How to Design a modern Yacht

SA Yacht Blog: RCOD

During the 2008 Vasco we regularly surfed at speeds of 18 kts. After the race the log and gps showed max speeds of 22 and 23.5 kts respectively.

the 2006 Cape to Bahia race, where Suidoos-2 arrived 3rd on corrected time. Skippered by the Ancient Mariner Gawie Fagan (80 years old!!!), they achieved 250 miles per day for the first three days! - in a 9m boat! If you think about it, that’s nearly 2x hull speed for 3 days . . . on average!!

Royal Cape One Design - Information - Cruisers & Sailing Forums

I sailed RCOD's for 6 years. My Dad, my brother and I raced "Reaction" (RCOD 38) from Richards Bay to Durban (about 80+Nm) and came second over the line behind a 76' maxi. We clubbed the rest of the fleet and won on handicap.

 

(One Ton WindSurf board)

1) young oceanic adventurer or grumpy old man, in both cases sitting in a safe and comfortable cockpit

2) a single winch, note the proximity of the mast, it is a true small boat: the deck only reaches around where the mast is

3) to hold on with your hands

4) racket of one of the two rudders

5) boom vang, mainsheet, preventer: 3 in 1 on a large 2 meter rail

6) ballast tank for Upwind with lot of wind

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Now I think my estimates are too cautious

A young man with this 1 ton WindSurf board hoisting a good amount of sail, I think that with young Waves Force 7 in the Atlantic he would perhaps make 9 knots in the valley and 18 knots "falling with style" with the sum of the Wind Force and the powerful Force of the Earth

 

Whether the sailboat will make 8 knots in the valley and 14 knots falling or whether it will make 9 knots in the valley and 18 knots falling is not important.

The important thing is a good Hull Attitude stern down and bow up so that the boat can accelerate and not crash into a wall of resistance that also inevitably has a lateral component.

Dynamic capsizes of a modern Yacht begin (1979) with the bow sinking, and then the sailboat yaws and capsizes or the stern flies over the bow.

Of course (1979 and 1997) when it comes to doing a nice somersault helps a lot a modern Keel/daggerboard (large 1979 or gigantic 1997) forward of the Yacht Center of Gravity.

In this case (1 Ton WindSurf board Thomas Harrison Butler in Memoriam) the centerboard is Neutralized.

 

question: how to design a modern yacht

answer: cutting out the waterplane area out of cardboard and balancing it finding the primordial center of the yacht:

the Center of Flotation

and then centering the yacht reconciling the centers with this Primordial Center of the Yacht

 

But

But if one wanted to carry the house on his back or go sailing in the southern Indian Ocean or Cape Horn ...

The design principles of a yacht do not change: Centered Yacht with its various centers well reconciled

but the solution would not be a small 1 ton surfboard, but a 10 ton yacht based largely on low pressure, suction, at the stern, in addition to of course a reasonable bow.

 

But, 2

Let's be honest, the vast majority of yachts are not made to navigate comfortably and safely, but to win a regatta or spend the summer in the Mediterranean.

 

A race boat and a F1 car share the quality of beign uncomfortable. If you want comfort, buy a cruising boat or a Cadillac.

 

If you agree that a Baroudeur will not beat a fully crewed 73ft maxi of the same era then you're implicitly agreeing that the claim that the Baroudeur can go just about as fast when singlehanded with cruising sails is rubbish. That was the point.

One can easily be "surfing" but on a craft that goes much slower than the swell, as anyone can tell by (for example) surfing on a Laser while a windsurfer is surfing the same wave. The Laser will not surf as fast as a big swell - it will get a speed boost for a while but will then end up falling behind the swell, while a windsurfer can keep with the swell (or if the swell is smaller, actually go faster than it and go much faster.

I'm fairly sure I specifically said that one had to compare boats of similar type, not a lightweight Black Soo with a heavy boat. The RCOD/Soo is a great boat and they can do brilliantly in the right conditions against heavier boats. Was the maxi you raced against Wesbank? That was obviously an excellent effort by you guys in very tough conditions.

