Navigation
Navigation requires a few basics:
1. Know where you are
2. Know where you are going
3. Know your average speed
4. Know how to plot and follow a compass course
5. Know how to use the tide & Current tables for the area
6. Know the wind & weather tendencies for the area
-Nautical charts, and knowing how to use them, help with these basics.
-Figure the current and tide info for the area, and BRING IT WITH YOU!
-Know how to use, and carry, a compass. Pre-plotting course bearings on your chart saves a lot of time in case fog or darkness descend upon you.
-Know the weather patterns for the area, esp. regarding wind conditions, and carry a weather radio/VHF to keep updated.
-Identify potential danger spots, and how to avoid them.
-Plan escape routes in case conditions become too severe.
Signal flares and VHF radios are good for summoning help, but do not make you any safer - they only help you when things have gotten out of hand.
Tides
Tides are defined as the vertical movement of water, and current as the horizontal movement of water.
Tides rise and fall, and currents flood and ebb. A flooding current flows toward shore and an ebbing current flows away from shore. For example, the continuous current in a river is an ebbing current.
Tides and currents are mainly caused by the gravity of the moon and the sun. They are also affected by the moon's orbit around the Earth and the Earth's orbit around the sun. Since the moon is closer to the Earth, its tide producing force is more than twice that of the sun's influence.
When the sun and moon are on opposite sides or the same side of the Earth, they create the strongest tides. This happens during the new moon and full moon. Other factors such as barometric pressure, heat and wind contribute to tides and currents as well.
For example, a continuous on shore wind has a tendency to raise the tide level and increase flooding currents.
The meteorological effects on tides and currents can be quite dramatic during storms. Tide and current tables do not consider weather or other unpredictable factors. They only predict tides and currents based on set data.
Lookup your tides and currents on the NOAA website
How do Tides and Currents Relate?
In general terms, a rising tide brings water onshore or into a bay causing a flooding current. When the tide has reached its maximum, there is a related period of slack water (slack before ebb).
A falling tide takes water away from shore or out of the bay causing an ebbing current.
When the tide is at its lowest point, a period of slack water occurs (slack before flood).
It is important to note, however, that the times for high and low tides do not necessarily coincide with slack water times. Nor do the times of maximum flood or ebb always coincide with the greatest change in tide.
Especially in locations where there are strong permanent currents such as rivers, the times for slack water may be quite different from that of the corresponding high or low tide.
NOAA and other agencies observe the tide and current at various stations throughout the world. Over time these observations are collected and turned into a set of factors. When added together, these factors model the tide or current at that specific location.
Each of these factors is called a harmonic constant, and is based on the sun or the moon. Stations that have harmonic constant data available are called harmonic stations.
Chart Datum
Soundings (depths) on the charts are based on the 0 point (Chart Datum) of the tide. You add positive tides to, and subtract negative tides from, the soundings on the chart to get the actual depth. Since the zero point is lower during spring tides, there may be less water than you think at those times.
What About Tide Books?
Tide books provide as much information as they can in a small amount of space. Many of the books that used to graph current flow are now out of print, replaced by Online apps like DeepZoom, The PNW Current Atlas (Apple and Android app stores) and the Navionics app are great tools.
They show a visual representation of the currents in real time. Some can also track you with GPS. Service is not available everywhere on the water, so make sure you have charts and written tide and current info with you.
Sea Kayaking Navigation Tips
Distance on a chart is measured in Nautical Miles. People measure speed in Nautical Miles per hour, or knots.
1 Nautical Mile=6080'= 1.15 Statute miles
Charts are small pieces of the earth laid out flat for navigational purposes. You can locate positions for any spot on Earth using latitude and longitude.
Latitude tells you how far you are from the equator, measured in degrees north or south.
Longitude shows your position east or west of Greenwich, England. For example, Seattle is 48°N latitude, 122°W longitude.
For purposes of measurement, we can use the degrees and minutes of latitude on the left and right sides of the chart.
1° of Lat=60 NM
1°=60' ('=minutes)
1'=1NM=60" ("=seconds) 1"=.02NM, =100 feet
1Knot=100 ft./minute
Average paddling speeds: 2.5 - 4 knots
The longitude scale does not work for measuring distances. When using a compass, remember that charts point to True North, where Santa lives. They do not point to Magnetic North, where your compass points.
To find the difference, locate one of the Compass Roses on the chart. The outer ring of the Rose points to True North.
