Hmm. I might have to go against the crowd on this one. I have a C-Dory 22' Angler, and am looking to buy a 24' or 27' Seasport. I've looked at the Parkers, Ospreys, Skagits, Trophys, Olympics, etc. The Seasport is the best of the bunch in my opinion.
One of the most important measurements of a boat is chronology. The length of years of the production run is a great indicator of quality. Both of these boats have been around of a long time, which to me is significant.
I think there might be a lack of objectivity on our site here regarding this subject tough. I love my C-Dory, and for it's size I think they have done a brilliant job, but I'm going to represent the other side. The Arima Rangers are a better comparable (and I think the C-Dory is far superior), but if your are looking at the Seasport, then that's what we are discussing. I agree that the two boats are hard to compare, but I think some important aspects haven't been brought up.
1. C-Dorys pound you. No two ways about it. It's nice to talk about "going the right speed", and trimming the nose down, but there is no substitute for a deep V, and a heavier boat.
2. The Seaport 24 and 27 both come with a head. Comparing the porta-poti that sits under my bow cushion to a sit down head with shower is not even do-able. My wife and daughters could defintiely expound on this subject.
3. Inboard vs. outboard. You can go either way with the Seasport, or you can even go diesel. Regardless, outboard is the only option on a C-Dory, and you don't get too much cabin heat from that baby.
4. Electricity. Outboards in general just don't generate enough electricity. You start running alot of electronics, a (gasp) microwave, refrigerator, etc. on a C-Dory, and it starts getting tough, or impossible to manage the juice. You get a few deepcycles getting juice from an inboard, and things are a lot different.
5. Beam. Ya, the deep Vs roll a little more when you are sitting there, but the beam on the Seasport is bigger, and that makes that roll diminish quite a bit.
6. Trailerability. This is where the C-Dory wins. I can tow the Seasport 24 with my Expedition, but the 27 probably does require either a new vehicle, or a slip. The C-Dory is about the best truly trailerable boat out there in my opinion.
7. Flybridge. Sitting up in a flybridge when it's sunny, when there is a ton of traffic, going thru the locks, or while docking is huge. C-Dorys don't have flybridges.
8. Capacity. I scuba dive. With two of my buddies, all our gear, and my kid on board, we were barely able to get on step. With a Seasport, this just woudln't happen. Also the swimstep on my C-Doy is pretty damn small.
9. Forward facing seat. My wife gets tired of having to kneel, or stand when she wants to look out the window. Sitting in a Seasport, looking forward, and up a little higher makes for better and comfort and safety. It's hard to see a deadhead when your back is toward the bow.
10. Speed. I work during the week so most of my trips are weekend trips. In chop, that Seasport is going to be traveling at least twice as fast as the C-Dory. This is the difference between getting out to where the fish are or not, and sometimes between going out at all.
11. Walkaround. It's way easier to walk around the Seasports to get to the bow. In rough weather, that walk to the bow if the C-Dory is pretty frightening.
12. Overnight. You can do four overnight on 24' Seasport. That way another couple can come along. It's still a big squeeze though. On the 27' it's no problem, in fact quite comfy. In the C-Dory, it's just not an option. You can do a camperback, but I could do that on a skiff too.
13. Bilge / Deck. I get tired of water in the back of my C-Dory. Whether it's from rain, scuba diving, crabbing, or just a spilled beer, I don't like a wet deck. I have mats on mine, some people have the factory decking, and some people use that dri-decking stuff. Regardless, it's a none issue on a standard, deep V hull design.
Anyway. Those are my thoughts.