Index | Use chart | 57 mm | 75 mm | 100 mm | 125 mm & 150 mm | Teardrop | Crossover | Mastbase Halyard Lead & Flip-Flop | Footblocks | AirRunners | Stainless Steel Runners | Opening Foot Blocks | Snatch | ESP Blocks | Stainless Steel ESP | Stainless Steel Blocks | Specifications
Big Boat blocks > Use Chart
This chart is designed to help you select the correct size hardware for each system on your boat. Match the specified dimensions on your boat to the maximum values shown in the chart.
Note: These hardware specifications assume a boat of moderate displacement sailing in normal conditions. ULDB's may often use smaller hardware. Heavy displacement boats and multihulls often require stronger hardware. Please contact Harken if you have any questions regarding the suitability of hardware for your applications.
Mainsheet
| Maximum mainsail area | ||||||||||||||
| 57 mm Low-load Black Magic® | 57 mm High-load Black Magic® | 75 mm Low-load Black Magic®/ 75 mm ESP | 75 mm High-load Black Magic®/ 75 mm Stainless | 100 mm Black Magic®/ 100 mm Stainless | 125 mm Black Magic® | 150 mm Black Magic®/ 150 mm Stainless | ||||||||
| ft2 | m2 | ft2 | m2 | ft2 | m2 | ft2 | m2 | ft2 | m2 | ft2 | m2 | ft2 | m2 | |
| End-boom | ||||||||||||||
| Single Attachment | 450 | 41 | 550 | 51 | 600 | 56 | 750 | 70 | 900 | 84 | 1250 | 116 | 1550 | 144 |
| Multiple Attachment* | 500 | 46 | 675 | 63 | 720 | 67 | 900 | 84 | 1100 | 102 | 1500 | 139 | 1750 | 163 |
| Mid-boom | ||||||||||||||
| Single Attachment | 400 | 37 | 400 | 37 | 450 | 42 | 550 | 51 | 700 | 65 | 1000 | 93 | 1375 | 128 |
| Multiple Attachment* | 450 | 41 | 575 | 53 | 600 | 56 | 700 | 65 | 950 | 88 | 1300 | 121 | 1525 | 142 |
* - Assumes two or more shackles share load on both boom and deck
Running Backstays
| Breaking strength of runner | ||||||||||||||||
| 3" Stainless steel runners | 4" Stainless Black Magic® | 5" Stainless Black Magic® | 57 mm High-load Black Magic® | 75 mm Black Magic® | 100 mm Black Magic® | 125 mm Black Magic® | 150 mm Black Magic® | |||||||||
| Ib | kg | Ib | kg | Ib | kg | Ib | kg | Ib | kg | Ib | kg | Ib | kg | Ib | kg | |
| Flying Blocks | 10000 | 4535 | 12500 | 5670 | 19000 | 8618 | 2500 | 1134 | 10000 | 4535 | 15000 | 6800 | 22000 | 10000 | 30000 | 13605 |
| 2:1 Separate Deck Blocks | 12100 | 5490 | 15250 | 6920 | 23150 | 10500 | 3025 | 1372 | 12100 | 5490 | 17550 | 7960 | 26500 | 12020 | 36136 | 16388 |
| 2:1 Becket Deck Blocks | 7500 | 3400 | 9470 | 4295 | 16500 | 7485 | 1875 | 850 | 7500 | 3400 | 10900 | 4945 | 16500 | 7485 | 22500 | 10204 |
| 3:1 Deck Blocks (Block #1) | 14850 | 6735 | 18750 | 8505 | 28500 | 12928 | 3713 | 1684 | 14850 | 6735 | 21600 | 9800 | 32700 | 14835 | 44550 | 20203 |
| 3:1 Deck Blocks (Block #2) | 18100 | 8210 | 22875 | 10375 | 34750 | 15760 | 4525 | 2052 | 18100 | 8210 | 26300 | 11930 | 39850 | 18075 | 54300 | 24625 |
Mastbase Lead Blocks
| 57 mm Low-load Black Magic® | 57 mm High-load Black Magic® & fixed MBL* blocks | 75 mm Low-load Black Magic® & Mastcollar post block/ 75 mm ESP | 75 mm High-load Black Magic® & fixed MBL* blocks/ 75 mm Stainless | 100 mm Black Magic®/ 100 mm Stainless | 125 mm Black Magic® | |||||||
