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Diving in South Africa/HMS Birkenhead wreck

9,808 bytes added, 18:36, 1 September 2012
<!--[[Image:Map or aerial photoBirkenhead site map.png|400px|thumb|Map (or aerial photo) of the dive site]]-->
[[Image:The Wreck of the Birkenhead.jpg|thumb|400px|Painting of the wrecking of the Birkenhead]]
[[Image:Wreck of the Birkenhead.jpg|thumb|The soldiers standing in ranks while the boats were loaded]]
[[Image:The Birkenhead-Troopship.jpg|thumb|HMS Birkenhead]]
[[Image:Approaching the engines along the reef P4065209.JPG|thumb|Approaching the engines along the edge of the reef]]
[[Image:Diver over an anchor P4065363.JPG|thumb|A diver caught in the act of photographing the anchor]]
[[Image:Diver over the paddle shaft P4065278.JPG|thumb|One of the paddle wheel drive shafts]]
[[Image:Remains of a boiler P4065316.JPG|thumb|The remains of a boiler lies between the paddle shafts]]
[[Image:View of the top of the upper engine P4065248.JPG|thumb|View of the original upper surfaces of an engine, now lying on its side]]
[[Image:Divers at the engines P4065387.JPG|thumb|Divers looking at the engines]]
 <!--why dive here? add This is an important historical wreck for both engineering and cultural reasons. The vessel was one of the earliest iron steamships, one of the last paddle steamers of the Royal Navy, and the epic story of the wreck is a short note if significant item of British and South African history and folklore. The wreck of the site Birkenhead is special famed for the story of the soldiers who stood by while the women and children were loaded into the few boats that were seaworthy. There are various tales of heroism and stupidity, and a large number of apocryphal anecdotes about shark attacks and bodies being eaten by huge red steenbras.The engines are still in fairly intact condition, and differ considerably from later triple expansion steam engines which were more or less standardised in some way-->general layout for a long time.
[[Image:The Birkenhead-Troopship.jpg|thumb|HMS Birkenhead]]
The name "HMS Birkenhead" is the name of the ship wrecked on 26 February 1852 at this site
| Construction || align=right | || || Iron
| Ship class || alighalign=right | || || Designed as a Frigate, later but served as a troopship
| Propulsion || align=right | || || Sail, plus 2x 2 x Forrester & Co side lever steam engines driving 6m paddle wheels
| Speed || align=right | 10 || || kt as troopship
Maximum depth is about 28m. and the top of the adjacent reef is about (depth)m. (Average depth on the wreckage is likely to be about 25m26m, and the highest part of the wreckage, on top of the engines, is at about 24m.)
Visibility will vary, but may exceed 15m on a good day. Visibility at depth may differ considerably from nearer the surface, but you will not know until you dive.
Lighting will also vary, and will be better on a sunny day, though the amount of light that penetrates to the bottom is very much dependant on the surface visibility, and depth of the thermocline. The sand bottom reflects light, so those parts of the wreck near the sand may be better illuminated that parts on the darker reef areas.
<!--description of the layout, landmarks and geographical arrangement of the site-->
Large The large sandstone reef to the south east of the wreckage (with a pinnacle at the blinder known as Birkenhead Rock) sloping slopes down to about 27m at the edge of the sand. Edge of sand , which runs roughly east-west magnetic. Bottom The slope of this reef is quite steep to the east, but flattens out a bit where the engines of the wreck lie stached at the edge of the sand.  The bottom is fairly flat to the northof this reef, and is sandy patches and low rock reef with scattered wreckage. To the north the reef starts flat but gets a bit more profile further north, bit never more than about a metre. To the west the reef is low and sandy, with odd chunks of wreckage as the highest points. Reef to the east is scattered boulders with sand between. The ship ran aground while travelling roughly south-east, and the wreckage is aligned more or less north west to south east, with the stern to the north west. Much of the wreckage is on or around a patch of white sand, and is concentrated in two main areas: * The engines are lying on their sides at the edge of the high reef to the south, with the tops facing north, and one engine lying fairly flat on the bottom with some components under the sand. The other engine is partly on top of the first, with the large cylinder propped on top of the first engine at the east side, furthest from the equivalent cylinder of the first engine. At first glance the engines appear to have only one cylinder, at the extreme end, but on closer inspection there appears to be a smaller cylinder in line and closer to the output end. These appear to have been double expansion side lever type engines, similar in principle to the beam engines which were popular at that time for stationary work, but how the second cylinder is linked in is unclear (some similar engines have an air pump cylinder). The engines appear to be based on substantial foundations, and