The Harlem River is an interesting eight-mile-long piece of water that flows from the East River at Hell Gate north to the Hudson River about two miles north of the George Washington Bridge. Although there are no marina facilities along the way, the river does shave off 20 miles versus traveling around Manhattan into the East River.
Along its length, the Harlem River is crossed by 15 bridges, and the controlling vertical clearance is 24 feet. If your vessel is less than 24 feet tall, you will only need to open the Spuyten Duyvil Railroad Swing Bridge (pictured above) at the confluence of the Harlem and Hudson Rivers. The bridge tender monitors VHF Channel 13 and will open the bridge on request if there is no rail traffic approaching. If your boat is taller than 24 feet, you will need to make four-hour advance arrangements to have all of the bridges opened for you, but keep in mind that they will not open the first bridge until after 10 a.m., and you must finish the passage by 5 p.m. Call the New York City Department of Transportation to make arrangements (212-371-7836).
Use NOAA Charts 12339, 12342 and 12343.
The area around Hell Gate and the Harlem River have often been described as spectacular in regard to the currents that flow through the area. If you arrive in the area during the time of maximum current, be prepared for large eddies, current-formed waves and confused water. This area is not necessarily dangerous, but being prepared for what you might encounter is recommended (check the tide before you arrive).
From Hell Gate, you can exit into the Harlem River either at the south or north end of Mill Rock, which is marked by flashing red 16 and flashing green 1, respectively. From either side, you can then position yourself to head into the mouth of the Harlem River between Wards Island and Harlem. The first of fifteen bridges crosses the river here, and if you tower more than 55 feet, you will need to make arrangements to have it and the next 14 bridges opened for you by the New York City Department of Transportation (see introduction above for details).
Keep in mind that the rivers tide floods to the south and ebbs to the north. If you can (depending on whether you have to have bridges opened or not), try and schedule your passage with a favorable current. If you do end up transiting the river during a foul current, remember to give yourself and others plenty of room at bridge crossings.