miscellanea

castle cook book replaced by nutrition

qajaq

aikido

body reset

polymath consulting

private

Cook Strait kayak crossing


From chart NZ463: click on chart for enlargement (0.6 MB)

These notes summarise information available from a variety of sources, add my views and experience, and point to further reading. I hope that it is of use to planning and executing safe kayak crossings, or more importantly discouraging you from unsafe ones.

My experience includes 21 crossings, most of them solo double crossings, as importantly many aborted crossings, and prolonged Strait watching.

Following the following advice does not guarantee a successful crossing: the Cook Strait can be an unpredictable and unforgiving place!

The trouble with kayak crossings of the Cook Strait is not the distance itself but the Strait's notorious tides and winds, and the interplay of the two. Following the golden rules, below are sections on:

This page does not cover the critical aspects common to kayak safety anywhere: paddling and self-rescue skills, training, experience, fitness, equipment, support, safety, communications...

Golden rules

  • Don't underestimate Cook Strait
  • Be prepared to cancel before
  • Be prepared to abort during
  • Plan to cross at neaps
  • Plan for slack water in the western strait
  • Cross with a high after a southerly or a trough between lows
  • Don't trust the weather forecast
  • Enjoy

Tidal streams

You will need at least the following:

  • Tide times for Wellington, Picton and Taranaki, and (if you're going that way) a tide stream table for Tory Channel.
  • Charts NZ46 (Cook Strait, 1:200,000) or, better, NZ463 (Approaches to Wellington, 1:100,000, see image above). Topographical maps are useful also, but do not show the critical areas of rips and overfalls. Chart NZ 6154 covers Tory Channel Entrance in more detail. If you are unsure of chart symbols, you will also need the Hydrographic Office's Symbols, Terms and Abbreviations used on charts publication.

Tidal streams are critical around the strait because they can be so fast relative to the speed of a kayak, because of the rips and overfalls they create when they clash or race over reefs, and because they can steepen seas against the wind.

Herein lies the problem: the Strait could be simulated by putting an almost complete obstruction across the middle of a half-full bath, and see-sawing the bath in phase with the slosh until full force is reached.

The particular problem with the Strait is not only that it is a narrow channel, but that the positioning of New Zealand's North and South Islands in the Pacific Ocean happens to be such that, as the Pilot describes it: high water on the western side of Cook Strait occurs about 5 hours later than on the eastern side, so that when it is high water on one side it is nearly low water on the other. The tidal streams are occasioned by these differences in level. If in addition meteorological conditions are such that mean sea level is raised on one side of the strait, then the flow from that side will be considerably increased in strength and duration, while the flow from the other side is correspondingly reduced or, under extreme conditions, even reversed.

Rate of tidal flow

"In the middle and narrowest part of Cook Strait, between Cape Terawhiti and Wellington Head [the rate of both the north going and south going streams] is from one to 3½ knots, but during spring tides and gales the stream setting with the wind may attain a rate of 5 knots", says the Pilot. As 3½ to 5 knots is, or more often exceeds, the speed range of kayaks, it is crucial to take account of these tidal streams.

The 18 hour non-crossing: legend has it that veteran Strait paddler the late David Herrington was once caught by the tidal streams to the extent that he had to paddle for 18 hours before he could reach any landing, and that was where he started.

The tidal streams rarely run in the same direction as the kayaker wants to. In the narrows they run along the length of the strait while the kayaker is trying to cross it (and avoid being swept out of it), and inshore they cause strong tide rips: it is a question of avoiding the stronger tidal streams rather than using them.

The areas with the main tidal rips and overfalls are generally marked on the chart, the most interesting being:

  • The Terawhiti and Karori rips off the south-west coast of the North Island, extending along some ten miles of coast and several miles out to sea, with speeds up to five knots at springs;
  • off Perano Head just north of Tory Channel entrance; and
  • northeast of Cape Koamaru (out to Cook Rock), around The Brothers, Fisherman's Rock in mid-Strait, and Mana bridge.

Other areas of rip can occur, but can usually be seen and heard from a distance and avoided. On one crossing, I could hear the rip east of The Brothers 45 minutes before riding it.

