this method. Others have
designed asymmetrical bilge boards and catamaran hulls to give greater lift.

The keel's lift is *not* negated. A symmetrical foil can produce lift
just fine. Some aerobatic planes have symmetrical airfoils.

The moment the boat starts to move a little sideways in addition to
forward, the keel will have a positive angle of attack and it will
produce lift.


Do not sweat it - just sail and enjoy
stu



"Mike" wrote in message
...
In books about sailing, I have read that the keel, going through water,
produces lift in a similar way to a sail. Given that water is a
non-compressible medium, I wonder how this can be so. Has it ever been
documented?


--
Michael Hobbs
Minneapolis, Minnesota







--
Alan Baker
Vancouver, British Columbia
"If you raise the ceiling 4 feet, move the fireplace from that wall
to that wall, you'll still only get the full stereophonic effect
if you sit in the bottom of that cupboard."

Keel lift
 

wrote...

But remember the keel/fin/centerboard are symmetrical in shape so you get
equal lift on both tacks. So the keel's lift is negated.

Not so.

Just as with an airplane with a symmetric wing section (many aerobatic planes,
including the Pitts Special) generates lift when the angle of attack is 0, so
does a symmetric keel. It does so by sideslipping a bit through the water,
imparting a relative angle of attack. Same with the rudder.

Keel lift
 

"Mike" wrote...
In books about sailing, I have read that the keel, going through water,
produces lift in a similar way to a sail. Given that water is a
non-compressible medium, I wonder how this can be so. Has it ever been
documented?

Air flowing at subsonic speed is also treated as incompressible. Both are well
documented in all kinds of fluid mechanics and aerodynamics texts, experiments,
and studies.

Keel lift
 

I agree with Alan, a keel produces lift (in this case the lift is sideways)
by changing the direction of the water, just in the same way your sail is
working.
It needs an angle of attack to do so, and this angle of attack generates the
leeward way you are making.
compressibility of the fluid (air or water) does not matter for the
principle.
on www.sailtheory.com/sail.html this is explained in more detail.

Alan Baker schreef in berichtnieuws
...
| In article ,
| "Mike" wrote:
|
| In books about sailing, I have read that the keel, going through water,
| produces lift in a similar way to a sail. Given that water is a
| non-compressible medium, I wonder how this can be so. Has it ever been
| documented?
|
| What makes you think that lift depends on compressibility?
|
| As has been pointed out before, lift really depends on changing the
| momentum of the fluid through which the foil is moving, and you can
| certainly do that regardless of whether or not the fluid is compressible.
|
| --
| Alan Baker
| Vancouver, British Columbia
| "If you raise the ceiling 4 feet, move the fireplace from that wall
| to that wall, you'll still only get the full stereophonic effect
| if you sit in the bottom of that cupboard."


--
Posted by news://news.nb.nu

Keel lift
 

The book is "Sailing Theory and Practice", C A Marchaj , Dodd Mead & Co NY
NY

He has another excellent book: "Stability, the Forgotten Factor" on modern
yacht design which is very good as well.

His ideas (some iconoclastic) are backed up 100% by referenced research. A
tough chew, but wholesome and nutritious.

Bruce



"Marty Browne" wrote in message
...
Many, many ways and times.

There is a book about sailing physics by C.A. Marchaj. (I hope I got the
author's name right.) It will have enough information about sailing
physics to satisfy even a graduate level physics person.

Keel lift
 

Mike wrote:

In books about sailing, I have read that the keel, going through water,
produces lift in a similar way to a sail. Given that water is a
non-compressible medium, I wonder how this can be so. Has it ever been
documented?


Incompressible, but not immobile.

The same as with a sail inthe air,the water is free to move away
from the keel. The equal reaction to that motion is what makes
the keel work, and planing boats plane, and wakes, which may push
the after quarters foreward on a boat with a pretty bum in
displacement mode, or get left behind by a boat approaching the
plane.

This is a document.

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