Fitment Guide

Anchor Sizing Guide

There’s a Rocna or Vulcan anchor to suit just about any vessel – including larger sizes not featured here. To choose the correctly sized Rocna or Vulcan anchor for your boat, follow the chart and instructions.

To choose the correctly sized Rocna or Vulcan anchor, find your vessel’s length from the column on the left, then track across that row until you find the first column with a displacement (in tonnes or pounds) the same or larger than the displacement of your vessel. The top of the column with the selected displacement indicates the recommended Rocna or Vulcan anchor.

Use the tabs to navigate between Metric Tonnes (t), Short Tonnes (T), and Pounds (lb).

Our Anchor Sizing is Conservative

Unlike other manufacturers, our anchor sizing recommendations are intended to provide an anchor adequate for use in most all conditions. We base our calculations on 50 knots of wind, associated surge, and poor holding bottoms. For more on our philosophy and rationale, please consult our Knowledge Base article on our sizing recommendations.

This chart is a guideline only, so if you’d like further information please enquire with us for further advice.

The Rocna 150 (331 lb) and Larger

We do not provide standard recommendations for boats larger than those for which the Rocna 110 (243 lb) would be the recommended size. This is because of increasing complexities of the factors involved. Furthermore, classification society rules and/or legal requirements are likely to dictate the anchor sizes mandated for these vessels.

(*) Classification Rules Sizing

Rocna anchors from size 110 kg (243 lb) and above may be sized based on classification society Rules for Ships for SHHP anchors. Modern rules permit a mass 33% lighter than HHP types, or 50% lighter than “standard stockless” types. Anchor sizing is based on a vessel’s separately calculated Equipment Number (EN). For more information, please consult the Rocna Knowledge Base articles on our sizing recommendations and Classification and Certification.

Rocna and Vulcan Anchor Bow Compatibility

To confirm that which Rocna or Vulcan anchor will fit your vessel, there are a number of resources below to assist you.

Basic Dimensions

Measurements important to the fitting of the anchor on a bow roller are reproduced on this sheet. Using these drawings and a tape measure, many boaters can easily determine that a Rocna or Vulcan will fit their boat.

Shank Hole Rocna Anchors

Vulcan Shank Hole Dimensions

PID L, mm W, mm T, mm
VLC4GS, VLC4SS 26.4 9.2 8.9
VLC6GS, VLC6SS 30.3 10.6 10.2
VLC9GS, VLC9SS 34.6 12.2 11.7
VLC12GS, VLC12SS 38.1 13.4 12.9
VLC15GS, VLC15SS 41.1 14.4 13.9
VLC20GS, VLC20SS 45.2 15.8 15.3
VLC25GS, VLC25SS 48.7 17 16.4
VLC33GS, VLC33SS 53.4 18.8 18
VLC40GS, VLC40SS 56.9 20 19.2
VLC55GS, VLC55SS 63.3 22.2 21.4

Full Scale Patterns

A 2D side-profile of any size anchor may be produced by using the below full scale patterns. The pattern may be printed on any standard printer on A4 or letter paper, then assembled to form a full scale mockup. You may use these patterns to evaluate a fit that may be more difficult to determine just from the basic dimensions above.

For larger sizes, please contact us.

Rocna Original Patterns
No Packages Found
    Vulcan Patterns
    No Packages Found

      Knowledge Base

      The Rocna Knowledge Base features a large and ever-growing collection of “boat fit cases”, with photos and other information, under Rocna bow compatibility. Popular production boats are covered, and examples of other owners of your boat type successfully fitting a Rocna or Vulcan will allow you to invest with confidence.

      Also included are articles and recommendations on the topic of custom bow roller assembly design.

      3D or 2D CAD Files

      We are able to supply naval architects or boat builders with accurate CAD files of all Rocna and Vulcan models to support the proper integration of the anchor into a boat’s ground tackle system. Contact us, and with the execution of a simple terms of use agreement these CAD files may be made available.

      Will a Rocna or Vulcan Self-Launch?

      Both the Rocna and Vulcan anchors have shank shapes that are designed to self-launch and encourage self-righting on retrieval, ensuring ease of use for all operators.

      Which Will Fit Best, Rocna or Vulcan?

      The Rocna anchor has set the bar for the highest performance and reliability when put to the test. The Vulcan infuses as many as possible of the proven performance advantages of its elder sibling, while being specifically designed to fit a wider range of vessels. For the Vulcan, the omission of a roll-bar along with a carefully designed shank profile ensures a snug fit on bows. Platforms, bowsprits, prods, stays, and other protrusions are easily cleared.

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