Greetings & Welcome~

The short answer to your question is Yes the SMX II can be used…I have installed them on all kinds of systems (even home systems) but…

The long answer is will Mermaid honor the warranty after you make the conversion ?

And do you really want to ?…It will be quite in depth to do it, and depending on what model Cruisair unit you have…Where & what to steal from it to make the change….It's not just a matter of the keypad/display (which is just that) The brains for the SMX are generally mounted on the unit (in a metal box) or in a box that is remotely mounted (this is likely if the Cruisair was converted from the 3 knob control)

The other question is what Mermaid unit are you buying ?…Many of their units control circuits are 24 VAC like in your home, and all of that will need to be removed & rewired for SMX connection…It's not likely a job for DIY'ers unless their electrical knowledge is really good.

Another consideration is Ductwork…Stepping up in unit size will require up-sizing the duct to 7″ (from 6″)

Lastly…I know the Mermaid is less money…But the new Cruisair "Turbo" that is ready for the SMX II keypad will outperform & outlast the Mermaid…Cruisair's 12K will likely cool as well as Mermaid's 16.5K….Last year I removed a older 16 that had 6″ duct installed on it, and replaced it with a Cruisair Turbo 12 using the same 6″ duct…The owner claims the boat has never been so cool or quiet…

What boat are we talking about and what is your locale ?

Steve~