[BigWalleye]

Originally Posted by in_vino_vomitus

I have a feeling I won't be the first person to think of this, so all those for whom this is old hat, my apologies, however I found it useful and it doesn't seem to have been mentioned in the thread so far, so here goes.....

You can use the reverse side of the SACF to do simple TSD calculations by lining up the distance in yards with the time taken to travel it and reading the speed off the sine scale at the pointer, but lining the time and distance scales is dependent on a good eye, which I don't have. Anyway. it's a relatively simple matter to make another index pointer and mount it on to of the time scale/inner wheel, which is what I did. It's really useful for say getting speed by timing the target through the crosshairs, because all you need to do is use the floating index pointer you've just added to line up target length and time taken, at which point the speed can be read off the inner wheel pointer.

I haven't tried it yet, but I imagine it would work just as well for points obtained from say a radar plot or active sonar maybe.

Anyway, like I say, I doubt it's an original idea, but it's handy and it doesn't get in the way and is worth considering, I think for anyone planning to build one of these.

In lieu of a thousand word description, here's a photo. It's set up to show 117 yards in 25 seconds - 8.5 knots or thereabouts....

Brilliant!

IVV, how do you fab the plastic parts and put the markings on them? What kind of stock do you use and where do you get it?