5/5/2012

1. Determine block size and type
The tables below are a guideline for typical applications.
2. Contact
If you have any questions, please contact your dealer or Harken Technical Service.
Note: These hardware specifications assume a boat of moderate displacement sailing in normal conditions. Ultra Light Displacement Boats may use smaller hardware. Heavy displacement boats and multihulls often require stronger hardware.
Technical Service:
Email: Harken Technical Service
262-691-3320 phone 7:30-4:30 CST
Mainsheet |
Mainsheets are usually attached near the end or the middle of the boom, depending on accessibility and whether the boat is used for racing or cruising. The farther forward a mainsheet system is on the boom, the higher the loads it sees. Systems with multiple attachment points spread the load over the boom. Use the table to choose the appropriate Black Magic, Element, or stainless steel blocks for your mainsail area. See Mainsheet Systems for common configurations.
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Maximum mainsail area (P x E x .5 x 1.1**) |
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45 mm Element*,
57 mm low-load
Black Magic | 60 mm Element*,
57 mm high-load
Black Magic | 75 mm low-load
Black Magic/
75 mm ESP | 80 mm Element*,
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 |
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End-boom single attachment |
450 | 41 | 550 | 51 | 600 | 56 | 750 | 70 | 900 | 84 | 1250 | 116 | 1550 | 144 |
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End-boom multiple attachment* ‡ |
500 | 46 | 675 | 63 | 720 | 67 | 900 | 84 | 1100 | 102 | 1500 | 139 | 1750 | 163 |
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Mid-boom single attachment |
400 | 37 | 400 | 37 | 450 | 42 | 550 | 51 | 700 | 65 | 1000 | 93 | 1375 | 128 |
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Mid-boom Multiple Attachment** |
450 | 41 | 575 | 53 | 600 | 56 | 700 | 65 | 950 | 88 | 1300 | 121 | 1525 | 142 |
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*Element blocks are appropriate for most cruising boats. For high-performance boats, choose Black Magic blocks
**Assumes 10% roach. ‡ Assumes two or more shackles share load on both boom and deck. |
Running Backstays |
Crews use running backstays to adjust mast bend for different wind conditions. This controls headsail sag as well as the camber (depth) of the mainsail. Use Black Magic runner blocks with higher breaking strengths than your runner wire. |
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Maximum breaking load of runner wire |
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57 mm Black Magic Air Runner | 75 mm
Black Magic Air Runner | 100 mm
Black Magic Air Runner | 125 mm
Black Magic Air Runner | 150 mm
Black Magic Air Runner |
lb | kg | lb | kg | lb | kg | lb | kg | lb | kg |
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Flying blocks |
2500 | 1134 | 10000 | 4535 | 15000 | 6800 | 22000 | 10000 | 30000 | 13605 |
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2:1 Separate deck blocks |
3025 | 1372 | 12100 | 5490 | 17550 | 7960 | 26500 | 12020 | 36136 | 16388 |
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2:1 Becket deck blocks |
1875 | 850 | 7500 | 3400 | 10900 | 4945 | 16500 | 7485 | 22500 | 10204 |
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3:1 Deck blocks (block #1) |
3713 | 1684 | 14850 | 6735 | 21600 | 9800 | 32700 | 14835 | 44550 | 2023 |
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3:1 Deck blocks (block #2) |
4525 | 2052 | 18100 | 8210 | 26300 | 11930 | 39850 | 18075 | 54300 | 24625 |
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Mastbase Lead Blocks |
Leading halyards and control lines aft allows crews to raise and lower sails or make tuning adjustments from the cockpit. Attach blocks to the mast collar post or padeyes, or mount mastbase halyard leads to the deck. The table below sizes Black Magic, stainless steel, Element, ESP, and mastbase blocks for different foretriangle heights and luff lengths. See Mastbase and Cabintop Blocks for common configurations. |
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45 mm Element*,
57 mm low-load
Black Magic | 60 mm Element*,
57 mm high-load
Black Magic &
fixed MBL** blocks | 75 mm low-load
Black Magic &
mast collar post block/
75 mm ESP | 80 mm Element*,
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 |
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Main halyard - Maximum "P" dimension |
47 | 14.3 | 52 | 15.8 | 60 | 18.3 | 74 | 22.6 | 80 | 25 | 90 | 27.5 |
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Genoa halyard - Maximum "I" dimension |
45 | 13.7 | 50 | 15.2 | 58 | 17.7 | 72 | 21.9 | 76 | 23.2 | 87 | 26.5 |
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Spinnaker halyard - Maximum "I" dimension |
47 | 14.3 | 53 | 16.1 | 60 | 18.3 | 74 | 22.6 | 82 | 25 | 93 | 28.4 |
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*Element blocks are appropriate for most cruising boats. For high-performance boats, choose Black Magic blocks.
