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The Challenge of Passage Planning in the SW Indian Ocean

By Anne Lloyd of SV Sofia — last modified Mar 14, 2018 01:01 PM
With the route out of the Indian Ocean to the Mediterranean still significantly affected by the threat of Somali piracy most yachts on a world circumnavigation are now faced with the prospect of a passage across the Southwest Indian Ocean to South Africa and round her southern capes into the South Atlantic.

Published: 2018-03-14 00:00:00
Topics: Indian Ocean
Countries: South Africa , Madagascar , Mozambique , Reunion Island

The Challenge of Passage Planning in the SW Indian Ocean

Madagascar cruising - taken by SV Totem

Yachts starting from Southeast Asia are most likely to take the northern route involving Sri Lanka, the Maldives, Chagos archipelago, the Seychelles, North West Madagascar and Mozambique, while yachts starting in Darwin Australia usually take the southern route involving Christmas Island, Cocos Keeling, Rodrigues, Mauritius and Reunion.

While yachts can combine elements of these two routes, the focus of this article is on what happens when a yacht reaches Madagascar on the northern route or Reunion on the southern route. Up until this point passage planning is relatively straightforward given that the South East trade winds predominate.

From here on two significant weather factors affect passage planning.

The first is the Agulhas current, which starts up in the Mozambique Channel and flows southward down the South African coast as far as Cape Agulhas. Given that the continental shelf is close inshore for much of the coast between Richards Bay and Port Elisabeth, the current flows strongest inshore; often as close as the 200 metre depth contour. The rate of flow varies along its length and is at its strongest between Durban and East London where it can be flowing at up to 4 to 5 knots. While this can give a yacht considerable benefit in terms of a fast passage down the coast, with many yachts recording their fastest 24 hour run down this stretch, there is a major downside in terms of passage planning caused by the other significant weather factors in this part of the world.

These are the Southwest depressions, which roll up the east coast of South Africa from the southern ocean up as far as southern Madagascar at regular intervals often as short as 2 to 3 days apart. When one of these depressions meets the south flowing Agulhas current, the resulting seas become very short and steep creating very unpleasant and often dangerous conditions. In a severe SW gale, waves as high as 20 metres have been recorded in the Agulhas current. Consequently it is not a place to be caught out in these conditions.

There are two further complicating factors when voyaging in these waters.

The first is the cyclone season, which affects the waters around Madagascar, Reunion and Mauritius from December to May. This means that yachts need to leave NW Madagascar or Reunion for South Africa by the end of November at the latest.

The second is the lack of safe harbours between Richards Bay and Cape Town. The only realistic options before the Cape Town area in the event of bad weather are Durban, East London, Port Elizabeth and Mossel Bay.

Knysna is only a realistic option in benign conditions. The entrance is tricky and potentially dangerous. This fact was highlighted to me by a British yacht that we met on arrival in Cape Town. The yacht was hit by two monster waves just after crossing the bar at Knysna on departure, which bent the steering column and spinnaker pole, did considerable damage to the stainless steel deck gear as well as drowning all of the electronic equipment. The owner told me that if they had been a lighter yacht they would almost certainly have broached and rolled over ending up on the rocks. As it was, their 21 ton yacht was just able to punch through these waves and survive the experience. In my view they had a very lucky escape!

It should also be noted that Mossel Bay is only really safe, if you can get inside the harbour. If a strong easterly is blowing, the anchorage outside in front of the yacht club is on a lee shore and subject to large swells. While we were there sheltering from a strong easterly, a yacht anchored outside dragged its anchor and ended up on the beach. They were extremely fortunate to be towed off by the lifeboat with minimal damage.

Both these incidents highlighted to me the fact that this coast deserves real respect and very careful consideration when it comes to passage planning.

Cyclone Patterns

On average the SW Indian ocean gets 5-9 cyclones annually (some years more and some less) and they have to be differentiated between those that originate south of Chagos (BIOT) and those that develop in the Mozambique channel south of Mayotte.

