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post #3651 of Old 01-12-2013 Thread Starter
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On design

Along this thread I have refused to take sides in what regards the ideal type of hull for a sailing boat and for a good reason: that depends on the sail conditions the boat is mostly used (downwind, upwind, with waves, without waves) and also in what regards the crew number.

A boat can be faster but require a numerous crew to be sailed. That same boat if sailed solo will be much slower than a well designed solo boat that if sailed by a crew would be a lot slower than the first.

But beside the maximization of the boat performance to a given criteria, even if that criteria remains constant, the NA are always learning and improving design. In as little as 10 years we can see big differences.

Let’s have a look at it. I don’t want to write much because I don’t want to make this post long but also because for the ones that can read the hull lines, the differences are obvious.

Nothing better than start with the old AC monohulls. The last year they were raced was 2007 and at that time the sailors were complaining that the boats were too much balanced to upwind sailing and that downwind the boats were just SLOW and that in the overall balance they were not fast sailboats, for top racing boats.

Anyway, upwind they could sail very fast at incredible angles and that’s what those hulls were maximized for. We can see that in just 17 years the design improvements are HUGE. Of course these boats heel a lot, have a small hull form stability and the major contribution in what regards the RM generated come from the big ballast on a bulb at the end of a very big draft.

And to go on, we are looking to the opposite hull shape, the best hull form maximized for downwind sail and most of all designed to be sailed solo, the Open 60. First a 1996 Finot design and then a Juan K 2007/2012 Design. Again a huge difference in a bit more than 10 years.

The Open 60 shape is not the fastest shape to go fast downwind but the best shape to go SOLO fast downwind. As we can see even if the boat carries a considerable ballast on a canting keel and has water ballasts, hull form has a huge importance here in what regards stability.

With this kind of hull the boat minimizes the more dangerous movement downwind, the lateral roll with provoked by lateral waves. On a narrow hull when the boat is hit laterally (on aft part of the boat) by a wave the boat will heel till that big ballast can generate the force to bring the boat back but then, because the hull has little form stability, the opposite roll induces by the boat RM will not stop at the vertical and will continue to the other side (in a lesser extent).

This movement can become synchronous with the waves and can create a very dangerous situation. It is needed a crew (at the sails) and a good hand at the helm to stop that. It would be very dangerous on a boat with one guy and unthinkable on autopilot.

On the same situation, those fat asses on the Open 60 will damp immediately that movement. The hull form stability is so big that the boat don’t need to heel to stop that movement and if it will heel, that opposite movement would be damped by the hull form stability and the boat will not oscillate from side to side like a narrow boat will do.

Many think that these boats are very poor upwind. Well they are worst then narrow boats and there are some technical reasons for that in what regards pointing ability (that I will not discuss here) but they manage to have a bigger waterline (a transversal one) and the wet area is a very slim one (they have a small wetted surface).

Things become much worse for them if they face waves. When the wave passes by the hull it increases a lot the wet surface that is in contact with the water and that’s why they have a big wave drag that slows them a lot.

They are really bad upwind (and very uncomfortable)in that situation but in flat water upwind their difference in performance compared with a narrower boat is much smaller and in some cases they can even take advantage of their smaller weight (less ballast needed) to create some surprises.

Some very interesting computer images that show the wet surface on those boats sailing in flat water (Owen Clark Design):

The Open60 can go solo downwind much faster than an America Cup monohull boat with a full crew because its flatter and beamier hull make is much more easier to plan than an AC cup, that will never manage to go much faster than its hull speed while the Open60 can easily go at two times hull speed…. and on autopilot.

But the Open60 it is not the best hull shape to go fast downwind with a crew.

A narrower boat, even if a lot more beamier than the AC cup boat, can do better but will be more difficult to control and in many cases impossible to control on autopilot or solo.

A good example of that type of boat is the VOR 70. Also here we can see the huge evolution in hull design in just about 10 years, between a 2001 design from Bruce Farr and the Juan K that won the last edition: Groupama

Regarding more overall balanced boats, between upwind and downwind sailing, probably one of the best is the Maxi Rambler, also a Juan K design:

And even if bigger boats are proportionally less beamy than smaller boats, we can see the boat is less beamier than an Vor70. But of course, even on this size, if the boat goes against a lot of waves and is mostly sailed upwind, a less beamier boat will do even better and that’s why the chronic winner of the Sydney-Hobart race is Wild Oates, a Reichel/Puig design.

Have a look at it. As all know that race is mostly an upwind race with bad weather. On most conditions and probably even on that race if the percentage of upwind sailing is not too big, the Rambler will be faster, but on an edition with contrary winds, the Wild Oates will only be beaten by a more modern designed boat maximized for upwind sailing.

Some will think that this has nothing with the design of cruising sailboats, well they are wrong.

Of course cruising sailboats are designed with different criteria but many of the developments that come from top racing design have an application in the design of cruising boats. You have only to look at the change of hulls on the last 15 years to see that many of those improvements have already made its way to cruising deigns. First to performance cruisers and then to mass production cruisers. After all they are designed by the same NAs.

But remember, except cruising racers that are occasionally raced with a crew, almost all cruising boats are sailed by a very small crew. That’s why the major influence come from solo racing boats, not only the Open 60 but the smaller Benetau Figaro and this ones are not only used on downwind races (transat) but more than half the time in mixed wind races and that’s why they are more balanced (downwind/upwind) than an Open 60.

If you cannot see any resemblances on these designs, both very ahead of its time, and the cruising boats that were designed after, well, you have a problem in your eyes.

The first Figaro Benetau was a 1990 Finot design and the second and actual design a 2002 Marc Lombard design:

Very soon we will have a new Benetau Figaro Design and I cannot wait to see it. Probably, like this two, it will be a major influence on the cruising boats to come.
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