The anchoring equipment fitted to the majority of vessels consists of two matched units, offering a degree of redundancy.
These units consists of an anchor, chain (or for smaller vessels wire), a gypsum or chain lifter wheel, brake, lift motor and various chain stopper arrangements.
When not in he use the chain is stowed in a chain locker, systems fitted with wire are stowed on a drum in the same way as winches.
A false bottom is fitted to the chain locker consisting of a perforated plate. This allows water and mud to be removed from the space. The end of the chain is attached to the hull by a quick release mechanism known as the 'bitter end'.
The strength of the 'Bitter End' fixing arrangement for a moderately large vessel is in the region of 6 Н tons, this will not be sufficient to prevent a run away unbraked chain. The arrangement must be easily accessible.
The proof load for the windlass (the load the windlass must withstand without being pulled from the deck) is given by;
6.18 dc2 (44 + 0.08dc) [kN]
Where dc is the diameter of the chain metal
This will prove that it is strong enough. It must also be as strong as the braking load on the cable.
The windlass must be capable of pulling the anchor from a depth of 25% of the total cable carried, i.e. 50% of the length of chain on one side
It should be capable of lifting the anchor from 82.5m to 27.5m at 9m/min.
May be steam, electrical, hydraulic or even engine driven although the latter is rare. A gear box arrangement, heavy tooth pitch on final drive, are fitted
Generally consists of ferodo lined half cylinder steel bands which are joined by a pivot point at the rear. The bands are closed and opened by the action of a threaded brake wheel spindle acting on the fixings at the front of the band ends
The chain is led overboard by a strengthened and reinforced pipe called a Hawser
One of the reasons for bow flare is to allow the anchor and chain to lie well clear of the hull when in use, preventing damage.
For anchoring operations the stopper bar is locked upright. When it is required to fix the position of the chain the stopper is lowered into the position shown. This allows the brake to be released and is typically used for stowing the anchor. chain stopper arrangements are not design to stop a runaway chain. Alternately an arrangement known as the 'devil's claw' may be used which has a forked locking piece. For smaller vessels, and where extra security is required bottle jacks with wire strops passed though the chain may be used.
End pull will cause the link to collapse in. This repeated many times will lead to fatigue failure. Hence, stud linked chain is insisted upon
Here a stud is welded on one side in the link to brace it against deformation. An alternative to this albeit in limited use is shown below
Each vessel is given an equipment number which is calculated with use of a formula and tkaens into account the vessels size, underwater area and sail area. From this a 'look-up' table may be used to give an appropriate size of cable. The diameter of the chain may be read from this table and differs depending on the grade of steel. This grade of steel varies from U1 ( mild steel), U2 (Special Steel) to U3 (extra special steel).
The size of cable that is to be used is found by the use of a formula which is
Equipment number = D2/3 + 2Bh +A
D = Displacement
B = beam
h = Freeboard + height of deckhouses over B/4 wide
A = Transverse area including deckhouses over B/4 wide
Connecting chain and components
To join two sections of chain a 'kenter' (don't quote me on the name) shackle is used. This consists of two half sections and removable bridge all held together by a tapered pin. This arrangement works remarkably well and can be found on all sizes of chain.
Ranging Anchor Chain
During docking the anchor chain is lowered from the chain locker to the dock bottom and laid out for inspection.
All of the anchors shown below are of the 'flipper' type. Regulations allows these
to be smaller than standard types
Below is an anchor of typical design seen in many small to medium sized tankers
Below is a high grip anchor typical of that used for four point mooring of vessels required to fix their positions accurately
This anchor weighs about 20 tonnes without attachments. The chain link in comparison the anchor size probably indicates this came from a jack up barge. For vessels the holding comes not only from the anchor but the weight and lay of the anchor chain
Again the chain link in comparison the anchor size probably indicates this came from a jack up barge
Designs to reduce propeller vibration and increase propulsive efficiency.
As the wash of the propeller does not enter at the same angle rudders (sometimes called 'slopped') with uneven inlet angles are sometimes fitted to even the flow from the propeller.
Another design involves the use of design. The water is directed in the same direction as the blade rotation and hence the shock loading occurring when the blade hits relatively still water is removed
Increasing number of blades and skewing
An overlap can be arranged to reduce the pressure fluctuations and change the forcing frequency
Half Kort (Port Nozzles)
Consists of two half loops mounted either side of the hull which smooths the flow of water into the propeller