Tidal variability

While tides are more predictable than wind, around the Strait even they have their idiosyncrasies. For example the nautical almanac, which reserves special cautions on tidal streams to Cook Strait (and French Pass), states:


I wonder what those squirly things are?
"The tidal streams in and around Cook Strait are unreliable, and mariners are warned to exercise every precaution when travelling in the vicinity. The streams often run in one direction for eight to 10 hours, while cases have been reported of them going so for 18 hours or more. When the streams have been running in one direction, for say eight to 10 hours, it has been found that the opposite stream is much weaker and, in some cases, hardly noticeable. The maximum rates shown on the chart which are usually attained at springs are also liable to be experienced at any other time. In the vicinity of Karori Rock and Cape Terawhiti a rate of up to 7 knots is frequently experienced, but as a rule it does not last for more than an hour. Small vessels are warned to keep well clear of tide rips, as they may lose steerage way and may, in extreme cases, capsize."

The Pilot cautions that "The influence of heavy gales upon the tidal streams is felt when the disturbance is 24 to 48 hours distant". The Navy's Tidal Officer, with military conservatism, notes that the passage of storms will affect Cook Strait tides up to five days afterwards, which is worrying but not very useful, as weather patterns there typically follow a five-day cycle. The charts note simply that "Weather conditions may considerably affect the tidal streams in the Cook Strait".

Swells

Ocean swells do not really affect kayak crossings, as you will be travelling parallel to them, and the entrances or landing are protected from the prevailing southerly swells.

Choosing a day with gentle tides

Given the variability, it may be unwise to venture into the Strait shortly after (or before) a storm, or the passage or approach of a significant depression, even if the forecast tides and weather are promising. All the more reason to plan for minimum tides, develop a keen weather eye, be prepared to cancel or abort, and have a reserve of fitness.

Choosing a day to minimise likely tides is simply a question of choosing one as close as possible to neaps and ideally, if you have a large enough window to cross in, choosing a day with particularly shallow neap tides. Neap tides are easily identified from tide tables by the minimum differences between high and low. Neaps are from one to three days after each half moon, i.e. around five days before each new or full moon, and so occur every two weeks.

The New Zealand Hydrographic Office calculates full tide predictions for 16 standard ports around New Zealand, with difference tables for secondary ports, each relative to the standard port with the most similar tidal pattern. The three standard ports against which Cook Strait tides are predicted are Port Taranaki, Picton and Wellington. The following table indicates the areas those standard ports affect.

Standard portArea referenced against itSecondary port(s)Mean neap tidal rangeMean spring tidal range
(Port) TarankiNorth Island coast north of Cape Terawhiti (from Makara Bay north)Porirua (Titahi Bay) (+20 min) and Makara (-40 min)3.0m1.7m
PictonQueen Charlotte Sound and the Western Strait out to about the line of the Brothers (Queen Charlotte Sound, Tory Channel and Cook Strait)Fisherman's rock0.5m1.5m
WellingtonEastern Strait south and east of Turakirae Head (from Oteranga Bay east)Cape Terawhiti, Karori Rock0.9m1.0m

The table indicates also the mean tidal height range at both neaps and springs for the secondary port considered most relevant to strait tides. The large difference between the neap and spring tidal ranges (a factor of up to three) reflects the importance of choosing neap tides.

Inspection of the tide tables shows that there can be a factor of 1.5 to 2 between the tidal height ranges for 'deep' neaps and 'shallow' neaps. For example, for Picton, the deepest neap range is 0.7m (0.3m low tide and 1.0m high tide) and the shallowest is 0.4m (0.5m low tide and 0.9m high tide). This reflects the lesser but still significant importance of choosing 'shallow' neaps.

Tide rips, overfalls and races are varying degrees of turbulence occurring in a tidal stream, and are caused by the stream being suddenly increased, or forced over an obstruction or through a constriction. They can, therefore, be expected where two streams or eddies converge, or where the sea bed shelves suddenly or becomes uneven, and in bottle-necks and straits. Eddies, tide rips, overfalls, and races can, in some circumstances, cause capsizing or complete loss of control in a boat. They should, therefore, be avoided. (This impeccable logic from the nautical almanac)

Neaps might span up to three days of similar tide heights before tidal differences rise towards their spring levels, so the timing is not exact. The tidal ranges of days close to neaps are, of course, indicated in tide tables.

