Real meaning of "twice the speed"

Originally posted by Eric Sponberg:

"As to your last question, the performance of "drag-only" downwind sailing and "lift" downwind sailing is very pronounced. I can (and have before) report the experience of Eric Hall, owner of Hall Spars, who in the mid 1990s equipped his J-90 sloop with a sloop-rigged free-standing wingmast with the same total sail area and then raced it against other conventionally rigged J-90s. He could swing the boom forward of the beam so that the rig generated lift downwind. He found that upwind, both boats (his and the others) sailed comparably--same speed, same pointing ability. However, downwind, he found that he was about twice as fast as the other boats--that's right, twice as fast downwind."

In " cat ketch downwind" downwind tread this caused quite a discussion...

In my opinion, the reason is no one really know the real meaning of "twice the speed".

When racer says "twice the speed", what it really mean, technically?
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Here is my little thought on the subject:

Handicap races are lost or won by time margin of ~0.2%.
Races in competitive fleets of monotype conventional boats are won or lost by few boatlengts, i.e. with time difference even less than 0.2%. This have fundamental influence to speed perception of racing sailors. They constantly tune their perception to notice VERY SMALL increase or decrease in speed and VMG. Very small I mean much less than 0.2%. So when racer gain, say 2% or 3% of speed, he could easily say "my speed has doubled!" and grin from ear to ear.
Have noticed it many times in conversations with racing sailors, grown up in monotype boats.
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So, the question is:
WHEN A RACER SAY, "I'VE GOT TWICE THE SPEED", WHAT DOES IT REALLY MEAN?
IN CONVENTIONAL KEELBOATS, HIGH PERFORMANCE KEELBOATS, MULTIS, CONVENTIONAL DINGHIES, HIGH PERFORMANCE DINGHIES?

 

Twice means two times. If it is not two times, they are exagerating or lying.

 

I know perfectly well they are exaggerating. I know perfectly well it looks like two times, when actually racing.
But I suspect it is possible to "extract" a true technical meaning of such claim.
This is the purpose of tread: to find, how much % really mean "twice the speed".

 

Technically, twice the speed in 200%.

 

From a mathematical point of view, twice the speed means that a boat moving at 8 meters per second is twice as fast as a boat that is moving 4 m/sec. On a percentage basis, the faster boat is moving at 200% of the speed of the slower boat. Math types often state that percentage should not be stated in terms that exceed 100%. With that in mind we should say that the faster boat is moving at 100% and the slower boat at 50%.

The subject is moot. We can show that a boat that moves twice as fast may not reach an appointed destination as soon as one who is moveing at half that speed. An example would be a race on a hard beat to windward. A boat that is close winded, but slower, might get to the windward mark before another boat who is sailing to windward on a close reach. We could complicate the question even more by arguing speed through the water versus speed over the ground.

My experience, in regattas, has me sailing fast in a 5 meter LOA boat, a larger 8 meter LOA boat, with more sail area, passes me so fast that he looks like a freight train. In fact I was sailing at about 6 knots and the bigger boat might have been doing 8.5 knots. Later in the club house I would complain that the E-scow, or whatever it was, passed me going twice as fast. I'd be bitching about his having disturbed my air in an ungentlemanly manner. After a few more beers I might claim that he was going three times as fast and therefore endangered my life and limb. Sailors and sport fisherman alike are prone to exaggerate and furthermore they are permitted to do so because everyone knows that the size of the fish or the speed of the boat is subject to verbal embellishment.

 

Let's refine the question:
what is the meaning of "twice the speed", when it is claimed by racers about identical or very similar boats.

 

Is the racer a liar or a stickler for technical terms?

 

joke appreciated.

Please note the following from first post :

"In my opinion, the reason is no one really know the real meaning of "twice the speed".

When racer says "twice the speed", what it really mean, technically?"

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This is theme, offered for discussion.
Any one with casual experience in sailboat races know how big speed differences look like, when actually racing.

While very few guys outside of handicap team do care to compare the numbers, like total time on distance.
However, my feeling is "twice the speed" DO have a measurable technical meaning. When racing, especially close racing, actual speed over the water is quickly moved to "background noise" category, whether it is 2 knots or 10 knots; but small difference between you and closest competitor became the main focus for attention.
Maybe "twice the speed" is 2% more as competitor, may be 10%. Or maybe "two boatlengts in a minute/15 minutes/half an hour". Maybe "I vent over the horizon in 1/2/4 hours".

Opinions, please.

 

This sounds like trying to apply Principles of Alchemy to sail racing.

If we talk about the boat speed in a sense of course speed or ground speed, then it is, imho, not possible to obtain any quantitative information from the claim "this boat is going twice the speed of the other one" - if the meaning of the claim is not "exactly 2 times the speed of the other one".

But if you consider a component of the ground speed in some direction, for example a VMG, then you have another parameter (the angle to the wind) which theoretically could make it possible to have one boat go twice the VMG of the other - tough not with "everything else being equal". If you put some real numbers into formulas for VMG, you will see that a boat A will have twice the VMG of the boat B only if the boat A makes 45° angle to the wind vs. about 65-70° of the boat B. Such a big difference doesn't sound much probable to me, unless the boat B has a huge nylon bag attached to the keel or something like that...

So, the short answer, imho, is - no, not practically possible to extract a "technical" meaning of that claim.
I think it should be considered with a grain of salt, just like when you hear a fisherman's story about that big fish he catched years ago, so big that... etc.

 

You guys just haven't been getting enough catsup in your diet. Or, if you prefer, ketchup.

 

I have been a "racer" of sailboats for more than 35 years. I have sailed at every level from club racing to International regattas.

I have never used the term "twice the speed" and have never heard anyone else use it when discussing the day's racing.

At times people do exaggerate and use terms like "he was going a knot faster", or "we eased the main an inch and went a knot faster."

 

What would be your impression, now, with cool thinking?
Was it really a knot faster?
Or maybe it is possible to find (after examining "the video records") some other quantitative term like gained boat lengths, noticeable change in trend (we start consistently close on forward boats and walk away from aft boats)?

I do not mean to bother anyone; from times immemorial speed claims tended to be exaggerated and not believed. But I still have the feeling, that "twice the speed", "a knot faster" actually could be pretty accurate terms, only the words "twice" or "a knot" are used inappropriately.
My feeling is based on the fact, that top level racers are able to notice and quantify many, including quite small, differences in speed, pointing, VMG, and use this information in practice. So whatever they say about speed gains or losses, MUST be pretty accurate. However, it is obviously not the kind of accuracy the engineers use. My general feeling is that engineers use "linear scale" , while racers tend to use "variable scale", where area closely below actual boatspeed at the moment is "compressed", while area around the actual boatspeed and up is greatly "extended".
I also feel, that some quite useful, if not scientifically accurate "translation" could be made.

 

Useful, maybe. It tells you that one boat was faster than the other one.

Scientifically accurate - not possible. Unless the claim is honestly reporting a reliable instrumental measurement which was showing the speed of the boat A as double the speed of the boat B.

 

I use the term 'twice the speed' quiet often...
when sailing a cat past a lead belly

2 kts is twice 1 kts

 

I don't think so.

Everyone seems to have their own shorthand when determining their position and speed when making trim or tactical decisions.

It seems to me the better the sailor, the less the exaggeration. When you are in a position where a couple of feet is the difference between getting rolled vs sawing the guy off people need to be pretty accurate. Same with crossing situations.