Increments
Hello,
Efficient sailing is the result of an accumulation of details: center of gravity; tune; scantlings; relative sail area; rudder shape; sheet block locations; and many more. One of those details involves spreader shape. Going from oval to an appropriate airfoil section, with perhaps a taper thrown in, will certainly improve performance, because physics. Whether the difference will be readily measurable, or sensible in a cost/benefit sense, is another thing. I vote airfoil, but it might be hard to convince you, judging just by how you phrased the question, which contains the phrase, "on a 17 ton cruising ketch." What seems implicit there is that you already see your boat as heavy and inefficient, so why bother with good spreaders. Another way to look at it might be, "In order to have a roomy and seakindly boat, I got a 17-ton cruising ketch. What basic, non-exotic rig details might I pursue that will help get the best performance?" Put that way, good spreaders are low-hanging fruit, and you are likely to look, not just at shape, but length, weight, and angle. You are more likely to see if the wires that go over those spreaders are the right size, if the tangs the wires attach to are sound and appropriate, and so on, right through the rig. Your spreaders are a window into your rig. Wander around in it for a while, get to know it as a system, and then see what you can improve without cutting too deeply into your budget. You might be amazed at the difference to your boat.
Fair leads,
Brion Toss
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