It is hard to answer your question specifically. To a great extent this is a question of definition. Much of this is rather long discussion is exerpted from early discussions on the topic of what makes an offshore capable vessel;
As I have noted in prior discussions, the term ''bluewater capable'' seems to get bandied about as if it had some kind of fixed meaning that can be measured on some absolute scale. To some, this term seems to mean that the boat is safe to take on an offshore passage, while to others it seems to imply an ability to distance cruise to remote locations. This range of interpretations would imply a broad spectrum containing very different kinds of boats.
Most well constructed coastal cruisers are perfectly seaworthy for a carefully timed offshore passage. What they often lack is the kind of layout and design details that make offshore passages comfortable.
Where coastal cruisers fail as long distance offshore cruising boats is in the ability to withstand the large amount of wear and tear that long distance cruisers incur in a very short period of time. As I have noted before in these discussions, a heavily used coastal cruiser might sail something on the order of 1000 miles in a year with most boats sailing considerably less than that. A boat being used for distance voyaging can often sail well in excess of 10,000 miles in a year, with much of that passagemaking in the harsh environment of the tropics.
There is often a tendancy to focus on such items as the AVS (angle of vanishing stability, which by the way I personally prefer the older, more widely accepted, and more linguistically accurate term LPS- limit of positive stability)or STIX (CE Stability Index) as key elements of the overall safety of a boat offshore.
These numbers represent a very small snapshot of the real safety of a boat and as such can be grossly misleading. An extremely high AVS or STIX can be easily achieved simply by designing an excessively narrow boat with lots of freeboard, but with that excessively narrow beam and high tophamper, comes a greatly increased likelihood of a capsize or roll over and a deterioration in motion comfort and carrying capacity.
In following the research process that resulted in STIX, it should be understood that the purpose in developing the CE Directive for Recreational Watercraft, of which STIX is a component, was never to extablish an absolute standard for vessels going offshore. Instead it was intended to develop a minimum and easily quantifiable standard that all of the CE countries could agree upon. In doing so, key calculations and measurements were omitted from the standards because member nations considered them to be onerous. Instead simplified surrogate formulas were substituted for actual more sophisticated calculations resulting in very loose and sometimes missleading approximations. This is especially unfortunate since there was adequate detailed research to have permitted very accurate stability assessments to made.
AVS suffers from another problem as well. As has been pointed out many times on this forum, there is no uniform standard for calculating AVS. It is not unusual to see very high AVS figures quoted in ads, but they mean little in an absolute sense because of the wide range of methods used to calculate a boat''s AVS. Some published angles are for boats in their most advantageous loadings (full water tanks and empty lockers) while other are at their worst (IMS calcs with empty tanks, and which do not include the volume of the cabin). None of these numbers take into account the weight distribution and buoyancy of the vessel in the inverted condition which can greatly alter the relative stability of individual vessels as the approach their limits of positive stability.
When I think of a coastal cruiser vs. a dedicated offshore boat, there are a number attributes that I look for:
On a coastal cruiser there should be good wide berths, with enough seaberths for at least half of the crew for that night run back to make it to work the next day. An offshore cruiser is often handled by a smaller crew and so fewer berths and fewer seaberths are necessary. The berths on an offshore boat should be narrower and have leeboards or lee cloths to keep the crew in place on either tack. On both types I would look for a well-equipped galley but the galley needs to be larger on a coastal cruiser so that there is adequate space to prepare meals for a larger crew or a raft-up. For coastal cruising large un-interupted counter tops are great for preparing elegant spreads and are easier to keep clean, but for offshore use can result in flying food. Deep sturdy fiddles that divide the counter into smaller segments work better for offshore cruising. Refrigeration is less important on a coastal cruiser although the case can be made for no refrigeration or icebox if you are going distance voyaging offshore. Large open cabin soles make coastal cruisers seem air and roomy, but offshore provide little foothold for crew moving around a heeled and bucking cabin.
A comfortable cockpit for lounging is very important on a coastal cruiser. It should be larger than an offshore boat to accommodate a larger number of people, which is OK since pooping is less likely to occur doing coastal work.
While gear for offshore boats need to be simple and very robust, coastal cruisers need to be able to quickly adapt to changing conditions. Greater purchase, lower friction hardware, easy to reach cockpit-lead control lines, all make for quicker and easier adjustments to the changes in wind speed and angle that occur with greater frequency. There is a big difference in the gear needed when ‘we’ll tack tomorrow or the next day vs. auto-tacking or short tacking up a creek.
Offshore boats need to be heavier. They carry more stuff, period. The traditional rule of thumb was that an offshore boat needs to weigh somewhere between 2 1/2 (5400 lbs) and 5 long tons (11,000) per person. A coastal cruiser can get by with less weight per crew person but generally is cruised by a larger crew. The problem that I have with most selection processes is that most offshore sailors and many coastal cruisers seem to start out looking for a certain length boat and then screen out the boats that are lighter than the displacement that they think that they need. This results in offshore boats and some coastal cruisers that are generally comparatively heavy for their length. There is a big price paid in motion comfort, difficulty of handling, performance and seaworthiness when too much weight is crammed into a short sailing length.
