Can mooring lines pull my boat underwater when water rises?

Yes. I have seen it happen on the upper tidal Thames where boaters familiar with the non-tidal river have made a rare visit into the tidal part and forgotten to allow sufficient slack in their mooring ropes. Sometimes the ropes or deck cleats give way first, in which case the boat may drift away, but often the boat heels over and then water spills in over the gunnels and it sinks.

I see such a casualty about every third or fourth time I go canoeing in the highest tidal reaches, usually boaters making the transit between Teddington Lock, where the tide ends, and the lock into the Grand Union Canal at Brentford about six miles downstream. Being used to canals or the non-tidal upper river, they forget to allow for tides.

2' rise is nothing try 10 meter tides!!. You just make sure that there is enough slack in the mooring lines to allow the boat to move up & and down by a bit more than the expected tidal range. A 2' change will not pull a boat under (unless it is very shallow draft) It will however put a lot of strain on ropes cleats & hull structure

I've never seen a solid wooden dock that regularly goes underwater. They are usually well above high-tide level. If there's not a floating dock, I've seen vertical iron rails with metal rings; you moor your boat to the rings and everything rises when the tide comes in. If you tied your boat direct to a low part of the dock itself, there would be many tons of force on the rope when the boat tried to rise, if it's large enough to live on. I'd assume something would break, perhaps the deck fittings.

If this is even a question in your mind then you have not tied your boat off correctly. you need to tie it off in such a way that you can account for the tides. this means you need to have some slack in the lines.. the easiest way to gain the flex you need is to legthen the lines

1. Take the bow line and tie it 10+ feet in front of your bow. and take the stern line and place it 10+feet back.. the extra line length will give you the flexibility you need.

2. if you have a small ski boat, boat they make special bungie cord that flexes you can use So you dont need to worry about it you need to change the way you tie your boat off.

As the water rises the boat will list. It won't stay level, so it is unlikley to be pulled under.

Oh yes. I have seen it happen.

I have also seen a boat left hanging from the dock by the mooring lines.

Yes, and whilst the tide falls, if the lines are tight, they'll pull the cleats off your deck

Yes, and when the tide falls, if the lines are tight, they will pull the cleats off your deck

Yes it can pull your boat under

Yup, many a craft has met its end this way.

What can also happen is the cleat gets ripped off, usually taking a section of toe-rail with it.