Summary of the hydroDynamic Problem of small yachts at sea

[CarlosK2]

On July 5, 2007, the Pogo 8.50 "Yum" capsized, and Pierre-André Huglo was trapped for an hour and a half and spent about four hours sitting on top of the hull, photographed by an airplane, and rescued by a merchant ship.

On January 29, 2015, the Pogo 8.50 "Zinzolin" capsized. It had set sail on January 24 from Quinta do Lorde. There were two crew members, and one was trapped inside, breathing through the toilet pump as the water, filled with spilled fuel, rose and rose. This case impressed me greatly because it could have been me: because of the date, the place (they set sail from Quinta do Lorde on the island of Madeira), and the boat: a Pogo 8.50, the boat I wanted.

 

[CarlosK2]

A lightweight or ultralight Surfboard (especially one with excellent longitudinal balance) solves the hydroDynamic problem of navigating in/on a small yacht offshore in/with big ocean waves ...

But we must be aware of the danger we can create if we get carried away with the idea and forget about passive safety.

 

[CarlosK2]

"American Express" is magnificent: note the position of the keel

https://www.histoiredeshalfs.com/Histoire des Minis/49.htm

and the size of its beam is from before the MiniTransat became a kind of aircraft carrier

what is missing is

+ more ballast, more lead
+ a deeper keel
+ more freeboard, and
+ a deep cockpit

Beam (2.5 m) / (1.28 m) =< 2
from 6 to 8 sailor Seat

American Express (AE) and
1 Ton WindSurf Board

(The length is drawn the same to avoid complicating the comparison)

At the stern the true freeboard is only the height of the seawater ballast tanks (though visually the freeboard is higher)

And an oversized and closed Mast

 

[CarlosK2]

The bow points to the left (like an airplane)

The lead ballast is very deep

The hull is 20 centimeters below the waterline, plus 1.08 meters of freeboard (= 1.28 m) relative to the 2.5 meter maximum beam: B / D =< 2

The mast is completely enclosed, made of wood and carbon fiber, with a weight similar (2.2 kg / m) to a well-proportioned aluminum Mast

Dyneema shrouds

 

[CarlosK2]

The keel's center of gravity is at a depth of 1.5 meters.

Therefore, the ballast equivalent to 1 meter of draft is 1.5 x 270 kg (220 kg bulb + 50 kg) = 405 kg

And the lightship displacement is around 810 kg

Equivalent Ballast @ 1 meter of draft / lightship displacement = 50%

And ballast / displacement < 33%

With the ballast and a good freeboard, we have a good lever arm at 90 degrees

The area that determines capsizing resistance is the 90-120 degree zone

The mast is 12 cm x 10 cm

It is oversized compared to the figures calculated with NBS, Nordic Boat Standard

It's not that it's particularly thick; the word above -"oversized"- might not be correct in English, I don't know.

 

[CarlosK2]

Without a crew member (or with the crew member in the water) ... the center of gravity is located approximately -7 cm below the LWL

I mean, I don't know how others calculate these curves; in fact, after dedicating a lot of time to this issue, I don't believe the published curves.

In any case, I consider a moderate hull shape (B/D ≤ 2) essential, along with very good ballast, and ensuring that the cockpit, after capsizing, doesn't become the two hulls of a catamaran.

If we also add a very strong and completely enclosed Mast ...

on a boat very resistant to sinking in case of impact (with a semi-submerged container or a whale) with 30 watertight compartments and the bow compartments filled with very low-density material ...

the result is a fairly safe ocean windsurf board

 

[CarlosK2]

The longitudinal position of the Center of Flotation (CF) is the primordial Center of a small sailing yacht

It is calculated from the area of the waterplane

The longitudinal position of the Center of Flotation (CF) is calculated numerically And by cutting out the area of the waterplane from cardboard and finding its Center

In the photograph above, it may appear that the SurfBoard bow is sharp and therefore the Lifting Wing is small

The wingspan is actually quite wide (we could even say 'enormous') when the SurfBoard rises above the bow wave (Froude number => 0.50) due to a very low chine at the bow

 

[CarlosK2]

Safety in Maneuvers on the 1 Ton WindSurf Board Plywood Epoxy

With a 3/4 fractional rig, we don't need to change the headsails

The bowsprit rotates aft, and the small A5 gennaker can be easily hoisted and lowered

The mast is located 40 cm from the cockpit

The staysail is mounted on a boom with no upward movement, allowing us to:

a) Trim the angle of attack (10-15-20 degrees) beating upwind

b) Trim downwind at 30-45 degrees

c) Install a reef to reduce the sail area to just 3 square meters

The final downwind settings in an extreme case (Force 10 Downwind) would be:

A) Penultimate setting: mainsail at its third reef and staysail reefed

B) Final setting: only the staysail reefed and centered, the sailor enclosed inside, and the boat sails itself.

