Monday, June 2, 2014

Sailing the North Pacific Roller Coaster

Hawaii to Sitka, Days 12-17

There is a reason why sailors love trade wind sailing. Actually, there are several reasons. The trade winds are reliable. In their season, they blow from a consistent direction at a fairly constant speed. If you choose your route wisely---that is, you choose to travel with the trade winds instead of against them---you are running downwind on a fairly comfortable point of sail. Sailors (including ourselves) give glowing reports of setting the sails and never having to touch them again, except for making very minor adjustments, for two to three weeks at a time. You don't have to constantly change the sail configuration when you're in the trades. No striking and hoisting sails. No setting and furling. No reefing and shaking out reefs. Actually, we did put a reef in the main at night on our trade wind passage from the Galapagos to the Marquesas. But that was when we were still fairly inexperienced ocean voyagers and still shaken from our first encounter with a squall in the Inter-Tropical Convergence Zone. I wonder if we'd make that choice as often now? (Patrick says, "yes.")

The type of sailing we are doing right now, and that we did on our passages from New Zealand to Hawaii last year---sailing outside the trade wind belt---is a more active kind of sailing and in some respects, more challenging. We have to make frequent adjustments to sail plan and strategy in order to meet the changing conditions. As we do that, a pattern is starting to emerge. Where do these changing conditions come from? On this passage, they are a result of the low pressure systems marching across the North Pacific from west to east: the North Pacific Roller Coaster. Instead of steady trade winds, these weather systems bring rotational winds, often strongest (and therefore, more "usable" to sailors-if not too strong) in their fronts.

In his article titled "Crossing the Pacific High," Richard Ian-Frese of the sailing vessel Anna observed that during their North Pacific crossing, "the lows were stacked up across the North Pacific, like planes on a busy runway." That's a very good analogy.

As these low pressure systems pass over us, bringing their rotational winds, our goal is to skate along as quickly as possible making miles good in the favorable winds (on our desired course, winds from the E, SE, S, and SW are favorable), and to lose as little ground as possible in the contrary winds (N, and NE winds.) To avoid losing ground, we point as high as we can and choose the most favorable tack.

After we punch through one of these systems, there is typically a period of light and variable winds. It is also challenging trying to keep the boat going during these times. We either ghost along under sail at one or two knots; or, if the sails are slatting too much, we motor in fuel conservation mode at about the same speed. Another option is to drift and wait for wind, but we usually choose to keep the boat moving if we can.

As we begin to enter the next weather system, the pattern starts up again. It usually begin with contrary winds from the N, or NE, and we are hard on the wind. As the wind clocks around to the east, we are still beating to maintain our course. As the wind further shifts to the SE---Ah, finally!---we can ease the sheets, speed up, and settle by turns into a broad reach or a comfortable downwind run. We usually try to reserve activities that require the boat to be somewhat level, such as baking bread or taking a shower, for the broad-reaching and downwind runs.

At the same time, we try to avoid the strongest winds and heaviest precipitation carried in the fronts of these low pressure systems. We do this by studying the weather files ahead of time and trying to choose a course that will keep us moving towards our goal but also leave us outside of dangerous weather. That choice is made easier at this time of year, because the winds in the low pressure systems are not as strong as they were during winter storms. (There's a reason why we spent the winter in Hawaii!)

To be honest, you don't have a lot of choice in the matter. There's a little wiggle room, but once you board the North Pacific Roller Coaster, you can't get off until the end of the ride. You take what you get and you deal with it. One of the things that makes a crossing to the Pacific Northwest when leaving Hawaii at this time of year difficult is that the price of admission to the North Pacific Roller Coaster is crossing the northeast trades at the start. Before you can board the ride, you have to get across the northeast trade winds---which typically blow from 17 to 25 knots at this time of year, out of exactly the direction you want to go---making it difficult to time when and where you board the roller coaster. Later in the summer, as the Pacific High (a stabile high pressure system now to our east) further establishes itself, grows bigger in size and strengthens, the High deflects the trade winds so they become more easterly, making it easier to get an offing from the islands. We chose not to wait to leave Hawaii until later in the summer in order to spend more time in southeast Alaska.