For example, if you wanted to cross the Strait around June 2006, the tide tables predict fairly deep neap tides (average about 0.6m difference at Picton) around 5 to 7 June (about six days before full moon) and nearly as deep neaps (average about 0.75m difference) on 20 to 22 June. In between, there are spring tides (up to 1.4m difference) around 14 June. Thus, neither neaps are ideal, but early June would be a slightly better time to cross (ignoring weather for the moment) than late June.

Choosing the hour

The western narrows is the term I use for the section of the Cook Strait alongside Arapawa Island, and extending south towards Port Underwood - in width about a third of the narrows of the strait, or some 10 km at its narrowest. You have to pass through it to leave or enter the Sounds from the narrows. The western narrows has stronger tidal streams then the eastern strait (with the exception of Cape Terawhiti), resulting in rips around both Tory Channel or Cape Koamaru (and around Perano Head between them).

The western strait also often has significantly stronger winds than the eastern side, often by as much as 10 knots (see the section on weather). The most important consideration in timing a crossing, in my view, is therefore to cross the western narrows at slack tide.

In general, the times of slack tidal streams do not correspond to those of the high and low water given in the tide tables. This is certainly true in the strait, where high or low water at one end means maximum gradient, and hence strongest tidal force, through the Strait. There are various sources of information about the timing of the tidal flows.


Tidal streams at the chart lozenges

The only point around the Strait which has actual tidal stream tables is Tory Channel. Calculating the tidal stream times for other areas has to be done from the textual descriptions in the Pilot and Charts, or other guides, referenced to tables of times relative to a Standard Port's tides.

The Charts also give tidal stream strength and direction at chosen points (indicated by lozenges). On NZ463, lozenge <A> is in the Western Strait off Tory Channel, and lozenge <B> is mid strait on the Tory Channel to Makara run. They indicate that the water's as slack as it gets there about at low water and (to a lesser degree) at high water at Wellington (for <A>), and about an hour before or five hours after high water Wellington (for <B>).

A useful guide based on the chart information is a set of small maps printed in the New Zealand Cruising Guide. They can be cut and joined in sequence to form a flip-chart (and laminated for use at sea). For a given day, once you have determined the time corresponding to one of them (e.g. "2 hours before high water Wellington" is 9am that day), you can flip through hour by hour to see how the tidal streams will develop during your day.

Weather

Don't trust weather forecasts The MetService forecasts are based on a global atmospheric model (run from London). The model calculates the most likely weather future. It does not consider other possibilities, so it is simply one scenario of what might happen, albeit a well educated guess. Reality might be quite different, especially in Cook Strait, when a minor change in the prevailing direction (westerly) can swing a wind from a northerly to a southerly through the Strait, and accelerate it too. Make your own judgments on how wrong the forecasts might be.

The tides can be bad, but the wind can be worse. It is more variable and, around Cook Strait, has practically no upper limit on ferocity. Closer to the day, you will also need weather forecasts, and an understanding of their strengths and weaknesses (which can only be gained from experience of matching forecasts to reality).

The forecast wind speed is for an average, and is made on the basis that winds will gust up to 50% over the stated average wind speed. I find it salutary to remember that the force of wind goes up as the cube of its speed; and so you can expect to experience gusts exceeding three times the force of the average wind (1.5 cubed is 3.4). In choosing in what average wind speed to cross, allow for this as well as the risk of an increase in average wind speed.

Whichever direction the prevailing wind over New Zealand is (often westerly), strong winds will invariably be venturied through the strait as either southerlies (including south-easterlies) or nor'westers (including northerlies). Both can reach extreme strength. Southerlies are more dangerous in that a cold front can bring them suddenly and violently (the "southerly gutbuster"), and that the time of arrival of a front is often forecast wrongly. Usually southerlies arrive later than forecast, but sometimes earlier which is doubly dangerous as they are moving faster than forecast, and will therefore tend to be stronger. Nor'westers tend to build up more gradually and predictably, but as they can easily rise in strength by 10 knots per hour, they can still change significantly in the course of a crossing. Southerlies also tend to peak in strength around the western narrows, which is just where you don't want them, whereas nor'westers tend to affect the strait more evenly.

