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Alex Samano
November 6, 2025

Ultimate Guide to Perf. Cunningham ILCA Systems

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Before reading this article, we strongly recommend you read our Introduction to Sailing Purchase Systems article. It will help understand how they work and how different systems affect the amount of line you will need to pull and the mechanical benefit - there is always a trade-off.

ILCA Class System Lines and Blocks Rules

The type of lines and blocks that you can use on an ILCA system are governed by PART 2 > Rule 3(a): Control Systems, Control Lines, and Fittings > Control Systems Definitions, of the ILCA Class Rules, which state the following (in PDF version):

  1. The Cunningham, outhaul, vang, traveller, and mainsheet are the Control Line Systems. The Cunningham, Outhaul, and Vang Control Line Systems may include more than one Control Line as allowed in Rules 3(d)i, 3(e)i, and 3(f)
  2. Each Control Line shall be a single piece of uniform thickness and material. A line is a Control Line if any of the line moves along its axis during the adjustment of the Control Line System. A line that exclusively attaches items together is a Tie Line.

In addition, PART 2 > Rule 3(a): Control Systems, Control Lines, and Fittings > Control Lines and Fittings, states the following:

  1. Control lines shall be natural or synthetic rope.
  2. Control lines shall be of uniform thickness, but may vary in thickness for the purpose of a splice at the load-bearing attachment point.
  3. iii. In a control line system where more than one control line is permitted, lines of different diameters shall not be joined together.
  4. iv. “Optional” blocks allowed in Cunningham, Vang, or Outhaul control systems shall have sheaves of diameter not less than 15 mm and not more than 30 mm. Thimbles allowed to reinforce rope loops used as “Turning Points” in the Cunningham, Van,g and Outhaul control line systems shall not exceed 40mm in length.
  5. v. Only single or double “Optional” blocks shall be used. A single block means a block with one sheave; a double block means a block with two sheaves. “Optional” blocks may include a becket, a swivel, and/or a shackle.

ILCA Class Cunningham Rules

The ILCA class rules on the Cunningham system are found in ILCA CLASS Rules> PART 2, Rule 3(e), Section 3: Control System Definitions > Subsection (i) "Cunningham" of the ILCA Class. Here is a summary of the Cunningham requirements.

  1. The Cunningham system shall consist of a maximum of three control lines, “Optional” blocks or loops for purchase with a maximum of 5 “Turning Points”.
  2. The Cunningham control line shall be securely attached to any of the mast, gooseneck, mast tang, swivel or shackle that may be used to attach the vang cleat block to the mast tang, the Cunningham attachment point on the “Builder Supplied” vang cleating fitting, or the becket of an optional becket block fixed on the Cunningham attachment point on the “Builder Supplied” vang.
  3. The Cunningham control line shall pass through the sail tack cringle (sail grommet) as a moving line.
  4. The sail tack cringle (sail grommet) shall be at least one of the maximum of 5 “Turning Points” permitted.
  5. Additional purchases may be obtained using rope loops, “Optional” blocks, and using any of the boom, sail tack cringle, gooseneck fitting, mast tang, shackle attaching vang cleat block, or swivel, the swivel, or the Cunningham attachment point on a “Builder Supplied” vang cleating fitting.
  6. The Cunningham control line shall pass only once through the Cunningham fairlead or “Optional” single block attached to the “Builder Supplied” deck block fitting and shall pass only once through the Cunningham clam cleat or “Optional” cam cleat attached to the “Builder Supplied” deck cleat base.

The exact purchase ratio allowed by the class rules is not explicitly stated. Class-legal Cunningham systems are commonly available in 6:1, 8:1, and 10:1 purchase ratios.

Cunningham System Lines and Blocks

To build a Cunningham System, you will need two different types of lines and two different types of blocks, depending on the system you want to build.

Downhaul Lines

The thickness and type of line depend on your preference and are usually 3, 4, or 5 mm in diameter, and 12 ft. in length. At 12 ft., it will accommodate a 4:1 to a 10:1 system. We recommend any of the following lines.

# Line Use Material Diam. Length No Notes Recommendations
1 Downhaul Control Line This is the line you will hold on your hands and run through the Cam Cleat, Deck Block, and up to the Sail Block. Dyneema Core Poly Double Braided 3 mm, 4 mm, or 5 mm 12 ft. 1 The Robline Dinghy control is softer than the PolyTech or Marlow lines. Since the line runs through blocks (no friction), there is no major impact on durability.
2 Sail Side Anchor Line This is the line that will run from the vang anchor through the sail grommet and hold the Sail Side block. Vectran or Dyneema - no stretch 5 mm 5 ft. 1 You can buy 3 ft. for systems with only one block on the sail side.
2 Tang Loop Lines These are the lines that hold or anchor blocks to the lower mast, usually on a Tang Loop. Vectran or Dyneema - no stretch 4 mm 4 ft. 1 You can buy 2 ft. for systems with only one block on the tang loop. The lower mast is 2.5” in diameter.

System Blocks

We like Harken blocks in general, but Ronstan blocks will be just fine as well. The important thing is that the blocks you choose fit the diameter of the control line you prefer. The block sizes we recommend are based on a max. 5 mm control line. If you are using a smaller line, you can use smaller blocks - always check the max. line size and load of the block. Here are the sizes we recommend.

# Block Use Options Size No Notes Recommendations
1 Primary System Blocks Main blocks of the purchase system used on the sail and mast sides. 29 mm (for up to 5mm line) 1 The smallest Harken Carbo Air block is the 29 mm. If you want to go smaller, you’ll need to switch brands.
2 Secondary System Blocks These are used as secondary (lower) blocks on multi-block setups. Cannot splice two together; must splice into a bigger block. 18 or 20 mm 1 Heads-up: 18 mm Fly or 20mm Ronstan blocks don’t have room for a 5 mm line without splicing.

Building your Cunningham System

4:1 Cunningham System

This is the most basic system. It requires a spliced Dyneema anchor line and block on the sail side, which runs through the sail’s grommet and attaches to the vang system or another anchor point on the hull. The control line is attached to the same anchor point on the vang system or haul and runs through the block and then the haul control lines block. Pre-made 4:1 systems are not usually available for purchase.

ILCA 4:1 Cunningham System

6:1 Cunningham System

To build a 6:1 system, you add a 32 block on a Dyneema ‘tang loop’, which is a piece of rope passed through the hole in the tang and then tied, spliced, or looped back onto itself. This secondary block should be the same size as your sail side block, and should be attached to the lowest section of the lower mast before you put the mast in. 

ILCA 6:1 Cunningham System

Recommended pre-made options for purchase:

8:1 System

To build an 8:1 system, you add one more smaller block to the sail side block. The additional block should preferably be smaller to keep the lines from touching. However, it should not be less than size 18 to allow you to use up to a 5 mm control line. The control line will now attach to the lower mast block.

ILCA 8:1 Cunningham System

Recommended pre-made options for purchase:

10:1 System

To build a 10:1 system, you will once again add one more smaller block, but this time it will be to the lower mast block. The additional block should be the same size as the smaller block on the top be smaller to keep the lines from touching. However, it should not be less than size 18 mm to allow you to use up to a 5 mm control line. The control line will now attach to the lower mast block.

ILCA 10:1 Cunningham System

Recommended pre-made options for purchase:

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Related Articles

  1. Introduction to Sailing Purchase Systems.
  2. Ultimate Guide to Performance ILCA Outhaul Systems

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