The Ronstan shock block takes its name from “SHeaveless blOCK” and reflects a growing trend in modern sailing systems: replacing traditional ball-bearing blocks with low-friction rings or sheaveless blocks.
By removing moving parts entirely, a shock block offers a lightweight, compact, and highly durable alternative for many control-line applications. These blocks are particularly suited to small purchase systems and line deflection setups, where simplicity, strength, and low weight are more important than rolling efficiency.
With no bearings, no sheave, and no internal components, shock blocks provide a maintenance-free solution that can be easily integrated into many sailing systems.
What Is a Shock Block?
A shock block is a sheaveless block designed to guide or redirect a line without the use of traditional bearings or rotating parts.
Instead of a rotating sheave, the line runs across a smooth, anodised aluminium surface that distributes load efficiently while keeping friction low enough for many applications.
This design approach offers several advantages:
- Lower weight than conventional blocks
- No moving parts, eliminating bearing wear and maintenance
- High strength relative to size
- Very compact geometry
For many modern sailing systems — especially those using Dyneema® control lines — a shock block provides a simple and robust solution.
Ronstan Shock Block Design
The Ronstan shock block is manufactured from anodised aluminium and is designed specifically for soft attachment methods, which are increasingly common in high-performance rigging.
Typical attachment methods include:
- Spliced directly onto a line
- Dyneema lashings
- Webbing strops
The elongated attachment aperture ensures that the block naturally aligns with the direction of load. This helps reduce side-loading and improves efficiency in dynamic systems.
Ronstan has also designed the block with a smooth 3-dimensional geometry, allowing the running line to move smoothly across the surface while remaining tolerant of lead-angle variations.
Ronstan Shock Block Sizes
Ronstan shock blocks are available in two sizes, covering a range of common control-line diameters.
|
|
Line Min (mm) |
Line Max (mm) |
Height (mm) |
Width (mm) |
Length (mm) |
BL (kg) |
Weight (g) |
|
Shock 5mm |
1.5 |
5.0 |
8.5 |
14.9 |
22.9 |
350 |
2.5 |
|
Shock 10mm |
3.0 |
10.0 |
14.5 |
24.8 |
36.0 |
1000 |
12 |
The blocks are colour coded (Blue, Red, and Grey), making it easy to identify sizes within a rigging system.
Shock Block Key Benefits
A shock block offers several practical advantages for modern sailboats:
- Lightweight construction
- Compact design
- High strength-to-weight ratio
- No moving parts – maintenance free
- Impact resistant aluminium body
- Colour coded sizes
- Designed for soft attachment
- Cost-effective alternative to traditional blocks
These characteristics make shock blocks particularly attractive for dinghies, sportsboats, and lightweight performance yachts.
Typical Shock Block Applications
Shock blocks are commonly used wherever a simple line deflector or small purchase system is required.
Typical sailing applications include:
- Line deflectors
- Small purchase systems
- In-hauls and out-hauls
- Tweakers
- Lazy jacks
- Dinghy vangs
- Cunningham systems
In many cases, a shock block can replace a conventional block where low friction is sufficient but bearing efficiency is not critical.
Summary: When to Use a Shock Block
The Ronstan shock block is a good example of how thoughtful engineering can simplify sailing systems. By removing unnecessary mechanical components, these blocks provide a lightweight, durable, and maintenance-free alternative for many rigging setups.
For boats using small-diameter control lines, a handful of shock blocks combined with Dyneema® lashings and single-braid line can significantly simplify onboard systems while reducing weight and complexity.
Shock blocks are particularly useful on:
- Dinghies
- Sportsboats
- Performance cruising yachts
- Lightweight control line systems
If you have questions about deck hardware or rigging systems, feel free to contact us and talk to one of our sailing experts or click below and explore our full range of low friction rings and soft-attachment blocks for modern sailing systems:
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Ronstan SHOCK Blocks - Simple Efficient Low Friction Rings