Windward performance?

Lets say I was only interested in a yachts performance to windward and could ignore other points of sail. What hull shape charactersitics would be optimum given a fixed and pre-determined fin length and bulb? Thanks, Ron.

[SailDesign]

Let me guess - you found a keel on the beach?
;-)

[shu]

This would make for an interesting development class, no? Start with a fixed draft and ballast weight. Everything else is open.

I would imagine you would end up with very long hulls with a L/B of say 6 and an elliptical midship section with B/T of 4 to 5 and nearly circular sections forward. Unless you can get most of the crew out on trapezes, a planing hull form is useless to windward.

Note, for above:
L = hull length
B = beam
T = hull draft

Of course the hulls might get very deep at the keel root, in order to cheat the keel downward.

[SailDesign]

shu says:
"Unless you can get most of the crew out on trapezes, a planing hull form is useless to windward."

I woudl beg to differ with you there. Once you get past 40 feet or so, the planing hulls will plane uphill. Kinda scary if you get it right...

[shu]

With fixed ballast? I don't recall seeing anybody's average speed to windward (even the open 60's) exceed hull speed.

How do you do that?

[Paul B]

40+ footer planing to windward? Not likely.

As displacement goes up it becomes impossible to have the Sail Carrying Power to plane upwind.

Bethwaite has a non-scientific calculation in his book, and it seems to be proven out in real world experience. Do the calculations for any of the lighest monohulls over 20' LOA and you'll find them lacking the ability.

Big powerful boats with narrow heeled waterlines probably exceed 1.34*sq rt LWL, but they don't plane upwind.

Here is a thread on a similar subject from the Sailing World board a while ago.

http://old.sailingworld.com/forums/r....pl?read=10345

I did the Bethwaite calculation, using some modern examples. There is an interesting picture in one of my posts taken from Guy Dumas' design site of an attempt to make a small planing keelboat.

[SailDesign]

shu and PaulB. You can calculate all you want, but I have done 16 knots upwind in an Open 60. Not tight-tight on the wind, but within 50 degrees or so. And not a common occurence even on that boat. It was a real blast - of cold water mostly ;-)

If one were to use solid, asymetrical wings, a great amount of lift could be generated by positioning the leward wing down towards the horizontal position (perpendicular to the windward wing)

[Paul B]

So what you are saying is you have planed in an Open 60 while reaching. What was the TWS at the time, and what sort of heel angle were you sailing at? What was you sailplan at the time, and what sea conditions?

Your angle of 50 degrees, was that TWA or AWA? In 25 knots of breeze and 16 knots of boatspeed and AWA of 50 degrees is 80 degrees of TWA, nearly a true beam reach. The AWS would be about 32 knots. Bear off in the puffs and you might pop up.

I have surfed to windward on a ULDB on a big swell day with an offshore wind. That is very diferent from plaing.

[SailDesign]

Paul,
If memory serves, the angle stated was TWA, windspeed was about 20, and IIRC there was one reef in the main. Heel was variable but around 20 degrees, as that is where she liked to sail. Sea conditions were 3-4 ft waves, which never were a problem as for some reason she just went through them rather than over them. She had a very broad bow, which gave amazing longitudinal stability, to the point where the sailplan could hold the bow down in waves. If you backed off a bit, she would go over them, but was obviously slower.
Steve

[Paul B]

Full planing upwind in 20 knots of breeze.

You were there and believe it happened.

I was not there and don't believe it happened.

It is pointless to continue the conversation.

[SailDesign]

PaulB - why the hard feelings? Or am I reading you wrong?

[Paul B]

You have a belief and nothing I say is going to change that.

I have a belief and nothing you say is going to change that.

Therefore, it is pointless to continue on this topic.

[dionysis]

I would go for say a 13 to 1 length to beam ratio, around 60 displacement to length, and a ballast ratio of 70% - long, lean and light.

[Chris Krumm]

Hey, Dionysis -

How about pretty much as you spec'd, minus the 70% ballast ratio, and build a multihull! Long, lean, and lighter...