Blocks with soft attachments are seen more and more frequently on dinghies and sailboats. Here is a short blog post about the pros and cons and some tips to keep in mind. When used correctly, blocks with soft attachments are a very useful piece of equipment for your sailing and boating.
What is the difference between a traditional block and a block with a soft attachment?
The main difference between a traditional block and a block with a soft attachment is that the connection point on the block passes directly through the center of the sheave. In a traditional block, the side plates transfer the load from the sheave to the block head and then to the attachment point.
This fundamentally reduces the risk of blocks with soft attachments breaking because:
- There are fewer parts involved.
- Even if the sheave were to break, the attachment point will still hold the line.
Pros and cons of soft attachments:
Pros:
- Lightweight, strong, and safe
- Resistant to abrasion
- Corrosion-free
- Self-adjusting to the load, which reduces fatigue on the block and the loaded line
- Gentle on the mast, deck, and sails, with less noise
- Low maintenance cost
On the minus side:
- The strength of the attachment line is dependent on it being correctly installed
- It has some room to twist if the pull on the line is not perfectly aligned with the block. There is a risk, if the twisting is too great, that the attachment lines may chafe against each other. A block with a swivel should be considered if the twisting is excessive
- The knot on the attachment line represents a weak point
The knot is the weak link!
The knot is always the weakest link in a line attachment. It often breaks at about half the breaking strength of the line. For blocks with soft attachments, you should therefore choose a line that has twice the breaking strength of the block. Divide the breaking strength of the block by the number of loops and then double this number to account for the strength loss from the knot.
Choosing the right knot is important. Here are links to two good alternatives:
- Carrick Bend
- Double Fisherman's Bend