Station · shallow

Skellow Bar

Two high waters, four hours apart, and neither of them is the real one.

48 hours · height in metres above chart datum · all eight constituents · window starts at hour 168 of the spring–neap cycle, at springs

Mean spring range: 5.26 m
Mean neap range: 2.54 m
MHWS: 6.98 m
MLWS: 1.72 m
Form factor: 0.06
Classification: semidiurnal

Shallow-water station. M4 is large enough here to put a second high water on the tide.

Sand bar across the entrance, least depth 1.8 m. The bar is what makes the second high.

M4 is 43.6% of M2 here. Above about a quarter, and in the right phase, that is enough to flatten the crest of the tide into two — over one spring–neap cycle of 14.765 days this station carries a second high water on twelve of its twenty-nine tides. The two days drawn above are deliberately at springs, which is when it is clearest — a page that quietly picked its best two days without saying so would be a brochure. In them there are 8 high waters .

The constituent table

Amplitude and phase lag at Skellow Bar. The periods are astronomy and are the same everywhere; the two right-hand columns are the whole of what a tidal analysis produces.
Id	Constituent	Period, h	Amplitude, m	Phase g
M2	Principal lunar semidiurnal	12.4206012	1.95	340°
S2	Principal solar semidiurnal	12.0000000	0.68	26°
N2	Larger lunar elliptic semidiurnal	12.6583475	0.38	322°
K2	Lunisolar semidiurnal	11.9672348	0.19	24°
K1	Lunisolar diurnal	23.9344697	0.09	140°
O1	Principal lunar diurnal	25.8193417	0.08	6°
P1	Principal solar diurnal	24.0658902	0.03	136°
M4	Shallow water overtide of M2	6.2103006	0.85	140°

High and low water, 48 hours

Turning points of the curve above, read off the same series that draws it.
Time	Event	Height, m
day 1 02:57	High water	5.71
day 1 05:24	Low water	4.97
day 1 07:27	High water	5.41
day 1 11:19	Low water	2.31
day 1 15:11	High water	5.64
day 1 17:48	Low water	4.73
day 1 19:56	High water	5.24
day 1 23:48	Low water	2.14
day 2 03:40	High water	5.31
day 2 05:56	Low water	4.68
day 2 08:32	High water	5.61
day 2 12:20	Low water	2.54
day 2 15:58	High water	5.21
day 2 18:19	Low water	4.51
day 2 21:00	High water	5.53

Survey sheet SB/3

229 soundings on run lines 52 units apart, 16 of them drying heights, deepest 20.9 m. One stroke on the sheet — the coastline — and no depth contours. Why.

Get Wrackline

Wrackline is an aid to planning and is not a substitute for an official tide table. Do not navigate on it.