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Old 14-03-2019, 20:38   #46
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Re: A question for our Antipodean cousins

I regularly race in Australia on a few different yachts and each seems to have better boat speed on starboard
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Old 22-03-2019, 20:37   #47
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Re: A question for our Antipodean cousins

Of course it's not possible for the speedometer sensor to be off center...
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Old 23-03-2019, 14:00   #48
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Re: A question for our Antipodean cousins

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Of course it's not possible for the speedometer sensor to be off center...
That may be an issue for some but my log is on the centreline immediately in front of the (lift) keel...
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Old 23-03-2019, 14:08   #49
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Re: A question for our Antipodean cousins

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From what I understand, after reading David Burch’s excellent book “Modern Marine Weather”, it is not the Coriolis effect on the boat itself. That would be negligible, unlike high speed military missiles where it is very important. It is the Coriolis effect on the prevailing winds and what happens during gusts. Higher altitude winds, which have less earth surface friction to deal with are curving to the right due to unopposed Coriolis effect (unimpeded by the friction of the earth’s surface). On the other hand, surface winds are affected by the friction of the earth’s surface. This friction slows the wind and somewhat opposes the rightward turning force of the Coriolis effect, resulting in less rightward turning. Therefore, upper level winds, compared to surface winds are more veered to the right (and are stronger). This can easily be seen by looking at the direction that the clouds are moving. Their direction of travel is usually about 15 to 30 degrees veered compared to the surface winds you’re sailing in (and more friction due to rougher sea-state equals more veering). Wind gusts (away from the expected turbulence around shorelines, cliffs etc.) are due to vertical instability of the air. That is, they are patches of higher altitude air that have dropped down to surface level. Therefore, they are higher velocity than the prevailing surface wind and, in the northern hemisphere, are more veered to the right. That translates to more of a beam reach during a gust on a starboard tack (wind shift away from the bow). On a port tack, the same rightward shift of the wind during the gust, means heading up or more close-hauled (wind shift toward the bow). That would certainly affect the performance difference, port tack versus starboard tack on a gusty day. In the northern hemisphere, a gust on a starboard tack would be a “lift”, whereas a gust on a port tack would be a “header”. When sailing to weather, a header impedes progress. The opposite would be true in the southern hemisphere where a gust would come more from the left compared to prevailing surface wind.
I highly recommend reading David Burch's book: Modern Marine Weather
Vchild, I concur with what you have written which is why I asked the question since it will obviously be opposite in the Southern hemisphere, but, from the replies I have seen from our southern brethen it appears that they still find their boats sail better on starboard, so i guess there must be another reason 'though what is is I'm still trying to figure out...
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Old 23-03-2019, 14:39   #50
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Re: A question for our Antipodean cousins

Has the effect of a furling headsail been mentioned yet?

Mine 'wraps from the right' so for much of the time there will be a purer air flow over it when on starboard than on port.....
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Old 24-03-2019, 09:51   #51
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Re: A question for our Antipodean cousins

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That may be an issue for some but my log is on the centreline immediately in front of the (lift) keel...
But if the paddlewheel or spinner is not also oriented EXACTLY in line with the boat's centerline, it will provide different readings, depending upon the tack you are on. Ours, for example, has a through-hull tube on the centerline that is marked to indicate the correct spot for the arrow on the speedo unit to line up with, when the latter is slid into position. O-rings make the fit snug and keep water out, but allow the unit to be turned in any direction. Who is to say that the tube is actually marked in the right place, or that it was installed correctly?
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