5/5/2012
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%.
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| 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. |
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| | | Maximum mainsail area
(P x E x .5 x 1.1*) |
| | | ft² | m² |
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| End-boom system | Single attachment | 500 | 46 |
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| Multiple attachment** | 540 | 50 |
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| Mid-boom system | Single attachment | 425 | 39 |
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| Multiple attachment** | 500 | 46 |
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*Assumes 10% roach.
**Assumes two or more shackles share load on both boom and deck.
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|
| 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. |
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|
Turning blocks | | Maximum 100% foretriangle sail area at 35 knots
(I x J x .5) |
|
180° turn | 150 | 14 |
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Turning blocks | | |
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90° turn | 215 | 20 |
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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
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| | | Standard | High-load |
| | | ft2 | m2 | ft2 | m2 |
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Sheet | Plain | 1100 | 100 | 1300 | 120 |
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| Ratchet | 900 | 83 | - | - |
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Afterguy* | Mounted amidships | 1100 | 100 | 1250 | 115 |
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| Mounted on transom | 900 | 83 | 1000 | 93 |
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Maximum "I" dimension
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| | | |
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Masthead halyard | | 48 ft | 14.6 m | 53 ft | 16 m |
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*Assumes maximum deflection of 45° |
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| 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. |
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| |  | Maximum "P" dimension |
| | Standard | High-load |
| | ft | m | ft | m |
|
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Main halyard lead | 48 | 14.6 | 52 | 15.8 |
|
|
| | Maximum "I" dimension |
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Genoa halyard lead | 46 | 14 | 50 | 15.3 |
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|
| | Maximum "I" dimension |
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Spinnaker halyard lead | 48 | 14.6 | 53 | 16 |
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|
| 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 |
| | | lb | kg | lb | kg |
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Flying block | 2:1 | 3600 | 1633 | 4600 | 2086 |
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Afterguy | 1:1 | 2200 | 998 | 2800 | 1270 |
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| 2:1 Becket | 3600 | 1633 | 3600 | 1633 |
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| 2:1 Single | 4500 | 2040 | 5000 | 2268 |
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