drill out the ones holding the present deck on and it should pull right off
exactly.
Use whatever tools necessary to cut off the parts that make it convexed. (I am fond of the 4" grinder)
The cross braces run from side to side, (port to starboard) not down the middle. As many as your want.
There are several ways to attach angle brackets to the boat hull.
don't use the store bought shelf brackets. they are steel and will rust by next week.
make your own by cutting off a section of angle aluminum.
BOLT it through the hull.
some people swear by brass (myself included) and some swear by stainless. Your choice.
either use thread lock or nylock nuts of the same metal to bolt it secure in place to the desired place.
then, attach your cross angle braces with screws, rivets, or bolts. up to you.
The bracket goes UNDER the cross brace.
Important note - - - if you are going to use the same metal that you took off . . . .
put that metal back on, adjust everything so it is as flat as you want it,
then, make a 2x4 wood splint that will hold the sides of the
boat in the correct width and not slip while you are working on installing the cross braces
or you run the chance of the metal not fitting exactly as it came off after the braces are in place.
In the best world, you can put some metal screws in the rivet holes just to hold it all together
while you get the measurements for the cross braces.
In other words, use your noggin to find a way to hold the sides of the boat in place so it will NOT move.
then, after you have your new cross braces in place, re-attach your bow metal with as
many rivets as you feel comfortable with. The standard 3/16" pop rivets will do fine (IMO).
Then, mount your trolling motor with as many bolts as you think will do the job.
try to bolt through the cross braces for this.
I guess a good idea would be to dry fit your TM first, use a marker where the hold down bolts will go,
then, put the braces in those places.
If you don't have it already, get some edge guard for the sheet metal edge.
There are MANY fine threads on just how to do this . . . just use the SEARCH button.