Almost mounting my mast so it would be underwater got me thinking (as
it should). Why not underwater sails? Force on a sail is
proportional to the density of the medium and that makes a 5 knot
water current give about 50X the force of a 5 kt air current on the
same size sail. This means you could sail across the Gulf Stream with
an underwater foil. However, I am not sure where your rudder and
centerboard would be, in the air? Could you make a planing boat with
an underwater foil taking advantage of the water current? That way
you would not be limited to the 1.2Xsqrt(waterline length) in speed
anf might get up to absurd speeds.
Then again, maybe this idea is the result of breathing epoxy fumes.

A lot of folks don't appreciate the difficulties Admiral Rickhover faced
developing the nuclear submarine. The first nuke power plants were
anything but reliable and the admiral insisted on auxillary sail power.
It was so successful that every nuclear sub since the Nautilus has
had a sail. Of course the darn sail only works when the wheels are
touching bottom, but that's why they call it an auxillary.
-------------------
Parallax wrote:
Almost mounting my mast so it would be underwater got me thinking (as
it should). Why not underwater sails? Force on a sail is
proportional to the density of the medium and that makes a 5 knot
water current give about 50X the force of a 5 kt air current on the
same size sail. This means you could sail across the Gulf Stream with
an underwater foil. However, I am not sure where your rudder and
centerboard would be, in the air? Could you make a planing boat with
an underwater foil taking advantage of the water current? That way
you would not be limited to the 1.2Xsqrt(waterline length) in speed
anf might get up to absurd speeds.
Then again, maybe this idea is the result of breathing epoxy fumes.

Parallax asks:

Why not underwater sails?

Because the size of the "keel" would be about the size of a normal sail, and
would have much the same effect. You already have one, in other words... ;-)

Steve

On 05 May 2004 12:33:50 GMT, ospam (Stephen Baker)
wrote:

Parallax asks:

Why not underwater sails?

Because the size of the "keel" would be about the size of a normal sail, and
would have much the same effect. You already have one, in other words... ;-)

Steve

More on this theme:

where a sail boat reacts the force from an airfoil against a waterfoil
for traction,
to react the force from a waterfoil against an airfoil would call for
a rather huge sail, because the speed potential from most water
currents is less than 5 knots and to provide considerable resistance
by an airfoil to a 5 knot movement calls for area - lotsa area.

And if an adverse wind springs up, you still need to strike sail.

Brian W

On Wed, 05 May 2004 17:16:13 GMT, Brian Whatcott
wrote:

On 05 May 2004 12:33:50 GMT, ospam (Stephen Baker)
wrote:

Parallax asks:

Why not underwater sails?

Because the size of the "keel" would be about the size of a normal sail, and
would have much the same effect. You already have one, in other words... ;-)

Steve

Another way of looking at this:

A sailboat glides on the boundary between two fluids. There must be
shear between the fluids for sailing to work. If there is no shear,
you are becalmed.

The foils must be of a size commensurate with the density of the
fluids. Hence, the keel is smaller than the sail.

The foils can be of suboptimal shapes and still sort of work. This is
the normal situation. Many successful centerboard boats have flat
plate centerboards (Snipe, Finn, Lightning). Many keelboats have keels
that would hardly be recognized as foils.


Rodney Myrvaagnes J36 Gjo/a


Ask not where the buck stops . . .

Parallax wrote:
Almost mounting my mast so it would be underwater got me thinking (as
it should). Why not underwater sails? Force on a sail is
proportional to the density of the medium and that makes a 5 knot
water current give about 50X the force of a 5 kt air current on the
same size sail. This means you could sail across the Gulf Stream with
an underwater foil.

Except for one small detail... such a boat could only sail in one
direction, with the current. The ability to sail "across" the Gulf
Stream or any other current would require some counter force, such as
the sails in the wind are countered by the centerboard.

... However, I am not sure where your rudder and
centerboard would be, in the air? Could you make a planing boat with
an underwater foil taking advantage of the water current?

And when it planed, using force from the current instead of the air, it
would do what... submerge?

... That way
you would not be limited to the 1.2Xsqrt(waterline length) in speed
anf might get up to absurd speeds.
Then again, maybe this idea is the result of breathing epoxy fumes.