This possibility must be considered to ensure safety

it's important to keep in mind that Mini Transat boats cross the Atlantic (together and accompanied) and don't return, and the same goes for 300-400k Euro sports yachts: they cross to the Caribbean; but it's very rare for them to sail back.

Anyway, I think it's better to return via a lower latitude early in the year and thus avoid getting caught up in the typical Force 10 demolition derby heading towards Horta in the Azores.

 

[CarlosK2]

With prudent navigation (not heading too far north until the middle of the Atlantic) ... and with a shortwave receiver we could receive an early warning: a RadioFax of the 500 mb map/chart from Ocean Prediction Center ...

Ocean Prediction Center - Atlantic Marine https://ocean.weather.gov/Atl_tab.php

Atlantic Ocean RADIOFAX Schedule https://ocean.weather.gov/shtml/atlsch.php

and the speedy windsurfboard would head south ... or perhaps in the future young adventurers will seek the big waves, I don't know

 

[CarlosK2]

Radio Fax, Ocean Prediction Center
96-Hour 500 MB Forecast

It could give us, for example, let's say 60 hours, and with the surfboard going at full speed southeast, we'd be free.

But I don't think that's even necessary with a prudent navigation; however, I want to point out that safety is a combination of factors.

 

[CarlosK2]

And if Force 8 - Force 10 catches the surfboard sailing upwind, then it anchors in the sea and clings and hugs the sea, bow to the waves like an ocean rowing boat.

As Robert Manry anchored in the sea ... taking the rudder out of the water

The Robert Manry Project - THE MAN - The Robert Manry Project https://www.robertmanryproject.com/the-man/

 

[CarlosK2]

1 The Nature of the Problem

"It may even be worth remembering that there may be on board a gentleman and a lady who regard each other with something warmer than mere tolerance, and would like to have an oportunity of proving it"

"They want to carry their house with them"

CA Marchaj, "Seaworthiness. The Forgotten Factor"

Half the problem is how to make a lightweight or ultralight surfboard safe, and the other half is how to surf comfortably and safely on a slow, heavy, snail-like yacht that's carrying the house on its back.

And the same principles apply: Pitch and Yaw control, hull Trim under acceleration, and a comfortable rig.

Look at the position of the Keel:

Articles https://ericwsponberg.com/articles/

 

[CarlosK2]

Tom Wylie "American Express" (1979)

Look at the position of the Keel:
fundamental centers reconciled

Profesional Boatbuilder, Number 75, 2002

by Steven Callahan

Steven Callahan - Wikipedia https://en.wikipedia.org/wiki/Steven_Callahan

The next step is to move the ballast even further back: "Aqua Quorum", which performed magnificently in the 1997 demolition derby where four yachts capsized and one disappeared.

https://www.histoiredeshalfs.com/50' monos/C10 Aqua.htm

And I've simply centered the Mast so that the keel holding the ballast acts as the centerboard for beating Upwind.

---

Snail-yachts for "a gentleman and a lady", Yachts who carry their home on their backs and with their fundamental centers reconciled around, say, 54% LWL, and small sporty surfboards for 1 sailor, young or old, with their fundamental centers reconciled around 60% LWL

 

[CarlosK2]

"Zinzolin" (2015)

The Zinzolin case is very striking to me because everything is typical: the date, the wind, the route... and a modern sailboat, and a crew member trapped in the capsized yacht that won't right itself: the foul-smelling water filled with spilled fuel rises and rises, and he sees a photograph of his 6-year-old daughter that says, "Daddy, come back for my birthday."

Yesterday I saw that the expression "rogue wave" is used for giant waves of 25-30 meters high; but the most typical thing is a very violent and wild wave of 6-7 meters high created from 4-meter waves that intersect with other waves.

And wave crossing is a very typical and normal phenomenon.

This, therefore, is the great complication for a light-and-wide surfboard once the hydrodynamic problem of being able to accelerate in a controlled manner with great pitch and yaw control has been solved.

 

[CarlosK2]

From my point of view, reordering the European design categories would result in the following:

Design Category E: Exploration of polar regions: steel and aluminum yachts

Design Category Aa: Heavy ocean surfboard => 8 tons for the Southern Indian Ocean

Design Category Ab: Lightweight ocean surfboard => 800 kg for the Atlantic

Design Category C: Coastal

Design Category D: Dinghy

In heavy surfboards, great emphasis would be placed on good longitudinal balance given their low relative speed compared to the wave speed and the push (a push that should not be destabilizing) of the Froude-Krylov force to initiate surfing in the arms of the large wave

And in wide-and-light surfboards, special emphasis would be placed on their ability to right themselves after a capsize