It is simply incorrect to consider the mast in isolation. For instance if
you weld a metal plate edge on, to the back of the cylinder then the drag
drops remarkably. The combination acts more like a very rough airfoil of
thickness to chord ratio cylinder diameter to plate width plus cylinder
diameter. Someone who lives near South Hampton Uni UK should go and pull
their yacht research data from the late 60's

-----Original Message-----
From: International 14 Mailing List [mailto:14list@i14.org]On Behalf Of
fast14riot@comcast.net
Sent: Monday, 15 March 2004 1:22 PM
To: Andy Loukes
Cc: 14list@i14.org
Subject: Re: [i14] bendy spinnaker poles and Bethwaite

well as to the boat speed educing in higher breezes is not totally from
being overpowered but mainly from the equality of forces being much closer,
i.e. force on the sails = hull drag. In the 470 class I know that there is
about 22-25 kg of hull drag (at displacement) and in about 10-13kts of wind
the sails provide roughly around 20-25 kgs of force but as the laws of lift
provide the force is at a right angle to the foil and this is why these are
marginal planning comditions up-wind but off the breeze you can plane much
easier. Also the heavier you are the more drag the boat has due to wetted
surface and frontal area. Also the drag of a cylindrical object is 16 times
greater than an airfoil of equal chord. So with the tubular mast section
this shouldn't be too hard to calculate.

Alexander Holman
Stockton, CA
I-14
USA 1096 RIOT!
J35
USA 28390 Raptor
j35raptor.org
E-27
USA 22 Hurricane
> On Thu, 11 Mar 2004, Jason Werner wrote:
>
> > The trick is achieving the speeds necessary for smaller sails to be
> > faster. In the case of a 14, it has a high drag bucket until planing,
so
> > you need enough power in the sails to get the boat planing fast, then
you
> > can reef. Oh...can anyone reef while sailing a 14...if so I want a
video of
>
> I can reef my Irwin spinnaker, just pull on the cunningham and the bottom
> 10 inches disappear :)
>
> > that! But realistically, the trick is to select a sail tht fits the
> > conditions. If it is blowing 30+ you are not going to put on your big
main
> > and spin...you have plenty of power to get planing, so you put on a
smaller
> > set of sails that are easier to control, and are also faster due to less
> > drag!
>
> OK, that does make sense. But it's more complicated than that, isn't it?
>
> I wish I hadn't started thinking about this and I wish I had practiced
> maths a bit more since university!
>
> I would be interesting to know what proportion of drag is from the stuff
> in the air (rig, crew etc) and what is from the hull and foils in 25 kts
> of wind.
>
> What do people think limits maximum VMG downwind? Presumably once
> overpowered the apparent wind start moving aft, you need to ease the
> spinnaker sheet and the wind speed to boat speed ratio reduces. In about
> 7 knots of wind you can do about 14kts and in 20 kts of wind you do
> around 22kts.
>
> So once overpowered you probably want a bigger spinnaker?
>
> --
> Andy Loukes
> Crew, GBR 1445 Pantomime Horse http://gbr.i14.org
> I14 Webmaster http://www.i14.org
>
>
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Received on Mon Mar 15 03:38:50 2004