Same Boat, Same Shadow, New Graphic!

Two days ago I posted an article here about wind shadow for Trudeau One. ONE is the first serious race boat from Trudeau Yachts since the legendary  J-Class, and ONE’s shadow engine is a truly powerful, tactical weapon. I think any serious sail racer owes this feature considerable thought and attention.
(But I’ve been wrong before.) 🙂

As I mentioned in the last article, I wasn’t too happy with the graphic displays  I came up with for shadow effects, and was still working on it. Today I went back and repeated all the measurements, trying to come up with a simpler graphic that might illustrate the effects but still be useful for race skippers.

Here’s that second attempt below; this time I ran around measuring the shadow intensity leeward of the ‘wind-blocking boat,‘ trying to define the borders of the “WS>20%” blanket zone.

The blue coordinates below show the points where WS=.20 (in other words, a ‘20% windshadow effect’). That new data matches rather nicely with what I posted two days ago.

Here’s the Bottom Line: A boat in the ‘orange bubble zone’ on the below graph will fall into a substantial shadow effect with a serious drop in wind impulse power. At the edges of the Orange bubble the effect is 20%… but central to the bubble and closer to the windward vessel the shadow strength goes to 100%.

In my hands, in this boat there is no noticeable turbulence effects on the Windward side of the shadow vessel; it’s all about Downwind Shadow, and that influence projects a strong, realistically-sized blanket on leeward boats within several mast-height distances from the ONE root prim.

The graphic below also shows the two features I emphasized previously:

  • There is a relatively small but very definite bias for stronger shadow effects aft of the shadowing boat. A boat approaching the windward shadow-caster from behind will get hit sooner with a heavier hammer than one on an opposing tack that passes from the front.
  • Since the shadow script radiates from the root prim, the effective area is shaped like a funnel… or actually a cartoon chat bubble :-). In other words, the Shadow Zone is very narrow immediately next to the boat, but then expands out fairly quickly.
  • A lee boat that that passes very close to the shadowing vessel  [2-4 min horizontal separation) therefore may only see a shadow effect for 5-6m of linear distance while passing. The shadow will be maximal for that short spurt, but if a crew has enough forward momentum, they might well be able to glide through that segment and find clean air on the other side.
  • What’s that line from Winston Churchill? “If you’re going through hell… JUST KEEP GOING.

It’s worth commenting briefly on three more points:

  • Watch out for sim edges. As Alain pointed out yesterday, shadow doesn’t transmit well over sim boundaries. You might play those boundaries  to tactical advantage.
  • For two boats traveling  perfectly parallel on a beam reach, the shadow effect is 100% with boat separations of 2.0 m – 14 m (beyond that, the shadow effect decays progressively with distance; it is minimal around 50m separation).
    This means that a boat passing leeward with 14 m separation sees the same maximum shadow as a boat passing with a scant 2.0 m separation.
  • There is, however, no advantage to giving the Windward boat extra room; the shadow effect will be just as bad a boat length away. I’m bringing this up here to illustrate that ‘funnel shape’ I talked about before.
    With a small 2.0-4.0 m interboat separation, the shadow effect on the passing boat has a very short geographic range. In contrast, if you “stay a safe 12 m away from the windward boat,” the actual intensity of shadow is the same, but the linear effective range while passing is far, far greater.
    Passing a Trudeau ONE on a course set 2m leeward to the shadowing boat is an interesting tactical option in my opinion… a gutsy crew might be able to pull that one off and grab the lead.
  • However, if you trying that same leeward maneuver with a larger 14 m interboat separation, the ‘course distance” you’ll spend under strong shadow is far greater. In my opinion, passing parallel and leeward at 14 m isn’t ‘tactics…‘ it’s suicide. 🙂
  • Hey! You try it!

    And please tell me if the new graphic makes more sense to show effective shadowing than the last one I posted!

2 responses to “Same Boat, Same Shadow, New Graphic!

  1. Hi Jane,
    That graphic is more intuitive, what you also might like to try (because we all know how much time you have) is do the same thing at 50% effect and overlay that with a different color

    • Yes I agree with Alain; Two things would help, maybe:
      1. A simple ‘color gradient’ to show fading shadow intensity; and
      2. A clearly marked ‘proximity area’ from zero to around 14m where the shadow is a constant 100%
      Here is a posted graphic of one of the VS ACC shadow blankets. Its very pretty, but doesn’t have quickly accessibly information. I know it can be set up different ways, so I’m not complaining about it, just saying this one view would not help me much racing. 🙂

      Maybe someone who knows VS well could comment on it.

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