Tide Clocks

[FWB]

Just bought one of these for home so I thought I'd do some checks------no I dont have anything better to do.
It makes one revolution every 12 hours and 25 minutes. Instructions are to set it to high water local on the day of the full moon and it should then stay 'roughly' in tune with the tides.
OK I know that there are various methods for tidal predictions but with this thing I can see why it's not so straightforward.
Full moon this month is on 14th, so if I set it up then---- by the 21st it will be ahead of the tide tables by 2h24, it will agree on the 29th, be ahead again by 1h37 on the 5th April,lag by 44mins on the 9th and be ok again by the full moon on the 13th.
Just thought I'd share that.

 

[bdsweeting]

Yup, they're not perfect, well mine isn't anyway but it looks good so that's OK.

 

[Gin]

You just confirmed my doubts about these things.

Thinking that I could well be buying a frustration with one of these, I just cut out a disc of hard white poly(something) from a sheet of same from the local aircraft modellers shop and inscribed it with position for HW, -1 / +1, -2/ +2, -3/ +3 and so on around the 'dial' either side of HW until reaching 6 which has neither - or + signs.

This disc has a circular hole cut out of its centre to fit over the bulkhead clock and three small brass lugs cut from thin brass from said model shop, which act as retainers for the disc, positioned over the mounting holes of the clock and clamped by the bulkhead screws.

The disc can then be rotated by hand to position the HW position at the appropriate hour for the next high tide, which then avoids the problems you have commented upon- assuming of course around the +5/ 6 time you reposition the HW indicator for the next high water time.

Crude, simple but effective

 

[Superstrath]

That's what this does, and tells you whether you're at springs, neaps or in between.

 

[Twister_Ken]

Hey mister!

Do you wear them both on the same wrist, or one on each?

 

[pampas]

Most of these clocks for UK use are geared to the Dover HW and duration, therefor they will always have an error shown when away from Dover, Falmouth time is approx 6hrs difference and I have found that it keeps in step reasonably well albeit 180 degrees out.

 

[FWB]

The clocks are geared to the moon. I dont think that Dover has a 12h 25min tidal period.

 

[dulcibella]

I bought one because it was the only brass clock that I could find that had proper Arabic numerals rather than Roman nonsense. I became allergic to Roman numerals because of my old Halmatic 30 "Dipper", which had a lovingly crafted piece of dowel as a fuel dipstick. Each gallon was marked by a flat on the dowel with the gallons marked in Roman numerals. Distinguishing IV from IX in the middle of a dark night in the middle of the Channel is no joke, even without presbyopia. I can now admire my nice tide clock without any bad associations. The one good thing is that the Romans didn't have a symbol for 0, so I never ran out of fuel. Presumably they don't make Roman-numeral tide clocks because Mare Nostrum has little or no tides.