View Full Version : Hydrodynamic Drag
Sm0akes
03-09-2004, 05:48 PM
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
03-09-2004, 07:21 PM
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
03-10-2004, 05:12 AM
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
03-10-2004, 06:47 AM
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
03-10-2004, 09:06 AM
Ok, but what are the constants of proportionality, roughly
sorenfdk
03-10-2004, 10:38 AM
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...
Sψren Flening
SeaDrive
03-10-2004, 10:47 AM
You can try the applet-based calcuator here: http://www.users.globalnet.co.uk/~fsinc/yachts/index.htm
Doing a little googing on "amateur yacht research" will raise of host of alternatives.
View Full Version : Hydrodynamic Drag