Those Deceptive But ‘orrible Offshore Winds
Wind is the curse of sea kayakers. It generates the bulk of problems that arise, choppy seas, capsizes, wind chill, weather tide effects, surf and so on.
There is however an exception; a following breeze, or one quartering from astern, can be a real boon in aiding progress through surfing rides. A breeze on the beam requires continuous corrections for drift and more concentration on balancing the boat. A breeze on the nose, or quartering from the bow, generates soul destroying, tiring, very wet, slogs.
The most deceptive and horrible wind blows offshore. Deceptive in that conditions may appear flat calm against shore with a light breeze wafting offshore, but with increasing distance offshore wind strength increases dramatically. Cliffed coastlines or those with marked topographic relief such as dune ridges, or swathes of forest, are particularly deceptive. Lurking sea kayaker traps are wherever those continuous cliffs or dune ridges are broken by gorges, fiords, steep sided valleys and narrow entrance bays.
Recently I received a swag of E mail messages from Sandy Ferguson relating to a party of New South Wales sea kayakers who were subjected to the deceptive but ‘orrible offshore winds at Jervis Bay, south of Sydney. I can sympathise with the N.S.W. paddlers’ predicament, for yours truly was caught during the Australian trip a long way offshore immediately south of Jervis Bay by a sudden, dramatic wind shift, that left me with such a struggle against an offshore wind that I felt like throwing in the towel and abandoning the trip. Limping into the lee of St. Georges Head I coined the phrase, ‘Wind was definitely the curse of the canoeing class.’
An article on offshore winds is pertinent, particularly after the article by John RamweII in the last magazine on the Lyme Bay tragedy.
Above an altitude of 500 to 600m, wind has an unobstructed flow over the sea while below that height, there is increasing frictional or drag effect between the air and the surface over which the wind is blowing, resulting in a diminishing of wind speed as the ground or sea is approached.
The amount of wind strength reduction depends on the nature of the surface; over forested hilly terrain the air flow will be less than that over open sea because of greater frictional drag.
Approximate values have been determined for frictional drag: over open sea a wind 500m above the sea reduces by about 33% at sea level, while over land the reduction is 66%. Thus a 30 knot wind at 500m will produce a 20 knot wind over the sea and 10 knots over land.
There is where the ‘deceptive’ description for offshore wind applies, for a factor of 50% can be applied to wind when it blows from land out to sea. A gentle breeze of 6 knots inland becomes a moderate wind of 12 knots offshore and a 15 knot wind inland becomes a near gale of 30 knots at sea.
The height and nature of a coastline govern the zone width of calm, sheltered water in offshore wind conditions:
a. a long beach with a low sand dune ridge providing minimum relief, dictates a minimum width with the offshore wind felt at the water’s edge.
b. a continuous line of vertical cliffs will provide a maximum width of calm, sheltered water, naturally depending on the height of the cliffs which govern where the offshore wind hits the sea
The obvious problem with offshore winds is being blown offshore. Where there is no off-lying shelter, such as a reef or island, and the next continent is thousands of miles away, the chances of survival without a radio or batphone are zilch. I maintain that once a wind rises over 30 knots, paddling progress into the wind grinds to a halt.
Any misadventure such as a dropped paddle or capsize, both occurred with two paddlers off lervis Bay, resulting in instant seawards drift and a greater distance to reach shore after recovering from the misadventure.
By way of example to those who have yet to experience such conditions, I struck diabolical offshore conditions during my first day in the Bering Sea, on the northern side of the Alaska Peninsula with a gale force wind blowing offshore over a low dune ridge and flat tundra inland. The sea was flat calm, a low surge against a gravel beach, wind ripples close inshore and an increasing density of whitecaps with distance out from the beach. Deceptively good paddling conditions, but bear in mind the 50% increase in wind strength from land to sea, and conditions more than 10m offshore were well beyond my limit to reach the beach. I spent many hours crabbing my way along the beach, the kayak at a 45 degree angle to the line of the beach to check offshore wind drift, the bow rising and falling against the beach with each surge. I was fully aware of the risk, realising the next stop offshore was the ice pack and unbearable polar bear country.
At the base of a long continuous line of cliffs, excellent shelter is afforded in strong offshore winds. Steep hillsides close to the coast, continuous dune Adges and tall forest also offer shelter dose to a beach.
But wherever that continuous line of shelter is broken abruptly, for instance by a narrow fiord, narrow bay or harbour entrance, gorge, river or stream valley, the offshore wind is funnelled through that break with unbridled force, causing williwaws and violent gusts or bullets of wind. And it is the violence of the turbulence that can cause the loss of a paddle or a capsize.
Manye sheltered bays and harbours have narrow entrances which open back into broad areas of calm water. Jervis Bay in New South Wales is a classic sheltered bay, which has a narrow entrance with tall cliffed headlands on both sides and we have many such examples in New Zealand. Offshore winds funnel through such narrow entrances with double or triple the wind strength of that inland.
Also where a continuous line of cliffs of steep coastline is broken by a headland or cape projecting seawards, increasing wind strength must be expected often accompanied by williwaws and strong gusts or bullets of wind.
What to Look For
An increasing density of whitecaps with progressive distance offshore are the best indicator of strong offshore winds, along with spray fanning seawards off breaking wave crests.
White spray dancing over the water, indicates a wind funnel with bullet like gusts of wind lifting spray off the sea.
Suggestions for Remedial Action
- If an offshore wind is blowing at the launch site, be prepared to abort or shorten the length of the trip.
- if caught in a sudden or gradual change to an offshore wind, turn tail immediately and run for the beach or nearest shelter. Sea conditions will deteriorate as the wind continues to blow offshore.
When faced by a wind violently funnelling out of a harbour or fiord etc., either return to the launch site or attempt to land and wait until the wind strength abates.
Patience is the order of the day. If there is any doubt, it is better to wait.
- When caught on an exposed coast by a change to offshore wind conditions, hug the coast intimately, even if this adds considerably to the distance paddled for example by paddling around the curve of a bay.
- Do not make straight line crossings of the narrow entrances to bays, fiords or harbours. Paddle upwind into the feature far enough before kicking out on the crossing. This is to combat ensuing wind and chop drift during the crossing and ensure reaching the far side safely.
Marine forecasts relate to powered vessels and not paddler powered kayaks. Offshore winds commonly knock down the sea state, diminishing swell size and generating reasonable fishing conditions for powered vessels. Listen to the marine forecast and if the stated wind direction is offshore in your area, be extra wary before commencing a paddle. We know forecasts are not always accurate, hence a final decision to paddle or not must be made at the launch site.
Points to Remember
- Offshore wind conditions are deceptive, with calm water and light breezes against the beach. Always look for whitecaps offshore.
- Wind strength increases by 50% when passing from land to open sea.
- Narrow topographic features funnel offshore winds, with dramatic turbulence.
(With reference to the now infamous Jervis Bay incident – wind speeds measured at the airbase on the south west side of JB at 4pm on that day averaged 27 knots gusting to 35. This wind then travelled over a fetch of 12 km before meeting up with our paddlers (and I was one of them) as they rounded Point Perpendicular. Paul Caffyns factor of 50% would mean we faced gusts of up to 70 knots – veritable supermen! Comment from our experienced sea paddlers who wish to argue with the sea-kayaking legends theory are welcome and should be directed to the Dear Editor page – Ed.)