You stay on board here.

You can be of no use to me on the journey, and may be of use here.

I will telegraph to you from Ostend.

Possibly I may want the yacht to sail at once to Dover to meet me there, or you may have to go up to town to do something for me.
"Now I must go down and tell Lady Greendale as much as is necessary.

It will, of course, be the best thing for her to go up to town with me, but if she is not well enough for that, of course she must stay on board." Lady Greendale had just come into the saloon when he went down.
"I think I have got a clue--a very faint one," he said.