You can troll crankbaits at kayak speeds. It does get a bit faster if you can troll them with the wind and current. If you need to get your crankbaits down use a rubber band and a weight (called the poor man's downrigger). Here is one video on you tube. I'm sure there are plenty more.
I troll crankbaits here in Hawaii all the time.
https://www.youtube.com/watch?v=4MfQJskQOyQ