Liverpool Marina Lock - Approaching with 3 knot tidal flow past the lock entrance!

[Jaguar 25]

Came into the lock yesterday with about a 3 knot tidal flow past the entrance. We are talking a Jaguar 25 with 9.8 outboard.

Usually we aim to enter just after HW when it is pretty slack but we were a bit late getting back and then held up for another 15 or twenty minutes as the small racing yachts were using that lock-in. So it was about three-quarters of an hour past HW when we were called in. I tried to crab in pointing almost 45 degrees up river but once we were in the entrance area i.e. out of the tidal flow suddenly I was heading for the wall! Used reverse and just missed the wall and then everything was fine getting into the lock but a bit of a panic initially and definitely not a well controlled approach.

Question is "what is the best way of entering the lock when going across a 3 knot tidal flow?"

Any advise would be appreciated.

 

[guernseyman]

3 knot is 5 ft/sec. Assume your boat speed is 5 knot, which is 8.3 ft/sec, and your boat is 30 ft long and you start your approach level with the upstream wall, 10 ft away.

To get into the lock, your stern needs to advance 40 ft at 5 knot, which takes 4.8 sec.
During that 4.8 sec your stern will have travelled downstream at 3 knot, i.e. a distance of 24 ft.

I don't know how wide the lock is, but if it is 30 ft, and your boat has a beam of 9 ft, your downstream side is very close to the downstream wall.

This not intended as a solution, but an indication that the problem may be best solved by waiting for slackish water.

By the way I once saw a boat trying to enter Trequier Marina at full flood, by pointing somewhat upstream and charging at the gap between pontoons. Very similar to what you might have to do, except that you have still water in the lock. He hit about six boats before coming to rest.

 

[macd]

Surely it's about anticipating the moment when the tidal flow stops and you cease to ferry glide, rather than simply reacting to it after the event? I'm sure you'll be forewarned and forearmed next time.

 

[savageseadog]

I do that lock regularly. Always approach from the uptide direction and things are easier.

 

[garvellachs]

Not done it but it sounds very hard once the ebb is flowing strongly - the entrance is angled to enter on the flood I think? Your entrance sounds very skilled in the circumstances!

Is there a patch of slacker water close in? I think I would watch a few others doing it who are used to it, or maybe in our boat I'd try holding against the tide in reverse and ferry-gliding across the tide into the entrance area? An outboard is good for this if you are actually steering using it, but not if you are only using the boat's rudder; if you don't have a prop/rudder combination that will enable you to turn whilst almost stationary then probably slack tide is your friend?

Have you joined a club? The waters you are exploring are tricky and joining a club/sailing in company will provide access to a wealth of experience that will build confidence quickly. That's how we got to know the N Wales/Anglesey area.

 

[ffiill]

3 knot is 5 ft/sec. Assume your boat speed is 5 knot, which is 8.3 ft/sec, and your boat is 30 ft long and you start your approach level with the upstream wall, 10 ft away.

To get into the lock, your stern needs to advance 40 ft at 5 knot, which takes 4.8 sec.
During that 4.8 sec your stern will have travelled downstream at 3 knot, i.e. a distance of 24 ft.

I don't know how wide the lock is, but if it is 30 ft, and your boat has a beam of 9 ft, your downstream side is very close to the downstream wall.

This not intended as a solution, but an indication that the problem may be best solved by waiting for slackish water.

By the way I once saw a boat trying to enter Trequier Marina at full flood, by pointing somewhat upstream and charging at the gap between pontoons. Very similar to what you might have to do, except that you have still water in the lock. He hit about six boats before coming to rest.

You can get this effect entering into the Caley Canal at Corpach Loch.
My advice would be to approach from a good distance aiming well to the up current side;go in slowly and speed up where necessary to enter the lock on the up current side.

 

[Jaguar 25]

I do that lock regularly. Always approach from the uptide direction and things are easier.

Thanks for the suggestion, however:

Given that we only usually go out and back in on a single HW tide with lock opening 2 hours each side of HW. Therefore, the tide is slack or on the ebb when we come back in. So, if we are a little late the ebb flow is down river. So, are you suggesting by approach from uptide you meads motoring against the tidal flow? This would mean doing about 5 knots through the water (towards max of the outboard's capability) to get a 2 knot over ground speed. Doesn't this mean that as soon as you turn in to the entrance the boat "accelerates" in SOG terms and would be difficult to control?

 

[onesea]

A long time since I have done that lock, its a fun entrance... Strong tidal flow across the lock along the line of the river that are basically 2 stone walls and then suddenly nothing when you cross the tide line..