A typically weather pattern around the strait is for alternating highs and lows passing over from the west. After the low winds of a high, nor'westers will gradually rise in strength until a cold southerly front heralds an approaching high, and the initially strong Southerlies die down to the low winds of the high. The best time to cross, therefore, is at the tail end of a southerly (those calm, blue days) to give the maximum leeway before the nor'westers get too strong. The late and greatly missed Dave Herrington, who survived more Cook Strait kayak crossings than anyone (at least until my crossing count got to current levels), recommended crossing on the trough between two stationary depressions (those silvery grey misty days). At neaps, of course.

Handy hint for calculating wind in Cook Strait: look at the difference in pressure (read the isobars) between Wellington and Kaikoura. In a southerly, which always makes Cook Strait rough, multiply this difference by 10 to set the Cook Strait wind speed in knots. So if isobars between Wellington and Kaikoura are 5 hectopascals apart, go for 50 knots through Cook Strait (from Bob McDavitt, source)

The best possible forecast is for 5 or 10 knot light variable winds. Knowing that 30 knots is hard work, and 40 knots is getting marginal, I prefer to cross in forecast average wind speeds of below 20 knots (i.e. up to 15 knots) to give an appropriate margin for safety, and in stable conditions.

In summer, sea breezes tend to pick up from around 11am until the evening, and rather than set in a particular direction seem to amplify the existing wind. The ideal is therefore either an early start or late one. If either takes you into darkness, using the moon can help considerably. The ideal days for early morning paddling are the neaps before a new moon, when there will be a nascent (e.g. 40%) moon in the sky from the early hours, and for evening paddling the neaps before a full moon, when there will be a gibbous (e.g. 60%) moon until around midnight.

The calmest crossing. Thankfully, not all Cook Strait kayak crossings are tales of fighting tidal streams and rips. Max Grant of Quality Kayaks reports one crossing where the sand from his launching beach was still on the bow after crossing.

Above all, do not venture out if there is any risk of a strong southerly arriving. Anyone who has seen these pass over central New Zealand waters will appreciate this. The late Russel Ginn, a Cook Strait watcher for many decades, cautioned that a strong and unexpected southerly would often come through in February. My rule is that I'll never venture out if there's any hint of a southerly front north of Christchurch: I plan to be an ancient mariner. Be warned!

Routes

This section describes the main routes and the best times to paddle them, in either direction, to allow for the tidal streams.

There are two main entrances to the Marlborough Sounds from the narrows of Cook Strait: Tory Channel and the Queen Charlotte Sound, which meets the Strait at Cape Koamaru. The practical start or finish points on the North Island are dictated by road access: Makara Bay or Titahi Bay. For a kayak crossing, any combination is possible, but the most logical are:

  • Titahi Bay - Cape Koamaru (38 km)
  • Makara Bay - Tory Channel (29 km)

Crossings from South Wellington to Tory Channel are significantly longer and trickier, because the South Coast from Ohiro Bay to Cape Terawhiti is challenge enough without then crossing too: Karori rip can really rip. If one does cross from or to Cape Terawhiti, the Cook Strait section is similar to crossing to or from Makara Bay.

Go west, or head east?

There is generally some advantage to crossing west to east:

  • you can be more sure of being in the Western Narrows there at slack;
  • there is less time for the weather to change while committed in the Western Narrows;
  • the conditions are more likely (though certainly not guaranteed) to get better rather than worse as you head east;
  • there is a slight current assisting you in light variable winds.

The main disadvantage of paddling west to east (other than that it may not be the way you want to go) is psychological: as kayak (or boat) access to Tory Channel or Cape Koamaru is more difficult than road access to Makara Bay or Titahi Bay, it might be more tempting to push on when one should abort. Don't ever commit psychologically to crossing on a particular day.

