Ordering Big Boat Blocks

By Product Categories

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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Ordering Big Boat Blocks

1. Determine block size and type

2. Contact

Mainsheet

Running Backstays

Mastbase Lead Blocks

Spinnaker - Symmetrical/Asymmetrical

Genoa Foot Blocks

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