spreader shape

[mariner2k]

How important is it on a 17 ton cruising ketch to have an airfoil shape on the spreaders? Does it make any significant difference?
Is an oval shape acceptable?
Thanks, Kevin

[Brion Toss]

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

[mariner2k]

This one is not really budget related. I have the spreaders basically shaped but not yet into a foil. I can afford (strength wise) to remove more material to get an airfoil shape. That being said my choice is leave them with rounded edges, which I know offers more wind resistance, or shape them into a foil for better efficiency. Lift vs. resistance. I'm just not sure if the lift on that size vessel is a significant improvement on it's own, enough to outweigh strength. I can definitely see how that would improve a lighter racing vessels performance. Your vote for a foil, however, carries significant weight.
Thanks for the reply. Kevin

[Brion Toss]

Hi again,
It might not make enough difference to notice, but you might be surprised. Remember, you are adding weight as well as windage as well as losing lift as well as degrading the appearance of the boat. If you can address all of those issues without compromising structural integrity, why wouldn't you?
Fair leads,
Brion Toss

[mariner2k]

Hi, I was looking around the shipyard today and some spreaders were airfoiled and some not. (wooden). The airfoiled spreaders definitely looked more professionally done and probably were. So there you have it.
On another note, I am going from a very substantial box mast to a round mast. Aside from a couple of running backstays, I think the wind resistance works well toward my favor. Sort of the difference between driving a van into the wind, or a car.
Thanks, Brion