How to Design a modern Yacht

1- It is simply incorrect to say that "imitating highly competitive sailboats has been the iron law since 1850" and it's an insult to sailors and designers. Take a canoe yawl or the Seabird, designed in 1898 and arguably the first yacht design to spread significantly, and compare them to a highly competitive small racing boat of the same era and place. This is a Seabird;


And this is a typical "highly competitive yacht" of similar size of the era, the Herreshoff "Wee Win";




The "highly competitive racing yacht" of the era and place was a very light bulb keeler with a separate rudder and long overhangs, built in carvel planking. The most popular yacht of the era and place was a keel/centreboarder with a keelson-hung rudder, transom stern and short bow overhang, built in clinker planking.

The most popular yacht had the same LWL and sail area as Wee Win but was only 80% as long overall, was 25% wider and displaced almost twice as much. They are not the same!

This, of course, is one of the popular canoe yawls of the era, Holmes' Eel;


It is of similar mean length to Wee Win but has very else little in common with it. Eel displaces 270% of Wee Win and has 160% of Wee Win's beam. One is a sloop, the other a yawl. One is a keelboat, the other a centreboarder. One has a cabin, the other does not. One has a spade rudder, the other does not. One has long ends, the other does not. One is a double ender, the other is not.

To say that Eel and her ilk follow an "iron law" that they must be like highly competitive racing boats is absurd. The canoe yawls are almost nothing like the Herreshoff half rater.


2- To look at a later era let's use a boat you keep on referring to, Harrison Butler's Z4 of the late '30s, or the Folkboat design of the early '40s. Once again we see that these very popular boats had very little to do with contemporary "highly competitive racing boats", apart from the common features all keel yachts have. Almost all of the "highly competitive sailboats" had long counter sterns, yet the Folkboat and Z4 have transoms. When the Folkboat was designed most "highly competitive sailboats" had genoas and spinnakers, but the Folkboat has neither. Almost no "highly competitive sailboats" of the time had a bowsprit yet they are found on Z4s.

Compare the Z4 to a typical small "highly competitive racing boat" of its era and place and the same waterline length, the Dragon. The Z4 displaces over twice as much, is only 72% as long overall, has 12% more beam and vastly more freeboard and volume. No reasonable person can say that the Z4 "imitates" the Dragon.

The same can be said when comparing the Folkboat of the same era to a racing boat. It is simply not correct to say that the Folkboat imitates racing boats like the Square Metre boats that were the most popular racing design of the time and place.



The most popular highly competitive racing yacht in the world at the time was the Star, an almost flat-bottomed hard chine bulb keeler with skeg hung rudder. No reasonable person can say the Folkboat, Z4 or the similar H28 - all very popular yachts - were "imitations" of the Star.


Nor were the highly popular cruisers "imitations" of Metre boats, or of highly competitive offshore racing yachts of the time, like Bloodhound, Blitzen or Maid of Malham.

3- Earlier you showed photos of the Muscadet. You state that "imitating highly competitive sailboats has been the iron law since 1850" so therefore the Muscadet must imitate a highly competitive sailboat. Which such boat does the Muscadet imitate?


Come on, you made the insulting statement - back it up.


4 - Re "My creation is an amazing little sailboat......clever chine...".

Your combination of self-praise and abuse of others is rather off-putting. How have your other designs performed? If you are such a clever designer why don't you just go and sail one of your other clever designs?

5 - "In a small boat, a good hull attitude can be achieved simply by moving the crew towards the stern, thus achieving an Angle of Attack that, on a flat surface with sharp edges and large enough create hydrodynamic lift."

This is untrue. In most GOOD small boats, the crew's weight is normally enough to keep the bow up - but it is certainly not the case with extreme wedge shapes, which is why good designs don't normally have the extremely wide flat aft sections of your design.

Having sharp edges forward creates handling difficulties because of the abrupt change in effective CLR as the chines lift in or drop out. People who have actually sailed small fast boats with "sharp edges" are aware of this. It's why, for example, Farr's chine designs always had a curved surface under the chine. This is why the flat bottom "coffin boat" design, which has sharp chines forward, is known to be tricky to handle.

Another issue is that when a boat with very flat and hard chined forward section heels at speed, the "flat" surface becomes angled and hydrodynamic lift changes suddenly, causing handling issues. That's one reason why designers who have actually sailed small fast boats normally use a more rounded section, which can handle heel better.

What planing hull boats with a sharp chine angle forward have you sailed?

 

In summary

(1) Reconciliation of the longitudinal position of the centers with the longitudinal position of the primordial center. Cunning chine. And an enormous (= 3 x LWL) longitudinal metacentric height. With this we achieve, in a modern way, the equivalent of a magnificent classic yacht.

(2) Yaw Control: Mr. Max Michael Munk under house arrest. And centerboard neutralized. With this we get the equivalent of a classic yacht.

(3) 150 D/L and 20 sqm per Ton, with this we get a good launching ramp = 0.5 Froude

(4) hydroDynamic trim of the hull (stern down bow up) and the sailboat adapts to the size and speed of the majority of the waves, 10-15-20 knots

(5) obviously we must take into account that there are wild waves and, therefore, passive safety must be magnificent both in case of impact against an Iberian orca, and resistance to sinking or impact against a wild wave, capsizing, security of the cargo/payload, head and ribs of the sailor, and righting.