are held together by an open structure of pillars and beams, with assorted diagonal bracing. Most of this is well covered by invertebrate growth and is not easy to identify. However, there appears to be a long beam (the side lever) on the lower side of the engines, roughly parallel to the base structure, which may be the side lever which transfers piston movement to the paddle wheel drive shaft. To the south of the engines, slightly up the reef, is a large section of flat structure, which comprises closely spaced parallel frames, almost like a grating, but only one direction. There are also some odd bits of machinery or piping on the reef. * The paddle wheels and shafts are clustered several metres to the north of the engines in much the same alignment as when on the ship, with a boiler between them. Each paddle wheel had its own shaft and engine, and they could be rotated at different speeds, which could be used to maneuver the vessel. The paddle hubs are three parallel discs near the outboard end of the shafts, connected to each other by bars, and having a few short stumps of the paddle spokes remaining. At the inboard end of each shaft there is a large disc, which may have carried an eccentric stub shaft to act as the connection to the connecting rod. The port paddle shaft has what may be the remains of a shaft bearing close against the inboard disc. * The boiler is on top of a large mound of wreckage which includes what might be a spare low pressure piston, as it is a large flat iron disc about 150mm thick with a deep square groove round the edge which could be for a ring, and a hole in the centre which could be for a piston rod. Just north of this piston there is a structure with a lot of parallel pipes and three rounded edged castings in a neat row which could be firebox openings. There are also other groupds of parallel large diameter tubes to the west of this boiler which could be fireboxes from another boiler, and assorted bits of hull structure around this area, but most is not easily identifiable.
The engines are piled on top * An iron anchor lies in the sand to the east of each other at the edge of engines, near the reef edge, One fluke is buried and sand. They are recognisable from the illustration in Allan Kayle's book “Salvage of other sticks almost straiht up, with the Birkenhead”, but differ from shank on the illustration in some detailssand. No stock is visible.
Information More information is needed on what weather conditions are best for diving this site.<!--The site is exposed to (weather/sea condition), so should be dived in (weather/sea condition), and is often good in (weather/sea condition). The site is reasonably protected from (weather/sea condition), but if (weather/sea condition occurs) then (response to weather/sea condition)-->
<!--The site is (usually) at it's best Good conditions have neem experienced in (season1) December and April, but there are also occasional opportunities then again on other occasions in (season2) and (season3)the same months, conditions have been bad.-->
<!--This The site is exposed to wind and swells from south west through to south east, so should be dived when the forecast is for low swell and light winds, as the boat trip will be uncomfortable in a chop. The site is reasonably protected from northerly winds, but they may produce an area unpleasant chop.It is not clear which sometimes has (special circumstance)season is more likely to have good conditions. Water temperature may range from about 17&deg;C at the surface to 12&deg;C at the bottom, caused by (condition1), resulting in (condition2)-->with a strong thermocline.
[[Image:Noble corals on the reef at the Birkenhead DSC00501.JPG|thumb|Noble coral is common on the reef]]
[[Image:Invertebrate growth on the wreck of the Birkenhead DSC00506.JPG|thumb|parts of the wreck are heavily encrusted with invertebrates]]
[[Image:Invertebrates on wreckage of the Birkenhead P4065419.JPG|thumb|Some of the invertebrates living on the wreckage]]
===Marine life===
<!--General description of biota. Substitute “Aquatic life” for fresh water sites-->Lots Marine life in this area includes lots of sponges, colonial ascidians and small sea fans. There , and there are large numbers of noble corals on the reefs nearby. Much of the wreck is quite heavily overgrown with benthic invertebrates, but some areas are fairly clean, largely where crustose coralline algae have taken hold, or in a few cases where the wreckage is a copper based alloy. The benthos includes a variety of sponges, mostly fairly small, some small gorgonians, the occasional noble corsl, assorted bryozoans, hydroids, nudibranchs and anemones.  There are large numbers of West coast rock lobster sheltering in the wreckage, and quite a lot of fish. As usual, Hottentot seabream are everywhere, but there are also fair numbers of Red stumpnose, Redfingers, and possibly barred fingerfin. Also seen were Pyjama shark, Janbruin, Roman and Spotted gully shark.  Bryde's whales, jumping Bronze whalers, and gannets may be seen from the boat if you are lucky. Great white sharks have not been seen recently, but are known to frequent the general area.
