Is there a way to covert windspeed and Sailarea into hp like from the engine?

[Ibetitsthisway]

Id Find That very Handy when calculating boat speeds for a given wind and sailet as there are Formulas to make These calcs based on Kilowatts put into the water.

[psk125]

If you take the polar diagram for the concerned sailboat you can see what speed is expected on each point of sail for different wind speeds. Then, based on the weight of the vessel, you can calculate how much power would be needed to attain that speed.
You could try comparing this to the actual engine in the boat. Say a 50hp engine is able to push the boat at 8 knots. So...it would be easy to surmise that if the boat is sailing at 8 knots, the sails are generating 50hp. This fails to take into account variables like shaft angle, prop pitch, slippage, and cavitation, however, so it’s not a very good comparison.

[cal40john]

Amount of hp for a certain speed varies tremendously depending on waves.

[CSY Man]

. Is there a way to covert windspeed and Sailarea into hp like from the engine?

Yes.
The biggest sailing ship ever had the equivalent of 5000 HP.
My CSY 33 sailing at 5.3 knots would be the equivalent of the sails and the rig generating 15 HP.
Any naval architect can probably help out with the exact number for your own tub.

[Ibetitsthisway]

40 year old boat.

Architekt past away.



Thought thre is a way to calc myself.

[TrentePieds]

Quote: "Is there a way to covert windspeed and Sailarea into hp"

Yes, here is, as I remember it, the basic formula for the power contained in wind: (You might want to verify it by asking an engineer at a windturbine manufacturer's or some such)

P = Cp * 1/2 * rho * A * V^3 * k

Where:

P = Power output, kilowatts
Cp = Maximum power coefficient, ranging from 0.25 to 0.45, dimension less (theoretical maximum = 0.59)
rho = Air density, lb/ft3
A = Sail Area
V = Wind speed, mph
k = 0.000133* A constant to yield power in kilowatts. (Multiplying the above kilowatt answer by 1.340 converts it to horse- power [i.e., 1 kW = 1.340 horsepower]).

Note that the value “Cp” ranges widely but cannot exceed .59. It is an expression of how much of the total power contained in wind a given extraction device, such as sails, can extract. This theoretical limit cannot be reached even by the most efficient very large wind turbines, much less by a sailboat's sails. This limit to extraction of 59% is known as the “Betz Limit” after the German physicist who determined it shortly after the Kaiser's War. I'm sure you'll remember that from you high school physics classes :-)

You can now set about figuring out for yourself how a rig should be designed to maximize Cp, but be careful, now, for Cp will vary with the Point of Sail, and is in part dependent (for every point of sail) on the rig having the optimum Aspect Ratio for that point of sail.

When you finish those considerations you can set about contemplating how each of the many coefficients that enter into designing the shape of the hull affects the ultimate force that propels the hull through the water. Again, exercise some caution, for that determination needs to consider the momentary Angle of Heel.

I say with all possible respect: You cannot learn yacht design by asking us amatoors questions in the disjointed, unsystematic fashion you have been doing. I recommend most highly that you turn to an accredited educational institution such as, perhaps, Westlawn School of Yacht Design. Be prepared for your tuition fees amounting, before you gain your accreditation, to considerably more than the cost of a vessel fully found and ready to take you anywhere you might want to go, s.a. the Denmark Strait, Cape Stiff and Rarotonga. This spring there was one such vessel, a thoroughly sound William Garden design built by what many, at the time of her building, considered the very best yard in this part of the world, for sale in my marina. She sold for Can$65K, I am told. Had I been forty years younger – i.e. had I been your age – she would have come to me!

Nochmals – viel Glück!

[Wotname]

Originally Posted by TrentePieds

Quote: "Is there a way to covert windspeed and Sailarea into hp"

Yes, here is, as I remember it, the basic formula for the power contained in wind: (You might want to verify it by asking an engineer at a windturbine manufacturer's or some such)

P = Cp * 1/2 * rho * A * V^3 * k

Where:

P = Power output, kilowatts
Cp = Maximum power coefficient, ranging from 0.25 to 0.45, dimension less (theoretical maximum = 0.59)
rho = Air density, lb/ft3
A = Sail Area
V = Wind speed, mph
k = 0.000133* A constant to yield power in kilowatts. (Multiplying the above kilowatt answer by 1.340 converts it to horse- power [i.e., 1 kW = 1.340 horsepower]).
.................

