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 systemSingle attachment50046

Multiple attachment**54050

Mid-boom systemSingle attachment42539

Multiple attachment**50046

*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.

Turning blocks
Maximum 100% foretriangle sail area at 35 knots
(I x J x .5)

180° turn

Turning blocks

90° turn


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



Mounted amidships11001001250115

Mounted on transom90083100093

Maximum "I" dimension


Masthead halyard
 48 ft14.6 m53 ft16 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


Main halyard lead


 Maximum "I" dimension


Genoa halyard lead


 Maximum "I" dimension


Spinnaker halyard lead


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
2:1 flying blockslbkglbkg
1:1 afterguy deck220099828001270
2:1 afterguy becket deck3600163336001633
2:1 afterguy single deck4500204050002268

Common vang configurations

  Maximum mainsail area P x E x .5 x 1.1*



*Assumes 10% roach

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