The bower anchor is worn, damaged or lost, and a replacement has to be ordered for a ship in class. The old certificate carries a mass, so the first enquiry asks for that mass.
Mass is the wrong place to stop. IACS UR A1 states its table mass for anchors of equal mass, then manages the total of the bower anchors rather than the equality of one unit to another [1]. Where an HHP or SHHP anchor is approved in that category, the permitted mass changes again [1], and approval of a high holding power design covers a size range worked out from tests, not every size the model is drawn in [1]. And two public drawings at the same 1,440 kg differ in every one of the six dimensions they letter [2][3].
Mass remains one field among several; the others — drawing, category approval, chain end, stowage, class record — decide whether the anchor can be installed and accepted.
Why the same mass is not a match
The mass basis sits in one clause. The mass per anchor in Table 1 is required for anchors of equal mass, and an individual anchor may vary by up to 7% of the table mass, provided the total mass of the bower anchors is not less than the table requirement [1].
Two things follow. The rule manages a total, so a pair that is individually lighter is not automatically out, and a pair reproducing an old certificate exactly is not automatically right — the question is what the bower anchors weigh together against the table. And the allowance belongs to the table figure for the ship: it is not a fit tolerance for a fabricated part, and it says nothing about whether a replacement enters the pocket or meets the chain end.
The category of the anchor moves the figure again. Where an anchor designated high holding power, of proven superior holding ability, is used as a bower anchor, UR A1 permits each anchor to be 75% of the mass required for ordinary stockless bower anchors in Table 1 [1]. For super high holding power anchors the permitted mass may be reduced to not less than 50% of that table mass, with use limited to restricted-service ships and the mass generally not exceeding 1,500 kg [1].
Both figures are easy to read backwards. They are permitted reductions where the anchor concerned is approved in that category, not a recommendation to trade mass for a category label on an existing ship, and they do not remove the need to establish the approved size range for the unit actually offered.
Then there is the drawing. Two public Sotra sheets — one AC-14 high holding power anchor, one SPEK stockless — each carry a dimension table with a row at 1,440 kg [2][3]. The letters are the manufacturer's labels on those sheets. Side by side at the same nominal mass:
Table 1 — same nominal mass, two designs
| Dimension (mm) | AC-14, 1,440 kg [2] | SPEK, 1,440 kg [3] |
|---|---|---|
| A | 1,795 | 1,710 |
| B | 1,610 | 1,300 |
| C | 497 | 570 |
| D | 311 | 279 |
| E | 1,093 | 950 |
| F | 862 | 950 |
Two observations survive that table. At the same nominal mass the designs differ in every lettered dimension, so a value copied from one sheet cannot check the other. And the letters are local: E equals F on the SPEK drawing and does not on the AC-14 drawing, enough to show that a letter does not name a fixed feature across designs.
Reading the dimensions on the drawing
The note under both tables says it in the supplier's own words: the measurements may vary between different models, and the company accepts no responsibility for deviation between the tables and the delivered equipment [2][3]. That is a supplier disclaimer, not a class requirement, but the effect holds either way: a published table is a reference, and the drawing that applies to the order governs.
So the dimensions worth matching are not the ones in a catalogue but the ones on the drawing approved for the ship, read against the anchor being offered. The difference between a design, its drawing and its approval is set out in the AC-14 anchor article; what matters here is that a mass row on a public sheet establishes none of the three.
If the ship's drawing is missing, the envelope has to be established from the ship itself — from the pocket, the hawse pipe and the chain end — which is a question for the yard and for the class, not something a table row answers.
The record to collect from the vessel
Three records need to be in one folder before quotations can be compared on anything except price.
The design and manufacture basis. UR A1 requires ordinary stockless anchors to be of a design in accordance with the classification society's rules or practice, and requires anchors and anchor cables to be manufactured in accordance with UR W29 and UR W18 [1]. Both are tied to a society and an approval behind it, not to a mass.
The test record. An ordinary anchor is proof tested to the UR A1 Table 2 load for its actual mass; an HHP anchor to the UR A1 Table 2 load for 1.33 times its actual mass [1]. The bases are not comparable, so a certificate carrying a load but no category cannot be checked against the old one.
The measured geometry. The sheet values, if the drawing survives, plus what can be measured on the ship: the mass of the unit that came out or is on offer, and the dimensions that decide stowage. At 1,440 kg the two Sotra sheets gave six different values, which is why this is a measurement and not a lookup [2][3].
Two further items are interfaces rather than documents: the chain-end form and size, and the condition of the hawse pipe, stowage position and stopper.
The interface chain
UR A1 treats the bower anchors as installed when they are connected to their cables and positioned on board ready for use [1]. The chain-end connection is therefore inside the delivery state the rule describes, not an accessory fitted afterwards. Which shackle or swivel belongs there is covered in anchor chain connections.
ABS names what else is in the picture. Its rules for survey after construction list anchors and chain cables, anchor windlass — including foundation, prime mover, shafting, wildcats, brakes, controls and chain stoppers — as items to be examined as far as possible, with a function test where the surveyor considers it necessary [4]. At special survey the same rules require the anchors and cables to be examined and their condition confirmed, with the hawse pipes, chain stoppers and chain locker examined [4].
Those clauses describe five interfaces a replacement has to satisfy: the chain end, the hawse pipe, the stowage position, the chain stopper, and the windlass with its wildcat. The component map is in the ship anchoring system overview.
