thanks dan.
i picked up a digital 2 foot level w/ a horizontal and vertical laser, as well as a small cubed shaped digital angle finder.
but i think the water level from chine to chine with some braided fishing line pulled down the keel and
a plumb bob is gonna solve finding center and locating X.

the most important hole you'l ever cut
 

locate center and X.
the boat is on the trailer, trailer is pretty close to level and there is 3 jackstands, 1 under the trailer up front
and 2 on the chines to tweak level 5/16 i.d. hose is attached to the rear jacks and is used as a water level.
a line is pulled down the keel and a plumb bob is dropped to locate dead center.

finding X was a fiasco and theres a thread in general discussion how the math had me going koo koo.
well it got even better, i used a digital level to draw the big plus sign on the transom and all it did was screw me up
so i went back to water level plumb bob and straight edge to remark.
2 or 3 day fiasco by this point

the paper template got a thin coat of elmers wood glue and was sqee gee'd on the transom and taped off.
then the cut was razored out and marked, follwed by center punching the bolt holes.

the jig got bolted up and was used only for the 8 bolt holes.
some one tell me how 2 mercury part numbered items that are supposed to do the same job not line up balls on

after the holes got drilled peel off the template and cut the hole.

what did you use to cut the hole, looks nice

the patch and cutout
 

as mentioned the boat had a #5 drive on it and the original owner patched the transom.
in the first pic you can see the #5 patch is outlined in pencil and the bravo is as well.

heres the deal, the bravo hole bottom is in virgin transom and the top is in the patch
the patch is bulged out 1/16 inside the boat, and is how i was able to trace it.

the transition can be clearly seen in the above posts pics of the hole.

i can see what i have to do to as far as making the inside flush for installing the transom assembly
but i'm not sure if the patch needs redone.

plan would be route out remaining #5 patch plus 3 inches on sides and top, but only to 7/8 depth
using new bravo bolt holes to hold the new ply in place until mat cured. then 1708 back up to thickness
out 3 inches past new ply.

steve told me the patch is good to go, will work no problem, and he is a professional glass guy and boat builder
so i believe him but if it rips out the boat will go down like 2 dollar tijuana you know what.

would really like to hear some opinions and get some advice.

f2 thank you, i used a hole saw to help out the corners and a sawzall to cut it.
started sanding it so it can get glassed and look nice

nice work! patience is key!

i responded in your other post also that got me over here reading this post. I wish I would have stumbled onto it sooner as I could have probably got you some ssm stuff on the cheap. But it’s alittle late now.

It may sound silly but before you go too far glassing the transom cutout up make sure your transom assembly fits well. Every boat I’ve ever cut out I’ve always had to sand and finesse some esp around the bottom 2 holes. I’d hate to see you glass it in perfect just to grind some back out.

By the way great job on the project. I like seeing someone going all out like that.

thank you, i appreciate the advice
yes the transom cut out isn't perfectly square, even with a new blade going, slow and trying hard the blade still
walked around on the inside
but in a good way, to tight rather than way opened up. it'll get squared off from the inside before it gets glass.

i have an idea to measure from the transom to the drive mounting face on both sides and holding it still w/ some shims
so 2 plumb bobs can get dropped off the drive mounting studs and measured for distance from a line pulled down the keel.
this way if the hole and stud holes need tweaking to keep the leading edge of the drive in line with the keel it can also happen
prior to glassing the cutout

engine room wrap up (almost)
 

the original firewall like a few other things that needed something done finally got the executive decision.

the multi tool is probably one of the best tools you can buy !
it filet'd the tabbing, fillets and what was left of the original firewall off like nothing.
the stringers got cut down ( i would never thought about them interfering with water distribution tubes, spark plugs etc)
that was another good call by class 6.

i made a jig to route out the transom and another one for the patch, last minute they got extended 3 inches.
not as nice as planned but it worked.
the transom was routed out and a patch made, the patch extends "past the original patch" into virgin transom
by 2 1/4 in the middle of the cutout, 3 1/2 inches just above that and 7 inches on top.

the original patch, no way it would have held up, i'm a little disappointed by how it was done but at least the hard and
dirty part of prepping it is over,

the bottom of the transom assy is in virgin transom, so that portion was left untouched.

next week the weather will be back up in the 70's so after the patch gets glassed in those pics will get posted
then maybe then it can start getting assembled