Cross tide (river) pontoon berth

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Ammonite

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This season I will be using a cross tide pontoon berth with a circa max. 2.5 - 3.0 knot tide on the ebb that will pin me to the pontoon. Should I want to leave on the ebb my current plan is to sprong myself off using a stern spring attached to the stern cleat furthest from the pontoon with the help of a 75kg thruster. However to make life even more interesting I will need to turn through 90 degrees in order to clear the boat in front so if needed I was thinking of attaching the sprong to the midship cleat and then on to the stern cleat so I could unhook this part way through to aid the turn.

Up to what ebb rate do you think this would work ignoring any wind effects?

Boat is a shallow fin Moody 36 drawing 1.45m with a 40hp engine.
 
My advice would be either find another mooring, or wait for the ebb to finish.

You may be able to drag the stern into the tide, but the likelyhood of getting pushed onto another boat and doing significant damage is very high.

Whatever you do, DO NOT try to spring the bow out and go out forwards. That is a recipe for disaster. The only option is to spring the stern out, use the bow thruster to keep the bow in tight to the pontoon, and reverse out.
 
Bobc said:
My advice would be either find another mooring, or wait for the ebb to finish.

You may be able to drag the stern into the tide, but the likelyhood of getting pushed onto another boat and doing significant damage is very high.

Whatever you do, DO NOT try to spring the bow out and go out forwards. That is a recipe for disaster. The only option is to spring the stern out, use the bow thruster to keep the bow in tight to the pontoon, and reverse out.
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I think you've misunderstood my post or I havent explained it very well. If I try to spring the stern out I will most likely hit the boat behind particulary as I dont have a stern thruster. Spronging off might not work if the ebb is too fast but I couldnt hit the boat in front as I'll be firmly attached to the pontoon by the "sprong" which would not be released until a 90 degree plus turn has been made. I'm very aware of the cockups made by people trying to go out forwards in this situation when using a regular spring which isnt what Im proposing. I am in essence turning the boat through 90 degrees in its berth.

I know it works in fairly benign conditions just not what sort of ebb the method could cope with however I am open to other suggestions and wouldnt do anything that risks damaging another boat
 
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with that rate of tide, I think the only 'safe' way would be if you could warp the bow out until the boat is positioned with its stern against the pontoon, i.e. at a right angle to the pontoon. Then motor away from the pontoon. Otherwise, I would wait for the ebb to ease. If I definitely needed to leave at that time, I would move the boat ahead of time to somewhere easier and leave from there.
 
Rappey said:
It's down to your boat handling skills and knowing exactly how your boats reacts in a given situation.
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Indeed but I was hoping that someone may have experience of a similar berthing situation. Im pretty handy when it comes to boat handling but just havent faced this particular challenge before!
 
Aeolus said:
with that rate of tide, I think the only 'safe' way would be if you could warp the bow out until the boat is positioned with its stern against the pontoon, i.e. at a right angle to the pontoon. Then motor away from the pontoon. Otherwise, I would wait for the ebb to ease. If I definitely needed to leave at that time, I would move the boat ahead of time to somewhere easier and leave from there.
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This is in effect what Im proposing but using the sprong in conjunction with the thruster as I'd need to be able to walk on water to warp it around :-)
Im assuming there will be times when the ebb is just too strong but Im keen to work out what the window will be
 
Ammonite said:
This is in effect what Im proposing but using the sprong in conjunction with the thruster as I'd need to be able to walk on water to warp it around :)
Im assuming there will be times when the ebb is just too strong but Im keen to work out what the window will be
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Hmm. I see where you're going with this. Personally it's not something I'd attempt.
 
Ive a long keel and I don't think a 3knt current would allow me to get off a pontoon with boats in front and behind.
I have a wide transom so my only option is to motor forwards against a spring on full lock, if my stern goes out far enough the spring is released and I give it lots in reverse to get away
If It looks like I can't do it I just drift back to where I was.
 
I think this is one of those situations where you either haul yourself off with a kedge anchor, or a line run out to something (if there is anything!) uptide, or wait until slack water.

Or, if there is a boatman on duty in the marina, ask him to tow you off.

Or, ask for a more convenient berth.

BTW, what do those ahead and astern of you do?
 