The Chagos cyclones as a rule track W/SW and usually hit the east coast of Madagascar and then re-curve back SE crossing Mauritius and
Reunion. Very seldom do they actually cross Madagascar and get into the channel between Madagascar and Mozambique. The stats on these events are freely available and most cruisers would be aware of this pattern.

What many are not aware of is the incidence of the formation of RTS (Revolving Tropical Storms) in the Mozambique channel south of Mayotte. On average they occur 5 times a year and have their origins south of Mayotte in the region off Nacala in Mozambique. They then move down the channel and after making a few detours - invariably with a very erratic pattern - usually head SE and clip the southern tip of Madagascar, trashing Toliara on the SW coast of Madagascar. Whilst not as a rule classified as true cyclones, they have been known to have sustained wind speeds of 45-50kts+ and typically torrential rain, which is due to the system being trapped between the two land masses and the warm current to feed off.

Those yachts who elect to go via the northern route around the top of Madagascar and then down the Mozambique channel, should be aware that they could be exposed to this pattern from November and peaking in February when Mozambique, as regular as clock work, has torrential rain and floods in the Xai-Xai/Inhambane area.

Reunion to Richards Bay/Durban

However, before one has to tackle the challenge of this stretch of coast, one has to get there. In particular the passage between Reunion and Richards Bay or Durban poses its own considerable challenge. The aim here is to avoid getting caught out in a SW depression when rounding the southern tip of Madagascar and especially when crossing the Agulhas current. The length of passage is approximately 1400 nautical miles and so will take most yachts 10 to 12 days. However, as one encounters the Agulhas current at the end of the passage there are no accurate forecasts as to what the weather will be doing off Richards Bay or Durban at the time of departure from Reunion.

Consequently one has to set off “blind” in this respect and be prepared for whatever one might encounter later on in the passage. That said the first challenge is to round the southern tip of Madagascar. Shallow waters and a wind acceleration zone make this an unpleasant place to be in a SW depression. However, by paying careful attention to weather forecasts while in Reunion, one should be able to avoid this situation.

Once safely round Madagascar it is very important to be able to obtain accurate weather information on the weather in the Mozambique Channel and coastal waters of South Africa, either by email from a weather router or from GRIB files. An Iridium Go system is probably best for this purpose as Sailmail via HF radio is not particularly reliable until well into the Mozambique Channel.  At this juncture one should be in a position to head directly to Richards Bay or Durban if there is a clear weather window before the next SW depression comes through. If a weather window has not opened up at this stage, the sensible strategy is to stay further North and head west along latitude 26S. This keeps one above the path of most SW depressions and keeps one’s options open. One is in a position either to head down to Richards Bay or Durban when a window opens up or to head north to Inhaca Island off Maputo if one needs to shelter from a SW depression.

The alternative to facing the dilemma posed by a direct passage from Reunion to South Africa, is instead to head North West from Reunion to North West Madagascar and thence down the Mozambique Channel to Richards Bay or Durban. The advantage of this option is that it breaks down the passage into shorter legs and provides more accurate weather windows during the latter stages of the passage down the Mozambique Channel, as well as several options for seeking shelter in the event of bad weather. However, it should be noted that this option will take substantially longer, especially if one intends to spend time cruising in the waters of NW Madagascar, which is reputed to be a delightful cruising ground. Accordingly this needs to be planned for well in advance and factored into one’s overall plan for crossing the Indian Ocean. Given the vagaries of the cyclone season, it is not a realistic last minute option.

Richards Bay/Durban to Cape Town

Once safely in Richards Bay or Durban, the next challenge is to negotiate the South African coast round to Cape Town.

The overall length of the passage is 800 nautical miles from Durban and a further 85 from Richards Bay. With SW depressions barrelling up the coast every 2 to 3 days, one would be lucky to make the trip in one go. Therefore the trick is to work out how much progress one can make in the window between SW depressions before the next one comes through. It should be remembered that the Agulhas current can provide a significant boost to progress, especially between Durban and East London, where it really kicks in 40 nautical miles south of Durban. In favourable conditions it is quite possible to achieve a 240 mile day on this stretch of coast and this needs to be taken into account.