The class question
A replacement anchor is not only a purchase. ABS's rules for survey after construction state that no alterations which affect or may affect classification — including substitutions of steel differing from that originally installed and changes to the original structural configuration — are to be made to a classed vessel unless plans of the proposed alterations are submitted to and approved by an ABS Technical Office before the work begins [4].
Two cautions belong on that clause. It is ABS's wording, read in ABS's own rules; other societies write their own. And whether a particular replacement is an alteration affecting classification is a question for the society, not something a purchaser can conclude from the clause. Either way the step is the same: put the proposal to the vessel's own class before the work is committed, and let the answer define what the submission must contain.
Replacement data checklist
The ten items below are what a quotation package should cover. Each one supports a decision, and each one has a failure mode when it is missing.
| # | Item | Source | Decision it supports | If it is missing |
|---|---|---|---|---|
| 1 | Drawing revision offered for the ship | Supplier, against the ship's file | Whether the envelope is the approved one | Letters compared across unrelated sheets |
| 2 | Anchor category: ordinary, HHP or SHHP | Class approval of the design | Which mass basis applies | Mass checked against the wrong table figure |
| 3 | Approved size range | Class approval of the design | Whether this mass sits inside the range | A model approval read as a size approval |
| 4 | Weighed mass of the old unit or the offered unit | Weighing record | Position against the table mass and its allowance | "Same as the certificate" assumed |
| 5 | Dimensions measured on the unit or on the ship | Drawing, or measurement at the pocket | Stowage and hawse fit | Fit inferred from a catalogue row |
| 6 | Chain-end form and size | Cable record | Whether the anchor connects to the cable | Connection left to the yard to improvise |
| 7 | Certificate and proof-test record, with its basis | Class file | Whether test figures can be compared | Test loads compared across categories |
| 8 | Condition of hawse pipe, stowage position and stopper | Survey report | Whether the interface still accepts the anchor | A new anchor ordered against a worn interface |
| 9 | Windlass and wildcat data | Windlass documentation | Whether hauling and stowing still work | Mismatch discovered at installation |
| 10 | Class notation and society | Certificate of class | Which rule the submission goes to | Proposal prepared against the wrong rule |
Questions to put to a supplier
Six questions cover the gaps a mass-only enquiry leaves open, and are worth asking in writing: the answers are what make two quotations comparable.
- Which drawing revision are you quoting, and is it the drawing approved for this ship?
- In which category is the design approved, and what approved size range sits behind that approval?
- For this mass, what proof-test load will appear on the certificate, and was it struck on the actual-mass basis or the 1.33 times basis?
- Which chain-end arrangement does the anchor accept, and to which cable end?
- What deviation from the table mass are you proposing for each anchor, and does the pair still meet the table total?
- Has the vessel's class been asked whether the replacement is an alteration, and what does its answer require?
A quotation that answers all six can be checked against the ship's records. One that answers only the first and the fifth is a price for a weight.
What this checklist does not decide
Three things stay outside this article. UR A1 defines the anchoring equipment as intended for temporary mooring of a ship within a harbour or sheltered area, and states that it is not designed to hold a ship off fully exposed coasts in rough weather or to stop a ship that is moving or drifting [1]. The capability being matched is that one, not a larger sea state. Acceptance of a specific unit by a specific society is the society's decision, not a property of a drawing. And service life is not addressed by any of these records; none of them carries a life figure or a wear allowance for the anchor.
What the records settle is narrower and more useful: whether the offered anchor is the approved design at an approved size, whether its mass basis is the right one, and whether it will connect to the cable and stow in the ship.
If the ship's drawing, the marks on the old anchor, the measured dimensions, the chain-end details and the class notation are in hand, send them to us with the notation the vessel is classed under, so the offer can be read against the same documents.
References
[1] International Association of Classification Societies, UR A1 — Anchoring Equipment (Rev.7 2020, Corr.1 2021), A1.1.1–A1.1.2 (scope of the anchoring equipment), A1.1.6 (manufacture to UR W29 and UR W18), A1.4.1.1 (design, and the table mass with the 7% individual allowance), A1.4.1.2 and A1.4.1.3 (HHP and SHHP mass), A1.4.2 (size-range approval), A1.4.3 (installation on board), A1.4.4.2 (proof-test basis) — https://ww2.eagle.org/content/dam/eagle/regulatory-news/2022/IACS-UR-A1.pdf
[2] Sotra Anchor & Chain AS, AC-14 high holding power anchor, dimension table, 1,440 kg row, and the note beneath the table — https://www.sotra.net/wp-content/uploads/2021/05/ac-14_anchor.pdf
[3] Sotra Anchor & Chain AS, SPEK stockless anchor, dimension table, 1,440 kg row, and the note beneath the table — https://www.sotra.net/wp-content/uploads/2021/04/Spek_anchor.pdf
[4] American Bureau of Shipping, Rules for Survey after Construction (2019), Part 7, Chapter 1 Section 1 (alterations; anchoring systems and mooring equipment) and Chapter 3 Section 2, 5.1.4 (anchor windlass, anchor and chain cable) — https://www.marineinspector.org/wp-content/uploads/wpforo/default_attachments/1608308620-Part-7-Survey-After-Construction-ABS-Rules-for-Building-and-Classing-Steel-Vessels.pdf