| ft | m | ft | m | ft | m | ft | m | ft | m | ft | m | |
| Maximum "P" Dimension | ||||||||||||
| Main Halyard | 47 | 14.3 | 52 | 15.8 | 60 | 18.3 | 74 | 22.6 | 80 | 25 | 90 | 27.5 |
| Maximum "I" Dimension | ||||||||||||
| Genoa Halyard | 45 | 13.7 | 50 | 15.2 | 58 | 17.7 | 72 | 21.9 | 76 | 23.2 | 87 | 26.5 |
| Spinnaker Halyard | 47 | 14.3 | 53 | 16.1 | 60 | 18.3 | 74 | 22.6 | 82 | 25 | 93 | 28.4 |
* - MBL = Mastbase Lead blocks
Spinnaker
Symmetrical/Asymmetrical| Maximum spinnaker area | ||||||||||||||
| 57 mm Low-load Black Magic® | 57 mm High-load Black Magic® | 75 mm Low-load Black Magic®/ 75 mm ESP | 75 mm High-load Black Magic®/ 75 mm Stainless | 100 mm Black Magic®/ 100 mm Stainless | 125mm Black Magic® | 150 mm Black Magic®/ 150 mm Stainless | ||||||||
| ft2 | m2 | ft2 | m2 | ft2 | m2 | ft2 | m2 | ft2 | m2 | ft2 | m2 | ft2 | m2 | |
| Spinnaker Sheet, Tack Line | 720 | 67 | 1200 | 111 | 1400 | 130 | 2000 | 186 | 2650 | 246 | 4300 | 400 | 5600 | 520 |
| Afterguy* | 790 | 73 | 1320 | 123 | 1500 | 140 | 2200 | 204 | 2900 | 269 | 4700 | 437 | 6100 | 567 |
* - Assumes maximum deflection of 45° to winch
Genoa
Adjustable Lead Car| Maximum sail area | |||||||||||
| Small Boat | Midrange | Big Boat | Mini-Maxi | ||||||||
| 3000 | 4500 | ||||||||||
| ft2 | m2 | ft2 | m2 | ft2 | m2 | ft2 | m2 | ft2 | m2 | ||
| #1 & #2 Genoa | 450 | 41 | 750 | 70 | 1500 | 139 | 2700 | 251 | 4400 | 409 | Assumes 155% Genoa/25 knots apparent wind/45° sheet lead angle |
| #3 Genoa | 175 | 16 | 330 | 31 | 435 | 40 | 650 | 60 | 1300 | 121 | Assumes 100% Genoa/40 knots apparent wind/60° sheet lead angle |
| Maximum 100% foretriangle sail area at 40 knots | ||||||||||||
| 57 mm Low-load Black Magic® | 57 mm High-load Black Magic® | 75 mm Black Magic®/ 75 mm Stainless | 100 mm Black Magic®/ 100 mm Stainless | 125 mm Black Magic® | 150 mm Black Magic®/ 150 mm Stainles | |||||||
| ft2 | m2 | ft2 | m2 | ft2 | m2 | ft2 | m2 | ft2 | m2 | ft2 | m2 | |
| 180° Turn | 110 | 10 | 180 | 17 | 365 | 34 | 540 | 50 | 800 | 74 | 1100 | 102 |
| 120° Turn | 125 | 12 | 210 | 20 | 420 | 39 | 630 | 59 | 920 | 85 | 1256 | 117 |
| 90° Turn | 155 | 14 | 260 | 24 | 515 | 48 | 770 | 72 | 1130 | 105 | 1540 | 143 |
| Maximum 100% foretriangle sail area at 40 knots* | ||||||||||
| 57 mm Low-load Black Magic® | 57 mm High-load Black Magic® | 75 mm Black Magic® | 100 mm Black Magic® | 125 mm Black Magic® | ||||||
| ft2 | m2 | ft2 | m2 | ft2 | m2 | ft2 | m2 | ft2 | m2 | |
| 180° Turn | 75 | 7 | 120 | 11 | 240 | 22 | 360 | 33 | 530 | 49 |
| 120° Turn | 85 | 8 | 140 | 13 | 275 | 26 | 415 | 39 | 610 | 57 |
| 90° Turn | 105 | 10 | 175 | 16 | 340 | 32 | 510 | 47 | 750 | 70 |
* - Based on load on upper sheave
Index | Use chart | 57 mm | 75 mm | 100 mm | 125 mm & 150 mm | Teardrop | Crossover | Mastbase Halyard Lead & Flip-Flop | Footblocks | AirRunners | Stainless Steel Runners | Opening Foot Blocks | Snatch | ESP Blocks | Stainless Steel ESP | Stainless Steel Blocks | Specifications