Hydrodynamic Drag

[Sm0akes]

I am trying to do some physics coursework and i need a ball park figure for the hydrodynamic drag of a sailing boat at a known velocity. OR a formula for drag.

It doesnt really matter what size of boat or yacht these figures are for.

Many thanks

[dougfrolich]

To help find Drag due to Skin friction figure
Turbulent boundry layer drag is proportional to Flow Velocity^9/5 x Wetted area
Laminar Boundry layer drag is proportional to Flow Velocity^3/2 x Wetted area

Turbulence will always occur if ( Length x Velocity )/ Viscosity = > 10^6 There are many other components to Hydrodynamic Drag but if the hull is Large and the Speed is Low then Skin Friction is the largest contributor.

[Sm0akes]

What i really need are some figures for the drag on a small dinghy or a formula.

Those formulae, without the constants of proportionality arent much help. What i am trying to do is apply some simple physics to a boat and work out its maximum possible speed. What would be really helpful would be a simple formulae, which doesnt need to be very accurate, which will give me the drag of a boat relative to its velocity

[SailDesign]

What would be really helpful would be a simple formulae,

Those _were_ the simple formulae. It just ain't as easy as you physicists assume.
Plus, for a displacement hull form, the "max" speed is relatively (dangerous word) well established. Flame wars notwithstanding.....

Steve

[Sm0akes]

Ok, but what are the constants of proportionality, roughly

[sorenfdk]

Go to www.sailboat-technology.com. Under "Online Articles" you'll find a link to "The Bare Hull Resistance of the Delft Systematic Yacht Hull Series" by J.A. Keuning et al. (and a lot of other interesting stuff).
The formulas are probably no good for dinghies, but at least you'll find out that the formulas aren't simple...

Søren Flening

[SeaDrive]

You can try the applet-based calcuator here: http://www.users.globalnet.co.uk/~fs...chts/index.htm

Doing a little googing on "amateur yacht research" will raise of host of alternatives.