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Old 13-02-2011, 17:27   #1
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What? Computer Dead Reckoning Mark 4

I am the proud but puzzled owner of a 'Computor Dead Reckoning Mark 4' (made by The London Name Plate Mfg Co Ltd. of London & Brighton) which came with my boat. I am not sure which category of equipment to place it into.



I have been categorising the equipment I have found on my boat. For example, three bilge pumps which were installed but 100% broken go into the 'totally-junk' category. The radio-communications aerial and two other aerial fittings installed on the stern but connected to nothing are in the 'practically-junk' category. The three life jackets go into the 'creative-use' category as they are to old to be legal as personal flotation devices but they look good. The metho stove is in the 'keep-&-treasure' category because surprisingly it works well and I love it.

What about the Computor Dead Reckoning thingo? All I can find on the 'net is that something like this was used for aircraft navigation. Any ideas on how to use it?

If nobody knows, then that is okay by me. It looks like it should be something awesome. I might simply put it into the 'props-for-acting-like-knowledgable-skipper-for-the-impressing-of-ladies' category.
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Old 13-02-2011, 17:43   #2
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No idea, but there is one on my boat also. The previous owner was a pilot as well.
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Old 13-02-2011, 17:51   #3
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Airplane pilots use them - you can do your VMG calculations (tide triangles) on the clear side and the backside is a speed-times-distance calculator. As the speed scale starts at 80 kts, I doubt it would be very useful - unless your boat is very quick
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Old 13-02-2011, 18:23   #4
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I'll give you the quickie tutorial, but it's been a long time since I used one of this type. Say you have a 30 kt North wind - you set the N to the True course triangle and measure 30 kts along the centre scale from the little hole in the centre; draw a dot or "x" with a 2B pencil. Now if you wanted to fly due East at 200 kts, you would spin the dial to put E on the True course marker, slide the centre hole over the 200 knot line and see the wind dot would be off to the left, telling you that you need to steer 7° to the left (steer 083°) and set the throttle for 204 kts to give you 090°/200kts. On the slide rule side, you set your speed to the 60, and then read minutes or hours/minutes on one scale and distance covered on the other. You can also convert NM to statute miles or kilometres, calculate altimeter settings and so forth.
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Old 13-02-2011, 18:38   #5
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In my business that useful device is called an E6B...before GPS they kept me out of alot of trouble.

Todd
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Old 14-02-2011, 08:46   #6
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It looks like a more complicated version of the plotter I use with my paper charts to figure headings. It's based on the Portland Plotter:

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Old 14-02-2011, 11:54   #7
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It looks more like a Kane Dead Reckoning Computer
Kane Dead Reckoning Computer :: squareCircleZ

Than an E6B Whiz Wheel
E6B - Wikipedia, the free encyclopedia
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Old 14-02-2011, 18:49   #8
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Lodesman: Yes, 80 knots is a bit fast for my boat so as you say, it is not much use. However, my dinghy does at least that so it may be useful there, except at that speed I am too busy on the oars to be mucking around with a slide rule thingo. Thanks for the tutorial.

S/V Alchemy: Unfortunately, this thing I have has no plotter function, I can't use it on paper maps. It only does slide rule sort of stuff, would have been good back in the days when ya had to figure it all out in ya head.

GordMay: It looks exactly like the Kane one. Following the link you gave, I found the manual for it and if I was really keen I could learn how to use it - wow! To use it properly I would need to have a plane . . . . oh, and a pilot's license.

Four winds: Amazing that there was one on your boat. Maybe there is some way they can be applied to sailing. For me, I think I would prefer to use a plotter like S/V Alchemy showed or similar or the GPS which came with the boat which does show projected path. That projected path I have found to be very useful ever since I was sailing upwind as much as possible to get around a serious rocky point but the GPS projected path had me hitting the end of it. Until I saw that, I did not realise I was slipping as far sidewards as what I was.
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Old 14-02-2011, 22:01   #9
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According to the very end of Gord's Wikipedia entry, it is a knockoff of the E6B from after the patent expired.

Haven't looked at it closely enough but you might be able to knock a 0 off every value and have it work for a sailboat, at least the dirft angle side. Alternatively you could easily renumber the scales since they are both to the same scale and linear.

The time/speed/distance on the back would be harder to rescale but possible.
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Old 14-02-2011, 22:45   #10
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It's been ages since I used an E6B, but they work very similar to a slide-rule. With that in mind many of the scales you can scaled by decimal places. It had never occured to me to dig one one of mine out and use it for calculating heading to correct for wind and current. - Ahhh another challenge
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