Rappey said:
Ive a long keel and I don't think a 3knt current would allow me to get off a pontoon with boats in front and behind.
I have a wide transom so my only option is to motor forwards against a spring on full lock, if my stern goes out far enough the spring is released and I give it lots in reverse to get away
If It looks like I can't do it I just drift back to where I was.
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My previous boat had a long keel and I wouldnt attempt it with that! It was a great introduction to boat handling though :-) If it doesn't work I'll be waiting for the tide to ease and going out backwards
 
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Poignard said:
I think this is one of those situations where you either haul yourself off with a kedge anchor, or a line run out to something (if there is anything!) uptide, or wait until slack water.

Or, if there is a boatman on duty in the marina, ask him to tow you off.

Or, ask for a more convenient berth.

BTW, what do those ahead and astern of you do?
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Poignard said:
I think this is one of those situations where you either haul yourself off with a kedge anchor, or a line run out to something (if there is anything!) uptide, or wait until slack water.

Or, if there is a boatman on duty in the marina, ask him to tow you off.

Or, ask for a more convenient berth.

BTW, what do those ahead and astern of you do?
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Their berths aren't cross tide! Dont worry im on the waiting list for one of those so hopefully this situation is temporary
 
Ammonite said:
Their berths aren't cross tide! Don't worry I
Their berths aren't cross tide! Dont worry im on the waiting list for one of those so hopefully this situation is temporary
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I'm sorry I must have misunderstood your situation. I thought you were berthed on a long cross-current pontoon with a boat ahead and astern of you.
 
Ammonite said:
Their berths aren't cross tide! Dont worry im on the waiting list for one of those so hopefully this situation is temporary
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Does that mean that their berths are at 90 degrees to yours? If so can you use a rope to pull the bows up to go alongside one of the other boats briefly, then depart from there ?

Frankly I would be worried about the pressure on the fenders and chafing or worse of the hull with a 3 knot tide from abeam when leaving the boat
 
2.5 - 3.0 knots, side on to a boat, is an awful lot of pressure.

It will also move the boat so fast you will not have any time to hesitate or err. By my calculations (do correct me if I'm wrong) 3 knots is about 5 feet per second.

You have to be able to get clear of the other boats and get the boat facing uptide or (only if your boat will manouvre in reverse) downtide, and under control, and no engine failure/forgotten lines still attached/rope round the prop etc. to get away safely.

I very much doubt that alone you would even be able to warp the boat round in such a current, even if there were the fixed points upstream to do that.

As others have said, either get the boat into a different position or location before the tide picks up, or wait until it has abated.
 
LittleSister said:
2.5 - 3.0 knots, side on to a boat, is an awful lot of pressure.

It will also move the boat so fast you will not have any time to hesitate or err. By my calculations (do correct me if I'm wrong) 3 knots is about 5 feet per second.

You have to be able to get clear of the other boats and get the boat facing uptide or (only if your boat will manouvre in reverse) downtide, and under control, and no engine failure/forgotten lines still attached/rope round the prop etc. to get away safely.

I very much doubt that alone you would even be able to warp the boat round in such a current, even if there were the fixed points upstream to do that.

As others have said, either get the boat into a different position or location before the tide picks up, or wait until it has abated.
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I think its probably closer to 2.0 - 2.5 knots in hindsight but there are a few berths like this and nothing untoward seems to happen. Besides I imagine a gale exerts a lot more pressure and at least this berth faces the prevailing winds. I suspect I will have to wait for the tide to abate but at least its a lot cheaper than a regular marina berth (for a reason) :-)
 
It sounds reasonable to me, reversing against a stern spring attached to the outside quarter should pivot the hull up in to the current, especially if aided by the bow thruster. As the hull swings up current, with the stern well off the pontoon, it will become easier for the thruster. You then get to a point where forward thrust will drive the bow into the current and you can slip the spring, while maintaining enough forward thrust to stop going down tide, then work the bow through the rest of the turn keeping her up current of your neighbours. Be ready to use positive, purposeful burst of power to get her to overcome the current, especially when going into ahead, snap out of reverse and get forward power on, as quickly as possible without crashing the gearbox.
 
Just looked at my Duncan Well's book, Stress Free Sailing and he describes your situation. An alternative to springing off, is to take a slip from the outside quarter, run it away from the stern to the pontoon, then drive ahead against this line while steering off. The boat will not move forward but the bows will pivot out. You need to fender the inboard quarter well as it will push against the pontoon. He does mention that it will get you 90 degrees out.

And a convenient video from BritSail: -

Note what they say about helm position and also read the comments below, which may help.
 
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