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Ordering Midrange Blocks

1. Determine block size and type

The tables below are guidelines for typical applications.

2. Contact

If you have any questions, please contact your dealer or Harken Technical Service.

Note: Multihulls and heavy displacement monohulls should reduce the maximum sail areas shown by as much as 25%.


The farther forward a mainsheet system is on the boom, the higher the loads. Systems with multiple attachment points spread the load over the boom. Use the table below to determine if Midrange blocks are strong enough for you mainsail area.

Maximum mainsail area
(P x E x .5 x 1.1*)
    ft²  m² 
End-boom system Single attachment 500 46
Multiple attachment** 540 50
Mid-boom system Single attachment 425 39
Multiple attachment** 500 46

*Assumes 10% roach.
**Assumes two or more shackles share load on both boom and deck.

Genoa Footblocks

Determine the area of your foretriangle and how many degrees the footblock will deflect the line to select footblock size. For system loading details, see the Block Loading vs. Angle of Deflection and Genoa System Loading sections.

Maximum 100% foretriangle sail area at 35 knots
(I x J x .5)
Turning blocks
180° turn
150 14
Turning blocks
90° turn
215 20

Spinnaker Blocks: Symmetrical/Asymmetrical

Use the spinnaker's sail area to determine what size Midrange or high-load Midrange blocks to use for the sheet and afterguy controls.

    Maximum spinnaker area
P x E x .5 x 1.8
    Standard High-load
    ft2 m2 ft2 m2
1100 100 1300 120
Ratchet 900 83 - -
Mounted amidships 1100 100 1250 115
Mounted on transom 900 83 1000 93

Maximum "I" dimension
Masthead halyard
  48 ft 14.6 m 53 ft 16 m

*Assumes maximum deflection of 45°

Mastbase Lead Blocks

Attach blocks to padeyes or 1634 Midrange ESP stand-up bases, or mount mastbase halyard leads to the deck. Use mainsail luff length and foretriangle height to determine what size Midrange or high-load Midrange blocks to use. Carbo blocks or 1986 mastbase halyard leads may be used for applications with lower loads.

  Maximum "P" dimension
  Standard High-load
  ft m ft m
Main halyard lead
48 14.6 52 15.8
  Maximum "I" dimension
Genoa halyard lead
46 14 50 15.3
  Maximum "I" dimension
Spinnaker halyard lead
48 14.6 53 16

Running Backstays

The table below shows whether Midrange of high-load Midrange blocks are strong enough for your backstay, based on the breaking strength of your runner wire.

Maximum breaking load of runner wire
  Standard High-load
2:1 flying blocks lb kg lb kg
1:1 afterguy deck 2200 998 2800 1270
2:1 afterguy becket deck 3600 1633 3600 1633
2:1 afterguy single deck 4500 2040 5000 2268


Maximum mainsail area P x E x .5 x 1.1*    
    ft2 m2
  400 37
  450 42

*Assumes 10% roach

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Valid on orders shipping within the United States