Oracle grindig mode

Windage is always a relevant part of the drag a boat has to overcome to sail. In foiling cats it has a much more significant impact, as apparent wind even in seven knots of breeze is always more than 30 knots. Looking back at AC32 on the slow mammuths that where those monohulls, all was done in order to reduce windage, from wingshaped spreders to Shosholoza reducing the runner cables all the time, having none that went all the way to the mast top, not even in stronger winds, to grinders laying flat in the cockpit going upwind… and fairing on all you could and tight lycras etc…

Aotearoa training in the Bermuda's Great Sound

Aotearoa in the Bermuda’s Great Sound

So when we see guys grinding standing out of the Oracle boat and helmsman and crew leaning out straight in the wind, I am, to say the least, really surprised, as I was really surprised when ETNZL last time around (SF, 2013) did not cut off the bowsprit they never used in the AC. Remember one starting reach, when TNZ had the gennaker up and never deployed, something that watching I could not believe my eyes, as they were so much slower due to the extra drag.

Compare these two pics… what’s better and more efficient for you?

Oracle grindig mode

Oracle grinding mode

 

kiwi's pedal mode

kiwi’s pedal mode

Oracle Team USA can change 10 % of their foil package in weight, for light winds they can try to get closer, but as the structure is shaped differently they will never be able to point as much. The systems in the wing of ETNZL allow for a much smoother twist profile and they can adjust it way more accurately. Not much can be done there by Oracle, as five day to change the entire system and mooving to pedal grinding, much more efficient in terms of generation of power, and that leaves the hands free to sailors to trim foils etc.

In this video the CFD fresh blood of ETNZL, Elise Beavis, explains how the kiwis put the right cards on the table with the pedal-grinding idea:

 

In the press conference both teams claimed they could improove and while Spithill looked like a gambler hoping for the magic card, Burling to me was just playing the part, TNZ will not improove much and so will Oracle, as a total rebuild is not possible right now, but what is interesting to understand is why they did not do anything when they first saw the kiwis sailing with pedal power down under. As to me that was a clearly superior package from day one. More power, less drag and more chance to have free hands to trim, that is why I bet with my friend Michele Tognozzi and we put all our cards on TNZ, though months ago all could have been changed if Oracle would have just had the intuition to be critical about their design.

Russell Coutts coul be a key factor in the next four days to help Oracle Team USA to hold the Cup?

Russell Coutts could be a key factor in the next four days to help Oracle Team USA to hold the Cup?

Probably Coutts, doing only the event organizing side, left a huge deficit in the team as last times around it was Russell to see and decide they needed a jib to win the dead of gift challenge, and again Russell understood they needed a change in the mode they sailed upwind, footing off and getting to higher speeds. I had with him a funny email exchange than, all in all intuition still palys a big role even at this level. Surely numbers can than confirm as designers can work out, how many kg/newton extra drag Oracle has towards Aotearoa, and how many seconds per mile they are slower just because of that.

Artemis showed the only area where TNZ is vulnerable, strong winds. Not a mistake there by the kiwis, just a decision in perfect line with the weather models for Bermuda at the end of June. All in all the kiwis did all they could to win and they are winning. Let’s see if weather forecast changes bringing some spice to the game, as in light winds chances are slim that we will see a close race…

Here a link to a really simple tool, http://www.engineeringtoolbox.com/wind-load-d_1775.html, you can work out how much difference it makes to be in the AC50 as Oracle and as TNZ…

So let’s make a rough estimation, let’s say 4 seconds a mile? If we are about right that is 35 seconds a race… right now they are 60 second a race slower, so in wing trim, foil shape etc they have to catch up 25 seconds and make better than tnz by 35 to become even, as they can do nothing for the windage… Me think no chance, but sailing is at times full of surprises and maybe I am overestimating crew drag , surely some good aerodinamicist can help out? Any of our beloved readers can come up with more accurate numbers?