I think that Steve B. hit the nail on the head... you don't need an
underwater sail, you've already got one.

Fresh Breezes... or Currents, whichever- Doug King

Epoxy Fumes

"Parallax" wrote in message
om...
Almost mounting my mast so it would be underwater got me thinking (as
it should). Why not underwater sails? Force on a sail is
proportional to the density of the medium and that makes a 5 knot
water current give about 50X the force of a 5 kt air current on the
same size sail. This means you could sail across the Gulf Stream with
an underwater foil. However, I am not sure where your rudder and
centerboard would be, in the air? Could you make a planing boat with
an underwater foil taking advantage of the water current? That way
you would not be limited to the 1.2Xsqrt(waterline length) in speed
anf might get up to absurd speeds.
Then again, maybe this idea is the result of breathing epoxy fumes.

Think of a sailing boat as an aircraft on its side. That's what, in
principle, happens and the principals that you have described are the reason
that your sail area is greater than your keel.
Install some ventilation for the epoxy fumes (5Litres/second/square metre of
workspace) and try a nice single malt whiskey - It's a much nicer method of
addling the greycells.


"Parallax" wrote in message
om...
Almost mounting my mast so it would be underwater got me thinking (as
it should). Why not underwater sails? Force on a sail is
proportional to the density of the medium and that makes a 5 knot
water current give about 50X the force of a 5 kt air current on the
same size sail. This means you could sail across the Gulf Stream with
an underwater foil. However, I am not sure where your rudder and
centerboard would be, in the air? Could you make a planing boat with
an underwater foil taking advantage of the water current? That way
you would not be limited to the 1.2Xsqrt(waterline length) in speed
anf might get up to absurd speeds.
Then again, maybe this idea is the result of breathing epoxy fumes.

Think of a sailing boat as an aircraft on its side. That's what, in
principle, happens and the principals that you have described are the reason
that your sail area is greater than your keel.
Install some ventilation for the epoxy fumes (5Litres/second/square metre of
workspace) and try a nice single malt whiskey - It's a much nicer method of
addling the greycells.


"Parallax" wrote in message
om...
Almost mounting my mast so it would be underwater got me thinking (as
it should). Why not underwater sails? Force on a sail is
proportional to the density of the medium and that makes a 5 knot
water current give about 50X the force of a 5 kt air current on the
same size sail. This means you could sail across the Gulf Stream with
an underwater foil. However, I am not sure where your rudder and
centerboard would be, in the air? Could you make a planing boat with
an underwater foil taking advantage of the water current? That way
you would not be limited to the 1.2Xsqrt(waterline length) in speed
anf might get up to absurd speeds.
Then again, maybe this idea is the result of breathing epoxy fumes.

"Newdirections Int [Australia]" wrote in message ...
Think of a sailing boat as an aircraft on its side. That's what, in
principle, happens and the principals that you have described are the reason
that your sail area is greater than your keel.
Install some ventilation for the epoxy fumes (5Litres/second/square metre of
workspace) and try a nice single malt whiskey - It's a much nicer method of
addling the greycells.


"Parallax" wrote in message
om...
Almost mounting my mast so it would be underwater got me thinking (as
it should). Why not underwater sails? Force on a sail is
proportional to the density of the medium and that makes a 5 knot
water current give about 50X the force of a 5 kt air current on the
same size sail. This means you could sail across the Gulf Stream with
an underwater foil. However, I am not sure where your rudder and
centerboard would be, in the air? Could you make a planing boat with
an underwater foil taking advantage of the water current? That way
you would not be limited to the 1.2Xsqrt(waterline length) in speed
anf might get up to absurd speeds.
Then again, maybe this idea is the result of breathing epoxy fumes.


At the risk of starting a flame war:

Most keels do NOT act as vertical wings but only provide a lateral
force to resist windage and to keep the boat going straight. To be a
good wing, they would have to have an assymetrical cross section.

In principle, you could sail across the current if you could minimize
windage (waterage) from the water current just as you sail across the
wind with a normal sail. Maybe use an enormous "Air Keel" instead of
a keel in the water.

I know, I know, its simply a mental excercise and not practical,
but.....