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 vessel, follow the chart and instructions below the chart.

1 t (metric tonne) = 1,000 kg

ROCNA OR VULCAN MODEL
  4 6 9 10 12 15 20 25 33 40 55 70 110
Vessel Length     Vulcan only Rocna only Vulcan only             Rocna only Rocna only
4 m ≤ 2 t                        
5 m ≤ 1 t ≤ 5 t                      
6 m ≤ ½ t ≤ 3.5 t ≤ 7 t                    
7 m ≤ ½ t ≤ 2 t ≤ 6 t ≤ 7 t ≤ 9 t                
8 m   ≤ 1 t ≤ 5 t ≤ 6 t ≤ 8 t ≤ 12 t              
9 m   ≤ ½ t ≤ 4 t ≤ 5 t ≤ 7 t ≤ 10 t ≤ 16 t            
10 m     ≤ 3 t ≤ 4 t ≤ 6 t ≤ 8.5 t ≤ 14 t ≤ 22 t          
11 m       ≤ 3 t ≤ 5 t ≤ 7 t ≤ 12 t ≤ 20 t          
12 m         ≤ 4 t ≤ 6 t ≤ 10 t ≤ 18 t ≤ 30 t        
14 m           ≤ 4 t ≤ 6 t ≤ 13 t ≤ 23 t ≤ 40 t      
16 m             ≤ 3 t ≤ 9 t ≤ 18 t ≤ 32 t ≤ 60 t    
18 m               ≤ 5 t ≤ 14 t ≤ 25 t ≤ 50 t ≤ 85 t  
20 m                 ≤ 10 t ≤ 18 t ≤ 40 t ≤ 75 t ≤ 165 t
22 m                 ≤ 6 t ≤ 12 t ≤ 33 t ≤ 65 t ≤ 150 t
24 m                   ≤ 7 t ≤ 25 t ≤ 55 t ≤ 135 t
26 m                     ≤ 18 t ≤ 45 t ≤ 120 t
28 m                       ≤ 35 t ≤ 105 t
30 m                         Use EN*
35 m                         Use EN*
Anchor weight 4 kg 6 kg 6 kg 10 kg 12 kg 15 kg 20 kg 25 kg 33 kg 40 kg 55 kg 70 kg 110 kg
9 lb 13 lb 13 lb 22 lb 27 lb 33 lb 44 lb 55 lb 73 lb 88 lb 121 lb 154 lb 243 lb
Rocna fluke area 460 cm² 590 cm² - 795 cm² - 1030 cm² 1140 cm² 1415 cm² 1695 cm² 1945 cm² 2300 cm² 2690 cm² 3330 cm²
Vulcan fluke area 420 cm² 560 cm² 730 cm² - 880 cm² 1020 cm² 1240 cm² 1440 cm² 1730 cm² 1970 cm² 2430 cm² - -
Rec. G40 chain 6 mm 6 mm 7 mm 7 mm 8 mm 8 mm 9 mm 10 mm  10 mm 11 mm 12 mm 14 mm 16 mm
1/4" 1/4" 1/4" 1/4" 5/16" 5/16" 5/16" 3/8" 3/8" 7/16" 7/16" 1/2" 5/8"
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1 short ton = 2,000 lb