The other factor which needs to be taken into account is the weather for rounding Cape Agulhas. In strong conditions with winds in excess of 20 knots from either direction, the sea state can rapidly become very unstable and unpleasant.  A further complicating factor is the likelihood of encountering a cut off low at some stage on passage. These are generated off the land and in most cases are of relatively short duration. Few last more than 6 hours. Consequently they are harder to forecast accurately. However, their potential impact on a passage plan in terms of imposing delay can be significant. Thus it is important to factor in some reserve time in one’s plan to allow for the possibility of encountering one.

Unlike the passage from Reunion, where one has to set off blind, there is no need to do so when sailing down the south African coast, as there is a wealth of accurate weather information available from the South African Meteorological Service and other weather sources such as Predict Wind, Passage Weather and Wind Guru.  However, it is important to monitor these sources very carefully as the detail changes on a daily basis; particularly with regard to timing.

With careful passage planning taking full advantage of the weather window on offer, there is no excuse for being caught out in bad weather on this stretch of coast unless one has the misfortune to suffer major gear failure. It is also important to maintain the average speed set out in the passage plan and be prepared to turn the engine on when wind strength does not allow one to maintain the required speed over the ground. Winds in a weather window can often be on the light side, so one should expect to motor for a considerable amount of time. That was certainly our experience down this stretch of coast.

So how did S/Y Sofia cope with these challenges as we crossed the Indian Ocean to South Africa in the autumn of 2017?

Mid October found S/Y Sofia berthed in Port de Galets marina in Reunion with her crew looking for a weather window to depart for Richards Bay.

Mindful of the challenges and uncertainties involved in the passage ahead, which had been on our minds for some time, we decided that it would be sensible to employ the services of a professional weather router. After reading an article in Yachting World on the internet on why international cruisers should consider using a weather router, we found Simon Rowell, who is meteorologist for the UK Sailing Team and the Clipper Race. He is also an ocean sailor, who has made two passages in these waters, so we were confident that we would receive the advice we needed.

We wanted input from him in two respects for our passage planning. The first was when was the appropriate window to depart Reunion and round the southern tip of Madagascar. The second was to provide ongoing weather advice as we approached the Agulhas current. His charges were very reasonable and his advice proved to be both helpful and accurate. However, having signed him on, Jenny Crickmore- Thompson (the OCC PO/POR Co-ordinator) told us about local South African weather expert Des Cason. Des is a retired ocean sailor based in Durban, who provides free and tailored weather advice to any yacht crossing from Reunion or Madagascar to South Africa or sailing down the coast of South Africa out of the goodness of his heart. His advice was to prove invaluable both on the passage from Reunion and then from Richards Bay to Cape Town. I would strongly advise any yacht sailing in these waters to make use of his services. Thus armed with advice from Des and Simon, we set off from Reunion on 16 October 2017 in company with another OCC yacht – S/Y Dreamcatcher (UK).

Conditions approaching the southern tip of Madagascar were relatively benign. However, at this point we noticed a major tear in our mainsail. In order to prevent further damage we took the sail off and replaced it with the storm trysail. This slowed us down somewhat and S/Y Dreamcatcher steadily pulled away from us. By now we were aware of the existence of a strong SW low making its way up the South African coast, although at this stage it was not entirely clear when it would reach Richards Bay.

