Straight luff furling is ideal for use with Code Zeros, Reachers and Gennakers, because they have more shape than a genoa but not so much that they can't be furled around a luff rope. They require an anti-torsion line to be sewn into a pocket on the luff of the sail.
When furling commences, the tack and head of the sail rotate at the same time to neatly bring the sail in. Once furled, the sail, complete with torsion rope can then be easily stowed and replaced making for easy sail changes.
Straight Luff Furlers also known as Bottom-up Furlers are Continuous Line Furling Systems that have have developed to make reaching sails such as the Code Zero much easier to handle. Although relatively deep and lightweight compared with a genoa, a certain degree of luff tension is still required to enable pointing, hence the term straight luff furler.
The torsional cable is enclosed in a pocket which runs up the luff of the sail.
The Tack is lashed to the bottom thimble eye in the torsional cable.
The Head is also lashed to the thimble eye of the torsional cable at the head.
The sail is stowed with the cable threaded through the luff pocket and firmly furled
Straight Luff Furler Deployment:
Attach the bottom thimble eye to the fork on the top of the drum and fix the top thimble eye to the fork on the swivel at the head
Hoist the complete system as a tightly furled unit and tighten the luff by hauling on the halyard to achieve the required tension
Spin the wheel to unfurl by pulling on the appropriate part of the continuous furling line
Spinning the wheel in the opposite direction by pulling on the other part of the continuous furling line results in the bottom of the sail wrapping around the torsional cable first and then the roll gradually rises up the luff – Hence the term bottom up
Bottom-up Furling Basics:
Straight luff reaching sails
Torsional cable runs through a luff pocket sewn into the sail
Head and Tack attached to either end of the torsional cable
Furling begins at the tack and works its way up the luff to the head
Straight Luff Furling (Bottom Up) Cables - Key Performance Factors
High Working Load Capability to achieve the required luff tension.
Cable stiffness
Minimum diameter to reduce upwind drag
Good Initial Anti Torsional Performance – after a few turns the increased diameter of the rolled sail will help to transfer the torque up the cable and adds to the effective torsion of the system with each successive roll.
PBO is generally regarded as the optimum core material for bottom-up furling cables
PBO is the stiffest, lightest and smallest diameter soft composite fibre available on the market
Zylon® PBO: Facts and Figures
- Developed in the 1980s
- The world’s strongest synthetic fibre
- The first organic fibre with cross-sectional strength superior to both steel and carbon fibre
- Excellent strength and modulus
- Good flame resistance
- Excellent thermal stability
- Excellent creep resistance
- Good chemical resistance
- Composition: rigid-rod isotropic crystal polymer, spun by a dry-jet wet spinning process
The Jimmy Green Rigging Team can guide you through a choice of systems from top manufacturers in the field - Profurl, Karver, Selden and Harken
