Anchoring Flashcards
How do you calculate the swing circle radius for planning an anchorage?
Max usable cable + Length of ship + safety factor (1 or 2 cables)
How much anchor cable should be ranged when anchoring?
Minimum of 4 x water depth
Recommended 6 or 7 x water depth
Very large vessels 8-10 x water depth
What are the considerations when choosing an anchor cable length?
- Depth of water
- Type of holding ground
- Length of time vessel is at anchor
- Sea room available for swinging
- Expected weather conditions
- Strength of tide
- Windage area
- Type of anchor and its holding power
How do you calculate the anchor holding power?
Anchor weight x seabed factor
shingle/sand = 3.5
rock/thin mud = 1.8
soft mud = 1.7
blue clay = 207
An anchors hold depends on the vertical pull exerted by the chain lying on the bottom.
True or False?
False. It is the horizontal pull that pulls the flukes into the seabed digging them in.
What is the safest method of using two anchors?
One at long stay and the other “under foot” at short stay.
Laying two anchors long stay can be dangerous if the wind or tide changes swinging the vessel and fouling the hawse.
Describe an open moor anchoring procedure
Vessel drops the port anchor and lays out 9 shackles.
Vessel turns to starboard 60 degrees and steams ahead until the anchor cable is lying 90 degrees to the ship.
Vessel drops starboard anchor and lays 6 cables as the port anchor is heaved in to 6 cables.
Why is the port anchor best to use in Northern latitudes and Starboard in Southern latitudes?
The predominant weather systems cause a veering wind in Northern hemisphere so the ship will remain to leeward of the anchor cable without it passing under the hull
In the Southern hemisphere the strong winds back and so the starboard anchor is used.
What considerations are there during an anchor watch?
- Mark the swing circle on GPS/ECDIS/Radar/Chart
- Plot and verify the position with visual fixes
- Mark distances to nearest vessels and dangers
- Keep a good radio listening watch
- Monitor surrounding water for small boats/security
- Hoist all access ladders when not in use
- Switch on all deck lights at night
- Display all relevant nav lights/signals and flags
What are the two anchor moorings used in tidal rivers?
- Standing Moor
- Running Moor
Describe a standing moor procedure
Let go the port anchor 100m ahead of the final position and range 10 shackles of cable.
Let the weight come on the cable and let go the starboard anchor.
Range 5 shackles on the starboard anchor whilst heaving in 5 cables on the port anchor.
Describe a running moor
Stop the vessel 100m short of the final position and let go the port anchor.
Pay out 10 shackles whilst steaming ahead.
Lower starboard anchor and pay out 5 shackles while heaving in the port anchor 5 shackles.
When is a Mediterranean moor used?
When berthing stern to the quay to allow multiple vessels to use the quay space
Describe a Mediterranean moor procedure
Whilst head on to the berth and 2 ship lengths from the berth, the starboard
The anchor is let go and held up and down/very short stay.
The vessel then swings around the anchor until stern facing the quay
Vessel moves astern slowly while paying out anchor chain, keeping it tight.
Anchor is used as a brake near the quay
The anchor can then be used to assist unberthing.
What maintenance should be carried out on the anchor equipment?
- Wash down anchors after use to remove all mud and debris
- Inspect the anchors for damage from the quayside when possible. Check the pin on the D anchor joining shackle and split pins
- Keep joining shackles painted
- Greasing of windlass and removal of old grease
- Check guillotine and chain stopper condition
- Check hawse pipe and spurling pipe covers for condition
- Check wire strop and senhouse slip for hanging off the anchor. Make sure spare joining shackles, D rings and links are well greased.
