Serve Application from my Mac over LAN
You shouldn't need a firewall rule to forward packets because Apache can listen on your selected port.  Leaving it as port 80 also won't conflict with anything. 

What you need to look at is your httpd.conf file.  Specifically, the "Listen" directive

# Listen: Allows you to bind Apache to specific IP addresses and/or
# Change this to Listen on specific IP addresses as shown below to 
#Listen 12.34.56.78:80
Listen 23736


Since it's working locally, but not on another client (I'm assuming on the same subnet), you may have the directive set as localhost:23736.

If that's the case, it would cause the symptoms that you are seeing.

What you should have is what I posted above, or to restrict it to a particular IP:

Listen 172.18.48.240:23736

Once you make the change, restart Apache.