Maine Island Kayak Company - Wind, Waves and Landforms

Wind, Waves, and the Effects of Landforms

Guiding Principle: Wind, above all environmental variables, has the greatest impact on the paddler. Predicting wind speed and direction and understanding the impact they have on the texture of the sea is essential to good seamanship.

Performance Objectives:

Obtain useful marine forecasts predicting wind direction and speed.
Predict the texture of the sea based on wind direction and speed .
Understand the effects of wind and waves on the kayak and how to compensate for it.

Wind: Movement of air caused by differences in temperature and pressure

Marine Forecasts for wind speed and direction:

Weather radio/VHF
Television
Internet
Newspaper
local knowledge – experienced mariners
make your own forecasts – watch the sky and the critters

NOAA Marine Weather Forecast

Wind speed (knots)	National Weather Service Advisories and Warnings	General meanings for kayakers
0 – 17 knots		Be aware of wind against current and local conditions
18 – 33 knots	Small Craft Advisory	Beginners stay home Intermediates have their hands full Advanced looking for surf
34 – 47 knots	Gale Warning	Beginners and intermediates stay home. Advanced have their hands full.
48+	Storm Warning	Read Sea Kayaker, Polish your kayak
Squalls and T-storms less than 2 hours in duration.	Special Marine Warning	Lightning and kayaking don’t mix well.

Wind Direction: from where wind is blowing.

Local conditions: Can vary significantly from the weather forecast. Keep an eye on the sky, understand cloud formations.

Thunderstorms and squalls are usually associated with approaching cold fronts. They form along the front or on a line 100 miles ahead of the front. Squall lines usually moving at 25kn, so gusts of 40-60kn are not uncommon. Keep an eye on the sky and listen to weather radio frequently.

Near-Shore Conditions. Coastal wind direction and speed can vary from a forecast. Winds blowing offshore usually veer and pick up speed. Due to Coastal Convergence stronger winds are created.

Sea and Land Breezes - Differential heating and cooling of the land and the sea. Afternoon onshore breezes are common in the summer along the New England Coast. Onshore clouds forming, onshore breeze beginning. Offshore clouds dissolve, sea breeze beginning.

Funneling and Channeling – Winds take the path of least resistance. Funnel between and wrap around islands and/or headlands.

Wind factors that generate waves:

Duration – Time that the wind blows
Velocity – Speed that the wind blows
Fetch – Distance over which the wind blows

Describing Waves:

Wave length – distance between crests or troughs
Wave height – distance from base to the crest
Wave period – Time for peaks to pass a point. Gives some sense for the amount of energy in waves.

A wave's energy is proportional to wave height squared. A four ft wave has 4 times the energy of a two ft wave. A long WL and large WH = lots of water involved.

Wave Generators/Types:

Wave type	Description	Example of WH and period
Wind Waves	Generated by local winds. Irregular and short-wavelength.	2’ every 6 sec
Swell Waves	Waves get organized into larger and longer forms. Can travel thousands of miles without loosing energy.	3’ every 14 sec.
Waves caused by currents	Waves are either stationary or move slowly upstream. Wind against current = steep breaking waves.
Seismic Activity & Glacial Calving	Tidal waves have huge wavelengths. Waves from icebergs breaking off can capsize even big boats.
Boat Wakes	Some can be surprisingly big.

Shallow Water Waves. When depth of water < half the WL (wavelength) swells begin to feel the bottom and slow down. As wave length shortens, wave height increases, period remains the same, so wave must get steeper.

Breaking Waves. Wave will steepen until water is 1.3 times wave height, then will begin to break. Winds & Current can vary this from 2x to .5x wave height.

Spillers and Dumpers: The way the wave breaks is determined by the shape of the sea bed. Boomers require a watchful eye, and may have an undertow. Spillers are ok for play.

Refraction: Wave over shoal slows while deeper portion continues on, Can refract up to 180 deg. Clapotis on sheltered side. Zones of convergence (building waves) and divergence (reduced waves) on beaches due to bars.

Reflection: Like a ball off a wall. Remember water depth and wave height WH equation.

Wave-Current Interaction: Waves moving against a current receive energy from the current. WL decreases, WH increases. Rapid steepening can lead to breaking. Example: a wind wave will nearly double on a 5K opposing current. Consider points, narrows, constrictions – called tidal races, overfalls. Study the geography.

Clapotis

SUMMARY OF EFFECTS ON WAVES:

Opposing winds or currents will                 STEEPEN WAVES
Underwater ledges or irregularities             CONFUSE WAVES
Narrow funneling passages                       HASTEN WAVES
Points of land                                  BEND    WAVES
Steep shorelines or bulkheads                   BOUNCE WAVES
Shallows, exposed rocks, beaches                BREAK   WAVES

Waves and Shoreline topography

Waves can travel for long distances without losing any energy … until they hit something. Understand the impacts and effects of wind, shallows, various shores, tidal currents on wind and swell shape.

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