I may be repeating myself, but I have a modified John Spencer 28 footer. It was put in the new boat category in our under-30ft offshore racing class (sadly now long gone) although by far the oldest boat in the fleet, so we didn't sail it badly. It's a bit heavier than a RCOD and a lot beamier, but the point is that we never got it surfing anywhere like as quickly as we got its big sister, the 73' Buccaneer, going with proportionately much less sail up - we got about half the speed. We could beat bigger heavy boats, but not bigger boats of the same style.

The same applies to other types; we could surf IOR half tonners but still get left behind by IOR one tonners of the same type. A Farr 30 or Melges like "Cone of Silence" is super quick downwind in a big breeze, but can't surf as fast as a TP52 or Farr 52. Even in skiffs, something like a 12 Foot Skiff has much better ratios than a 49er but isn't quicker downwind in a breeze, because the 12 suffers from its short length.

PS - I've actually done a fair bit of very close racing in dinghies with one of the guys on the crew list of Sun Tonic in the Richards Bay-Durban run mentioned on that blog. It's a small world.

 

It was not a claim i ever made. My only point was that a Baroudeur, if falling/surfing down the right size wave, could reach a speed similar to that others suggested a larger boat could sail at. I do not believe he was making the claim that a Baroudeur is going to cross any ocean at the same "pace" as a larger boat, that would be absurd.

Boats can and do exceed hull speed, but speeds of 20+ knots on otherwise displacement type hulls of this size will be, in my experience, quite possible but very rare.........and you will never look at rudder attachment the same way after.

 

Sorry, I was unclear. The claim that I was addressing was Carlos' statement that a heavy boat surfs faster than a light boat, because the heavy boat is accelerated more by gravity than the light boat. This ignores the fact that the drag of a non-planing design increases dramatically as it accelerates through the static water of the swell, until it quickly reaches a point where the increasing drag matches the acceleration created by gravity.

Carlos' "evidence" was that someone allegedly surfed a Baroudeur to 20 knots, which is about the same speed as the fastest maxis of its design type and era. My point is that is, to say the least, extremely unlikely. Even when surfing, big boats go faster than small boats of the same general design type. On top of that, the Baroudeur is slow even for a 22 foot long keeler.

Your experience with pushing that wonderful ultra-light RCOD to 18 knots also illustrates the point - if heavy boats surfed faster than light ones as Carlos claims, then the heavy 30ft Murias would surf faster than the light 30ft RCODs.

 

The bottom line is that a modern yacht will be from light to moderate displacement. Carlos is looking at antique designs. Modern necessarily follows fashion. Otherwise, he should call this thread "How to design a retro boat". There is nothing wrong with retro and antique recreations, but they will never be called modern.

 

The "Barouder" was sailing at 5-6 knots and, falling with the wave in a big 20-30 seconds Surf, it reached a top speed of 20 knots for perhaps 1 second

Speed is not the issue.

Don't look at the finger pointing at the moon, but at the moon:

Control of Pitch and Yaw

The helmsman of the 46-foot yacht "Vanguard" of the Hong Kong Admiral Cup team (1979) lost his intense concentration "an instant" (Peter Bruce)

and the yacht capsized doing a 360-degree roll

 

Andrew Claughton

Andrew Claughton around 1984 persuaded the management of Southampton Tank to buy a wave-making machine

and using radio-controlled models he was amazed at how well the heavy displacement classics Surfed ...

while also being struck by how modern (1970-) yachts capsized

 

why modern yachts capsize

because the wave coming from the stern sinks the bow, and

when the bow sinks, Mr. Max Michael Munk goes completely crazy, very very crazy

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

and to top it off Mr. Max Michael Munk finds the willing collaboration of a large modern centerboard/Keel with its hydrodynamic center forward of the center of gravity of the Yacht

 

How to design a modern yacht to be a good surfboard, as good as a classic yacht

1) place LCB at LCF or a little aft of LCF

2) design to achieve a high longitudinal metacentric height

3) design a bow and a stern that minimize lateral pressures

4) Keel Neutralized

5) size the rudder from various estimates of the Munk Moment family

6) design a bow that produces hydrodynamic lift and a stern that collaborates with low pressure, suction, thus achieving a good Hull Attitude for Surfing

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CB: Center of Buoyancy
CF: Center of Flotation
L: Longitudinal Position