I had to do this job a few years ago, and posted some pictures.
The first order of business (removal) involves the following:
1) remove the center water tank
2) underneath where the tank was, there are 4 nuts that hold in the strut (the bolt heads are captured in the underside of the strut mounting flange.   On some of our boats (mine, which is an '85), Catalina glassed over the top of the nuts, so you'll have to grind the glass off to get at them.   See second picture below.,
3) on the underside, the small fin in the area of the strut is just filler for -- give or take -- 10 cm on either side of so, you'll need to chop that out with a saw to free the strut. See first picture below. 

Here's a link to a picture of Gerry Douglas (the designer of the C36) at the factory showing the strut installation to some C36IA members a number of years ago: www.catalina36.org/community/photos/catalina-factory/prop-strut

In the links below, you'll find diagrams and photos showing the strut is bolted into a large cavity within the small fin that runs down the middle of the hull in that area, and the cavity is simply faired out with a bunch of  filler.

www.catalina36.org/forum/technical-discussion/propeller-strut-mounting-diagram

www.catalina36.org/members/technical/maintenance/replacing-prop-strut 
www.catalina36.org/comment/62604#comment-62604
www.catalina36.org/community/photos/catalina-yachts-strut-repair...

www.catalina36.org/forum/technical-discussion/water-pooling-aft-...
www.catalina36.org/forum/technical-discussion/prop-shaft-strut-n...
www.catalina36.org/forum/technical-discussion/strut-support
www.catalina36.org/forum/technical-discussion/propeller-strut-mo...
www.catalina36.org/forum/technical-discussion/strut-question
www.catalina36.org/forum/general-discussion/what-filling-should-...