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Support / Selection tools / How to choose

Ordering Big Boat Blocks

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 | Phone: 262-691-3320 | 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.

Maximum mainsail area (P x E x .5 x 1.1**)
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 
End-boom single attachment
450 41 550 51 600 56 750 70 900 84 1250 116 1550 144
End-boom 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
Mid-boom Multiple Attachment**
450 41 575 53 600 56 700 65 950 88 1300 121 1525 142

*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.

Maximum breaking load of runner wire
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
Flying blocks
2500 1134 10000 4535 15000 6800 22000 10000 30000 13605
2:1 Separate deck blocks
3025 1372 12100 5490 17550 7960 26500 12020 36136 16388
2:1 Becket deck blocks
1875 850 7500 3400 10900 4945 16500 7485 22500 10204
3:1 Deck blocks (block #1)
3713 1684 14850 6735 21600 9800 32700 14835 44550 2023
3:1 Deck blocks (block #2)
4525 2052 18100 8210 26300 11930 39850 18075 54300 24625

 

 

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.

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
Main halyard - Maximum "P" dimension
47 14.3 52 15.8 60 18.3 74 22.6 80 25 90 27.5
Genoa halyard - Maximum "I" dimension
45 13.7 50 15.2 58 17.7 72 21.9 76 23.2 87 26.5
Spinnaker halyard - Maximum "I" dimension
47 14.3 53 16.1 60 18.3 74 22.6 82 25 93 28.4

*Element blocks are appropriate for most cruising boats. For high-performance boats, choose Black Magic blocks.
**MBL = Mastbase lead blocks

 

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.

Maximum mainsail area
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 
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

*Element blocks are appropriate for most cruising boats. For high-performance boats, choose Black Magic blocks.
**Assumes maximum deflection of 45° to winch.

 

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.

Single Genoa Footblocks
Maximum 100% foretriangle sail area at 40 knots
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 
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

*Element blocks are appropriate for most cruising boats. For high-performance boats, choose Black Magic blocks.


Double Genoa Foot Blocks
Maximum 100% foretriangle sail area at 40 knots*
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 
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
**Element blocks are appropriate for most cruising boats. For high-performance boats, choose Black Magic blocks.

 

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