Summary of the hydroDynamic Problem of small yachts at sea

[CarlosK2]

(Mein Surfboard is bigger)

And it all culminates in European Legislation under the Stability Index (STIX) of the supreme pontiff Van Oossanen ...

Van Oossanen Naval Architects - Naval Architechts, Yacht Designers, Hydrodynamicists and Consultants https://oossanen.nl/

And ISO/TC Working Group 18

for the enjoyment of the old fogies

John Scott Russell - Wikipedia https://en.wikipedia.org/wiki/John_Scott_Russell

The Quantity of "stability under canvas" (John Scott Russell) ...

It is not a data or a parameter to judge the safety of a small 1-10 ton yacht on the high seas

Because the wind capsizes the big yachts, but the waves capsize the small ones.

It's the world turned upside down. As always: demanding of the small, lax with the big.

Bayesian (yacht) - Wikipedia https://en.wikipedia.org/wiki/Bayesian_(yacht)

 

[CarlosK2]

John Scott Russell was right.

That doesn't mean we have to go back to the narrow, heavy British sailing yachts he advocated against wide American yachts: the old (ca. 1850-1880) cutter vs. sloop debate.

But it does give us pause for thought and makes us realize some simple, basic facts:

1) Yachts of 1-10 tons are objectively small; large yachts are 30 tons or more

2) Length is not a parameter for judging the safety of small yachts of 1-10 tons

3) The amount of transverse static stability is not a parameter for judging the safety of small yachts of 1-10 tons

4) Wind is one thing, and Waves are another.

 

[CarlosK2]

In short: the question for the small 1-10 ton ocean yacht is how to make an ultralight surfboard safe and how to surf with a heavy yacht

 

[CarlosK2]

"Such a vessel will be able to carry plenty of sail, will be very stiff under canvas (...) The great danger of a ship which is all shoulder, and has no underwater body, is that across a sharp sea she is liable to capsize." (John Scott Russell, "On the Rolling of Ships as influenced by their Forms", 1863)

John Scott Russell prophesied the capsize of the brand-new IMOCA "Hugo Boss"

"The effort of stability is the lever by which a wave forces a ship into motion: if a ship were destitute of this stability ["stability under canvas"] no wave that the ocean produces would serve to put her in motion" (W. Froude, "On the Rolling of Ships", 1861)

 

[CarlosK2]

There are at least five types of capsizes: four are preventable, and one is unavoidable

1) Dynamic capsize due to the inability to Surf a big wave

2) Static capsize due to poor positioning relative to the waves

3) Ignorance or recklessness: large waves with a long wavelength (e.g., 250 meters) that are affected by the seabed (e.g., 25 meters deep): the paradigmatic case of the two Danish couples who drowned off the coast of Portugal after setting sail from Peniche just the day after a major storm, and on top of that, they did not quickly head out to sea but instead sailed parallel to the coast

4) Distraction: the Class 40 that fell into the trough created by the seamount en route to Horta in the Azores: the seabed rises from a depth of 3,000 meters to 30 meters

5) The impact of a rogue wave

 

[CarlosK2]

5) The impact of a rogue wave: the capsize of two Pogo 8.50

The issue here isn't about avoiding capsizing

because that's impossible with small 1-10 tons yacht, and it's completely ridiculous to claim that a 3-ton surfboard is ocean-going based on its length and "stability under canvas"

When, ironically, and to add insult to injury, it's easy to capsize in the waves precisely because of its great stability ... under canvas

The issue here is righting the boat after it capsizes.

 

[CarlosK2]

Between the old British proponents of very narrow and deep yachts and the new French follies, I believe we can find a middle ground

A) A restriction on hull shape: a red line:

Beam (the maximum beam of the hull) / Draft (draft of the hull without the keel) ≤ 2

B) Vertical position of the center of gravity (VCG) at LWL

C) That the cockpit, when the sailboat is capsized, doesn't become the two hulls of a stable catamaran (!)

Look at a MiniTransat and imagine it capsized: the cockpits of sport yachts inspired by the MiniTransat are essentially the two hulls of a catamaran

D) And in the smallest boats, we can include a fully enclosed mast, which has a tremendous effect on a small ultralight sailboat

 

[CarlosK2]

Closed Mast
Huuuge on a small ultralight boat

The mast is sacred, like the rudder, the keel, or the hull.

Drilling holes in the mast is a caveman superstition.

Sealing the mast both protects its structural integrity and improves the passive safety of a small boat at sea.

