This is not so, however, because so far we have only considered the effect of a steady wind on a boat at rest, whereas, in fact, her speed must be taken into account in order to determine the effective power of a wind to drive the boat ahead.
Le nto ayikho njalo, kuba ukuzo kuthi ga ngoku siqwalasele iziphumo zomoya owomileyo kwisikhephe esiphumileyo, nangona, isantya kufuneka sithathelwe ingqalelo ukuze kucace amandla angawo omoya wokuqhubela isikhephe phambili.