Value w - t propulsion

[bit]

Sorry, what are the values of w and t propulsion for sailboats "modern" than the last 30 years? About...
Thank you

[pavel915]

w is the wake fraction;
t is the thrust deduction co-efficient.

you can see "principal of naval architecture" for details

[jehardiman]

It is really going to depend on the hull shape and the shafting selection.

It will be very different for outboard, inboard, or saildrive. And very different if fullkeel or finkeel.

[Corsair266]

Can u explain for me to understand clearly , how are the Coefficients W , t created ?

[pavel915]

W(Wake fraction):
If the ship travels at speed V then the relative velocity between water and propeller is not equal ot V it is less than V and named speed of advance Va.

w=(V-Va)/V

t(thrust deduction coefficient):
The total thrust to delivered by the propeller to tow the ship in speed V is not just equal to the total resistance R at that speed .
If thrust is named T

t=(T-R)/T

[Corsair266]

Originally Posted by pavel915

W(Wake fraction):
If the ship travels at speed V then the relative velocity between water and propeller is not equal ot V it is less than V and named speed of advance Va.

w=(V-Va)/V

t(thrust deduction coefficient):
The total thrust to delivered by the propeller to tow the ship in speed V is not just equal to the total resistance R at that speed .
If thrust is named T

t=(T-R)/T

I know that thrust deduction coefficient is calculated as fomulea t = (T-R)/T
but i want to know the substand of generating of thrust deduction coefficient ,i know when the ship moves in calm water ,pressuse at the stern is less than
pressure at the bow ,because of the interaction between propeller and the hull of the ship.So ,differemce of pressure between the bow and stern generate thrust deduction coefficient ,Can u give me more details ?

[jehardiman]

w is determined from model or full scale testing by using a wake rake (a moveable structure that measures the wake field using pitot heads). You can also use similar hulls or CFD to determine it.

t is actualy the decrease in static pressure aft by the propeller due to propeller flow, this generates an apparent reduction in thrust that is actually an increase in drag due to the intergral of pressure over the hull. It is determined either by self propulsion model tests or is calculated based upon vertical section area aft using the del V pressure loss calculated using w.