I think that after many voyages, and many passages, sailors develop a sixth sense about when the best time to start a passage is. They know from experience, from living the systems, the general patterns of weather on the oceans at various times of year. However, it may be more difficult to develop this "sixth sense" now than it used to be, in a world of changing climate. While many technological advances have made sailing easier---from the standpoint of materials, equipment, and communications---some things have made sailing more difficult than in the past. Climate change is one of them. Global weather systems are less predictable than they used to be.

Our passage did not have an auspicious start, but we are doing better now. In fact, we have fallen into what seems to be an incredible piece of luck: We have a forecast of southerly winds (from the SE, S, and SW) stretching ahead of us for the foreseeable future, for the next week. One of the weather systems affecting our passage is the Pacific High, the high pressure system east of us. Silhouette is positioned between the Pacific High and the procession of lows on the North Pacific Roller Coaster. As the low pressure systems butt up against the Pacific High, they affect its shape, compressing the calm eye in the center of the high and "squishing" its edges. The Pacific High also interacts with an approaching low, deflecting it away from the High, much the way two magnets with opposite poles repel each other. ("More like a billiard ball hitting another billiard ball," says Patrick, which is actually a more accurate comparison, because it includes the idea of deformation) Currently, the High is deflecting an approaching low from the west to the north and west of us, fending off some of its stronger winds. At the same time, the remaining southeasterly winds from the approaching low are merging with the southeasterly winds in the lengthened edge of the High, giving us a period of sustained southerly winds. 

The following image captures from our GRIB (GRIdded Binary) weather files better illustrate this scenario. We experienced an even more dramatic example of this a couple of days later, but I think this example is particularly clear. 

The "normal" condition of the High, showing its generally roundish shape with winds rotating in a clockwise direction around the center

An approaching low from the west begins to "squish" the High, lengthening its eastern and western boundaries and deforming its center

At the same time, the low is deflected by the High, and the counter-clockwise rotating southerly winds in the low merge with the clockwise rotating southerly winds in the high, producing an oceanic freeway of southerlies
 
At present, we are rolling along on the North Pacific Roller Coaster, making excellent progress towards Sitka. We have 1703 NM under the keel and 831 NM to go. I think it's time to put our hands up in the air and do the wave!

In other news...

Life Aboard: We have reached the shipping lanes, and night watches are kept busy keeping track of the positions of large container ships and tankers, in relation to Silhouette's position, as they ply the waters between Asia and the large ports on the west coast of North America. The sound of voices over the radio, some in foreign languages we can't quite place, adds an element of intrigue to our nights. We have also reached the land of fog, which makes keeping track of those large ships all the more difficult. A ship passed within three miles of us last night, and we couldn't even make out the glow of its lights in the fog.

Our outer wear has metamorphosed once again. We started this passage in shorts, T-shirts, and bare feet. We are now donning the Northwest Uniform: a layer of long underwear, a layer of fleece, and a layer of rain gear (in this case, foul weather gear.) The cotton sheets on our pilot berth have been exchanged for fleece ones, and we have one to three blankets (depending on if we are running our diesel heater or not) on the berth as well. Needless to say, the pilot berth is snug and toasty and neither of us leaves it willingly.

The Critter Report: We're starting to see more life out here. A whale (I'm pretty sure it was a minke) surfaced next to the boat several nights ago. The whale was swimming parallel to Silhouette at a fast clip and surfaced four times before it disappeared. We have also had a Laysan albatross and possibly, a black-footed albatross, following the boat at different times. We still haven't caught any fish. Although it has sometimes been too rough to fish, I set my lines out whenever possible. Sadly, I think the North Pacific has been pretty well fished out by the driftnet fisheries; but I'm still hoping to catch an ocean-going salmon before we make landfall.

_____
Posted from sea via Ham Radio.
Edited for clarity and images added after arrival in port. 

No comments:

Post a Comment

Follow by Email