Ordering Big Boat Blocks

5/5/2012

Big Boat Chart
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, ESP, 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* )

 
57 mm low-load
Black Magic
57 mm high-load
Black Magic
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 

 
End-boom single attachment
450415505160056750709008412501161550144

 
End-boom multiple attachment* **
50046675637206790084110010215001391750163

 
Mid-boom single attachment
40037400374504255051700651000931375128

 
Mid-boom Multiple Attachment*
450415755360056700659508813001211525142

 
*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 Runner75 mm
Black Magic Air Runner
100 mm
Black Magic Air Runner
125 mm
Black Magic Air Runner
150 mm
Black Magic Air Runner
lbkglbkglbkglbkglbkg

 
Flying blocks
2500113410000453515000680022000100003000013605

 
2:1 Separate deck blocks
3025137212100549017550796026500120203613616388

 
2:1 Becket deck blocks
1875850750034001090049451650074852250010204

 
3:1 Deck blocks (block #1)
371316841485067352160098003270014835445502023

 
3:1 Deck blocks (block #2)
45252052181008210263001193039850180755430024625

 

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, ESP, and mastbase blocks for different foretriangle heights and luff lengths. See Mastbase and Cabintop Blocks for common configurations.
 

 
57 mm low-load
Black Magic
57 mm high-load
Black Magic &
fixed MBL* blocks
75 mm low-load
Black Magic &
mast collar post block/
75 mm ESP
75 mm high-load
Black Magic &
fixed MBL* blocks/
75 mm stainless
100 mm
Black Magic/
100 mm stainless
125 mm
Black Magic
ftmftmftmftmftmftm

 
Main halyard - Maximum "P" dimension
4714.35215.86018.37422.680259027.5

 
Genoa halyard - Maximum "I" dimension
4513.75015.25817.77221.97623.28726.5

 
Spinnaker halyard - Maximum "I" dimension
4714.35316.16018.37422.682259328.4

 
*MBL = Mastbase lead blocks

Spinnaker - Symmetrical/Asymmetrical
Use the spinnaker's sail area to determine what size Black Magic, stainless steel, or ESP blocks to use for the sheet and afterguy controls. Spinnaker Systems for common configurations.
 

 
Maximum mainsail area

 
57 mm low-load
Black Magic
57 mm high-load
Black Magic
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
72067120011114001302000186265024643004005600520

 
Afterguy*
79073132012315001402200204290026947004376100567

 
*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

 
57 mm low-load
Black Magic
57 mm high-load
Black Magic
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
11010180173653454050800741100102

 
120° turn
12512210204203963059920851256117

 
90° turn
1551426024515487707211301051540143

 

Double Genoa Foot Blocks

 
Maximum 100% foretriangle sail area at 40 knots*

 
57 mm low-load
Black Magic
57 mm high-load
Black Magic
75 mm
Black Magic
100 mm
Black Magic
125 mm
Black Magic
ft² m² ft² m² ft² m² ft² m² ft² m² 

 
180° turn
75712011240223603353049

 
120° turn
85814013275264153961057

 
90° turn
1051017516340325104775070

 
*Based on load on upper sheave
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