Mooring Definitions..

[wipe_out]

Just looking at all the mooring options available but the definitions are not clear to me.. I get "Deep Water" means deep enough for a fin keel boat at any state of tide and I get that "Drying" means that at low tide there is no water there at all so I assume only useful to bilge keel boats and power boats (unless you are happy for you boat to lay over on its side! )..

These are the ones that are unclear to me..

Semi-Tidal Mooring
1/4 Tide Mooring
1/2 Tide Mooring
3/4 Tide Mooring

What do these mean exactly?

I would have thought something like "minimum water depth at low spring tide" or some similar depth measurement would have been far better to work out if a mooring was suitable..

 

[chewi]

Just looking at all the mooring options available but the definitions are not clear to me.. I get "Deep Water" means deep enough for a fin keel boat at any state of tide and I get that "Drying" means that at low tide there is no water there at all so I assume only useful to bilge keel boats and power boats (unless you are happy for you boat to lay over on its side! )..

These are the ones that are unclear to me..

Semi-Tidal Mooring
1/4 Tide Mooring
1/2 Tide Mooring
3/4 Tide Mooring

What do these mean exactly?

I would have thought something like "minimum water depth at low spring tide" or some similar depth measurement would have been far better to work out if a mooring was suitable..

I don't know, but I could hazard a guess.

how would "minimum water depth at low spring tide" work for moorings that would dry out at LWS and long before that?.

 

[l'escargot]

I would interpret that as when your boat would be afloat on an average tide - 1/4 tide, your boat will be aground most of the time; 1/2 tide, your boat will be afloat half the time & 3/4 tide, your boat will be afloat most of the time. Probably based on bilge keelers on a drying mooring and looking at a common draught of about a metre - although check with them, what are the majority of boats on other moorings?

 

[Searush]

Firstly, they are estimates. Tides vary & boats have different draughts so they are not cut & dried definitions, but my take is as follows.

Semi-tidal; this mooring will dry out for most boats on some tides (usually the Springs, but could be only the bigger springs)

1/4 tidal; most boats will be aground for around 3 hours twice a day
1/2 tide; you will be afloat for about 3hours either side of HW
3/4 tide; you will be afloat for only about 3 hours a day.

Now, depending on the point of view of the person who wrote the descriptions 1/4 & 3/4 could be transposed, a quick look at a chart should tell you which is which - or go see the moorings with a tide table in your hand.

FWIW, I have a 1/2 tide berth on neaps, but probably get almost 4 hours either side of HW on springs, especially the bigger ones.

EDIT: I see that the snail has taken the opposite point of view to me which illustrates the ambivalence of the definitions.

 

[wipe_out]

I don't know, but I could hazard a guess.

how would "minimum water depth at low spring tide" work for moorings that would dry out at LWS and long before that?.

No idea! I guess those would fall into the "drying" category..

Just thought there must be a more "measured" way of doing it.. For example some moorings might have a minimum depth at any time of say 1.5m then you know a boat with a 1.2m draft would be fine there all the time but a boat with a 2m draft wouldn't..

 

[l'escargot]

No idea! I guess those would fall into the "drying" category..

Just thought there must be a more "measured" way of doing it.. For example some moorings might have a minimum depth at any time of say 1.5m then you know a boat with a 1.2m draft would be fine there all the time but a boat with a 2m draft wouldn't..

Don't get too bogged down with exact measurements otherwise you are going to have to start considering wind direction and atmospheric pressure - which can alter things up to 1/2 a metre in either direction on occasions. It is no more than a general guide in the vague world of tidal predictions. I would never trust a tidal calculation that claimed to be accurate within 1/3 of a metre anyway.

 

[Searush]

No idea! I guess those would fall into the "drying" category..

Just thought there must be a more "measured" way of doing it.. For example some moorings might have a minimum depth at any time of say 1.5m then you know a boat with a 1.2m draft would be fine there all the time but a boat with a 2m draft wouldn't..

You are expecting a lot of precision when tidal predictions can easily be a meter out due to the weather & the sea bed can fluctuate a couple of feet after a gale, not to mention that where your boat settles on a drying mooring can be almost anywhere in a 30' circle (plus length of boat) and the sea bed is seldom flat. We are not talking parking cars in a numbered parking slot here.

 

[guernseyman]

A half-tide rock is one awash at half-tide, and that is true for both spring tides and neap tides and all between.

I have no idea whether a half-tide mooring is awash at half-tide or has enough water for, say, a boat with a nominal 2 metre draft.

The other terms are even more vague as they would depend on the tide height.

 

[wipe_out]

We are not talking parking cars in a numbered parking slot here.

Haha..