 

Sagitta 30 vs. Shuttleworth 31

two friends cross the Atlantic together

"My 30' Sagitta catamaran surfs too fast - 18 knots in a force 7 with no sail up"

"When I crossed the Atlantic, I set off alongside a Shuttleworth 31 open"

Why does my boat surf so fast? https://www.boatdesign.net/threads/why-does-my-boat-surf-so-fast.50195/

similarly two friends in two monohull

one in a classic with 19.19 LWL sails in the valley at 6 knots of speed, and Surf, "Surf Gliding", "falling with style" at 14 knots and reaches a top speed of 20 (!) knots

the other old friend sails in a modern 19.64 LWL monohull and in the valley he sails at 7.5 knots maybe 8 and "falls with style" and in a controlled manner towards the center of the earth with a speed of 14 knots and makes a maximum of 18 (?) knots

 

The great advantage of the classic heavy surfboard like a small British yacht from 100 years ago is that the hydrodynamic hull trim is largely based on low pressure, suction, and is immune to the angle of attack and adapts wonderfully to that rough and changing environment

If it weren't for the fact that a lot of water was entering inside (that is, leaving aside this old constructive aspect) small classic British yachts have surfed Force 11 without anyone at the helm

I mean they set the bar very high

Yes, Eric said that when he grew up it would be difficult for him to reach the end of the bowsprit (!)*

I don't think my modern light surfboard is that good; but something more comfortable for an old sailor

---
*: "I suppose that when I get too old and fat to sit on the bowsprit end (...)"

(Eric Hiscock, Wandering under Sail)

 

I usually say that the Scow is a good solution because, being a rectangular shape, almost anyone will be able to find the Primordial Center of the Yacht without having to cut out the waterplane area out of cardboard and balance it on a sharp knife

 

After twice going thru the two pages that you have so far posted, I come back to the first sentence of the first post.
Yes, words do mean things.
If you were in a court of law the judge might ask you, "Barrister, make your case".
What is the case you're trying to prove? Is there an exit strategy or end point?
Are you trying to develop/invent a mathematical way to design the perfect hull?

 

I don't understand the complaint, unless he was bragging about his speed. Surfing is exciting and entertaining.

 

"I suppose that when I get too old and fat to sit on the bowsprit end (...)"

Nah

consulted the resistance curves

Force 7 and young Wave

Heavy Surfboard 300 D/L

19.19 LWL
6 knots
"Falling with style": 20 knots

Light Surfboard 150 D/L

19.64 LWL
8 knots
"Falling with style": 1 Froude: 3.33 SLR: 14.77 knots

 

In 40 knots of wind the hull of my light surfboard is half out of the water, but the big difference with the motorboats is that there is not as much reduction in wet surface: a large daggerboard, a lead bulb and two good rudders, The friction at high speed is atrocious and at the end of the resistance curve at 20 knots it is around 3000 Newtons

We must also keep in mind that with the speed of the sailboat the speed of the apparent wind decreases, and although the bulk of "falling with style" is the force of the earth, a little help from the sails does not hurt

so it is difficult to tie with Roman Sánchez and his old surfboard

 

Roman Sánchez's old heavy Surfboard is a classic and very clean hydrodynamic marvel, in comparison my modern light Surfboard with its three large appendages looks like a Christmas tree

 

It is difficult to compete with a classic surfboard in the category of falling with style, Surf Gliding

But my light surfboard will be spectacular in the Surf Riding category, this is when the sea wave destroys the hull wave which in this case is Froude 0.5

 

So we have up to four ratio speed indicators in different circunstances:

A) surface of sails hoisted / wet surface

B) Power % Displacement: GZ / h (vertical distance between wind force and lateral water force)

C) hoisted surface of sails / Displacement

D) sine of the slope of a young wave x mass of the sailboat x 9.8 gravity / wet surface

 

Speed in absolute terms is not a goal to pursue in the real world beyond the crazy world of competitions

What we want as good disciples of our teacher Thomas Harrison Butler is good control of the band of outlaws: Yaw, Pitch and Roll

Airplane Stability and Control https://www.cambridge.org/core/books/airplane-stability-and-control/69376B1ABCDDC3A2AE9F934D37A6F1B9

We want a sailboat at the height of the aeronautical technology of 1914, which was exactly the year in which "Curlew", a Falmouth Quay Punt, was retired

And we want speed in relation to the speed of the Waves

A young Wave Force 7 sails at about 14-15 knots

 

Munk Moment

H: High pressure
L: Low pressure

How we put Mr. Max Michael Munk under house arrest

Max Munk - Wikipedia https://en.m.wikipedia.org/wiki/Max_Munk

Eric Hiscock's professionally designed "Wanderer II" seems the epitome, the exemplary example, of a classic British small yacht. And yet, it is not comparable from a hydrodynamic point of view with the Z4 of Thomas Harrison Butler, an amateur that is: a passionate

The bow design of "Wanderer II" produced a lot of lateral High pressure.

Well

With a careful design of the stern and bow we can greatly reduce the Munk Moment

We also Neutralize the centerboard

The axis of rotation Yaw passes halfway between the Buoyancy center and the Center of Gravity.

So we Neutralize the lateral force of the daggerboard by placing its hydrodynamic center below the center of gravity of the Yacht

And we make a reasonable estimate of the Munk Moment with Yaw and Roll, and thus we size the size of the rudder blade, in such a way that the Yacht has a Stable balance, that is, the sum of the lateral forces is aft of the Center of Gravity

A 1 ton yacht is a 1914 one ton aircraft

A 1 ton yacht is not a miniature ship

 

This is a still photograph of a long sequence of events and calculations

It begins with the boat sailing at 7.5-8 knots, continues with the arrival of a young Wave Force 7, continues through the strict control of Pitch and Yaw...

And here is captured (Froude 0.60) the moment of takeoff of the small aircraft

Here Munk's Noment is practically insignificant: bow out of the water, and stern that does not create Low lateral pressures (but vertical Low pressure): 5

And when the machine flies (Froude > 0.60) Munk's Moment is zero, nothing.

And the magic carpet can be driven by a small child.