Some questions on polars and upwind/downwind performance

Now let's look at the typical slow yacht that imitates high-performance racing yachts with wide sterns

The center of Flotation is located aft of the center of gravity (CG) and when the wave hits the entire stern and/or when the yacht heels/Roll the center of Flotation moves further aft (CF)

On the other hand, there's a typical longitudinal misalignment between the center of Buoyancy and the center of Flotation, the old "heavy quarters" problem: Heel/Roll dips the bow

The sum of these two effects, let's say, dips/Pitch the bow -2° down

The wave pushes the slow yacht, which was sailing at 0.30-0.35 Froude, against a wall of resistance and destabilizing lateral forces

A typical yacht that lacks stable balance on the Yaw axis with Roll/Heel + yaw/Leeway appears very unbalanced with Roll + Yaw + Pitch (!)

Because

Munk_Moment_(Yaw + Roll + Pitch) => 2 (!) x Munk_Moment (Yaw + Roll)

And

HydroDynamic Center of a powerful Keel is ahead of the Yacht Center of Gravity

 

1) We neutralize the powerful keel by placing its hydrodynamic center (CH) below the yacht's center of gravity

2) We order the yacht's fundamental centers longitudinally, as Poseidon, god of the seas, command:

L_CG > L_CB > L_CF

(Center of Flotation calculated with all the stern in a Wave)

3) We design a bow capable of generating hydrodynamic lift, and

4) We give it the Force to achieve 0.5 Froude

And there you have it, a magic carpet to surf the waves

 

1979

The young helmsman lost his concentration for a moment, a brief "lapse" (Peter Bruce, Heavy Weather Sailing) ...

and the yacht capsized, completing a 360-degree somersault like a church bell

My suggestion is simple: pay attention to the center of Flotation which is the yacht's primordial Center

L_CF: 58% LWL

OK

L_CB: 60% (!)
L_CG: 62% (!!)

And

HydroDynamic Center of the Keel: 62% (!!!)

 

Breton fishing boats were a marvel (?)

André Béneteau racked his brains to design a spectacular surfboard (!?)

No, it was coincidence

1) The traditional shapes, plus the addition of an engine, ensured a yacht Center of gravity Aft of the Center of Flotation, and

2) the curve created at the stern when accelerating creates low pressure (suction) giving the hull the right Hull Attitude (trim) for surfing at high speed, and

3) it didn't have a modern keel at the bow to trip over

 

MiniTransat 247

Rogers Yacht Design

"her canting keel which also slides fore and aft 800mm; this feature is paramount for fast downwind sailing in big seas"

E x a c t l y

 

A really idiotic suggestion. Look down the hatch at the "center of Flotation" instead of the sea conditions, deck, sails, etc.