ROCNA OR VULCAN MODEL
  4 6 9 10 12 15 20 25 33 40 55 70 110
Vessel Length     Vulcan only Rocna only Vulcan only             Rocna only Rocna only
13 ft ≤ 2.2 T                        
16 ft ≤ 1.1 T ≤ 5.5 T                      
20 ft ≤ 0.55 T ≤ 3.85 T ≤ 7.7 T                    
23 ft ≤ 0.55 T ≤ 2.2 T ≤ 6.6 T ≤ 7.7 T ≤ 9.9 T                
26 ft   ≤ 1.1 T ≤ 5.5 T ≤ 6.6 T ≤ 8.8 T ≤ 13.2 T              
30 ft   ≤ 0.55 T ≤ 4.4 T ≤ 5.5 T ≤ 7.7 T ≤ 11 T ≤ 17.6 T            
 33 ft     ≤ 3.3 T ≤ 4.4 T ≤ 6.6 T ≤ 9.4 T ≤ 15.4 T ≤ 24.3 T          
36 ft       ≤ 3.3 T ≤ 5.5 T ≤ 7.7 T ≤ 13.2 T ≤ 22.1 T          
39 ft         ≤ 4.4 T ≤ 6.6 T ≤ 11 T ≤ 19.8 T ≤ 33.1 T        
46 ft           ≤ 4.4 T ≤ 6.6 T ≤ 14.3 T ≤ 25.4 T ≤ 44.1 T      
 52 ft             ≤ 3.3 T ≤ 9.9 T ≤ 19.8 T ≤ 35.3 T ≤ 66.1 T    
59 ft               ≤ 5.5 T ≤ 15.4 T ≤ 27.6 T ≤ 55.1 T ≤ 93.7 T  
66 ft                 ≤ 11 T ≤ 19.8 T ≤ 44.1 T ≤ 82.7 T ≤ 181.9 T
72 ft                 ≤ 6.6 T ≤ 13.2 T ≤ 36.4 T ≤ 71.7 T ≤ 165.4 T
79 ft                   ≤ 7.7 T ≤ 27.6 T ≤ 60.6 T ≤ 148.8 T
85 ft                     ≤ 19.8 T ≤ 49.6 T ≤ 132.3 T
92 ft                       ≤ 38.6 T ≤ 115.7 T
98 ft                         Use EN*
 115 ft                         Use EN*
Anchor weight 4 kg 6 kg 6 kg 10 kg 12 kg 15 kg 20 kg 25 kg 33 kg 40 kg 55 kg 70 kg 110 kg
9 lb 13 lb 13 lb 22 lb 27 lb 33 lb 44 lb 55 lb 73 lb 88 lb 121 lb 154 lb 243 lb
Rocna fluke area 71 in² 91 in² - 123 in² - 160 in² 177 in² 219 in² 263 in² 301 in² 357 in² 417 in² 516 in²
Vulcan fluke area 65 in² 87 in² 113 in² - 136 in² 158 in² 192 in² 223 in² 268 in² 305 in² 377 in² - -
Rec. G40 chain 6mm 6mm 7mm 7mm 8mm 8mm 9mm 10mm 10mm 11mm 12mm 14mm 16mm
1/4" 1/4" 1/4" 1/4" 1/4" 5/16" 5/16" 3/8" 3/8" 7/16" 7/16" 1/2" 5/8"
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ROCNA OR VULCAN MODEL
  4 6 9 10 12 15 20 25 33 40 55 70 110
Vessel Length     Vulcan only Rocna only Vulcan only             Rocna only Rocna only
13 ft ≤4,400                        
16 ft ≤2,200 ≤11,020                      
20 ft ≤1,100 ≤7,720 ≤15,430                    
23 ft ≤1,100 ≤4,410 ≤13,230 ≤15,430 ≤19,840                
26 ft   ≤2,210 ≤11,020 ≤13,230 ≤17,640 ≤26,460              
30 ft   ≤1,100 ≤8,820 ≤11,020 ≤15,430 ≤22,050 ≤35,270            
 33 ft     ≤6,610 ≤8,820 ≤13,230 ≤18,740 ≤30,860 ≤48,500          
36 ft       ≤6,610 ≤11,020 ≤15,430 ≤26,460 ≤44,090          
39 ft         ≤8,820 ≤13,230 ≤22,050 ≤39,680 ≤66,140        
46 ft           ≤8,820 ≤13,230 ≤28,660 ≤50,710 ≤88,180      
 52 ft             ≤6,610 ≤19,840 ≤39,680 ≤70,550 ≤132,300    
59 ft               ≤11,020 ≤30,860 ≤55,120 ≤110,230 ≤187,400  
66 ft                 ≤22,050 ≤39,680 ≤88,180 ≤165,300 ≤363,000
72 ft                 ≤13,230 ≤26,460 ≤72,750 ≤143,300 ≤330,000
79 ft                   ≤15,430 ≤55,120 ≤121,300 ≤297,000
85 ft                     ≤39,680 ≤99,200 ≤265,000
92 ft                       ≤77,200 ≤231,000
98 ft                         Use EN*
 115 ft                         Use EN*
Anchor weight 4 kg 6 kg 6 kg 10 kg 12 kg 15 kg 20 kg 25 kg 33 kg 40 kg 55 kg 70 kg 110 kg
9 lb 13 lb 13 lb 22 lb 27 lb 33 lb 44 lb 55 lb 73 lb 88 lb 121 lb 154 lb 243 lb
Rocna fluke area 71 in² 91 in² - 123 in² - 160 in² 177 in² 219 in² 263 in² 301 in² 357 in² 417 in² 516 in²
Vulcan fluke area 65 in² 87 in² 113 in² - 136 in² 158 in² 192 in² 223 in² 268 in² 305 in² 377 in² - -
Rec. G40 chain 6 mm 6 mm 7 mm 7 mm 8 mm 8 mm 9 mm 10 mm  10 mm 11 mm 12 mm 14 mm 16 mm
1/4" 1/4" 1/4" 1/4" 5/16" 5/16" 5/16" 3/8" 3/8" 7/16" 7/16" 1/2" 5/8"
                           
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To choose the correctly sized Rocna or Vulcan anchor, find your vessel’s length from column on the left, then track across that row until you find the first column with a displacement (in tonnes) 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.

For multi-hulls: use the chart as instructed, then select the model one size larger.

Our sizing is conservative

Unlike other manufacturers, our 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 sized 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.

Equipment Number (EN) range (applies to Lloyd's, RINA)
50–70 70–110 110–130 130–175 > 175
ROCNA MODEL 110 150 200 275 Please
enquire
Anchor weight 110 kg 150 kg 200 kg 275 kg
243 lb 331 lb 441 lb 606 lb
Fluke surface area 2300 cm² 4470 cm² 5560 cm² 6510 cm²