[[Image:Paddle wheel shaft and hub DSC00491.JPG|thumb|Paddle wheel hub and shaft at the wreck of the Birkenhead]]
[[Image:Copper pipe under the engines P4065383.JPG|thumb|]]
Scattered wreckage of a historical wreck of great cultural significance. The wreckage includes remains of the paddle wheels, boiler and engine, which is a very early model and quite interesting in design. There are also a few anchors, cannon and similar generic type artifacts.
<!--General description of routes-->
<!--#List of specific route instructions-->
The wreck site is fairly small, and it is possible to see all the major features on a single dive
The recommended places for dropping the shot are near to the engines, at the edge of the high reef, which is relatively easy to confirm with an echo sounder, and as near as possible to the boiler, which is central and therefore makes it likely that a bit of error will not make you miss the whole site, The route description is based on a shotline position near the engines.
*Descend to the shot, and see if you can spot the engines, or failing that, the high reef to the south. If neither of these can be seen, look around for other wreckage.
*If you land on the sand, head south to the high reef, and if you land on reef shallower than 25m, head north until you get to the sand. When at the border between reef and sand, check for wreckage again. If you see the anchor or large boulders you are likely to the east of the engins, so swim west along the edge of the sand. If the bottom is flat and sandy or just sand north of the reef you are more likely to the west of the engines, so swim east along the reef edge.
*Once at the engines, spend a bit of time looking at them as you may never see this type of engine again. There are two, One lies on its side on the sand with the other lying on its side partly supported by the bottom one. The big cylinders are the low pressure cyinders, and the beam across the top transfers the force and movement of the piston to rods at the sides which move the beams, which are parallel to the base of the engine, and pivoted on a bearing about half way along the base. The far end of the beam was connected to a connecting rod which drove the propeller shaft. This style of engine structure is similar to the original stationary beam engines, but with beams at the bottoms of the sides instead of a single beam on top. There is a second cylinder, which is smaller, next to the big cylinder. This was a high pressure cylinder, and the steam would go through this first, then the low pressure cylinder.
*When you have looked at the engines, swim magnetic morth from the east end of the engines. This will take you across the sand to the paddle shafts. The paddle shafts had the paddle wheels at the outboard ends, and the hubs are still easily recognisable as triple discs near the ends of the shafts. The inboard end of each shaft would be driven by the connecting rod from an engine and there would have been a couple of large bearings supporting the shafts.
*The other shaft is in line with the first one you found, in the direction of the big solid disc at the shaft end furthest from the paddle hub.
*Half way between the shafts you can see the spare piston, and just north of that, the boiler. The fireboxes are on the north side.
*There is an assortment of unidentified wreckage around the boiler, extending about 10m or more in an arc to the north.
*The last item on the tour is the anchor, which is south of the eastern paddle hub, on the sand almost back at the high reef, and to the east of the engines.
==Stay safe==
<!--Site specific hazards, entry hazards-->
If a large swell is running, there may will be a break at the rock. This could be dangerous to the boat, and it should stay clear, however in those conditions there may also be strong surge on the wreck and poor visibility. Even on a flat day at low tide the pinnacle will break, and on days when there are soth west and south east components to the swell, both may break at the same time. This may happen sporadically and without warning, so be careful.
The site is near to one of the world hotspots for the Great White shark. This may be considered a hazard, and the reports of survivors indicated that many of the shipwrecked crew and passengers were taken by sharks. Most Scuba divers report that they have seen no sharks during the dive, nevertheless this may not be the best place to dive in low visibility. It is also recommended not to spend a long time at the surface, or to plan to do long decompression stops, as the visibility is often worst near the surface.
There may be slight currents, and the biggest hazard from this is not finding the wreck. These may change over a short period, and can be strong enough to require mild effort to remain in place near the bottom. Currents of this strength may be associated with incoming tide, and deteriorating visibility, and are known to set east on some occasions.
This is a wreck that is not easy to get to, so it is desirable to maximise your dive time by using Nitrox. It is also recommended to carry a compass, and a DSM to alert the boat that you are surfacing, so it can pick you up without a long delay on the surface.
===See also===
The Wikipedia article includes a substantial list of references
Back to [[Diving in South Africa#Gansbaai]]
{{usabletopicguidetopic}} [[Wikipedia:HMS Birkenhead (1845)]]

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