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Old 19-10-2014, 01:49   #16
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Re: Question re Mast/Boom Tracks

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So your 1 inch stretch will allow well over a foot of deflection at the centre point
Good point, overlooked that.

But that means the forestay is experiencing a similar deflection - apparently without adverse effect on headsail performance. So why should it be a problem for the mainsail?
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Old 19-10-2014, 02:05   #17
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Re: Question re Mast/Boom Tracks

Because:

1. The aerodynamics of a headsail and a mast/mainsail combination are two completely different things.

2. You don't have a bl**dy great lump of steel/aluminium/timber sitting to windward ahead of the deflected headsail, blocking the draught.
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Old 19-10-2014, 02:21   #18
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Re: Question re Mast/Boom Tracks

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2. You don't have a bl**dy great lump of steel/aluminium/timber sitting to windward ahead of the deflected headsail, blocking the draught.
That's true, windage of mast v. windage of forestay.

Alright, you've convinced me.

Case closed.
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Old 19-10-2014, 05:54   #19
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Re: Question re Mast/Boom Tracks

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(...)

1. The aerodynamics of a headsail and a mast/mainsail combination are two completely different things.

(...)
How come?

There is a flow, there is a foil, there is something ahead of the foil. Sounds same rules should apply.

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Old 19-10-2014, 05:57   #20
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Re: Question re Mast/Boom Tracks

Plenty of deflection in my OK-dinghy mast. Seems designed-in somehow. I tried stiffer masts they seemed slower.

How do we know deflection is all bad then?

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Old 19-10-2014, 12:11   #21
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Re: Question re Mast/Boom Tracks

barnakiel,

It makes intuitive sense that a bigger object to windward of the sail would pose a bigger problem, but you raise an interesting point re your dinghy. And on that note, aren't masts on boats designed to flex a certain amount too? Which necessarily puts the mast to windward of the sail at certain points of sail?
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Old 19-10-2014, 13:27   #22
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Re: Question re Mast/Boom Tracks

Intuition can be misleading.

Which one will generate better flow / lift / force:

- a jib with hanks on a stay,
- a jib set inside an alloy extrusion?

And why do racers use extrusions/jib foils?

Which will create more drag / spoil the flow more:

- a thick spar (like a mast),
- a fine rod run an inch ahead of the sail (stay and hanks jib).

And why was such a rod tested / used on airplanes and why was it abandoned.

Trust intuitions if you want, just do not expect others to follow. Part of physics is counter-intuitive. You only want intuition to form questions. Then you want experiment and measurements to find answers. Intuition DOES NOT give valid answers.

Read books on aero and hydrodynamics, esp those written by hull and sail designers. You will learn heaps.

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