..................
Nochmals – viel Glück!

Nice explanation TP, perhaps you expand it by telling us what units should be used for the sail area?

[TrentePieds]

Ah, yes! Getting old and careless. Or perhaps old and forgetful :-)

Since we've got rho in lbs per foot^3, and velocity in mph, let's keep things simple and do Sail Area in SqFt.

But remember that where you are, the wind blows backwards ;-)

TP

[Ibetitsthisway]

Hi TP


Well.. What shall i say... These Kind of top 1% posts cannot be appreciated highly enough.


Thanks a lot... You just made my day :-)

Looking foreward to getting to my spreedsheet.

[Auspicious]

Originally Posted by Ibetitsthisway

Id Find That very Handy when calculating boat speeds for a given wind and sailet as there are Formulas to make These calcs based on Kilowatts put into the water.

Originally Posted by TrentePieds

Quote: "Is there a way to covert windspeed and Sailarea into hp"

Yes, here is, as I remember it, the basic formula for the power contained in wind: (You might want to verify it by asking an engineer at a windturbine manufacturer's or some such)

P = Cp * 1/2 * rho * A * V^3 * k

I don't think that works very well. You are better off doing lift-drag calculations for the sails to get a force number at various wind speeds. This is going to be really tedious over the range of angle of attack and then there is reefing. You'll really want to generate a numerical model so you can generate tables or graphs. Remember that the force is a vector and you'll want to break it down into components so you can get the amount of force applied along the centerline of the boat. The force perpendicular to that just heels the boat. *grin*

[Ibetitsthisway]

sensible or not - I must be getting something wrong with the formula.


Excel gives me 2,5kw at 100m² Sailarea and 12mph wind speed.!?


100m² SA (1076ft²)

Wind: 12 mph
air density: 0,08lb/ft³


? hmmm... maybe one zero too many in k?

[ggray]

Ok,I have a simple formula.

As a kid, had a book on sail published by National Geographic that had a picture of Preussen in a gale. Caption read more than 6000 hp from 60,000 sq feet of sail.

So I figure 1 hp per 10 sq ft., max in heavy wind.

Seems reasonable.

[Ibetitsthisway]

I found this somewhere in the web with the same topic:

Hi Bob,
Such high teck replies to a simple question. Yikes! I found this info from either a book or magazine article many years ago-- so memory is foggy!
0.015 hp/sqr ft of sail @ 7-10 kts wind speed
0.020 hp/sqr ft of sail @ 11-16 kts ''
0.040 hp/sqr ft of sail @ 17-21 kts "
0.070 hp/sqr ft of sail @ 22-27 kts "

I hope this is what you were looking for!
Have a Great Day!
Earl

[David M]

One more factor, as a sailboat heels, the resistance through the water increases because it then has a less efficient hull shape. Except for catamarans if the weather hull leaves the water, then there is less overall wetted surface area. But that only applies to smaller cats that do this relatively frequently. Planing vessel also applies where once on a plane the resistance is a bit less than when stepping onto the plane.

But I guess we are just talking about displacement monohulls?

[Ibetitsthisway]

Originally Posted by Ibetitsthisway

I found this somewhere in the web with the same topic:

Hi Bob,
Such high teck replies to a simple question. Yikes! I found this info from either a book or magazine article many years ago-- so memory is foggy!
0.015 hp/sqr ft of sail @ 7-10 kts wind speed
0.020 hp/sqr ft of sail @ 11-16 kts ''
0.040 hp/sqr ft of sail @ 17-21 kts "
0.070 hp/sqr ft of sail @ 22-27 kts "

I hope this is what you were looking for!
Have a Great Day!
Earl

YES - its all about displacement





I filled some spreedsheets With this and it Works quite well for me and myexperience!
Maybe some one wants to try and report..


I used this graph from fisher panda for the relationship