Narrow Channels

[DAKA]

Any chance you can wait for adequate tide plus .5 meter please ?

I'm posting this well after the event so please don't feel that I am having a go at an individual , this isn't a one off incident or one off location .

We recently entered Chichester Marina, I checked the tides and I waited for adequate water plus 1/2 meter spare.

We were in the fairway heading towards an open lock and green light (indicating the lock was open ready for us).

There was a yacht heading out of the very narrow channel wafting his arms up and down (simulating a flightless bird trying to fly).

We were close to tick over , almost wash free and as close to starboard side of the channel as I dare be.

As we got level with him he shouted , we only have 2 cm of water

I presume that he meant he only had 2 cm of water between his keel and the mud

If he had hit the bottom the current would have swung him round to block the channel for everyone for an hour or so.

The lock keeper had questioned his draft and stated the indicated water hight.

So what does the forum think ?
I have added a poll but please feel free to comment .

 

[ProDave]

Rising or falling tide?

 

[Minerva]

So altercation between mono and sail boat? Clearly the mobo at fault!

In more seriousness some folk have an over confidence that the real world tides work just like their tidal calcs on their chart table. Measuring to 20mm spare is somewhat bold

 

[ProDave]

So altercation between mono and sail boat? Clearly the mobo at fault!

In more seriousness some folk have an over confidence that the real world tides work just like their tidal calcs on their chart table. Measuring to 20mm spare is somewhat bold

And assuming the sea bed is flat to that degree of tolerance as well.

 

[justanothersailboat]

... nobody's depth sounder is accurate to 2cm, no chart is accurate to 2cm, what is this guy playing at?

Coping with the existence of the tide is a basic prerequisite of going to the beach, let alone getting on a boat.

 

[benjenbav]

First, I hope there was no collision. Also that nobody got stuck in the mud or otherwise blocked the lock channel.

Second, having spent quite a few years using that lock on a regular basis (albeit some time ago now), if the lock-keeper didn’t think there was enough water in the channel for the outgoing yacht and you to cross, I would have expected them to hold you on red until the yacht had completed its transition of the channel.

Which leads me to think that you did the right thing (keeping reasonably to starboard) and that the other skipper was perhaps a little more nervous than circumstances demanded.

But, I wasn’t there. What do I know?

 

[Minerva]

... nobody's depth sounder is accurate to 2cm, no chart is accurate to 2cm, what is this guy playing at?

Coping with the existence of the tide is a basic prerequisite of going to the beach, let alone getting on a boat.

During my YM course we were expected to get within 10mm when doing tidal height calcs. Just silly really.

 

[MoodySabre]

As someone who has never made a mistake I would not like to judge others. As in all walks of life there are those less capable and less confident. We can’t compensate for all of them. Act sensibly and sleep at night.

 

[dunedin]

During my YM course we were expected to get within 10mm when doing tidal height calcs. Just silly really.

Did you ask the examiner what the air pressure was, and what direction the winds had been blowing the last 48 hours?

 

[Sticky Fingers]

First, I hope there was no collision. Also that nobody got stuck in the mud or otherwise blocked the lock channel.

Second, having spent quite a few years using that lock on a regular basis (albeit some time ago now), if the lock-keeper didn’t think there was enough water in the channel for the outgoing yacht and you to cross, I would have expected them to hold you on red until the yacht had completed its transition of the channel.

Which leads me to think that you did the right thing (keeping reasonably to starboard) and that the other skipper was perhaps a little more nervous than circumstances demanded.

But, I wasn’t there. What do I know?

I’m with you on this. I had a running-aground-inbound incident not unlike this at that marina the first time I went there, but was on a rising tide and just waited for the inevitable refloat. A stiff cross wind made it slightly more interesting.

 

[Sticky Fingers]

I’m with you on this. I had a running-aground-inbound incident not unlike this at that marina the first time I went there, but was on a rising tide and just waited for the inevitable refloat. A stiff cross wind made it slightly more interesting

Did you ask the examiner what the air pressure was, and what direction the winds had been blowing the last 48 hours?

Just seen this - those two factors were the exact reason I had less water than expected.

 

[justanothersailboat]

During my YM course we were expected to get within 10mm when doing tidal height calcs. Just silly really.

Fine (ish) if the examiner expects you to then tell them why you don't rely on that...

 

[Sticky Fingers]

Fine (ish) if the examiner expects you to then tell them why you don't rely on that...

Well, the model answers in the YM theory course are 2 dec pl of metres, but no sensible person doing the DS or CS or YM practical would ever expect you to rely on those to that degree of accuracy.

 

[capnsensible]

Did you ask the examiner what the air pressure was, and what direction the winds had been blowing the last 48 hours?

Separate subject. Learn how do do simple tide heights. Walk. Then learn what other factors can alter the calculated height. Run.

 

[Egret]

Thames Estuary you can easily have a surge of +1m or more or -0.5m - seems to be +0.5m quite often - +0.3m at Harwich at the moment - was +0.5m earlier at noon today - was minus 0.09m at 0630 - it can change quite rapidly - and what about the waves - so 2cm is quite academic

 

[Sailing steve]

During my YM course we were expected to get within 10mm when doing tidal height calcs. Just silly really.

Indeed.

I don't think I've used anything I learned at YM theory that actually gave me any advantage or indeed made any noticeable difference in the real world and yes relying on calculating tidal heights to +/- 1cm or a CST to +/- one degree is taking small boat sailing to a whole new level of nurdishness at best and downright bloody dangerous at worst.

 

[Chiara’s slave]

Separate subject. Learn how do do simple tide heights. Walk. Then learn what other factors can alter the calculated height. Run.

You’d expect to get the answer to the second decimal in the theory exam then, but even 1 decimal is pushing your luck in the real world. As far as I recall in my practical, I gave a within 10cm answer, and qualified it by saying we were clear by 40cm and were safe as there were no unusual circumstances. If this incident was in the last few weeks, there certainly were factors to be taken into account in Lake Solent, and Chichester, most particularly the Ichenor channel. I’m surprised the guy got away with it.

 

[Iliade]

Surely it all depends upon how powerful his engine is? I have plowed many a furrow in the pursuit of leaving before the tide wanted me to...

Equally I've sat on the mud overnight waiting for the Neptune's return after taking a few moments too long making my way up the rythe.

 

[Pye_End]

During my YM course we were expected to get within 10mm when doing tidal height calcs. Just silly really.

Makes it much easier for a teacher to know if a pupil has got the correct methodology if they come up with the correct answer. In the real world less precision may well be appropriate.

 

[Mark-1]

I'm pretty sure at Chi the lock cill is shallower than the channel so if they got over the cill they had way more than 2cm in the channel. Also the deepest part part of the channel is a few metres North of the posts, so that might be a factor.in them thinking it was shallower than they were expecting.

Most of the lock keepers are helpful, I've heard them warn vessels too close to the posts and advise vessels it was too shallow, so I don't think they'd let a vessel out if they weren't confident it could safely make it. (In my case with merciless piss taking when without checking I rocked up after work on a low spring when there wasn't enough water even for me.)

In my years at Chi I was one the few people who could still get in and out at most low tides so I'm something of an expert at pushing my luck in and out of Chi Marina.