Minimum depth under keel

[BigAl.NZ]

Originally Posted by Bobby Lex

Like Benz said, there are lots of variables. Too many to have one hard-and-fast rule. Add to his list: 1. wave action. You may have enough depth if the water is flat. But with 1' waves you may be bouncing off the bottom with the same depth. 2. bottom type. I'm much more willing to risk a soft grounding with a forgiving bottom (sand, silt, etc.) than with a hard bottom (coral, rock, etc.). 3. lastly, one the OP mentions, rising vs falling tide. If a soft grounding is quite possible due to little depth, I'm much more likely to risk it if I know the tide is rising and I can float off after a bit of a wait. OTOH, if the tide is falling I'm very wary of risking a grounding, knowing that I could get stuck there for hours.

Bob

Nothing worse than creeping in with 100mm under keel then a big ferry comes along and its wake lifts you then slams you into the mud!

[Shaneesprit]

[QUOTE=thomm225;3551164]I'd say it also depends on your boat, the type keel you have, and how it's connected.

My boat can handle bouncing off the bottom a bit to get over a low spot if necessary without damage and since it only draws 4' I could go overboard and give it a push if necessary

/QUOTE]
Been there done that, off the back of my CAT at night on a 5.8m tide to give it a push at night too. In an area the chart say’s Navigate with local knowledge or something like that, I never plan to leave this spot without 6m of tide as that’s about the point I know the boat will float, if there is only 5m then the boat doesn’t even get wet. It was a need must, when I took over a mooring then found it wasn’t in the condition it was supposed to be.
Lots of interesting mooring spots in the UK needing good tides to get over obstacles. Sometimes the tide won’t touch my boat for many days.
Someone I know hit the bottom on a sandbank on his boats first voyage. Big ferro cement boat, the tide went out and it snapped in two, took 10 years to build his next 58ft in steel

[paul2884]

Originally Posted by sail sfbay

I would NOT enter any tidal harbor that has inadequate depth for my sailboat at low tide. I always time my entry and departure at close to high tide. Rising vs. falling, onshore vs. offshore and night vs. day does not matter as long as it is close to high tide and you have the recommended electronisc. However, always best to enter on a rising tide and during the day.

Good luck around somewhere like north brittany (France) at low water you can stand in the middle of the approach channel and maybe see the sea in the distance!
Sand or mud and a rising tide no swell we may follow the tide in with a few inches under, with swell it would need quite a bit more depth, rocky bottom and lots more depth although you can be more confident about the soundings and channel with rock as it wont have moved..

[Seabeau]

My Presto 36, at heavy ship weight, with her centerboard up, drafts approx. 2'-8"to10”. Board down, approx. 6'-00". If the depth is at least 6 ft+a few inches, I'll sail her thru, bumpin the board if necessary. Less than 6ft. , I'll motor thru with the board up. A (9"X6"X16' lead grounding shoe, takes out all the worry of close encounters of the dirt kind. Designed in 1884 by Ralph Middleton Munroe.