Hello Ralph,
As you may have noticed over in my Eilean Mòr thread (**LINK**), I am currently fitting our her dinghy with oars, so I was asking myself exactly the same question a couple of weeks ago, and tdid some research to try and come up with an answer …
At 1:12, a 14" boat does of course correspond to 14' at full scale and my dinghy, too, at 7" and 1:24 scale also represents a classic 14' dinghy/jolly boat/tender type of rowing boat.
Some googling of full scale practice seemed to indicate that 7' oars are very common in smaller rowing boats, although 8' or 9' are not unheard of either.
Harold A. Underhill, on his plan #789 of two clinker built life boats (one double-ended, the other transom sterned), states that "no oar, mast spar or fitting must exceed 2/3 the length of the boat", which at 14' would put the upper limit at 9'4".
The white metal oars that came with my kit were 3.5", i.e. represent 7' oars. However, in the end I decided to go one step up, and make 4" = 8' oars for my dinghy, as I thought that 7' oars looked just a tad stubby for my taste.
Hope this is of some help 
/Mattias
Edited By Banjoman on 06/08/2015 20:53:59