Saturday, February 14, 2015


This is a special example of the Laurent Giles designed Vertue Class. She is Number 61. Her name is 'Virtue'. (With the "i" rather than an "e" [ There is a whole story about that for another day ] ). The pedigree of the Vertue Class yacht is impeccable. (See Post Below 06/02/2015 ).

'Virtue' was built of Cor-ten Steel in the land where they are exceptionally good at building steel boats of all sizes (Probably because they have chopped down all the trees ).

I like this video for three reasons.

1 - The owner is obviously so very proud of his little ship. I can feel that. I understand that.
2 - I like the piano accompaniment.
3 - It proves that this anecdote (below) is not just some sort of urban (or marine) myth.

"One of my most vivid memories of a Vertue is of trying to catch a halyard that had come adrift and was just out of reach. "Here - use this!" said the helmsmen, and handed me the tiller as the boat sailed on. "


Ben said...

Hi Alden,

Can you explain why you don’t need a rudder on this ship going a straight course?
The ships I sailed occasionally (Dufour 36 for example) needed sometimes heavy rudder action to maintain course. Wind force 5 approximately.

Alden Smith said...

The reasons some yachts are able to self steer under sail are both scientific and mysterious.

Also 'self steering' is a matter of degree in that some yachts will self steer when close hauled but not self steer with the wind on the quarter or running down wind.

The icon of self steering is the famous yacht 'Spray' (owned by the legendary sailor Joshua Slocum who was the first solo circumnavigator of the world). Spray was able to self steer on any point of sailing.

There are 3 attributes that a yacht requires for self steering. Different mixtures of these attributes give differing outcomes.

1 - A hull that has good balance (similar shape) between her fore body and aft body (bow and stern), BUT more importantly a balance that does not change to any extreme degree when the hull is heeled - some yachts will steer themselves when upright, but when heeled and the hull immersed, the different fore and aft shapes that are in contact with the water brings about an imbalance (and changer of course direction) which require a movement of the rudder to correct.

2 - A hull that has a reasonable ‘forefoot’ - that is a boat that is not cut away too much in profile at the bow. Rather, the bow sweeps down to the keel in a big broad curve continuing the curve of the bow that is above the waterline. This forefoot allows a yacht to ‘hang onto’ the water, the bow not being continually pushed to either leeward or windward by waves. Of course this more old fashioned profile makes a yacht slower when tacking and doesn’t “turn on a penny” like a modern yacht profile.

3 - The way a yacht is rigged - this doesn’t mean the number of masts or sails but refers to the ‘Centre of Effort’ or drive of these sails - this is reduced in theory to what is called the Centre of Effort (CE).

4 - The ‘pivot point’ of the hull is important - this is reduced in theory to what is called the Centre of Lateral Resistance (CLR).

The relationship between the CLR and the CE seems to be important - If, when the hull heels, there is no great change in the position of these points, it means the hull is well balanced and more likely to self steer on varying points of sailing.

From a yacht design point of view which involves the laws of physics there is a lot more to this self steering malarky than this - There are a number of other changing (as the hull heels) factors that come into consideration. That is :

The CB (theoretical Center of Buoyancy)
The CG (theoretical Center of Gravity)
The Rl (theoretical Righting Lever) which is a function of the weight of ballast and how deep that is (draft of the boat).

All of these 5 calculable points change their position as the yacht heels and tosses around on the face of the ocean - it is the relationship and balance between these points that allows a yacht to self steer.

Having said all of that - Yacht design is as much an Art as it is a Science and there are yachts who have all the theoretical boxes ticked yet don’t self steer all that well. A case in point is the famous yacht “Wanderer 3” which Eric and Susan Hiscock sailed twice around the world - This great little cruising yacht is a larger edition of the famous ‘Vertue’ class yacht that I have blogged about. Despite the lauded self steering ability of the Vertues, Wanderer 3 failed to self steer, much to the frustration of the Hiscocks - so there is a bit of mystery in all of this - and perhaps that's that way it should be - What would life be without mystery and serendipity?

Alden Smith said...

...... and I forgot to add ---- Having reliable self steering (whether inherent in the yachts design or attained by a mechanical wind - vane self steering device, is like having an extra hand on board, one who is an expert helmsman (or woman), who doesn't eat, sleep, drink and doesn't talk back to the skipper.... and doesn't mind sitting out in the cockpit steering in bad weather.

Ben said...

Wauw, that is a lot of information to think about. Simple questions can have complicated answers! Thanks. As an engineer I find this interesting stuff. Great to study when I have the time. Also here you get nothing for free. With great self steering capabilities the designer sacrifices some fast maneuverability. The way how a wind vane works is also intriguing. The extra hand on board with all the properties you mentioned will be great. By the way, on the Classic boat forum you can vote for the 2015 awards for restorations. Ngataki is one of the nominees.

Alden Smith said...

Yes, I guess it seems very complicated to the uninitiated but like much in life yacht designing is a specialist area - those that study it deeply understand it. I don't make any claims to any great knowledge apart from that of an enthusiastic amateur.

Thanks for the note about the Ngataki - I will have a look at the Classic Boat Forum.