The goals of
nautical navigation can be described as
getting where you want to go, without hitting anything on the way. The
following information, with particular applicability to Boston Harbor
and sailboats without motors,
is
intended to help you with those goals. This is no substitute, however,
for a
coastal piloting and navigation course or a cruising course. I urge
any
serious
sailor to take one or both of these.
1.
Avoiding
Collision
Note: There are
no “right of way” rules applying to boats,
in the sense that a boat with “right of way” may
proceed with impunity and
other boats must avoid collision with it. Navigation rules (also known
as
“collision regulations” or
“COLREGS”) define which boats should
“stand on” and
which boats should “give way” in potential
collision situations, but each
boat in every situation remains obliged to avoid
collision.
a.
To
avoid collision, you must know what’s around you with which
you might collide.
Maintain a lookout all around. A tanker going 12 knots can come up from
behind
you very quickly. If you have crew, assign the lookout duty to them,
while you
concentrate on driving the boat. The responsibility
for the lookout is
still yours, though.
b.
Risk
of collision exists if it is obvious or if the bearing of the other
vessel does
not change. If you are in doubt, assume that there is a risk of
collision.
c. If you are sailing without using a motor, you are the “stand on” boat relative to motor powered boats (includes excursion boats and sailboats that are motoring) that aren’t restricted in their ability to maneuver around you.
d.
You are the
“give way” boat relative to:
(1)
Boats
that are anchored, drifting, or powered by oars or paddles. Keep a
sharp
lookout for kayaks!
(2)
Boats
that are fishing or tending traps.
(3)
Vessels that
can only navigate within the confines of a
channel that is narrow (compared to their size or
maneuverability). This
includes large
ocean-going vessels and tugs with and without barges. Don’t
tangle with tankers
or argue with the Subaru container ship!
(4)
LNG
tankers. By regulation, you are required to stay
clear at least two
nautical miles forward, one behind, and 500 yards to either side.
They’re big
and tall and surrounded by escort vessels with flashing lights.
e.
For other
sailboats, if
they’re not motoring,
the usual rules apply (i.e., starboard over port; leeward over
windward).
f.
Any overtaking
vessel must give way to
the vessel being overtaken, regardless of its motive force or yours
(oars,
sails, motor).
g.
If you
are the "give-way” vessel, required to alter course to avoid
collision,
make your change early and large enough to be readily apparent to the
other
vessel. You must use your boat to show your intent.
h. If you are the “stand-on” vessel, maintain course until you see what the other vessel is going to do. If the give-way vessel does not yield, you must take measures to avoid collision. If you can’t see the other boat’s crew or they don’t acknowledge your presence, assume they don’t see you and won’t give way. (Yells, screams, or five short blasts on your horn or whistle are in order here.) If you must turn to avoid collision, turn away from the other boat (Tiller Toward Trouble).
For
more information about the collision regulations, with commentary aimed
especially at sailboat sailors, see McLendon's Rules
for the Rest of Us
2.
Charts -
Use your chart of Boston Harbor to keep track of where you are and
what’s
around you, friend or foe.
a.
Aids
to Navigation. They come in several colors and may be lighted or
unlighted,
floating (buoys) or firmly attached to the seabed or land (daymarks,
beacons,
lighthouses).
(1)
Most
buoys and daymarks mark channel limits and are RED
or GREEN.
RED
aids
are
always even-numbered. They mark the starboard side as you sail from
seaward
toward a harbor. (Remember: RED RIGHT
RETURNING.) GREEN
aids are odd-numbered. Keep them to port as
you sail from
seaward. (In this hemisphere, but that’s where Boston Harbor
is.) The
charts show aid locations and descriptions. The identifying marking
actually on
the aid is shown in quotes on the chart.
(2)
Unlighted
buoys
(a)
RED
buoys are pointed on top and are called “Nuns”.
Red
Nun
(b)
GREEN
buoys are drum or can-shaped and are called “Cans”.
Green
Can
(3) Lighted buoys have similar shapes whether they are red or green and may also have sounds (e.g., bells).
Red Lighted Buoy Green Lighted Buoy
(4)
Buoys
are shown on charts as circles with diamond shapes on top. Unlit buoys
have
open, uncolored base circles. Lit buoys have a purple circle over the
base
circle. For red or green buoys, the diamond is colored to match.
(5)
Marks
on the chart looking like exclamation points (solid black dot with a
purple
stroke) show fixed aids (for example, lighthouses, daymarks, beacons).
(a) RED daymarks have triangular dayboards, pointed up, like nuns.
(b) GREEN daymarks have square dayboards, flat on top, like cans.
(c) Daymarks that mark dangers, rather than channel limits, usually have black and white dayboards. They usually have letters on the dayboard (“SL” for Sunken Ledge, for example). If you are close enough to read the letters with the naked eye, you are probably too close, however.
(d)
Daymarks around
the harbor are often
attached to dolphins (clusters of piles connected together). Sometimes
people
use the word “dolphin” to mean
“daymark”. The terms
“daybeacon” or “beacon” are
also used for fixed aids, whether they are lighted or not.
(6)
Examples
of aid designations: G
C “5A”
means an unlit green can buoy with “5A”on
it. G “17” Fl G 2.5s
means a green lighted buoy with “17” marked on it
and a light that flashes
green every 2.5 seconds. (If no color is given for a light,
it is white.)
