"Yarn is the way to go." - Yarn? This seems way too inexpensive for the typical yacht, just look around any shop handling marine
supplies - they would never carry something as cheap
Clearly what is needed here is some kind of expensive electronic gadget that needs power and can fail. Perhaps performing sail trimming using a strain gauge (aka load cell?)? One would think that a tension strain gauge could be built into a stainless steel
waterproof housing with an eye on each end. Connected to a common Bluetooth transmitter and powered by a (AAA?) battery
it could be connected to a PDA without wires getting in the way. This is more like the stuff one sees on the shelves.
In the simplest case, a flying headsail that is attached to the boat
by only three lines, it would seem that a maximum of three strain gauges would be needed (and possibly only one if it is confirmed that the total force generated by the sail is transmitted to the boat
with one third of the total force loading each line). Using the gauge, one could read the force developed by the sail directly and as one made adjustments in the trim, the effect of adjustment could be seen immediately on the readout. This would have the advantage of isolating the power developed by each sail in use and make it easier to learn the best combination of sail trim for each point of sail. Figuring out how to instrument sails
with more (cars) or continuous (furler, bolt rope) attachment points will likely be a tad trickier – but it might be easier to instrument the stays and/or the mast
until a force model is developed and needs only input from one strain gauge. One would think that much of this work
has been done in that the people who engineer
and design the sails
must have some serious idea of the loads that develop on the head
, tack, clew, and cars that attach a sail to the boat. Knowing the maximum forces gear
was designed to withstand should make it easier to accurately size the strain gauge needed. Since the area of the sail is known (usually – furlers might be tricky) and the apparent wind
speed is also typically being measured, it might be interesting to measure the instantaneous horsepower(?) being developed by each sail and collect this data for a baseline polar at various wind
conditions. Comparing the baseline with current
might provide a good measure of increased drag due to loading and/or marine
growth. One would think that racers would use this technology –but I think that it would be useful while learning
to sail a particular boat. Once learned, the instrumentation may not need to be left in place.
By collecting a series of data points – perhaps: 1) sail force measured by the strain gauge; 2) apparent wind strength; 3) apparent wind angle; 4) boat speed through the water; and 5) indicated course; one could generate polars for the boat which might be of some use. A more detailed polar might show the contribution of each sail in a series of internal lines which then add to give the polar of the total rig. This would enable comparisons to be made between different sail suites and/or locations – the strain gauges telling you which sails that are contributing. This information could be sampled periodically and collected and then displayed or printed out for closer scrutiny.