Golden Globe Race design rules?

[sharpii2]

I can not recall the competitor, but it was interesting to see the winner sailed a whole lot more sea miles, than the guy who stuck rigidly to the shortest route. Its much more using weather forcasting with favourable routing when all boats are running displacement speeds.

ULDB do not have to be expensive. Ply on frame 50ft is not in any way "exotic", and the lighter boat needs a smaller rig and sail area, much savings to be had there even if some semi-exotic fabric was put on the hull.

I recently did a bit of math noodling on Displacement/Length (D/L) ratios.

I started out with a boat of the following dimensions:
Length= 34 ft (10.4 m)
Beam = 11 ft (3.36 m)
Displ. = 9,856 lbs (4,460 kg)

Then, I played with its Load Water Line (LWL)

With a 32 ft (9.76 m) LWL, I got
a D/L of 134.

With a 27.2 ft (8.29m) LWL, I got
a D/L of 219

With a 24.5 ft (7.47 m) LWL, I got
a D/L of 300

And

With a 22.0 ft (6.71 m) LWL, I got
a D/L of 414.

And this was with the same Length, Beam, and Displacement.

My conclusion is that a boat with a low D/L can easily require as much Sail Area as a boat with a high one.

And it is likely that low D/L boat will have greater Sail Area than the boat with a high D/L, if it has the same displacement.

This is likely because it cannot only be driven harder, but because probably has greater form stability as well.

This is why I use a ratio I came up with which I call the Heft factor (Hf).

It is determined by taking a boat's displacement volume, multiplying by 20, then dividing it by the square of its Beam, then by it's Length. The resulting product is the rounded down to a two digit number such as: 0.50, 1.0, or 2.0.

A boat can have a high Hf, say 1.5 to 2.0 and above, and a low D/L only if it is very narrow for its length. Rowing shells and maybe kayaks are good examples of this.

A boat can have the inverse of this if it is very wide and short, such as a catboat. It can also have a more common Beam Length ratio of, say 0.30 to say 0.35, but have long overhangs and a short LWL.

Late 19th and early 20th century racing yacht designers were notorious for exploiting this loophole.

 

[skaraborgcraft]

My conclusion is that a boat with a low D/L can easily require as much Sail Area as a boat with a high one.

And it is likely that low D/L boat will have greater Sail Area than the boat with a high D/L, if it has the same displacement.

This is likely because it cannot only be driven harder, but because probably has greater form stability as well.

.

This seems contradictory to me. Any boat can be loaded down with stores, and it will increase its displacement, while also reducing its sail area to D ratio, but increasing its WL length. It also decreases its ballast ratio the more stores go onboard.
Working sail area with regards to displacement certainly averages out, but the full blown racer will almost certainly always carry more sail area than perhaps standard production line boats that most people sail.

I had a 7 ton gaffer with a low SA/D, but it could hold its working SA to the top end of a F5. My old Lightweight J.O.G yacht had a similar SA, but a third of the displacement and had to be reefed down accordingly. Daily runs while offshore were similar, but the J.O.G yacht would surf more easily if one was in the sporting mood. The ratios are a useful guide. The Ballast Ratio of the J.O.G yacht was well under 30% when fully loaded for a 35day passage, but it would still plane if one was gung-ho enough to carry enough sail, in strong wind. Why stick with displacement speed when if you choose, you can do a little better? Both boats were small enough to be uncomfortable in rough weather, so the edge in speed can make even a little difference, to me anyhoo.