The inner compass points to Magnetic North. Inside the Rose you will find the Variation, or difference between True and Magnetic North. The innermost rose is not used anymore.
Currents
Paddling in current at Deception Pass
Currents relate to the horizontal movement of water, while tides measure the vertical component. As the water flows through the constricted channels, and around the islands, it acts much like current in a river would.
Fortunately, there are current tables that tell us the direction and timing of the flows. They also tell us the times of Slack Water (sw), when the speed of the current is weakest.
In our area, there are generally 4 slacks and 4 current maximums each day, usually 2 ebbs and 2 floods.
In some areas , currents achieve velocities of 8 knots or more. It is important to know how to read the current tables.
Tide rips, eddies, and wave conditions are much more pronounced during times of fast current. A current that moves with the wind will lower wave height. In contrast, a current that goes against the wind and waves will make the waves steeper. It will also reduce the distance between the waves, creating very rough conditions.
Eddies or countercurrents tend to form on the downstream side of points, and in depressions in the shoreline. Eddies also form near shore in channels with fast currents, and where fast water flows into slow. The eddyline marks the edge of two currents moving in opposite directions. Whirlpools sometimes form there.
FINDING CURRENT INFO FOR YOUR DESTINATION
The sea rises and falls with the tide.
It is important to know how high the tide will be. This becomes clear for a paddler who wakes up to water lapping at their tent door. It also applies to someone who sees their kayak drifting away because they forgot to secure it or their gear on high ground.
It is also useful when paddling in shallow areas, like river deltas. These areas can dry up and leave you with a long walk through knee-deep mud, dragging your kayak behind you.
See also
Deepzoom.com or Navionics app
PNW Current Atlas app
60/90 Rule For Currents
The current tables tell you the times of slack, times of max speeds, and the max speeds.
To find out what is happening between the slack and max, you can use the rule of 3rds. Let's assume, for this example, that the currents look like this:
(SW=slack water, E=Ebb, F=Flood)
SW12:00 Max3:00pm 6.0E SW6pm Max9pm5.0F
Take the amount of time in between max and slack for when you will be in the area; Divide that by 3. In this case, it would be 60 minutes. This is your interval for the thirds.
SW 12:00 + 60 mins= 1pm + 60 mins=2pm +60 mins=3pm.
From the slack water, the current increases to 60% of max in the 1st 3rd, to 90% in the 2nd 3rd, and to max in the final 3rd. This would look like:
12:00 SW=0 current
1pm: 60% of 6.0= 3.6 knots Ebb
2pm 90% of 6.0= 5.4 knots Ebb
3pm 100% = 6.0 knots Ebb
4pm 90% of 6.0= 5.4 knots Ebb
5pm 60% of 6.0= 3.6 knots Ebb
6pm SW=0 current
The 60/90 rule offers a more conservative approach than the 50/90 rule, which people can use for most of the sound. When you are dealing with fast current areas, like Deception pass, 60/90 is a closer approximation.
You can use it anywhere and still be sure that the currents will not be faster than you expect. This is true as long as there are no strong winds or waves to make things more complicated.
If you are in the current for the whole cycle (SW to SW), your average drifting speed would be 63% of the maximum. This assumes you are moving with the current and there is no wind.
Duration of Slack: The Slow Water Rule
When making a crossing, you will be paddling at a right angle to the current, which means you will be pushed to the right or left of your course.
Doing so at Slack water will eliminate this sideward movement. This will also lessen the chance of encountering tide rips caused by the collision of current with opposing wind and waves. It also helps when paddling through a pass.
The duration of slack is not hard to figure. The harder part is getting there in time so you don't miss it. To figure the duration of slack, we will use this example:
Max 10am 3.0F
SW 1pm
Max 3pm 6.0 E
How long will the slack water last? By dividing the Max speeds into 60, we get the amount of time the water is moving at less than 1/2 knot, before and after the SW.
60/3=20 min, 60/6=10 min.
This means there will be 20 minutes of slow water before the SW at 1 PM. There will also be 10 minutes of slow water after.
In total, there will be 30 minutes of slow water. This starts about 20 minutes before the SW. Since the SW actually may occur up to 30-45 minutes earlier than predicted, it is always a good idea to get there early.
Kayaking Classes
Our Fundamentals of Sea Kayaking class offers the basic building blocks for safe kayaking on the inland waters: paddling and rescue techniques, current, wind and wave phenomena. On our day trip, we go to a place there is current so we can learn to work with, across, and against current, in a safe, supervised class setting.
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