" but from the great start he had had, Derick's boat led the chase"
"...at this juncture, the pequod's keels had shot by the three german boats last lowered, but from the great start he had had, Derick's boat led the chase." I'll "translate" a phrase at a time, explaining as I go. At this juncture = at this particular point in events or in time; now the Pequod's keels = the long structure(s) on the underside of a boat or ship which give it stability in water had shot by = had passed at great speed the three German boats last lowered = the final three German boats put into the water by being lowered from the deck but from the great start he had = because he was so far ahead Derick's boat led the chase = Derick's boat was closest to the prey of all the boats chasing it Paraphrasing: Now the Pequod had zipped past the last three German boats to go into the water, but Derick was so far ahead his boat led all of the others in the chase.
at this juncture - at this point in time. don't know what the others mean.