I have never liked the idea of steam cleaning after I found out that it dried out the wiring insulation on the ignition wires on a Mercedes...they were not cheap to replace....and some of the other wireing was the worse for wear....... and on a boat in a confined area......with other equipment in the immediate area.....even less so.....I am sure someone will come back having nothing but praise.....so this is just my .0000002 worth......
I have used Gunk.....really stinks up the boat, but does a good job with a medium bristle brush.....if really filthy might take a few more applications.....also there is a product I bought at the recomendation of my helpful hardware man at the local Ace a few years back called Challenger.....worked just great....no after smell and seemed to really clean the engine on my Ericson after the PO probably left the dipstick out....it was a really filthy black mess.....
All of the above FWIW....
Good Luck