(7)
Numbers
on aids increase from seaward. Numbers on aids repeat within Boston
Harbor,
because there are many different channels in the harbor.
Sometimes, as with Buoy "5A" above, an aid has been added to an
existing sequence. Rather than renumbering the whole string of aids,
the
previous number is repeated, with the "A" added. In other cases (for
example, Daymark 2A on False Spit) the "A" designates an aid that
marks a danger close to, but outside of, a marked channel.
Always read
your chart to know what it is that you are seeing.
(8)
Other
kinds of aids:
(a)
Yellow
buoys mark special areas (for example, anchorages).
Anchorage
Buoy
(b) Junction buoys show horizontal red and green stripes. The top color indicates the preferred channel (i.e., red means treat it like a nun; green means treat it like a can), but both channels are passable. They may be lighted or unlighted. Letters on the aid refer to the danger or channel they mark: for example, "CF" for Crow Point Flats, "HS" for Hospital Shoal, "PR" (not shown here) for the junction where North Channel and South Channel join at President Roads.
(c) Boston Harbor has one aid that is historic and unique. It's an unlit daymark, although it is designated "BN". Nixes Mate
(d)
Boston Light, the only remaining staffed US lighthouse, shows on the
chart with a simple beacon symbol. The information that it is 102 ft
high, visible for 27 miles, does tell us that it's more than a simple
beacon, though. Boston
Light
b.
Numbers
scattered over the Boston Harbor chart show water depths in feet at
average low
tide. (Other charts may have a different unit of depth –
meters, fathoms, etc. Always
look for the marginal note that tells you what the chart unit of depth
measure
is.)
c.
Colors
on the chart have meaning: Brown = dry land, Greenish-brown = you can
plow it
at low tide, Blue = shallow water, White = deep water, Asterisks =
rocks (Watch
out!)
d.
Popular
run-aground spots in Boston Harbor. Find these on your chart, not with your boat:
(1)
Area
between Castle Island and number “5A” green can
(mud flat and rocks).
(2)
Lower
Middle and Governors Island Flats off the east end of Logan Airport.
(3)
Area
between Deer Island and Deer Island Light.
(4) Ram Head Flats, the entire east side of Lovell’s Island.
(5) Shoals and rocks between red nun “10” and Lovell’s Island, at the north entrance to The Narrows.
(6) Great Brewster
Spit,
extending west a mile from Little Brewster and Great Brewster Islands
toward
Lovell’s. It’s a sand spit. Over the years it has
moved, so don’t depend on it
being exactly where it is shown on the chart.
(7)
Sunken
Ledge and Hangman Island in Quincy Bay
(8) Harry’s Rock off south side of Peddocks Island
(9)
(This one isn't clearly shown on the usual Boston
Harbor waterproof chart) Governors Island
shoal, at
the southeast corner of Logan Airport. Airport
Shoal
e.
If you are
tacking home, your best bet is Boston Main Channel. Here's how to find
it, and not the rocks or shoals:
Tacking
Home
f. Lower Middle (Small Ship) Channel is a quicker route in and out of the harbor, if you don't have to tack. Here's how to find it: Shortcut Channel
Note:
To improve readability, enlarge each of the preceding two links on your
browser and scroll around the chart. Firefox, just click the magnifying
glass cursor. Internet Explorer, hover your cursor and click
on
the "Expand" icon that will pop up
at the lower right.
3. Tides and Current
a.
Average tidal
height variation in Boston
Harbor is about 9½ feet, but tides can be as much as 12 feet
above and 2
feet
below the water depths shown on the chart. (The water depth datum
on the chart is the average of the low tide levels of the
lower of the two tides each day.) This site shows tide predictions for
Boston Harbor. By changing
the "Prediction Options", you can see the tide forecast for many
different periods, in many different formats. Boston
Tide
b.
Actual
water height can vary from the predicted tidal height if there are
strong
winds.
c. Tide is not just a raising and lowering of the water surface, but also an increase and decrease in the total amount of water in the harbor. As water flows in and out, tidal currents are created. During flood (close to, but not exactly the period from low to high tide), the currents flow into harbor. They reverse during ebb (approximately from high to low tide). Around high and low tide times, as the currents start to reverse, the water is slack (little current). Tidal currents are strongest when the tide height variation is greatest, and at narrow points in harbor entrances (between Deer and Long Islands, between Little Brewster and Point Allerton, through Hull Gut).
d. Tidal
currents near the surface can be affected by wind.
e. Times of high
tide
(and low tide) vary within a narrow range (less than 10 minutes)
throughout the
Boston Harbor sailing area. If
the tide table shows a high tide at 10:13 am, for example, the actual
time of high tide
at any point in the harbor will be within 10 minutes of that. Times of
peak and
slack currents vary much more. Current can be slack at Deer Island when
it is
still ebbing at 0.6 knots through Hull Gut. Don't
depend on a tide table to be your guide for the exact times of peak and
slack currents. Even published "Boston Harbor Current" tables try to
predict current only at Deer Island.
f. A 2-knot current ebbing by Deer Island, coupled with a 10-knot westerly breeze, can guarantee that you won’t be able to sail into the harbor from the east without a motor. You will tack back and forth, but you may actually be moved backwards (east).
May you sail with the wind always at 10-15 knots on your beam!
2/14/2007 DHK
