Sailcloth comparisons: how we see it

Here's an e-mail exchange with a curious customer.

Win,

Thank you for the revised quote on the sail for my boat.  I have a few quick questions trying to compare things.  What are the differences between Dimension Polyant 280 AP  6.5 oz Dacron and 7.7 oz. Challange Marblehead Dacron for a crosscut dacron sail?  What are the differences Dimension 310s Seatec square Dacron and Dimension Polyant TriRadial 6.5 oz Dacron in a TriRadial and finally what are the differences between Dimension Polyant CX7T Laminate, 8.1 oz Dimension Flex C 16 polyester laminate w/taffeta and North's Norlam for a laminate crosscut sail?

Sorry for all the questions, just trying to get a better understanding of the various sail cloths and the pro's and con's of each fabric and the various sail configurations.

Thank you for your help.  

M---

Hi M---

Don’t apologize for asking questions about sail fabrics.  A quality fabric is the key to the performance and durability of your sail, after all.

First of all, both Dimension Polyant and Challenge Sailcloth make high quality fabrics – meaning they are well engineered, and tightly woven, from high modulus yarns.

 The DP 280 AP 6.5 oz. is a 250 denier (warp direction) by 440 denier (fill directions) weave that weighs about 6.5 oz. per sailmakers yard (36” by 28.5”).  The Challenge 7.77 is a 300 x 440 weave weighing approximately 7.5 oz per sailmakers yard.  In a cross cut layout the fill yarn is aligned with the leech.  In a high aspect sail, like a mainsail or blade jib, the loads are concentrated along the leech so the fill yarns are doing most of the work.  In a lower aspect sail like a genoa the loads are more spread out, so a more balanced weave like the Challenge product helps the weave structure handle off thread line loads.  That said, the DP product is not as unbalanced as some weaves designed only for high aspect sails.

The DP 310s is a ripstop construction with a base weave of 250 x 250 interspersed every half inch with a pair of 1000 denier yarns in each direction weighing about 7.2 oz/smy.  The advantage of this structure is that the basic weave can be very tight (meaning the threads are heavily crimped implying some stretch in exchange for good off thread line performance) while the 1000 denier ripstop yarns can be held very straight for good thread line stretch resistance.  This is a very balanced weave and its strength in the warp direction, a rarity in woven fabrics, makes it appropriate for radial constructions, where the warp yarns are well aligned with the loads, especially in a low aspect sail where those loads are widely spread.  I am not sure just which fabric is meant by DP 6.5 oz Dacron.  The closest would be their 6.2 oz 265s.

Laminates can be more stretch resistant because their structural yarns do not need to be woven.  Instead they can be laid straight before being laminated between layers of Mylar film.  Having no crimp from weaving, they have very low initial stretch.  Moreover, the structural yarns are not limited to warp and fill directions.  Both the DP CX7T (8.4 0z/smy) and the DP Flex 16 C (8.1 oz/smy) have some off warp and fill yarns (generally referred to as x-ply).  The CX is designed to be strong in the warp direction and slightly off warp – x-ply at plus and minus 6 degrees from the warp.  This fabric is designed for triradial construction.  We used it for many years with great success.  The Flex is a newer style with x-plies at 20 and 30 degrees to the fill and is designed for crosscut construction with the x-plies providing support for the off thread line loads.  When built with this fabric, a cross cut sail behaves very much like a triradial sail.  Flex, by the way, is an acronym for Fill Laminate Extra X.  The main advantages of crosscut  Flex sails as opposed to triradial CX sails are that the cloth utilization is more efficient and that the shaping is all confined to seams perpendicular to the principal loads in the sail.   Better cloth utilization means that although Flex costs more than CX the sails are less expensive.  Cross load shaping means the sails are generally smoother than the triradial sails.  That said, the CX sails may have slightly better initial stretch resistance, but our testing shows better long term performance from the Flex sails.

I am afraid I can’t give you any information on the Norlam crosscut  laminate.  In the past, their warp oriented laminates have not included any unwoven yarns but relied solely on the external taffeta for stretch resistance (with no off thread line support beyond the film). 

The only negatives to laminates in general are weight and mildew.  At least for boats in your size range, the structure of cruising laminates, two layers of film, two layers of taffeta, and the base structural yarn framework, plus laminating adhesive, add up to extra weight, not all of which adds to performance.  Cruising laminates can on rare occasions become seriously contaminated with molds or mildew.  Because of the laminate structure, these contaminates can be difficult to remove completely.  Although they have no structural effect on the sail, they can be unsightly.

I hope this answers you questions.  Please don’t hesitate to call if my answers above have left you more confused.

Best,

Win