The choice of term, the decision to put it in inverted commas, in highly indicative of the hull shape. It would be helpful to have a photo, the name of the race or, indeed, information as to whether this is actually a hull designed by Mr. Libera. I think you have no reason to use anything other than the term as cited in inverted commas. That is why I have put a "high" confidence level without even being sure of the type of boat. I somehow have an Australian skiff in mind. Or a 49er?!

Optimists are familiarly described as "caisse à savon", I'm not surprised to see a high-performance race craft described as a "luge". I suspect it is a flat open hull affair with

In no way does the term "luge" point to a foil.

Can you not provide any more context?

Is it like this? https://www.youtube.com/watch?v=aJpzVpQgx4E and https://www.youtube.com/watch?v=ms3eBs6Hw0k

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Note added at 2 hrs (2017-04-12 16:57:21 GMT)
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Sorry, "flat open hull affair with a trapeze sest-up".

https://www.youtube.com/watch?v=YX-tC9NSVEM
https://www.youtube.com/watch?v=Xs1FMn-QuMQ
https://www.seabreeze.com.au/News/Sailing/Squall-wipes-out-e...

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Note added at 2 hrs (2017-04-12 16:58:15 GMT)
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From the last source:

"ake Garda is known for having fickle, and interesting wind patterns for sailors, but kiteboarders and windsurfers enjoy the frequent strong winds that start blowing from this time of year. It’s usually pretty tame though, with strong days reaching 30 knots at most. This day was not tame however, and nor was the racing with several of the obscenely complicated ‘Libera’ Class yachts (or should they be called dinghys?!) being toppled by the squall.

If you havn’t had the chance to see what these ‘Libera’ Class boats are like, imagine an 18ft skiff on steroids, scaled up to 45ft, with crews of 15, ALL on trapeze. Yes, ALL on trapeze. It’s insane, and something that only really happens on Lake Garda during the Centomiglia regatta."

I like the "like an 18ft skiff on steroids"!

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Note added at 3 hrs (2017-04-12 17:01:53 GMT)
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http://www.yachtsandyachting.com/class/Libera/

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Note added at 3 hrs (2017-04-12 17:08:19 GMT)
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Check out EN docs on Principessa, Centomiglia, Raffica...

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Note added at 3 hrs (2017-04-12 17:16:18 GMT)
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The Libera class sebsite is not up and running at the moment. There are references to the class in Hungarian and in Italian, but also in English. ;-)

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Note added at 3 hrs (2017-04-12 17:16:28 GMT)
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website

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Note added at 4 hrs (2017-04-12 18:59:02 GMT)
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I have rowed a little in the past. We called the beginner's boat the "bathtub". It is not unusual to use nicknames, affectionately, for boats.

Yes, it is highly likely that there are some fairly competent linguists among the crew and teams, often comprised of yachties from many countries. They oten know the technical vocab. Only those who speak French are likely to understand the allusion to "luge" though, but explained to an EN native yachtie, the idea will be clear.