Force 7 Ocean Wave

My "2 ton surfboard" had a D/L of 216



The ride from Madiera to Tenerife was "uncomfortable". High winds from the N-NE and accelerated made the first 2 nights challenging with steep waves. Easier going after day 3. I have found, after several deliveries to the Canary from the North, that steep wave conditions can happen, and that the appropriately sized rudder can help avoid broaching. High speed broach on a 40ft yacht can get messy.
Again, I can not follow your math, but i grok the reality. Surface water speed can increase a boats daily average, if they can ride it.

 

I get in soaked, i sit facing the bow on the enormous and fantastic 2.45 m x 60 cm board (!)

and hang the wet items to port,

I sit in S4-S5, collect water and clean the entrance

I change my clothes, and i sit lying on the large bed between S3 and S4 with a gigantic cushion to listen to music, read or write things that feel good to me like a ritual in a forum

 

The advantage of that hull shape, skaraborgcraft, is that it certainly does not sink the bow when heeling.

avoid broaching ...

is a sum

+ that the bow does not sink when heeling
+ that the wave and the force of the sails do not sink the bow
+ a large rudder

 

Rayner

Denys Rayner - Wikipedia https://en.wikipedia.org/wiki/Denys_Rayner

 

The stern of my surfboard is huge and completely wet (it's pointless to calculate with the sailboat stopped in port), and yet the Longitud Position of the Center of Flotation is like a 1979 yacht: ca. 58% LWL

1) I've taken care to draw a bow that balances the stern, and

2) I've centered the sailboat following this primordial center: the Center of Flotation

L_CF: 58%
L_CB: 60%
L_CG: 62%

Otherwise, the sailboat will dip its bow when heeling, and is prone to dip its bow when a wave comes in from the stern.

My WindSurf Board is a British Classic, haha

 

Yesterday I saw the video of the naval architect installing a second autopilot on his new 45-foot, 10-ton yacht, which for the second time condemned him to being chained to the wheel.

Question

How can you have a sailboat with a very wide stern and not have it be a complete disaster?

Answer

Moving everything aft

This is kind of silly. It's incredible we've been arguing about this issue since 1880.

 

The Satanita (!) what a name

The Satanita - Wikipedia https://en.wikipedia.org/wiki/The_Satanita

Roll/Heel
Pitch bow down
Yaaaw

Impact

 

8 knots, 6° Yaw/Leeway

Mister Max Michael Munk is equivalent to a 330 Newtons Vector at Stem

The Keel lateral Force is huuuge

But is Neutralized (!)

Keel hydroDynamic Center longitudinal position = WindSurf board center of Gravity longitudinal position

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If the bow sinks ... then Mister Max Michael Munk goes crazy and can become a vector of 750 Newtons.

If there are also differences in water speeds between the bow and stern ...

If the rudder also works by swallowing the vortex of the Keel ...

(More calculations are made when designing a washing machine than a 10-ton yacht)

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and Resistance (!)

If the bow sinks into its own bow wave... it hits a wall. A wall of Resistance.

The yacht is very uncomfortable, becomes uncontrollable, and in the worst case, capsizes/flip like a church bell.

The question, therefore, is the proper bow-up-stern-down hull attitude when the wave pushes the yacht and the yacht is propelled by the enormous, gigantic, and all-powerful force of the Earth =

Mass of the yacht in kilograms x sine of the Ocean wave slope x 9.8 = Newtons

 

A) The boat is sailing Downwind at 0.5 Froude, about 7.7 knots

The Ocean wave arrives ... it lifts the stern, pulls it out of the hole created by the displacement, also gives it a little push, and the orbital current plays in its favor ... and it goes into the arms of the wave ...

propelled by the force of the Wind ...
and the force of the Earth (!)

B) It's sailing at 0.60 Froude, 8.8 knots because there's more wind

Much simpler because it's already sailing at takeoff speed

And if it catches the wave ... it will reach the speed of the wave for a few seconds

(or maybe a spectacular 1 minute Surf, I don't know, it's very difficult to make an estimate or impossible with my means: paper and spreadsheets)

The top or peak speed is completely irrelevant; the issue is harmony, safety, comfort, control, balance, and beauty

 

If a sailboat is well balanced from a hydrodynamic point of view ...

... the rudder only moves to balance the imbalance created by the force of the sails

 

Let's imagine a 20-degree wave slope on a gale and a 5,000-kilo yacht.

The force of the Earth propels the sailboat with a force of 16,660 Newtons, equivalent to 34% (!!!) of its displacement.

A vessel that was designed to move with a force equivalent to 3-4% of its displacement is pushed by a monstrous force.

There are two solutions: launch a towing drag device from the stern to slow and stabilize the yacht ... or Surf like a SurfBoard

 

The amazing thing ...

is that we have everything naturally in our favor.

All it takes is a Herculean effort to understand a simple fact:

On a planing motorboat, the thrust of the propeller lifts the bow; on a sailboat that want surf-planing the force of the sails sinks the bow.

 

If the wind is strong enough, for example, 30 knots, and the wave has grown and is large ...

it gives time for the Force of the Earth to act between time 1 (t1) when the boat is sailing at 7 knots with the force of the Wind, and time 2 (t2) when the boat is sailing at > 16 knots with the combined forces of the Wind and the Almighty Force of the Earth.

Looking at it like this, the Surfing never stops.

In any case,

we've reduced the impact speed of the wave's crest.

And the bigger the wave, the faster the boat.

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PDF

David Glover

Surfski Science
The Physics of Surfing a Wave

Fonte: DKayak https://share.google/a9jM0RFezTgScgD4Q

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One question is which waves are surfable and which aren't for a particular sailboat, as the author of this lovely article calculates for kayaks.

Another question is how long the surf can last.

These are very complicated issues and ultimately, they are details.

From my point of view, the important thing is that a Yacht can accelerate in a controlled manner and Surf well. It seems logical to me. The tactic of braking with a drag device is cumbersome, and the waves hit constantly.

 

I never used a drag/drogue, but i found that particular boat ( 2 ton surfboard) would answer the helm in every situation. The 40ft boat i assisted delivery to the Canary that broached in steep waves, did an Atlantic crossing towing warps, I later heard from the owner; although a quick boat, the rudder seemed too small for proper directional changes in big seas, to the point he sold it on arrival in Barbados.

 

A long surf on a Force 7 ocean wave with 30 knots of wind isn't a force issue: a 12° slope gives us a propulsive force of 2,241 Newtons, and the sails 885 Newtons if the 1.1-ton windsurfer is already riding in the arms of the big wave at 20 knots. The problem is that the sweet spot for surfing is very small: on this 72-meter wave, the sweet spot for surfing is about 10 meters in size. The other issue is that everything happens very quickly: 1-2 seconds to catch the wave.