 

[CarlosK2]

Pogo 2

This video is great because it has two parts: Upwind and Surfing

And we can see the starting point of the issue

(half the issue: how to make an ultralight surfboard safe; the other half would be how to design heavy yachts that surf well)

The sailor

a) sits (?) uncomfortably
b) with the sailboat heeled sharply
c) aft in the cockpit, far from the sailboat's pitching axis, and

d) in one of the two hulls of a catamaran (!) if the sailboat capsizes

---

A less extreme hull and a generous 60 cm backrest in a deep cockpit simultaneously improve comfort and passive safety

And greatly enhancing the feeling of being protected rather than exposed: it's much harder to fall overboard from a deep cockpit

The sailor's position is easy to adjust and place closer to the pitching axis

And heeling is reduced by carrying 220 liters of seawater, which, because the cockpit is deep, can be emptied with simple plugs in the cockpit floor—simple and efficient

At the same time, the ballast tanks shift the sailboat's center of gravity even further aft, facilitating better wave passage and less violent pitching

 

[CarlosK2]

MiniTransat "American Express"
220 l sea water Ballast
2.5 m Beam

Magnificent

But note how exposed the sailor is

What's missing is increasing the freeboard, and with a deeper cockpit, we simultaneously improved comfort, passive safety, and the feeling of being protected on the high seas.

 

[CarlosK2]

Returning to the overall map, the conceptual framework that I propose as an alternative to working group 18 "It is extremely difficult to find rigorous criteria for the safety of offshore Yacht"

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1) Structural safety

1A) Hull
1B) Keel
1C) Rudder
1D) Mast

2) Passive safety

2A) Impact, significant water ingress, resistance to sinking
2B) Impact of a rogue wave, capsizing, and righting

3) Active safety

3A) Beating
3B) Hove-to
3C) Surfing

4) Maneuvering safety

 

[CarlosK2]

3B) Hove-to

Poor bow position relative to the waves

After the rescue, the skipper interviewed said the bow was at about a 60-65-degree angle to the waves, and it was probably more

Most modern yachts are sideways to the sea when stationary

Watch this short video; you can see from the footage that the boat is pointed sideways to the waves, and at the end, you can see the electronic wind vane indicator:

(And note that there are no fuxxx furled sails on the bow)

 

[CarlosK2]

Solution

First gear: We lift the rudder blades out of the water, and by adjusting the mainsail, we can properly position the bow relative to the waves

Second gear: We deploy an inexpensive sea anchor with 100 meters of line, which keeps the bow aligned with the waves and prevents them from dragging the boat, deployed the sea anchor then it's time to lower the mainsail

Note all the advantages:

a) Two gears in hove-to mode

b) The yacht is calm and secure at anchor anchored in sand or mud (or anchored to the sea) without pulling the anchor: there are no furled sails on the bow, the mast is centered, and the sailboat doesn't yaw

c) It's a sport yacht that lifts one blade out of the water like a sports yacht, solving the dilemma of one large blade or two small ones: two large ones

(JPK on a JPK 1050)

 

[CarlosK2]

(Here's the photo I can't find now of a yacht sinking: it anchored in the sea with a sea anchor, broke its rudder, and sank)

If the rudder isn't raised out of the water, the yacht yaws violently from side to side and either breaks the anchor line or the rudder.

By raising the rudder blades out of the water (and with a centered mast and no sails furled at the bow) a yacht remains calm whether anchored in sand, mud, or open sea

Remember the large motorboat with an astronomically large mast, "Bayesian", incapable of finding serenity at anchor if the wind picks up like most yachts with one mast

 

[CarlosK2]

The Aerodynamic fear of a large freeboard is unjustified

The Aerodynamic Drag of the Hull is certainly atrocious when the wind picks up (TWS: 30 knots)

A 21 ----> 309 Newtons (D 21)

but it's impossible to hide the hull of a modern sailboat that sails on top of the water instead of in the water, and on the other hand, we must consider that the main culprit is the significant effect of heeling

We overcome resistance with more power by taking on seawater: 220 liters: "American Express", 1979 winner

Even on a "Dragon", the main culprit behind the increased aero drag of the hull is heel

When heeling, the Pogo 2 exposes a lot of hull, and the keel root gets close to the water's surface and even breaks the waterline

Controlling upwind heel is very beneficial

Taking on water is excellent: it increases displacement, shifts the center of gravity to windward, and can shift the center of gravity aft.

---

Corollary

It's absurd to damage something as sacred as a Mast to hide halyards from the wind.

And let's not even mention a cruiser crammed with gadgets: from large solar panels to a barbecue or windbreaks ... and holes in the Mast to hide halyards from the wind

Look

Heavy weather dynamics: the behaviour of yachts sailing upwind in high winds | Nordkyn Design https://nordkyndesign.com/heavy-weather-dynamics-upwind-sailing-windage-and-resistance/