I suggest that a better way to go is to start with the displacement that makes sense for your needs and then look for a longer boat with that displacement. That will generally result in a boat that is more seaworthy, easier on the crew to sail, have a more comfortable motion, have a greater carrying capacity, have more room on board, and be faster as well. Since purchase, and maintenance costs are generally proportional to the displacement of the boat the longer boat of the same displacement will often have similar maintenance costs. Since sail area is displacement and drag dependent, the longer boat of an equal displacement will often have an easier to handle sail plan as well.
It is important to understand that in and of itself, weight does nothing good for a boat. Weight does not add strength. It does not make for a more comfortable motion. It does not add stability. It does not make for greater carrying capacity. Weight only breeds more weight. Adding weight begins a design cycle that can make a boat harder to handle and more expensive to build with few if any improvements to the boat itself. To explain, as a boat becomes heavier drag increases. As drag increases the sail plan needs to get larger. With increased sail area, there is a greater need for stability. To gain that greater stability, ballast weight and drag increases which starts the another cycle of weight increases. With greater sail area and stability, hull structure needs to get heavier, and, rigging and spar sizes need to increase, and with that greater weight comes the need for still more sail area and stability. With the greater weight aloft comes greater roll angles, a reduction in AVS and an increased likelihood of capsize or knockdown. When the cycles stops, the larger sail plans of a heavier displacement boat makes them harder to handle and that weight increase is in places that do not add to weight carrying capacity. Weight does nothing good for a boat!
-Keel and Rudder types:
I would say unequivocally that for coastal cruising a fin keel is the right way to go here. The greater speed, lesser leeway, higher stability and ability to stand to an efficient sail plan, greater maneuverability and superior windward performance of a fin keel with spade rudder (either skeg or post hung) are invaluable for coastal work. Besides fin keels/bulb keels are much easier to un-stick in a grounding. In shallower venues a daggerboard with a bulb or a keel/centerboard is also a good way to go.
There is a less obvious choice when it comes to the keel and rudder type for offshore cruising. Many people prefer long or full keels for offshore work but to a great extent this is an anachronistic thinking that emerges from recollections of early fin-keelers. Properly engineered and designed, a fin keel can be a better choice for offshore work. Here though is the rub. Few fin keelers in the size and price range that most people are considering are engineered and designed for dedicated offshore cruising.
Full or long keels offer quite a few advantages when cruising off of the beaten path, such as the ability to safely dry out on a remote beach or haul out on an old style marine railway.
Good ground tackle and rode-handling gear is important for both types but all-chain rodes and massive hurricane proof anchors are not generally required for coastal cruising.
At least along the US East Coast, (where I sail and so am most familiar with) light air performance and the ability to change gears is important for a coastal cruiser. It means more sailing time vs. motoring time and the ability to adjust to the ''if you don''t like the weather, wait a minute'' which is typical of East Coast or Great Lakes sailing. If you are going to gunkhole under sail, maneuverability is important. Windward and off wind performance is also important.
With all of that in mind I would suggest that a fractional sloop rig with a generous standing sail plan, non- or minimally overlapping jibs, and an easy to use backstay adjuster is ideal for a coastal cruiser. This combination is easy to tack and trim and change gears on. I would want two-line slab reefing for quick, on the fly, reefing. I would want an easy to deploy spinnaker as well.
More and more designers of offshore crusiers are turning to fractional rigs for distance cruisers as well. This switch seems to be especially popular in Europe rather in the States where the cutter rig still seems to the default answer for long distance voyaging.
I think that speed is especially important to coastal cruising. To me speed relates to range and range relates to more diverse opportunities. To explain, with speed comes a greater range that is comfortable to sail in a given day. In the sailing venues that I have typically sailed in, being able to sail farther in a day means a lot more places that can be reached under sail without flogging the crew or running the engine. When coastal cruising speed also relates to being able to duck in somewhere when things get dicey.
It is harder to make the case for the need for speed in an offshore or distance cruiser. Speed can be an asset to an offshore cruiser. More speed means fewer days at sea and less motoring time. That results in a greater range without restocking and so a reduced need for tankage and the need carry less supplies. Argueably greater speed allows an offshore vessel to strategically deal with weather patterns, which when coupled with better weather forecasting information can be a real safety advantage. That said, it is rare that even a very fast boat can ''out run a hurricane''.
Good ventilation is very critical to both types. Operable ports, hatches, dorades are very important. While offshore, small openings are structurally a good idea, for coastal work this is less of an issue.
-Visibility and a comfortable helm station:
Coastal boats are more likely to be hand steered in the more frequently changing conditions, and higher traffic found in coastal cruising and are more likely to have greater traffic to deal with as well. A comfortable helm position and good visibility is critical. Offshore, protection of the crew becomes more important.
Storage and Tankage:
There is a perception that coastal cruisers do not need as much storage. I disagree with that. Coastal cruisers need different kinds of storage than an offshore boat but not necessarily less storage. Good storage is needed to accommodate the larger crowds that are more likely to cruise on a short trip. Good water and holding tankage is important because people use water more liberally inshore assuming a nearby fill up, and with a larger crew this takes a toll quickly. Holding tanks are not needed offshore but they are being inspected with greater frequency in crowded inshore harbors and there are few things worse than cruising with a full holding tank and no way to empty it. Offshore boats generally need larger and segregated fuel tanks with fuel scrubbing capabilities. Offshore vessels can tolerate more less convenient long term storage areas.