1)
Who are "Kol Tofesei Mashot Malachim Kol Chovelei ha'Yam"?
1.
Malbim: They are, respectively, those who conduct small boat, medium size boats and great boats.
2)
Why will they stand "El ha'Aretz"?
1.
Rashi: What use do we have for boats? To where will we take merchandise? Radak ? "El" is like Al; the same applies to "El he'Harim Lo Achal" (18:6).