Jon Sanders blogs on the Agulhas Current and other ocean things
Jon’s 7th Blog
Since last Wednesday Perie Banou 2 has passed south of Madagascar. Dipping down on a angle from the north east. Passed 100 Nautical Miles South of Madagascar on non stop route to Cape Town South Africa.
Approaching the southern part of Madagascar and to the south of - the sea was sloppy. Even in zilch wind.
In this region "you get that".
Caused I suppose, by the very steep incline of the sea bottom, despite the favourable current. (Or the mountains under the sea).
It kinda makes this older specimen start getting younger and fitter! Forced by the compulsory isometrics of the situation. (The yacht is going every which way).
Interesting. Long long way elsewhere is Cape Horn at 56 degrees latitude south.
I have cleared that Cape 5 times solo. Never in summer. (Nor in winter).
Coming to and at Cape Horn have copped terrific, incredible gales and storms.
I have also been becalmed. Same place. Grey forbidding cliffs, snow-capped mountains and a grey cold oil calm sea. In other words when the gale stops the sea calms quite quickly.
Sir Robin Knox-Johnson says more people have climbed Mount Everest than sailed yachts around Cape Horn.
Blimey, I don't want to climb Mount Everest, I would avoid climbing a hill on Australia's Nullabor Plain. I'm useless.
Anyway ahead of me is the Cape of Storms. (Cape of Good Hope).
The Cape of Good Hope is not the most southerly point of Africa. It is, in fact, Cape Aghulas.
South of Cape Aghulas (and that southern portion) is the Aghulas Bank. A wide bank. The southern end is 120 Nautical Miles distant.
The edge of the bank is the 100 fathom line. (A fathom is 6ft in proper language). Want to know what that is in meters? "Buy a calculator".
In the north between Mozambique-Africa and Madagascar, sweeping south, is the Mozambique Current.
My paper chart says 1 to 4 knots. The current follows the African coast, broadens and is joined by currents from the North West, (the direction I am coming from) and is renamed "Aghulas Current". Flows at 1 1/2 to 4 knots, and 2 1/2 to 3 knots.
I am steering to a "way point" (I named St Francis) leads me to where I transit across the Aghulas Bank.
My US weather chart shows an increase in the potential for gales.
I have always fetched something rounding the bottom of Africa. This will be my 11th rounding.
The current doesn't help the wave formations and its ridiculous behaviour. To make things more awkward are ships, ships and more ships. All rounding the southern end of "all of Africa". Using the same track.
As always I will be following the route recommended by my bible, the British Admiralty publication "Ocean Passages for the World". (Sailing vessels section).
To quote "Ocean Passages for the World" reads -
"Keep in the strength of the Mozambique Current and the Aghulas Current. In rounding the Cape of Good Hope, if west winds prevail, keep over the Aghulas Bank not more than 40 to 50 miles from the coast. Here the wind will be smoother than elsewhere.
It should be borne in mind that there is much less sea over Aghulas Bank in depths from 110 meters to 130 meters, or less, during gales than there is near the edge and south of it".
Unquote - there goes 400 years of experience. One would have rocks in the head to be off the South East end of the bank in foul weather. Seas there can break the back of a super tanker.
This "Ocean Passages for the World" volume I have on board belongs to David Dicks. He reminds me now and again "have you still got my book?" I see his notes within.
David in the 90s was the youngest to sail around the world solo without stopping. Age 17. He sailed his S&S 34 sloop named Seaflight. (Jesse Martin and Jessica Watson followed).
All three sailed in S&S 34s. The yacht I am now sailing on is a 1971 built S&S 39. (Sparkman & Stephens).
Regards to all,
Jon’s 8th Blog
In my last blog I made mention of the Agulhas Current and the Agulhas Bank. I did.
Cape Town (Maritime) Radio carry warnings with their Ocean Forecasts. Give wind and predicted wave heights. Additional warnings for dangerous unpredictability in the Agulhas Current during westerly gales.
