Ocean Passage Planning

By John and Lyn Martin

It’s very satisfying to get to the end of an ocean passage and say to yourself, “I enjoyed that”.

It’s not always like that, but passages are not a lottery and you can improve your odds dramatically with good passage planning.

So where do we start? Let's assume you have a good boat, one that‘s well prepared and up to the task. The dream is swaying palm trees and white sand beaches. It's time to “head north until the butter melts”. Tonga is the usual pick for a first destination.

The South Pacific cyclone season runs from December through to late April so a May start looks promising. First step is to get the right information. Tides, currents, wind, both strength and direction and what’s the weather going to do? I use the Pilot Charts of the South Pacific Ocean, these charts show a multitude of information in a graphic presentation that’s easy to read.

Taking May as our start date and highlighting the route to Tonga from, in this instance the Bay of Islands, we can read the following: The greatest percentage of wind is from the south, southeast and east, the average wind strength is 15 to 20 knots and the percentage of calms is 2 percent, great, that’s perfect for where we want to go. The charts also give us ocean currents, the drift is mainly east to west but there is a hook to the south around the top of the Kermadec Islands. This will likely give us a lumpy seaway if the winds are south and east. If we look a little to the west there is another current line that looks like it will push us north. We can also see that if we keep a little west of the rhumb line the chance of gales drops.

Next out comes the chart, paper of coarse, in this case NZ 14605. Use paper charts for this part of your planning, a chart plotter will show only the major features, reefs and small islands don’t show until you scroll in.

So our thinking is keep a little west , let's plot this on the paper chart and add the waypoints into the GPS or chart plotter as an additional check. Our first waypoint is just off the Nine Pin at the Northern end of the Bay of Islands, great, nothing to hit until we get to 24 deg south, so we will put our second waypoint five miles off the southern of the two Minerva Reefs. North and South Minerva reefs make a great stop over taking this route, fun to visit, good diving or snorkelling and it breaks the passage up.

So how long is the passage going to take? This question is important for our next part of the planning, weather. We have seen what the averages are from the pilot Charts but the date of our departure will be dictated by the weather systems and our speed will tell us where we will be in relation to these systems not only at the start of our passage but as both we and the system progress.

A good reference for weather is the “Mariners Met Pack” by Bob McDavitt. In lay man's terms it explains weather and how it affects us. In short, highs (anti cyclones) revolve in an anticlockwise direction with more wind on the outer edges than the centre. Lows work the opposite.

Circulating lows tend to be restricted to the higher latitudes (further south) in May so as we head north we are more likely to be affected by the highs and the bigger or more intense the high the more edge effect it will have. As the high pressure pushes against the tropical low pressure zone a squeeze of the isobars occurs, the bigger the high the more squeeze and squeeze means wind. A 1030hpa high can give accelerated trades of 30 knots +.

There are a multitude of weather services available today, pick one and use only that one. Why?

There are different “Models” used for predicting weather which means sometimes the reports from different sources conflict. Picking just one avoids confusion. I use “Metvue” the Victoria University site, it seems to have the most consistent long range weather.

An average cruising yacht should cover 130 to 140 miles a day which will put it at South Minerva about 5 days out, plan to arrive here between 10am and 3pm for best visibility going in.

In May there is usually about 7 to 10 days between systems. We are looking for winds from a southerly quarter with a high that is forecast to be around 1020hpa in about 5 days. We want to be in the front half of the high when we get to Minerva. Remember as the high moves through the winds will back through east then northeast and north, not the direction we want.

So we have analysed the weather patterns, looked at the timing and conclude the best time to leave seems to be on the back of a low that’s just gone through, it may be a bit brisk but it’s in the South west so its aft of the beam. The wind should back and moderate as the high fills in and we should reach Minerva in five days with a bit of a push from the current we saw on the Pilot Charts. All things being equal the wind should be in the ESE by the time we get there so we will still be beam reaching . We can then spend a bit of time exploring the two reefs and head for Tonga in the next batch of South easterlies, these should come through on the front of the next high, about 4 day’s from when you arrived.

Well that’s the plan anyway. Keep an eye out for rotating lows forming in the tropic in your long range forecasts and avoid these.

My only other suggestion is if this is your first time offshore, go with a group. The support and sense of community is well worth it. In fact a lot of well healed sailors still prefer to go offshore in an organised group or event.

What ever you do, just do it, cruising the Pacific Islands and indeed further afield is the experience of a life time.

Tips for a safe passage

• Take the time to prepare your boat well. Work with your safety inspector on this.
• Plan your passage in advance, don’t try and do it on the fly. Have a back up route and destination in case of emergency.
• Make regular radio skeds and advise someone of your plans, destination and ETA.
• Prepare your crew. Practice sail work, explain the boat’s systems and talk about safety procedures and where to find everything.
• Check if your crew is on any medication, if they get seasick they wont be able to hold down their medication.
• If any of your crew are the least susceptible to sea sickness, have them start taking something for it, BEFORE you set sail.
• Have a grab bag handy at the foot of the companionway in case of emergency.
• Set up a watch system. Whether it’s two, three or more crew, set up a watch system so everyone knows what they are expected to do. Allways keep a good lookout.
• Set up a schedule for chores and make sure everyone has their fair share. Leaving all the cooking and cleaning up to the misses is one sure way to have a grumpy partner.
• Pre-cook some passage meals BEFORE you leave, one pot meals are best and where possible have them pre-frozen ashore.
• Make a box full of sandwiches to have available for the crew whenever they are hungry.
• Have lots of high energy snacks on hand.
• A well fed and rested crew is a happy crew.
• Reef down early, it’s easier and safer. It’s a good idea to reef down before dusk if the forecast is even a bit uncertain.
• Have a daily check around the boat for chafe and things that can come undone, like shackles etc.
• Most important of all, keep the skipper happy. Remember he or she takes ALL the responsibility and a tired skipper is more likely to make mistakes.
• To the skipper, remember you are the boss but also remember what happened to Captain Bligh.

What's in a grab bag?

A grab bag is just that, you grab it as you go past when every thing around you has turned to the proverbial.

You haven’t got time to pack one in a hurry and in an emergency your mind has a tendency to be spinning in circles. Not the time to be fumbling around, probably in the dark, trying to think what to take.

Grab Bag Contents

• Semi waterproof bag, preferably with floatation.
• Water proof bag with:
  • Passports
  • Money
  • Credit Cards
  • Boat papers
  • Clearance Papers
  • Cell phone
  • Hand held GPS + spare batteries
  • Ocean Chart.
  • 2x Travelers towels
  • Sea sick pills
  • Any crew medication.
  • Flares:- Hand held Orange 4x, Red Parachute 4x, dye marker 1x
  • Hand held VHF waterproof
  • Spare Batteries
  • Torch, Spare batteries, spare bulb.
• 406 Epirb Basic first aid kit
• Water, usually the packet type (keep a ¾ filled 20lt container on deck with a length of line attached with a clip on the end)
• Basic food, lunch bars, barley sugars, be aware some foods will make you thirsty.
• Packet electrolytes
• Survival blanket.
• Strobe light Anything else you feel you may need

John & Lyn Martin are directors of the ISLAND CRUISING ASSOCIATION and live aboard their boat “Windflower”. Based at Opua in New Zealand’s beautiful Bay of Islands, they have extensively cruised the South Pacific with their two children over the last 15 years.