I suspect that he is asking to compare a semi dory and a Down East type of boat. The lobster boats, Duffy, and the nearest to the C Dory is the Rosborough 246. There are a fair amount of cross over between these two boats--and some Rosborough owners have been C Dory owners.
The Down East type of boat is often straight run aft, flat buttocks with a round chine, , and a moderate V foreward. It is also a semidisplacement boat. My personal opinion is that all in all the C Dory is a more stable and better sea boat.
The Rosborough often are much slower than the C Dory and are run at displacement speeds--with twins up to 15 to 17 knots and occasionally with large engines up to 30 knots. My feeling is the C Dory is more effecient in use of fuel. But the Down East boats are less likely to pound.
They are good boats, and I had considered one when I was making the decision on the Tom Cat 255. I am still a member of their list and plan on making a cruise with this group later this year.
It is a little like comparing a C Dory and A Sea Sport--both have some good features. The Rosborough has pilot house doors on the side--I see this as a negitive, because of water intrusion. The Rosborough has perment foreward facing seats, the V Berth is slighly shorter than the C Dory, and the head is more cramped than the 25 or Tom Cat--and below the helm console. The side deck access is about the same as C Dory. There is an extended cabin top over the aft cockpit--and a high and low freeboard model.
There are a number of other down east boats--but the Rosborough comes to mind when thinking of comparison with the C Dory.