Titahi Bay - Cape Koamaru

Titahi Bay is easy to launch from and land at in all crossing conditions. I nearly always paddle this route, principally because I live in Titahi Bay (or, in a sense, vice versa - I live there for the good kayaking).

There is a small high-tide only beach just east of Cape Koamaru, and a rocky beach on Arapawa Island one mile west of the cape that can be accessed when there's no northerly swell.

The direct route (if the tides let you follow it) goes south of Fisherman's Rock, which lies submerged half way between Cape Koamaru and Mana Island. It's worth climbing the Cape to watch the rips working at peak flow: quite impressive. The Bothers raise tiresome rips, which can generally been seen and heard from some distance. Any stationary fishing boats in that area are probably over the rock.

The most unpredictable section is the western strait around the Brothers Islands and between them and Cape Koamaru. The tide rip markings on the chart are there with reason! The direct route goes north of The Brothers, although I usually paddle through them to have a look. The Brothers are a reserve so you cannot land there: in emergency a landing would be possible if a tad gnarly just north of the lighthouse.

If crossing east to west, best to leave Titahi Bay around high tide. Pass south of Mana Island (conditions can get choppy briefly over the bridge and off the south end of Mana). From the south end of Mana you can usually see The Brothers standing out against Cape Koamaru in the background. By night, the Brothers light house flashes white every ten seconds. The heading is close to due west.

If crossing west to east, best to leave the cape about an hour before low tide Picton, to be level with the Brothers around slack water which is generally around low or high tide Picton, and to catch the east going tidal stream in the eastern strait. Second best would be leaving an hour before high tide Picton, as it is more important to have slack water around the Brothers than the east going stream, which is neither reliable nor strong. Head to the south end of Mana Island. Mana Island can be difficult to make out from the western strait, as it merges with the mainland: even in broad daylight you might need to start on a compass bearing, east.

Makara - Tory Channel

Makara is usually easy to land at or launch from, but can have a small dumping surf when there's a northerly swell. It's sometimes best to use the stream mouth at the north end of the bay: at high tide one can paddle up it, which is best of all.

Tory Channel entrance does have fast tidal streams, but they generally swirl rather than raise a rip, so are not too troublesome. Neverthless, an experienced sea kayaker almost died off Tory Channel entrance in 2005. The main dangers here is when leaving the sheltered waters of the channel: a fast outgoing tidal stream could eject you into the Strait's Western Narrows before you've had time to check the conditions out there. Watch out for the ferries, of course.

Raukawa Rock on Arapawa Island is closer to Makara than Tory Channel entrance itself, and can make a good aiming point. But don't gaze upon the eye of the octopus....

One can launch or land easily below the triangular lead markers on Arapawa Island opposite Tory Channel entrance: it's reserve land and you can camp there.

Why?

In Cook Strait I've been airborne in rips, spun around in swirls, swept off by tidal streams. I've stared down into dark holes in the water, stared up at breaking crests, stared across at working rips. I've paddled in grey, glassy calms, seen meteorites, surfed with dolphins, paddled to Picton for tea, and all the time admired the stark beauty. Why not?

References

  • New Zealand Pilot, UK Hydrographic Office
  • New Zealand Nautical Almanac, Hydrographic Office, Royal New Zealand Navy, Auckland
  • Tide times for Wellington, Picton and Taranaki, LINZ
  • Tide stream table for Tory Channel, LINZ
  • Charts NZ46 Cook Strait
  • Chart NZ463 Approaches to Wellington (tif file copy at 0.6 MB)
  • Chart NZ6154 Tory Channel Entrance and Picton Harbour
  • Symbols, Terms and Abbreviations used on NZ charts, Hydrographic Office
  • New Zealand Tidal Streams Atlas
  • New Zealand Cruising Guide
  • Greater Cook Strait - Form and Flow, T F W Harris (a fascinating book if you can find a copy - no longer in print)
  • The Cook Strait Mariners' Weather Handbook, Jim Hessell, MetGen.
  • Paul Caffyn's cunning crossing plan (sorry this link seems to have died - let me know if you find it)
  • Various weather forecasts and metering: see my weather page
< kayaking stories | qajaq | kayak links >
Page last modified on September 09, 2014, at 07:38 AM