Minimum depth under keel

[acunningham]

When entering or leaving an unfamiliar tidal harbour that has inadequate depth for your boat at low tide, what's the minimum depth of water that you're willing to tolerate under your keel when planning your arrival or departure time? Does rising tide versus falling tide make a difference? How about onshore wind versus offshore wind, day versus night, etc?

[Benz]

One inch. Or half of one, which is all you get in South Florida sometimes.
I like to go into skinny water on a rising tide, but there are far more variables to consider: if the tide range is a whopping 25 feet rather than 2 feet (been there), then you have to work the tide tables, since depths change dramatically faster, and there can be lots of water under the keel or very little within an hour.
But there are more variables: is there weather? Do you need to get through a skinny channel before dark/squalls/drawbridge closures? Do you need this tide to get out so as to arrive at the next place before the turn (very important in the St. Lawrence seaway). Sometimes you must risk an inch or two to spare, hateful though it may be, for a greater purpose.
What you want to avoid is trapping yourself behind inflexible rules, that, while designed to keep you safe, limit the options--options you might need to stretch to their fullest potential sometimes in order to avoid a bad outcome.

[Pete7]

We have crept into some locations with just a few inches under the twin keels

However, you make a good point about tides. A good blow up the English Channel can change both time and height of tides as does the air pressure.

We touched bottom and had to wait quarter of an hour for a bit more tide to get in here, but that's half the fun creek crawling to a place fin keelers fear to tread

Pete

[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

[thomm225]

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

Plus knowledge of the bottom is also helpful so you have an idea what you may be hitting. (soft mud or rock)

[Tupaia]

I once tried to warn a following monohull not to follow me, people walking across the river in front of me should have been a give away, but there again my old cat only drew 10 inches with the rudders up.
The trick is not to get neaped.
I once had a mud berth only accessible on a few tides during the equinoxes.

[thomm225]

Originally Posted by Tupaia

I once tried to warn a following monohull not to follow me, people walking across the river in front of me should have been a give away, but there again my old cat only drew 10 inches with the rudders up.
The trick is not to get neaped.
I once had a mud berth only accessible on a few tides during the equinoxes.

I purchased my boat at a marina that I could only enter an hour or so either side of high tide so you had to plan your comings and goings.

The boat sat in the mud a lot at the dock also which made it quite stable!

It was Deep Creek Boatyard and Marina.

https://www.google.com/maps/place/De...!4d-75.7507708

https://charts.noaa.gov/OnLineViewer/12228.shtml

[Barkingmad]

High tide only! I really don't know if I was dragging on the way in or out, so much stirred up silt from the propwash you couldn't tell.
As the tide went out you just sunk into the ooze, I'd hate to know what/who is under there!

[chris mac]

In the Bahamas with mostly sand in the shallow areas, I try to go an hour or two before high tide. That way if I ground, I know I can float off and go back.

[sail sfbay]

Originally Posted by acunningham

When entering or leaving an unfamiliar tidal harbour that has inadequate depth for your boat at low tide, what's the minimum depth of water that you're willing to tolerate under your keel when planning your arrival or departure time? Does rising tide versus falling tide make a difference? How about onshore wind versus offshore wind, day versus night, etc?

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.

[rwidman]

An inch is all you really need.

Actually, it depends on the bottom. In some areas, the bottom is made up of soft mud and decomposed marine organisms. In South Carolina, we call this "pluff mud". You can drive right through it.

Hard packed sand or rock would be a different story. I would want a little more depth in these conditions.

[Halam]

I often get stopped by the mud as I try to push into my berth too early, it is soft mud and I'm going dead slow. On the other hand, I get alerts from the UK Environment Agency when local flooding is expected, sometimes tides are a meter above what the tables predict.

Clearly, there is a difference between planning and execution. With a soft bottom, I plan to scrape in and proceed dead slow. If I sailed a fin keeler and was approaching a hard cill then I'd prefer a meter. I wonder how many boats actually float at their documented draft.

[Bay Breeze]

A lot more careful in Maine with rocks than Florida with sand and mud. In Maine allowing a foot under keel at charted low tide minimum. In gulf and ICW up to Chesapeake, 6 inches. Cost of prop or rudder repair informs our choices.

[Scubaseas]

Depends. Prefer rising tide, soft mud and no waves then maybe 6". If rocky bottom two feet and consider wave height now and when leaving. Also there are places where wind can seriously affect how much water there is or not.
Currently off Galveston Bay. If I came in today I have 7 feet since there has been a strong South wind. If the wind blows out of the North hard for a day or two that could drop to 2 feet.

[Clivevon]

Originally Posted by rwidman

An inch is all you really need.

Actually, it depends on the bottom. In some areas, the bottom is made up of soft mud and decomposed marine organisms. In South Carolina, we call this "pluff mud". You can drive right through it.

Hard packed sand or rock would be a different story. I would want a little more depth in these conditions.

+1