A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Date: 2014 Jun 28, 06:25 +0100
I will try to write up detailed instructions over the next few weeks. However, I really am not a skilled craftsman or slide rule expert.
I rely on Scales from Wayne Harrison which can be easily re-sized in my old Photoshop 7 elements (just put PDF into photoshop, go to image>re-size, give dimensions and print on photo paper at best quality. (cheap HP standard printer). Takes multiple trial and error with plain paper drafts to get perfect fit for height and width. Has to be perfect ht on Fuller otherwise get incorrect results Attaching the scales is tricky and takes patience to get it perfect. Use double sided tape, one long piece along the joint edge..No glue .Attach one edge first, then carefully wrap the rest around, making sure the scales join up perfectly. Takes practice with plain paper drafts first. The inner tube for the Bygrave and mini fuller 2 (48mm ext dia, 44mm int) was originally a tube of silicone sealant, used emptied and cleaned out. Fits perfectly! Cost nothing.
The other PVC pipes were all cheap or free “off cuts” from my friendly local hardware store. Just basic water/drain pipes, but all seem precision made. Just need a few mms gap between tubes. Small strips of felt from a local store stuck with double sided tape. Trial and error for perfect degree of resistance between tubes without slippage. I have added a Gary type brake to my latest minifuller 2 prototype. This also now has cosines in red and green going the other way. Photoshop allows addition of text but not fundamental editing of the original scale numbers (postscript, I think. I cant do that. Waiting for Wayne to deliver those later.) But it works and with magnifiers, I’m getting similar results now to the big Fuller 2. I can now do all cel nav calcs with the Fuller 2 and will start on a comparison run next week. I use the “Chichester test”. What would be best for quick, accurate calcs in an open biplane in the middle of the pacific? In my experience, most mistakes are doing simple mental arithmetic calcs , looking up tables and writing down intermediate results. So the less of those the better. So far the mini fuller 2 with cosines wins (better than versines and logs) except for simple LOPs where the Bygrave still wins easily when LAH and Dec not off scale. Gary’s instructions re Bygrave use the best. I use his forms for this. I aim to get 1’ accuracy and usually manage this even with Bygrave at extreme angles. I think you would need a very big circular rule to match that and I think the cylindrical rules, with prefabricated PVC pipes are easier to make. Gary’s flat version probably the easiest, but I’ve no experience and wonder about overall size and slippage?
You seem at good spirits. I wish you further speedy recovery.
Let me go back somewhat.
As you know I have answered my own question as to why Bygrave may have chosen
his is particular equations on his slide rule. The answer in a nutshell: He made an excellent choice. The log tan/cot scale is relatively insensitive to reading errors as compared to log cos/sin scales. It is true, the log cos does appear in his equations but any reading errors of it have generally only a minor influence on the end result.
The same is true for versine and havsersine since those are equal to cos/sine plus a constant. Therefore, for my own - future - slide rule for sight reduction I will follow Bygrave's footsteps, too.
This certainly applies to the standard sight reduction. I have no idea if this is also true
In a different vein:
I have been mulling over your description of how to construct Fullers and Bygraves. Obviously, this is still a complicated process. Is there a way to be even more specific?
To give an example: What PVC pipes does one use? Are they irrigation pipes? If so what schedule? Can one buy them at Home Depot/ Lowes etc.? Do you happen to have even the SKU perhaps?
I venture not many CelNav aficionados have your mechanical and PC skills. For them
to successfully tackle such a project they probably need descriptions of the kind the Heath kits were. Remember them? Even if you never had built an electronic device before following them you would end up with a real functioning, useful oscilloscope. However, writing a how-to with so much detail would become a project of its own.
Nevertheless, I put a copy of your description on the wall of my office as an joyful encouragement!
On Fri, Jun 27, 2014 at 6:46 AM, Francis Upchurch <NoReply_Upchurch@fer3.com> wrote:
I'm just out of hospital post op, and doing fine. But beached and therefore restricted to sextant readings and playing with slide rules while lying down in the garden overlooking the ocean. Tough life!
Coming round from the anaesthetic, (great for lateral thinking!) I had an idea re the Fuller 2. The main problem is lack of cosine scale, which means I have to convert all cosines to sines first. Simple, but tedious, time consuming and an unecessry source of errors. I never use the log scale on the big fuller 2, so have replaced it with another sine scale,same size ,but with cosine numbers in red and green going the other way. So I can now do all my cosine formulae cel nav calcs direct which halves the time.
I have adapted the minifuller 2 , with the sine scale now having added cosines numbers in red going the other way too. Works ok, but the big fuller 2 replica is more accurate and best for shore based work.
Over the next few days I'll do some comparative LOP calculations using long hand Haversines or Versines, Fuller 2, mini Fuller 2 and Bygrave and see what we get in terms of accuracy and speed. For lunar clearance, I suspect the big fuller 2 will win, but the minifuller 2 probably adequate and more seaworthy and with the Otis King format, a bit faster with less moves.