roberto bormann (asker) Aug 20, 2011:

You are right. But for this context (specifically) it takes the same meaning, as it refers to the effect the wind causes on the water. The radar uses the reflection on the water surface waves, which is different for oil and water. If there are no waves, no reflection, no radar sensing. By leeward the effect of the wind is blocked by the vessel causing the wind shade. In this specific case they talk about the final effect, doesn't mind if there's a vessel or not... In the end it's the same.
That's why it took me some time to understand the sense. I had to ask the client. He probably knows better.
In any case, thank you anyway!

Salvador Scofano and Gry Midttun Aug 20, 2011:

Just for the records: sotavento (leeward) is not the same as "wind shade".

http://pt.bab.la/dicionario/ingles-portugues/leeward

Wind shade is an obstacle that masks (reduces) the wind in a certain area.

roberto bormann (asker) Aug 16, 2011:

Eu esperava que houvesse alguma expressão paralela a "Mar de almirante" e "Céu de brigadeiro" Mas como não há calm sea ou quiet sea ou flat sea servem perfeitamente.
Quanto a sombra de vento: Trata-se de leeward, que seria também chamado de sotavento em português, no jargão náutico.
Peço desculpas se não fui explícito o sufuciente para formular a pergunta.