As Savagesea dog says approaching from up-current and being quick with the rudder to correct when the boat crosses the tide line is a good start. If the boat is heavy slowing down before the lock can be interesting.

On one occasion I was a little late catching the tide up the river (Weekend in Douglass IOM with my friends, a late night ).

Started pushing the flood some where up the channel, by the time we got near gates the ebb was well underway.

Dad and I had discussed the option of using "bank effect" of the wall, it was agreed it was not something we wanted to try. Dad was on the knuckle watching as I made my approach. Mum trying to calm him, both for me nearly missing the tide and the approach I was making.

As I recall it went rather smoothly. I kept 10-20 feet of the wall and just motored round the knuckle corner, no heroics. Although after that we made sure we did push it that close again...

 

[maby]

Never done Liverpool, but we have to do similar quite often down south and it still scares the hell out of me. The only practical way is to approach uptide as suggested and turn in as you get into the dead spot just outside the lock - that way, you are approaching slowly over ground but, as you say, run the risk of going out of control as the current drops in the mouth of the lock. That should be manageable on a 25 footer - imagine what it's like on a 45 footer - you can still have a lot of current across the stern as the current on the bows drops off to zero!

I thought I had it pretty much worked out till a few weeks ago when we were invited to come in and moor aft in the lock - there was only a couple of feet clearance between us and the boat in front and it was very scary trying to maintain enough speed to make it through the gates, then stop fast enough to avoid hitting the guy in front of us - I did end up scuffing my gelcoat on the lock gate as I chickened out and braked a bit too early!

Free flow can be just as nerve wracking - a few months ago I got the approach wrong, coming in at too much of an angle and realising close to the entrance that I would not manage the turn without slowing down. I throttled back, managed the turn but then found myself progressing through a lock that is not that much wider than the boat doing four knots in a three knot following current - effectively doing one knot through the water. I don't have a lot of steerage at such low speeds - I really don't know how I got through without losing the anchor roller! Needed a very stiff brandy after that one!

 

[Searush]

First a caveat, I have never "done that entrance", however I do have a fair bit of white water canoeing experience.

If you want to approach from out in the river, you must "ferry glide" across the current - at 3kts forward, you will approach at 45deg, at 6knts forward the angle will be finer, but use your maths to work it out, I always ferry glide by eye, using landmarks to tell me if I am on target or not. As you hit dead water, straighten up & throttle back or you will hit the lock gate. Perhaps be ready to reverse or have a rope ready to throw to a helper on the quay.

You can approach with the tide, but as soon as your bow hits the dead water, the stern will be swept past & you risk hitting the far side, you may get away with a fast downstream approach to turn in quickly (much depends on your keel shape than) but you still risk the spinning effect of the stern left in the current longer than the bow.

You can approach against the tide, if you have a reasonable speed over the ground & turn late so as not to be swept onto the near corner of the lock entrance. Again, be ready for an apparent sudden acceleration as you enter the slack water & be ready to use a warp or hard astern to kill the speed.

If your boat handles like a narrowboat, just wait for the next available highwater somewhere else or move your boat to a safer bit of water.

 

[Storyline]

I have entered the lock many times but always with a powerful inboard engine. I always do what you did but try to balance the revs when stemming the tide so we are only just making when crabbing sideways then make a sudden turn to port when out of the tide. I have also tried it from upstream with the tide under us as Savageseadog suggests but personally I prefer your approach against the tide as I feel the boat is more under control. When coming down with the tide the boat speed through the water is actually quite slow even though you are zooming down towards the lock so you do not have much steerage.

If I was you I would practice with the start of the ebb and then slowly gain confidence by entering later and later after HW. The lock can be quite intimidating at first but you will soon get used to it. Saying that, I came on from the river for the first time in more than 10 years last winter and I had forgotten how little room there is out of the tide. It was dark and we only just made the last lock in so had 2 hours of ebb to deal with. All the confidence I had gained in the past had deserted me and it was bit alarming.

edit: - I have just read Searush's reply and he makes a good point about using landmarks to judge your speed as you ferry glide against the tide. There a lots of transits available as you approach the lock - from memory these are lamp posts with warehouses/buildings behind them. If you use them you can adjust your SOG so you are only just going forward so you have the minimum boat speed to contend with when you make your sudden turn to port and into the lock.

 

[dslittle]

Never done Liverpool, but we have to do similar quite often down south and it still scares the hell out of me. The only practical way is to approach uptide as suggested and turn in - That should be manageable on a 25 footer - imagine what it's like on a 45 footer - you can still have a lot of current across the stern as the current on the bows drops off to zero! Needed a very stiff brandy after that one!

