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Subject: Leeway angles
From: Joe Shields (jshields@XXX.XXX)
Date: Mon Jul 19 1999 - 23:34:16 EDT
I also have that formula: 58.5 * heel / boatspeed**3
as well as another: 8 * heel / boatspeed**2
for leeway angle (which I found somewhere and copied into my notebook)
but I also found (somewhere) a table that seems easier to use:
------------------- -----------------WIND STRENGTH & POINTS OF
SAIL------------------
BOAT TYPE 3-10 knots 11-21 knots 22-33 knots
34-65 knots
beat reach beat reach beat
reach beat reach
------------------- ---------------- -----------------
------------------ ------------------
shallow-keel 10 5 8 4 12
10 20 12
cruising sailboat
deep-keel racer 6 4 4 2 6
4 12 6
Large cruising 4 2 6 4 10
8 20 12
sailboat
under power
<same boat> 10 4 8 4 12
12 20 15
under sail
------------------------------------------------------------------------
-----------------------------------------------
LEEWAY ANGLES (in degrees)
I have no idea how accurate this is or how it was constructed. I've
used it as a guide in trying to keep a straight track to short range
destinations and have usually been rewarded by not needing an extra tack
to reach the harbor. (Other boats that crossed my path obviously
steering directly towards the lighthouse marking the mouth of the harbor
needed the extra jog). It also seems to put me on the mark when
practicing DR using the Coastal Crusing Simulator (by Posey Yacht
Design).
Anybody else familiar with this table? Can't remember where I got it.
Could be Dutton.
-- Joe Shields
> ----------
> From: Bill Murdoch[SMTP:WSMurdoch@XXX.XXX]
> Reply To: Navigation Mailing List
> Sent: Monday, July 19, 1999 10:03 PM
> To: NAVIGATION-L@XXX.XXX
> Subject: Re: True vs Magnetic
>
> In a message dated 7/18/99 12:19:28 PM EST, lu.abel@XXX.XXX writes:
>
> > PS - Does anyone know how to calculate leeway (for either power or
> sail)?
>
> Some time ago I wrote myself a note, "for modern sailing hulls: Leeway
> = 58.5
> * heel angle in degrees / boat speed in knots cubed, Ocean Navigator
> #45 3/92
> page 72. It makes sense that increasing heel would indicate
> increasing
> leeway and that lower speeds would indicate higher leeway, but the
> numbers do
> not seem to fit. Does anyone have the back issue to see if I wrote
> the
> formula correctly ? My own experience is that sea state also has a
> big
> effect.
>
> Bill Murdoch
>
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