NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: beginner
From: Willem Piccer
Date: 2005 Oct 2, 12:29 +0200
From: Willem Piccer
Date: 2005 Oct 2, 12:29 +0200
I suppose it is a personal matter: I feel more happy with a little bit ( more) weight and as a result of that more inertia. Less weight can also be a selling argument for instrumentmakers. Regarding your "skeleton"argument: if you make a disc like sextant it will be very prone to windinfluence A little bit out of the "navigation lane" : with bicycles in a race ( time trials) there is also the argument of using "open"wheels or "disc"wheels because with the wind in the wrong direction the disc wheels have a negative influence. I am Dutch that's why I bring up the bicycle! I short to me: skeleton frame with a certain weight is perfect! Willem Piccer ----- Original Message ----- From: "george huxtable"To: Sent: Wednesday, September 28, 2005 1:05 AM Subject: Re: beginner > At 10:56 19/09/2005, Willem Piccer wrote, about the weight of an observing > instrument-: > > >Weight is something which plays a minor role in the discussions we see here > >about the plastic sextant but to me it is important. > > > >If you use your sextant on a platform which is not stable than a sextant > >which has a certain weight will help you to obtain a more accurate > >observation because it is more stable. > >I know there is a sextant from John Bird ( around 1770) which has a "stick" > >on the backside to make it more stable. > > > >I suppose there is an optimum weight for a sextant : on one side not too > >heavy to handle and on the other side heavy enough to obtain a good > >observation. > >I remember when we started to use these light East German sextants that this > >was exactly what was noticed: easy to lift but more difficult to make a > >good observation > > ======================= > > I've seen that sentiment expressed before, by other seasoned professional > mariuners, and I would like to understand the basis for it. Why should a > heavy sextant be more stable, I ask (as someone who only ever owned a > plastic sextant, but has used others)? I respect the views of those who > have much more experience than I do, but remain as yet unconvinced. > > After all, the windage on a sextant is just the same, when made of a light > material or a heavy one, if they are the same shape and size. If a sextant > is physically smaller, as some yachtsman's models are, then wind forces > will be less. True, a heavy sextant will have more inertia, so it resists > initial movement, but when moving with the ship's roll, then it acquires > extra momentum, which makes it harder to bring it to a stop. > > Sextant makers all seem to go to a lot of trouble to skeletonize the frames > of their instruments. If there was as advantage in having a heavier > instrument, why would they bother to do so? > > The clinching argument, to my mind, against Willem's view, is that if > weight was a real advantage, mariners would "improve" their lightweight > instruments by simply adding lead ballast, to make the thing more "stable". > I have never heard of this being done, to any sextant, though it would be > easy to do in practice. Why not, then, if the extra weight would make it > somehow better? Convince me that it would. > > ======================= > > I've missed recent Nav-L discussions, having been away on a family holiday > (four aboard) on a hired motor-cruiser on the River Charente, in south-west > France. For me, a real change, in that the only navigational decision was > whether to set off upstream and return downstream, or vice versa. It made > for a good holiday, but reinforced my preference for salt water, and sails. > > George. > =============================================================== > Contact George at george@huxtable.u-net.com ,or by phone +44 1865 820222, > or from within UK 01865 820222. > Or by post- George Huxtable, 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 > 5HX, UK. >