As a USCG Licensed Master for 20 years, and the Captain of a Hydrographic Survey Vessel in Baltimore Harbor I find myself in many near collision situations with pleasure craft (Power and sail) operating in the 50 foot shipping channel, when in many areas from Baltimore to below the Bay Bridge, 20 foot+ exists outside of those channels for safe passage around me. We display the Black BALL-DIAMOND-BALL dayshape as required by USCG rules for Restricted Maneuverabity vessels. Night colors are RED-WHITE-RED displayed vertically. The nature of hydrographic surveying requires one to run a track line across the channel with a 10'' tolerance and steady speed. If I deviate, the line is rerun, which is costly. If you see that dayshape, POWER and SAIL vessels must stay clear and yield right of way (USCG Inland Rule 18). This may not be taught in all schools but is especially important in inland waters around dredging areas. Vessels trolling must also stay clear. As the captain of a survey vessel, I want boaters to understand their responsibility as vessel operators so I''m not the "bad" guy for "cutting others off". I''m only doing what''s required under USCG Navigation rules by maintaining course and speed. Pass astern of survey vessels after consulting a current nautical chart. I also monitor Channels 13/16. Most vessels will air security calls on VHF 16 to alert the public as to survey operations. Thanks, Tom Conroy Captain, Survey Vessel Linthicum, US Army COE.