@Lilliwyt—
Maybe.
It would be a real stretch for her father to rescue them under such circumstances. Further, their building a boat for four people does not result in a boat adequate for seven people, and in the absence of intersecting paths there's a problem with resolving the rescue of her father and of his two companions if the girls are simply successful — the girls don't know of those three, though those three know of the girls.
It wouldn't make good sense for her father and his two companions too have built a boat for seven people; a better plan for those three would be for them to escape and get help for the four girls.
It may be the intention of the author to have the boat project founder, or the structure of the boat be retasked in an emergency, which leaves the boat unusable for the purpose that the characters originally planned.