Poor ESC recommendation, no ESC will work. First off, you have a very hot setup for a boat that large, it is really a hydro motor more suited to a 30" hydroplane - ON 4S! There is no ESC that will handle that motor on 6S, you will burn down any of them as you will be drawing well over 200 amps. And never run any ESC at its maximum voltage rating on a 'hot' setup. They will ALL burn down eventually, even the $700 Schulze 40-160, I've seen it happen.

You have two choices. One, run the 1515/1Y on 4S with an m440 or x442 prop and watch for heat. The Turnigy 180 might work for this application.
Two, sell your motor and buy a more appropriate one for 6S - any similarly-sized motor with a Kv from 1250 to 1500 will work. Use an ESC with a voltage rating of at least 8S unless you can control yourself and not use too much prop for "just a little more speed."





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