Not a lock but did get the entrance to Exmouth Marina VERY wrong a couple of years ago. Came in as above but did not see eddy in the entrance. Went from about 3 knots into the ebb to about 7 knots into the wall!!! Nearly recovered it but managed to make a very loud noise and reasonably sized hole midships. I suppose that it was entertaining for the folk watching as they waited for us to go though and the bridge to go down...

 

[nigel1]

Done this many times, like others have suggested, stem the tide, get the boat settled, with a good view of the lock gates, and use a transit to keep the boat stopped over the ground. When you get the green light, angle in towards the bell mouth at the lock approach, adjust engine speed to keep on your transit. As you approach the bell mouth the tidal steam will start to ease, point the bow around more, ease up on the revs. Word of warning, on the ebb you can get a strong counter flow coming off the downstream wall, which can make it hard to turn to port for the final approach. Be ready for this, and use positive helm and a burst of power to get the bow around. Once in the bell mouth, it turns into a mill pond,and I find I'm covering the last 50 meters at idle revs/neutral.

I here there are a few users of the marina who just wont go in on the ebb. On the flood tide its much easier.

 

[[3889]]

If you want to approach from out in the river, you must "ferry glide" across the current - at 3kts forward, you will approach at 45deg, at 6knts forward the angle will be finer, but use your maths to work it out, I always ferry glide by eye, using landmarks to tell me if I am on target or not. As you hit dead water, straighten up & throttle back or you will hit the lock gate.

^^^This^^^ plus wait in the river until the outer gate is opened to give you a longer deceleration path. If you think Liverpool is hard try Fiddlers Ferry - same current, half the width and submerged bank in the entrance.

 

[davidpbo]

Crewing a 50 ft ex naval pinnace towing another, entering Albert Dock with the inner basin fairly full of boats was quite exciting in my limited experience of sailing at the time.

 

[Jaguar 25]

I have entered the lock many times but always with a powerful inboard engine. I always do what you did but try to balance the revs when stemming the tide so we are only just making when crabbing sideways then make a sudden turn to port when out of the tide. I have also tried it from upstream with the tide under us as Savageseadog suggests but personally I prefer your approach against the tide as I feel the boat is more under control. When coming down with the tide the boat speed through the water is actually quite slow even though you are zooming down towards the lock so you do not have much steerage.

If I was you I would practice with the start of the ebb and then slowly gain confidence by entering later and later after HW. The lock can be quite intimidating at first but you will soon get used to it. Saying that, I came on from the river for the first time in more than 10 years last winter and I had forgotten how little room there is out of the tide. It was dark and we only just made the last lock in so had 2 hours of ebb to deal with. All the confidence I had gained in the past had deserted me and it was bit alarming.

edit: - I have just read Searush's reply and he makes a good point about using landmarks to judge your speed as you ferry glide against the tide. There a lots of transits available as you approach the lock - from memory these are lamp posts with warehouses/buildings behind them. If you use them you can adjust your SOG so you are only just going forward so you have the minimum boat speed to contend with when you make your sudden turn to port and into the lock.

Pretty sound advice, thanks. I have entered the lock five times to date and only had a problem on Sunday (close to springs and tide on the ebb). Looks like the normal requirement of PRACTICE, PRACTICE, PRACTICE still applies! (And watch others at the lock coming in on the ebb from above).

Good discussion, many thanks.

 

[savageseadog]

I've realised what I suggested might not be clear. On the flood, approach with the tide, from North/West at your best speed aiming just off the North knuckle, throttle back just as you clear the the tide. On the ebb approach from the South/West, aim just off the South knuckle. I do the lock very regularly and it works.

The problem with approaching against the tide is that in a slower boat you will end up across the lock and when you turn it's easy to be pushed onto the downstream wall. There is plenty of room before the lock gates so it's not too bad.

 

[Deej]

My boat is a similar size and engine power to yours. I tend to reduce power a second before entering the slack water in the mouth of the lock and I'm also ready to pull sharply on the tiller to straighten up. I think once you've done it a few more times, you'll anticipate how your boat is going to behave and it will be easier.

Dave

 

[marklucas]

Surely the way to enter any lock / entrance / cross a river in a cross-tide situation is to take a transit of where you want to finish up and steer to stay on it.

No maths, no worries and constant feedback as to your progress.

 

[maby]

Surely the way to enter any lock / entrance / cross a river in a cross-tide situation is to take a transit of where you want to finish up and steer to stay on it.

No maths, no worries and constant feedback as to your progress.

Unless your boat is shorter than the lock entrance is wide, there will be circumstances under which this results in you getting stuck in the entrance! There comes a point at which you have to straighten up and, depending on the length of your boat, the strength of the current and the geometry of the lock approach, this can be a tricky situation!