[GeorgeB]

The old rule of thumb (at least for me) is a comfortable sea state is when the wave period (in seconds) is greater than the wave height (in feet). Note that this is for the predominant swell and not for any wind driven waves (which most likely be running at the same time but perhaps from a different direction). Five foot swells @ six seconds are definitely doable in a 28 footer. If you are sitting in the cockpit (assuming that you have a tiller), your eye height is probably between four and five feet above water line so you will probably loose sight of the horizon momentarily when in the wave trough. Another rule of thumb is wave heights taller than your boat’s beam starts increasing the risk of rolling over in a broach. The classic example of this is the (famous) photo sequence of Yachtsea being rolled under the Golden Gate Bridge. However, even “tall” waves can be benign if the wave period is long enough. On waves greater than five feet in a small boat you may start to lose wind in the lower part of the sails while in the troughs and your boat may not have the mass and momentum to carry you over the next crest. Breaking waves will compound your misery. There will be days when it will be more fun swapping lies and stories at the bar than it is sailing out there and breaking all sorts of equipment!