Seems Retractable Bollards were used for much more than just tieing up the sub in dock!
But, you are correct, they are "retractable bollards"...although exactly how
they retract or extend is a mystery to me.
Excerpt from the Interrogation Report of Survivors of U-459 (September 1943)
[Quote]
(b) Amounts of Fuel Supplied. U-boat may be supplied with any quantity from 8 to 80 tons of fuel,
these being the extremes supplied by U.459. A prisoner said that he had heard that U.511, when
proceeding to Japan, had been supplied with 85 tons of fuel by U.460.
(c) Description of Hose. The hose used for the transfer of fuel is made up of various lengths connected
together. Those have an internal diameter of 3.5". In the supply boat there is an additional 8 metre length
of rubber impregnated linen hose, to which is connected an 8 metre length of armored hose to prevent
damage through chafing, where the hose leaves the supply boat.
Between the supply boat the the U-boat being fueled are connected five 16-metre lengths of non-armored
hose, with a further 8 metre armored length, where the hose enters the boat being fueled.
In the boat being fueled three further 16 metre lengths of non armored hose are used.
Thus the total length of fueling hose is 152 metres (500 feet).
When lubricating oil is to be transferred, a similar hose of 2.16" internal diameter is also passed across.
(d) Method of Transfer. The hose is passed round the forward retractable bollards and then back along
the deck to the fuel supply valve which is near the galley hatch. Whilst fueling the U-boats proceed slowly
ahead and the hose falls in a catenary, the extreme ends being entirely on the deck of the U-boats. The two
U-boats lie about 50 yards apart, depending on the sea. The U-boat being supplied lies roughly with her bow
abreast the stern of the supply U-boat. The hose is passed from the supply U-boat using a rubber dinghy.