The electronic chart plotter has in small print (mid chart) "Current Agulhas see lower zooms".
Zoom in gives current direction and "the dangerous element in the navigation during and after gales".
So one does not want to end up being in the Agulhas current during a westerly gale.
I had warning (via Cape Town Radio weather forecast).
I put the 3rd heavy weather reef in. Tied it "as near as".
I checked all my halyards and everything.
Some days before I reorganised the fore peak department. Robin, Gareth, Vera and Colin would have been impressed.
The Almighty had other ideas. Reorganised the fore peak, turned it into a shambles.
In heavy weather I could liken the S&S34 and the S&S39 to putting a cork in a bottle, and if the bottle has lead on one side it will righten itself quickly.
Everything is only as strong as its weakest link. I.E. Have a good mast section and go up one on the rigging wires (if not more) etc.
Rolly Tasker used to say to me "Add more strength" "Add more lightness". "Add more simplicity".
The radio mentioned 20 to 50 knot winds in forecast. I took the 50kts to be squalls. Nup.
It seems to go 25 to 30. 30 to 40. & 40 to 50.
If you had to choose between 40 to 50 in the Aguhlas Current or a Siberian Salt Mine. (Both is unthinkable).
Jonathan Clough installed all my B&G equipment, he also installed a brand new VHF Arial on top of the mast and a vertical airial on my back rail. To that aerial I tied Royal Perth Yacht Club General Manager (Stuart Walton) his Club Burgee. The aerial went from vertical to horizontal. The Burgee remained trying to flay itself to pieces.
There is no shortage of electricity on this yacht. Specially in foul weather. The batteries being fully topped up. One can turn on all sorts of power, as much as I want. The "Superwind" generator with its 3 carbon fibre blades pumps the energy thru. The silent giant keeps the power going.
The gale did a bit of good. Cleaned the decks. A brilliant wash down. (Specially the cockpit).
To hove-to I put the (storm) 3rd reef in to the mainsail and set the self steerer to hold the yacht 50 degrees into the wind and boiling steep sea. Any angle into the oncoming sea is good. (Beam on one could find oneself walking on the roof).
Xmas day came and went. The wind was mild, the sea lumpy. The food remaining in my locker boring. Very boring. But Jon Readhead and his super nice wife left a Xmas package on board. "Walkers" - bit elite - Rich Fruit Cake and Scottish short bread biscuits. That will do. Par excellent.
Jon is Royal Perth Yacht Club member who works almost full time creating, making and recording Club Archives. I suspect Royal Perth Yacht Club have the best Archive records of any yacht club in Australia. Other clubs consult him.
In a few hours I shall clear Cape Agulhas. The most southern point in all of Africa. The sea and wind is mild.
The Agulhas Bank seems to have lots of ships, oil rigs and odd fishing boats. They always seem to be where I want to go.
Kindest and best regards to all,
Notes from Robin
Jon is abeam Durban, located within the Eastern Cape of South Africa. To his port is the Transkei Basin (up to 4,500m deep) underlain by oceanic crust. To his starboard is the Agulhas Bank (50 - 200m deep) underlain by African continental crust. The topographic transition is called the Agulhas Ridge. This “ridge” lies along the eastern end of the 1,200 km long Agulhas - Falklands Fracture Zone (AFFZ) - one of the largest strike-slip fracture zones on planet earth and one attributable to the separation of Africa and South America.
This ridge is a prominent topographic feature ranging in height between 4,900 ft (1,500m) and 8,200 ft (2,500m) above the abyssal plain, notionally at 4,000m deep. Refer to this video at the 3:03 mark (freeze frame) to put this tectonic structure into global perspective. Here you will see the Mid-Atlantic Ridge (red line) do a major eastward step along the AFFZ. Follow the AFFZ eastward to near the edge of the image and it becomes the Agulhas Ridge.