Anchors & Cable

“Holding on” in an unfamiliar anchorage in bad weather can be the most anxious time of any cruise. It is foolish and false economy to proceed on a cruise with anchors & cable inadequate for the very varied bottom conditions and weather that will be encountered during any voyage. It is a common sight in many vessels that the ground tackle supplied is often far to light for the conditions an ocean going passage maker will be expected to anchor in. The types of bottom most often encountered in anchorages are one of the following:

1) Mud
2) Sand
3) Rock
4) Rock overlaid with sand or mud

At one time or another each of these bottom types will be encountered so the type of anchor should be suitable, as far as possible, for each of these conditions. Broadly, anchors are of two types:

1) Stock type
2) Stockless type

The old style ‘Pick” or Kedge anchor, the Danforth, Moorfast and Stato anchors are all stock anchors. The stock in this type of anchor is designed to keep the anchor upright on the bottom. The big disadvantage with stock anchors is they are difficult to stow neatly on deck. This problem is overcome with the pick anchor by making the stock portable. Most other anchors are of the stockless type; their stability on the bottom is dependant on the size and weight of their “crown” or “head”.
The following is a diagram showing the most common types:
Anchor Types


Of the types shown the Hall, Spek, AC 14, Pool, Danforth, Bruce and the CQR anchors are the most suitable for Trawler Yachts.

Holding Power

The efficiency of an anchor is expressed as its holding power in lbs versus its weight in lbs. The holding power is proportional to its projected fluke area, shear strength of bottom material and depth of penetration of the anchor into the bottom. The following is a table showing the approx. holding power, for comparison purposes, of each anchor type in mud and sand:

Holding Power
Anchor
Mud
Sand
Hall
3:1
7:1
Spek
3:1
7:1
AC14
5:1
12:1
Pool
6:1
14:1
Danforth
9:1
20:1
CQR
9:1
20:1
Bruce
9:1
20:1

The Hall and Spek type are classed as low Holding Power (LHP) anchors and are most commonly seen on merchant ships.

The AC14 and Pool types are classed as High Holding Power (HHP) anchors.

The Danforth, CQR and Bruce anchors are classed as Very High Holding Power (VHP) anchors.

 

On the face of it the best choice of anchor for a Trawler Yacht would be one of the VHP types and certainly this is the case for bottom types 1 & 2. The trouble is in the other bottom types 3 & 4. No anchor can develop any bottom penetration and an anchors only asset in this situation is its dead weight. A better choice would be one of the HHP types which are smaller physically weight for weight than the VHP types. The HHP types are also much easier to stow on deck or in a hawse pipe. Weight of Anchor & Cable The best approach for assessing the weight of anchors and chain sizes is to use one of the Classification Societies Rules such as Lloyds. Each Society has formulae to calculate the Equipment Numeral (N.A.) for all types of Ships and Navigation Notations. The N.A. formulae is a very complex calculation which takes into account the vessels displacement, beam & length, frontal & profile areas, number of decks and freeboards. A table is provided from which the required number of anchors, their weight and the size and length of chain cable is derived.

The following is an example of one of these tables.
Windlass

 

21. As a rule a windlass of suitable power for the mass of anchors and the size of the chain is to be securely attached to the deck which is to be
efficiently strengthened and pillared.

22. The windlass is to be installed so that the chain
run between the hawse pipes and the chain locker
is as direct as possible. The moving parts of the windlass that are likely to cause accidents are to be properly guarded.

 

NA
Stockless Anchors
Chain Cables
Greater than
Less than
or
equal to
Number
Mess (kg)
Length of each
mooring line (m)
Nominal Diameter (mm)
Studless
Chain Cable
Stud Link chain cables
01
02
10
12
1
15
35
7
12
14
1
19
40
7
14
16
1
23
45
8
16
18
1
26
50
8
18
20
1
30
55
9
20
23
2(1)
33
60
9
23
26
2(1)
39
65
10
26
30
2(1)
45
70
10
30
35
2(1)
52
75
11
35
40
2(1)
62
80
12
40
45
2(1)
72
85
13
45
50
2
82
90
14
12.5
50
60
2
91
95
14
12.5
60
70
2
113
100
15
14
12.5
70
80
2
135
105
16
14
12.5
80
90
2
155
110
16
14
90
100
2
180
110
16
14
100
110
2
205
125
16
14
110
120
2
230
125
19
17.5
120
130
2
255
140
19
17.5
130
140
2
128
140
19
17.5
140
150
2
310
140
19
17.5
150
170
2
340
140
20.5
17.5
170
190
2
405
150
20.5
17.5
190
210
2
455
150
22
19
210
230
2
510
150
22
19
230
250
2
550
150
24
20.5
250
300
2
600
150
26
22

In the example in bold it can be seen that a vessel with N.A. between 70-80 requires 2 x 135kg (300lbs) anchors and 105 metres (345ft) of 14mm (9/16ths) chain.

The anchor weights in the table are for L.H.P. anchors. A reduction factor of 0.75 is allowed if a H.H.P. anchor is chosen. Q1 chain is mild steel and Q2 chain is high tensile steel. H.H.P. anchors must be coupled with Q2 chain.

Therefore the vessel in question could be equipped with the following: 2 x 100kg (220lb) Pool (N) Anchors 105metres (345ft) 12.5mm (1/2 inch) Q2 Cable This would provide holding power in mud of 600kg (1323lbs) and 1400kg (3100lbs) in sand.

The Watson 48™ for example has an N.A. of 50 and is specified with the following: 2 – 60Kg (132lb) Pool “N” High Holding Power Anchors. 180 metres (590ft) 13mm (1/2 inch) Short Link Chain.

Anchor Stowage

Anchors much over 60lbs are impossible to man handle and must self stow. This can be done with difficulty, by fitting a tilting bow roller system. By far the best is to have the anchors self stow in hawse pipes in the hull. This is not possible with most V.H.P types because they cannot be made to stow neatly against the hull. In steel vessels the hawse pipes need to be stainless steel with a stainless steel striker plate against the hull for the anchor to stow against. Yachts should always have both anchors connected for immediate deployment. Having the second (spare) anchor stowed on deck is not good practice.

A pair of 60Kg (135lb) Pool “N” anchors fitted to the Watson 48. The hawse pipes and striker plates are fabricated from 316 stainless steel and are designed so anchors self stow. Anchors and chain should always be procured from a reputable manufacturer and be supplied with traceable certificates.

Winches

For vessels up to about 60ft yacht windlasses such as those made by Maxwell and Muir are excellent except that they are not strong enough to ride on and must be fitted with chain stoppers. 24VDC electric systems are fine, however if the ship has a hydraulic system then this may be the preference. Larger vessels almost inevitably need custom built windlasses.

Chain Lockers

A Yacht should have watertight, self stowing chain lockers located immediately below the windlass spurling pipes. For safety their drains must be connected to the ships central bilge pumping system. Stud link chain is always preferable for stowing as it does not become knotted in the chain locker. In conclusion a ships anchoring gear, including the windlass, is of prime importance; it is always better to “kick for touch” when assessing anchor and cable requirements for an ocean passage maker.

©2006 T.C. Watson & Sons Ltd, Naval Architects, Whangarei, N.Z All rights reserved.

Last Updated (Tuesday, 07 September 2010 22:57)