I did a post for my mates ... on our small private group .... may be of interest:
Thought as we head towards a new season, I would put a bit of explanation to you on the tides.
I did this in detail on my Day Skipper course ... I’ll condense many pages and several Hrs into a 2 minute read.
It’s all about the lunar cycle.
Swansea bay is part of Bristol Channel, which has one of the largest tidal ranges in the world.
Each month we get 2 types of tides Spring & Neap.
Springs which are the high tides happen 1.5 days after a new and full moon, approx once a fortnight. Neaps (Low tides) occur halfway between each Spring tide.
The Spring tides give the lowest water, as tide goes out further.
Neaps the opposite highest low, and lowest high ... i.e. doesn’t go out very far.
The tidal range for normal Spring is around 8m and 4m for Neaps.
Spring is nothing to do with the season.
When Sun & Moon are in same side of the earth we get Spring tides.
The time between each tide is 6hr 13min ...Therefore 12hr 25min between successive high tides.
Now the clever bit ... the rise & fall is divided into 12 equal parts. (obviously pre-decimal)
This is known nautically as ‘The Rule of 12ths’
It is totally predictable, both for rate of rise or fall and water flow speed.
1st hr rise or fall = 1/12th of tidal range (runs at 1 knot)
2nd hr rise or fall = 2/12th of tidal range (runs at 2 knots)
3rd hr rise or fall = 3/12th of tidal range (runs at 3 knots)
4th hr rise or fall = 3/12th of tidal range (runs at 3 knots)
5th hr rise or fall = 2/12th of tidal range (runs at 2 knots)
6th hr rise or fall = 1/12th of tidal range (runs at 1 knots)
You can see slack water occurs at high water & low water.
Worth noting that the biggest mass of water is midway between high & low tide.
So if you lose power you will drift for 12 miles before tide turns.
The above is the normal Lunar cyclic tides, known as semi-diurnal.
If you remember physics, it’s a sinusoidal pattern, repeating every 6 Hrs.
Some places such as Oxwich point & Mumbles head for example also have tidal races where there is a significant increase in water flow due to coast geography.
An incoming tide coupled with a following wind would increase tide flow & height.
We get 2 particularly high springs each year - Known as equinoctial spring tides ...this year on 22 Mar. It’s a 10.3m And 29 Sept. 10.41m
At the low tide preceeding these you can walk out to exposed wrecks on many Gower bays.
Every 18 months when moon is closer to earth we get exceptionally high springs .. known as Proxigean Spring Tide. Every 31 yrs there are Extreme Proxigean tides ... the one in 1995 coincided with a following wind and caused extensive flooding ... 2026 is the next big one.
I have a great photo,of my Father as a Policeman rowing a boat along the Mumbles road .. to rescue stranded people ... that was during a Proxigean tide.