The Racing Rules of Sailing
Conditions to meet definition of surfing
Question primarily for other IJs : could a Dragon surf down the front of a wave that is no more than 70 cm high with a wind speed of 10-12 knots ?
At an ongoing event there seems to be some confusion as to what constitutes surfing, and so when pumping the mainsail is permitted. I know what I expect to see when a boat is surfing, but I'd like to hear other opinions please, should they differ.
At an ongoing event there seems to be some confusion as to what constitutes surfing, and so when pumping the mainsail is permitted. I know what I expect to see when a boat is surfing, but I'd like to hear other opinions please, should they differ.
Created: Yesterday 15:57
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then, no, these boats will not surf on a 70 cm high wave. I would say the boat is surging and not planing or surfing as a 70cm wave will not be long enough for surfing and in 10-12 knots this type of hull will not be planing.
You have to differentiate what is happening into three types: planing, surfing, and surging. Most people confuse surging with planing or surfing.
Planing occurs when the wind forces on the sails are suitably large enough to cause the hull to develop hydrodynamic lift that takes the boat beyond displacement mode. This is generally independent of any wave action.
Surfing happens when a boat accelerates down the face of a wave due to gravity. You can think of this like a skier going downhill. The effective wave length (the wave length that the boat sees because of its angle to the wave) must be greater than 2x the length of the boat in order to surf. The boat can then travel at the speed of the wave but no faster as it will run into the back of the wave ahead of it if it does. If you are not going 'downhill', you are not surfing.
Surging happens when a boat is initially going slower than the wave speed. In a wave the water molecules are primarily moving up and down, however, they also have a circulation that moves the water at the top of the wave in the same direction as the wave. This is the force that causes the boat to surge ahead. When the length of the wave is larger than the boat, the wave will lift the stern of the boat and push the boat forward. As the wave passes underneath the boat, the boat will level out and then as the wave passes the boat of the boat, it will lift the bow. Wave lengths that are shorter than the length of the boat will push the boat forward but not cause as much change in the trim. You can almost consider this as a little 'wave current' that is moving the boat forward at the top of the wave and in the opposite direction at the bottom of the wave.
When a boat is surging, you can trim the sails to the new apparent wind angle, but pumping the sails, etc. would break RRS 42.
The perfect answer with explanations of all the possibilities.
Can you provide a reference for your POV?
You can surf if the wave-train is moving faster than hull speed and you manage to jump on and stray with the wave. I have raced dragons quite a lot in the past and will certainly agree that the described situation is borderline, but it really depends on the waveform and the wave speed. But we can certainly agree that planing is categorically out of the question.
Take a look at:
https://www.yachtingmonthly.com/sailing-skills/sailing-in-waves-top-tips-to-keep-you-safe-at-speed-79670#:~:text=Once%20surfing%2C%20don't%20steer%20straight,wind%20angle%20will%20suddenly%20change.
This explains some of it. Most of the articles you will find on surfing are about surfboards and not sailboats, but the physics involved is the same. Pumping the sails is the equivalent of a surfer paddling to catch the wave. Once they catch the wave, they have accelerated beyond their initial speed and stop paddling. Same with a sailboat, once you are 'on the wave' you stop pumping because it doesn't help, you are already going fast.
You could write an entire disertation on the physics of this and likely someone has.
A boat of any length can ride a set of waves (such as a competitor’s bow waves) each of shorter “frequency” than her LWL for an extended period of time.
In so doing she rides down the greater combination of wave tops over the lesser combined opposing wave bottoms.
She is surfing one of those waves. You choose!
I have a problem, now I think of it, with the definition of surfing: "surfing (rapidly accelerating down the leeward side of a wave)". When one picks up a wave to surf on it there's an initial acceleration to wave speed, sure enough, but thereafter one will not normally be accelerating, but by any normal dictionary definition one is still surfing. Its I suppose a moot point for the rule, since one is only allowed a single action to promote the accceleration to pick up the wave, but it seems messy to me.
Once you start surfing, you accelerate by bearing off and slow down by heading up. If you hold your angle steady on the wave, you will reach equilibrium and stop accelerating. If you head up too much then the wave passes you by. Bear off too far and you go too fast and bury the bow into the wave ahead.
I think getting into all the subtleties of the definition of surfing is more than the rule writers want to get into. You would have to cover the initial acceleration and then the sustained boat speed due to continuing go downhill (down gravity?), when do you start and end surfing, etc. Ugh.
One thing you have to ask yourself is whether the sail is being pulled in response to the changing of the apparent wind angle because the boat has accelerated or because surfing is possible and you are trying to catch the wave. That is part of what the judges have to evaluate, is surfing (and not surging) possible? If it is, then the sailors get to try to do it, if not, they don't. And if they try and fail, then something has to change (more wind, bigger waves) before they get to try again, or they break RRS 42.
If this seems an easy answer for the dragin i frequently consider it in lighter winds in the ilca class