In our previous blog, we explained what we meant by the term “structural furling forestay”. In this article we look at when to use traditional wire vs a composite cable as the torsional stay.
Structural forestay furling systems using a normal wire stay are available on the market for boat lengths of up to approx. 10-11 m and a maximum of 7 mm wire diameter. If you look closely at the way a wire cable is made, it is wound in a spiral which lends itself quite nicely to handle torsional furling loads.
It should be noted that wires must be furled in one direction only. This is no different to composite cables, which rely on off-axis braid fibre alignment for their torsional strength / stiffness. For optimum performance any furling stay (wire or composite) should only be furled in a single direction.
At the upper 7 mm wire limit, a Dyform wire construction is preferable as this has a much more robust construction with fewer individual wire strands which are prone to break, resulting in potential tear hazards on standard 1x19 wire.
(N.B. we have supplied 8mm Dyform structural furling forestays but halyard swivels are not available at this size) which means the genoa is permanently lashed at the head
Above 11 m boat length and 7 mm wire diameter most manufacturers recommend a switch to a composite torsional cable as the structural furling forestay.
Re-use existing forestay
Cost
Halyard swivel
Windage
Benefits of composite structural forestays
Weight
Wear
Strength
Custom torsional stiffness / strength
Conclusion
Wire structural furling forestays are common on dinghy’s / sports boats and there are many, simple, lightweight and competitively priced systems available on the market for 3-5mm diameter wire.
5-7mm diameter wire sees a transition to keelboats from approx. 23ft – 34ft where all the specialist furling manufacturers offer wire furling forestay solutions.
8mm wire is the transition. It is still feasible to operate a wire furling forestay but this is the point most manufacturers recommend a transition to composite forestays
If you have a 10mm diameter wire forestay or bigger (38-40ft+ boat), then you will require a composite torsional cable to handle the torsional loads required.
Q: Could you use a composite forestay on a 27ft boat with a 6mm forestay?
A: You could but it is generally cost prohibitive. The cost of a custom torsional cable (at this size) normally doubles the cost of the package!
If you would like to know more about structural furling forestays – download our guide or if you have an enquiry contact us here.