Waves + reefs = Danger
Yea I too have found the Sugar reef area quite dangerous. Although my troubles were with rocks that became uncovered at low tide, I know the waves are also a concern on certain days. I think many fisherman fail to relize that much of the waves energy as it comes accross the water is under the surface. When a powerful wave encounters a reef most of the energy comes up over the reef hatching a much larger wave than what was visable the moment before it encountered the reef wall. I think all of us know that the waves are made even steeper to almost wall type conditions due to the influence of the current. The outgoing currents as opposed to incoming can make the worst conditions over a reef from what I have read on the subject.
The Merrimac river current plus the waves coming in can make the mouth of the river impassable at times tossing big boats around like rag dolls. The biggest examples of these condition current induced waves I have seen were actually out west at Neah Bay or in Alaska with 25 foot tides influencing the surf in a big way. The conditions were so treacherous that waiting till slack tides seemed like the only way to pass safely in all but the biggest boats. Something to keep in mind around reefs and river mouths.