I copied this from various websites and it is how i got the PROPER oars for my 12' 54"beam tinny
my oars are 7.5 feet long and they work really well, you can get going pretty good. i'm glad i got the right ones, it makes life waaaay easier. its bad enough to break down, but try getting back with 1 paddle from a canoe, i wish you luck...lol...
the standard way to calculate proper oar size depends on the span between the oarlocks, rather than length. here's how it goes:
measure the distance between the oarlocks. divide by 2, then add 2 inches. take this number, multply by 25, divide by 7, and that's your approximate answer in inches.
for example, if a boat is 48 inches between the oarlocks, then the proper size is: 48/2=24+2=26. 26x25=650/7= approx. 93. That's 7 feet, 9 inches. thus, either 7-1/2 or 8 foot oars should work well.
performance rowers with a rowing shell may do it differently, but this formula works well for most rowing craft.
Alumacraft reccommends a 7.5 to 8 foot oar for my 14.5 ft boat which has a 68 inch beam. Another formular is one half the beam times three plus 6 inches. Both seem to work fine.
As for the distance between hand grips...
Depend on the person.. Myself I like to leave a space about a width of my fist..
Some preferred the ends of the grips slightly overlapped about a inch, I don't like it because of pinch zone....
i hope it helps??