Re: dumb starter ?s. 25 '72 evinrude
6 gauge copper is probably enough.
A little bit of history may help you to understand things. Unless you are as old as I am, you probably don't remember when cars had a starter pedal. Yes, a pedal, located next to the accelerator pedal. It was a heavy duty switch, such as you advocate, combined with a shifting mechanism for engaging the starter gear.
By and by, improvements came along and the starter pedal was replaced with a push button on the dash. That neccesitated a solenoid because the push button was a light duty switch, not capable of carring the full starter current. But it carried the solenoid's coil current just fine. There was another reason for the solenoid: Even if the dash button were capable of carring the full starter current, the battery cable would have to go all the way to the button, then back to the starter motor. That means a long run of heavy battery cable, both expensive and power-robbing.
Not much has changed since those days. We use a solenoid for the same reasons. It would be absurd to run battery cables all the way forward to the start switch in a boat. That would amount to 30 feet or more of expensive battery cable. OK, so you say you just want to put the start button on the motor. You would still need a very heavy duty switch---similar to the one Grandpa tromped on in his old 1930 Chevy.
P.S. I am even older than that--I remember when cars didn't even have starters. You used a crank.