**MBL = Mastbase lead blocks |
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Spinnaker - Symmetrical/Asymmetrical |
Use the spinnaker's sail area to determine what size Black Magic, stainless steel, or Element blocks to use for the sheet and afterguy controls. Spinnaker Systems for common configurations. |
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Maximum mainsail area |
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45 mm Element*,
57 mm low-load
Black Magic | 60 mm Element*,
57 mm high-load
Black Magic | 80 mm Element*,
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 |
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Spinnaker sheet, tack line |
720 | 67 | 1200 | 111 | 1400 | 130 | 2000 | 186 | 2650 | 246 | 4300 | 400 | 5600 | 520 |
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Afterguy** |
790 | 73 | 1320 | 123 | 1500 | 140 | 2200 | 204 | 2900 | 269 | 4700 | 437 | 6100 | 567 |
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*Element blocks are appropriate for most cruising boats. For high-performance boats, choose Black Magic blocks.
**Assumes maximum deflection of 45° to winch |
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Genoa Foot Blocks |
Footblocks route genoa controls from the lead car to a winch. Double footblocks or snatch blocks enable faster sheet changes. Determine the area of your foretriangle and how many degrees the footblock will deflect the line to select footblock size. For system loading details, refer to Block Loading vs Angle of Deflection and Genoa System Loading. See Genoa Lead Car Systems for common configurations.
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Single Genoa Footblocks |
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Maximum 100% foretriangle sail area at 40 knots |
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45 mm Element*,
57 mm low-load
Black Magic | 60 mm Element*,
57 mm high-load
Black Magic | 80 mm Element*,
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 |
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180° turn |
110 | 10 | 180 | 17 | 365 | 34 | 540 | 50 | 800 | 74 | 1100 | 102 |
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120° turn |
125 | 12 | 210 | 20 | 420 | 39 | 630 | 59 | 920 | 85 | 1256 | 117 |
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90° turn |
155 | 14 | 260 | 24 | 515 | 48 | 770 | 72 | 1130 | 105 | 1540 | 143 |
*Element blocks are appropriate for most cruising boats. For high-performance boats, choose Black Magic blocks.
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Double Genoa Foot Blocks |
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Maximum 100% foretriangle sail area at 40 knots* |
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57 mm low-load
Black Magic | 60 mm Element**,
57 mm high-load
Black Magic | 80 mm Element**,
75 mm
Black Magic | 100 mm
Black Magic | 125 mm
Black Magic |
ft² | m² | ft² | m² | ft² | m² | ft² | m² | ft² | m² |
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180° turn |
75 | 7 | 120 | 11 | 240 | 22 | 360 | 33 | 530 | 49 |
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120° turn |
85 | 8 | 140 | 13 | 275 | 26 | 415 | 39 | 610 | 57 |
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90° turn |
105 | 10 | 175 | 16 | 340 | 32 | 510 | 47 | 750 | 70 |
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*Based on load on upper sheave
**Element blocks are appropriate for most cruising boats. For high-performance boats, choose Black Magic blocks. |
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