Yes I get that.. So I guess the way everyone plays it is either have a fin keel and stay in "deep water" or get a boat that can stand on it's own..

 

[wipe_out]

I have no idea whether a half-tide mooring is awash at half-tide or has enough water for, say, a boat with a nominal 2 metre draft.

The other terms are even more vague as they would depend on the tide height.

That's what I was getting at.. Does it mean there is enough water for the boat to sail in or out for that period or just that there is "some water" there?.. Doesn't appear to be a set definition so really could mean anything..

 

[Searush]

A half-tide rock is one awash at half-tide, and that is true for both spring tides and neap tides and all between.

I have no idea whether a half-tide mooring is awash at half-tide or has enough water for, say, a boat with a nominal 2 metre draft.

The other terms are even more vague as they would depend on the tide height.

If it is "awash" then some of it is above water if only between waves so there is no way anything could float over it.

The range of tides varies from springs to neaps, but 1/2 tide is not always the same depth above datum. Check your tide tables & plot the mid tide point over a series of tides, it will not be a flat straight line, it fluctuates. Wave heights also affect what is awash & what isn't, these terms are VERY imprecise simply because nature is not that predictable.

 

[l'escargot]

It is purely an indication of what to expect with an average boat on an average tide in that specific area - measurements 25% apart can never be considered accurate. Without knowing the specific moorings, only the mooring providers could give the OP anything other than a rough guess of what to expect from these particular moorings.

 

[l'escargot]

Haha..

Yes I get that.. So I guess the way everyone plays it is either have a fin keel and stay in "deep water" or get a boat that can stand on it's own..

There is no difference between a fin keeler and a bilge keeler in that respect, they both need to be afloat if you want to sail them...

 

[wipe_out]

There is no difference between a fin keeler and a bilge keeler in that respect, they both need to be afloat if you want to sail them...

Very true, but one will fall over while the other won't..

 

[l'escargot]

Very true, but one will fall over while the other won't..

Not if they're both afloat...which takes you back to your original question. People will keep fin keelers on 3/4 tide moorings in mud with the keel just aground for some of the tide.

 

[wipe_out]

Not if they're both afloat...which takes you back to your original question. People will keep fin keelers on 3/4 tide moorings in mud with the keel just aground for some of the tide.

So that suggests that 3/4 tide means roughly 2m of water or more for 3/4 of the time.. If so that answers my initial question on the definitions..

 

[l'escargot]

So that suggests that 3/4 tide means roughly 2m of water or more for 3/4 of the time.. If so that answers my initial question on the definitions..

Not necessarily it may only be 1/2 a meter of water for a quarter of the time. Too many variables without knowing where the moorings are and what type of boats generally use them. At what depth do you expect the boat to dry?

 

[chewi]

There is no apparent norm on the meaning. I can see a vendor might classify moorings to show that one mooring is deeper than another, but the meaning cannot assume the boats draught for an unknown boat! I'd think you would have to a ask whoever callas it halftide or other what THEY mean by it.

eg to some 3/4 tide could mean "good access for 3/4 of the tide cycle", or conversely could mean "needs 3/4 of the tide to be any use at all".

 

[Charlotte Anne]

You need to ask the mooring provider.

At our club 3/4 tide moorings like ours never dry but have less than 1m at LWS so our lifting keel boat is always afloat but they do not rent them to full keeled boats. The 1/2 tide moorings are dry for a period on every tide. The river has changed shape a lot over the years and so the definitions have changed and indeed most of the full-tide moorings are now 3/4 tide moorings....

 

[oldharry]

Just looking at all the mooring options available but the definitions are not clear to me.. I get "Deep Water" means deep enough for a fin keel boat at any state of tide and I get that "Drying" means that at low tide there is no water there at all so I assume only useful to bilge keel boats and power boats (unless you are happy for you boat to lay over on its side! )..

These are the ones that are unclear to me..

Semi-Tidal Mooring
1/4 Tide Mooring
1/2 Tide Mooring
3/4 Tide Mooring

What do these mean exactly?

.

Basically nothing, for the reasons outlined above. They dont define tidal height. They dont even define which way they run. The only approximation is a 'half tide' mooring, where you could expect to get 6 hours afloat and six aground. Even that is not accurate because in some places there can be as much as 2 hours difference in between the time it takes for the tide to run in and out again. In somewhere like Poole where the tide stands for several hours, it would be even more misleading!

Here in Chichester, the moorings are defined by their height above or below Chart Datum. So mine is in the range 0.5 to 1.5m above datum, which means that on springs I am aground for a couple of hours, but on neaps, I am afloat nearly all the time.

On your scale that could be a '1/4 tide' or '3/4 tide' mooring, though neither description would be accurate.

Height above CD is the only viable way to define a drying mooring.