Ya need to elaborate a touch here..I'm confused ..30hp kicker..most ALL kicker brackets are 15hp rated tops....(as more hp is not needed..ya just want that push factor, not ski behind it with the biggie shut down)
The answer is "if it fits, then you do can do it", checking to see if the shaft is long enough and that both motors can turn and not hit each other are the main concerns. A lot of people say to use large motors like this for kickers, but hear in the NW where almost every boat over 15' has one, you almost never see one larger than 15HP, the most popular motor by far is the Yamaha T8 and that's for boats up to 26'.
There usually isn't room on the transom for both motors plus turn clearance. That said, if you can do it, there's no reason not to.
ondarvr is right on about size. I recently went down from a 15hp to an 8hp on my 18'-er. I like that I troll further up in the rpm range now. I get more speed adjustment and there's always someplace to go down or up. I think the motor is much happier trolling for hours at 1/3 throttle than 1/5 too.