Consequently, rather than heading directly for Richards Bay, we followed advice from Des to keep our options open by keeping further north and heading west along latitude 26S.  By the time that we reached longitude 030E the situation regarding the depression was much clearer and we now had 48 hours in which to cross the Agulhas current and reach Richards Bay before the low arrived. However the prevailing light winds in the Mozambique Channel would mean motoring hard to cover the distance in the time available. As we had already motored for some of the way from Reunion to the southern tip of Madagascar, fuel consumption was now an issue. After some careful calculations we reckoned that we had just enough to make it, with a small reserve for emergencies. After motoring hard for 24 hours we were in a position to take advantage of the favourable winds that Des and Simon had forecast as we approached the South African coast. As the wind backed round from the North West to the South West we were able to follow the wind round and close reach our way down the coast to Richards Bay. At that pint we took a wave over the foredeck, which split the genoa at the foot, so we replaced it with the staysail and were able to make it into Richards Bay with 6 hours to spare on Thursday 26 October 2017 after an 11 day passage and were safely tied up in the small craft harbour in Tuzi Gazi when the SW gale arrived and roared through the rigging!

After 5 very pleasant weeks in Richards Bay at the Zululand Yacht Club it was time to head down to Cape Town at the end of November.

Most yachts head down in this time frame for a variety of reasons, although the best time of year for this passage is January to March. We felt confident that provided we allowed sufficient time for stopovers in the event of bad weather, we could make the 900 nautical mile passage in 10 to 14 days and reach Cape Town by mid December.  Armed with advice from Des we reckoned that we could reach East London in our first weather window, even though we might encounter a small cut off low south of Durban for 6 hours. Based on Des’ comment that conditions might be uncomfortable but not dangerous, we decided to press on rather than call in at Durban. After a bouncy 12 hours tacking south of Durban the wind backed to the south east and we picked up the Agulhas current. Given the boost from the current we rocked down the coast averaging 10 to 12 knots. Such was progress we decided to bypass East London and head for Port Elizabeth, where we would wait as the next SW depression came through.

It should be noted that in spite of a very welcoming yacht club there are two significant problems with Port Elizabeth. The first is surge within the harbour and the second is coal dust from the coal loading facility right next to the marina, which quickly coats everything. This problem is compounded by the severe water shortage here. Restrictions on water usage mean you cannot use fresh water to wash off the coal dust.

Once the depression had blown through we moved on to Mossel Bay. Unfortunately for us the strong easterlies, which would have been ideal for a quick passage to Cape Town, made rounding Cape Agulhas problematic while these conditions persisted, so we called into Mossel Bay and ended up on the harbour wall rafted on to a French yacht that we had met in Port Elizabeth. There we waited for a day for an appropriate opportunity to round Cape Agulhas. Given the go ahead by Des we set off at the crack of dawn in order to reach the Cape by midnight, when conditions would be starting to die down. We duly arrived at the appointed hour and had a relatively benign rounding. However, as we were motoring in calm winds and flat seas towards Cape Point, a cut off low suddenly materialised with 25 knots on the nose! Consequently we found ourselves beating our way up towards Cape Point, which delayed our arrival in Cape Town. Instead of arriving in daylight in reasonable winds, we found ourselves arriving at midnight in the teeth of the “Cape Doctor”. This made berthing in the Royal Cape Yacht Club marina, in the dark for the first time with the wind gusting over 30 knots, a somewhat nerve wracking experience!

With the benefit of hindsight, the passages between Reunion and Cape Town have certainly been the most challenging of our circumnavigation to date.

In the light of this experience the following advice might be useful for those following in our wake:

1)      Use the services of Des Cason at sygambit@gmail.com. In our experience his advice is timely, customized to your requirements and invariably accurate. I would disregard his advice at your peril.

2)      Consider additional input from a professional weather router. We found this very helpful and neither Des nor Simon had a problem with this.

3)      If you dislike uncertainty and have time in hand, consider taking the route from Reunion to the Mozambique Channel via northern Madagascar. This has the added bonus of beautiful cruising grounds in NW Madagascar.

4)      Consider waiting in Richards Bay or Durban until January when weather conditions are likely to improve, before heading down to Cape Town.

5)      Allow at least double the normal time for the passage from Richards Bay or Durban to Cape Town. A 900 mile passage would normally take us 6 days. We allowed 12 days and it took us 11.

Anne Lloyd
SV Sofia

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