What’s the minimum depth you would sail in?

[sail sfbay]

Sailing in shallow water risks running into submerged objects or sandbars in shallow rivers and tidal estuaries that feed into the San Francisco Bay. For that reason we sail in deep water AND waterways we are confident we will not hit submerged objects or sandbars.

[Letterkenny]

Originally Posted by Phyrcooler

You’re talking about east bay sailing. You are correct that it’s reputed to be mostly mud bottom. Regardless, you wouldn’t want to run aground, especially on a falling tide. Normal tidal swings in SD bay are 6-6.5 feet, but swings more based on time of the month and weather. Today’s low tide was -3.1’. A couple days ago, it was -3.7. There’s a lot of 11’s & 12’s on the chart - so most places you’re at 7’-9’ at low tide. I don’t like anything less than 3’ under my keel if I can.

Most often when I’ve heard folks grounded, they are just east of the channel going into Glorietta Bay - NE of the little peninsula where the Navy’s small boat group is. It’s shallow in there folks! Don’t cut the corner by the Green Buoy!

A good tide App is your best bet. Decide your comfort level and always make a tide check part of your pre-sail checklist.

I thought most of the charts show the depth at low tide? At least Navionics?

[Phyrcooler]

Originally Posted by Letterkenny

I thought most of the charts show the depth at low tide? At least Navionics?

You are correct. Depth only correct when tide is “0”. Which is why you will have actual depths of less when tides are in the negative range.

[MicHughV]

there are two kinds of sailors....

1. those that have run aground...
2. those that will run aground.....

[Mike OReilly]

Originally Posted by Letterkenny

I thought most of the charts show the depth at low tide? At least Navionics?

Yes, sort of... The charts show some version of the average depth of the lowest tides. Some, like the NOAA, use "Mean Lower Low Water", which means the average of the lower low water height. Other countries, such as Canada, use a slightly different standard. Here we use lower low water of the large tide, or "Lowest Normal Tide."

In simple terms, it's the lowest one would expect to see in most of the time. But because it is based on norms and averages, negative water heights are always possible.

[BillKny]

Originally Posted by MicHughV

there are two kinds of sailors....

1. those that have run aground...
2. those that will run aground.....

Actually there are at least two other kinds of sailors in addition to the above list:

3. Those that never go anywhere.
4. Those that lie about never running aground.

[Phyrcooler]

Originally Posted by Mike OReilly

Yes, sort of... The charts show some version of the average depth of the lowest tides. Some, like the NOAA, use "Mean Lower Low Water", which means the average of the lower low water height. Other countries, such as Canada, use a slightly different standard. Here we use lower low water of the large tide, or "Lowest Normal Tide."

In simple terms, it's the lowest one would expect to see in most of the time. But because it is based on norms and averages, negative water heights are always possible.

Mike is absolutely correct - and it’s a good reminder to make sure you are using the correct setting in your tides App. You can choose the correct tide datum in the settings.

[Adelie]

Originally Posted by Letterkenny

I thought most of the charts show the depth at low tide? At least Navionics?

In general charts show depth from:
A. Mean lower low water
B. Mean lower low springs
C. Mean lower low astronomical.

A. Approximately 1/4 or 1/8 of the lows are less than the number on the chart.
B. Approximately 1/30 or 1/60 of the lows are less than shown on the chart.
C. 1 predicted low sometime will be the same as shown on the chart.

In the US I believe most charts use MLLW. Lower low is averaged over 19yr for MLLW and MLLS.

You need a tide table to know when lows are and what their value is.

[belizesailor]

Like almost everything...it depends.

Crossing a shallow bar in calm conditions...an inch is as good as a mile.

Crossing a shallow bar in rough conditions...not so much.

Sailing in a shallow, well protected bay, with minimal wave action and a soft bottom with local knowledge...Id been be willing to cut it pretty damn close.

[Adelie]

Originally Posted by Phyrcooler

You’re talking about east bay sailing. You are correct that it’s reputed to be mostly mud bottom. Regardless, you wouldn’t want to run aground, especially on a falling tide. Normal tidal swings in SD bay are 6-6.5 feet, but swings more based on time of the month and weather. Today’s low tide was -3.1’. A couple days ago, it was -3.7. There’s a lot of 11’s & 12’s on the chart - so most places you’re at 7’-9’ at low tide. I don’t like anything less than 3’ under my keel if I can.

Most often when I’ve heard folks grounded, they are just east of the channel going into Glorietta Bay - NE of the little peninsula where the Navy’s small boat group is. It’s shallow in there folks! Don’t cut the corner by the Green Buoy!

A good tide App is your best bet. Decide your comfort level and always make a tide check part of your pre-sail checklist.

I think you are misreading the tide tables. NOAA says the lowest tide recently was about -1 on 7/10. I believe the lowest slows are about -2 and tats only every several years.

https://tidesandcurrents.noaa.gov/no...ion=dailychart

[Scorpius]

Originally Posted by Letterkenny

I thought most of the charts show the depth at low tide? At least Navionics?

American NOAA charts show depths above and below Mean (or average) Low Water - meaning that, for about half the low tides, the water is SHALLOWER than shown on the charts. So watch out!

On Canadian charts, depths are shown at either Lowest Normal Tides, or Lower Low Water, Large Tides - so we almost never have minus tides and water depths are pretty well always at least as deep as shown on the charts.

I guess in Florida, the Bahamas, etc. with very small tides, this isn't a big deal - but in Alaska with 40' tides (or even around here with 16' tides) it's critical and could mean life or death.

Then of course there's the fact that US charts are in fathoms (and feet in shallow water) whereas Canadian charts are pretty well all (I think) now in metres (and decimetres in shallow water). It was pretty confusing for a number of years there during the conversion with half our charts in fathoms (and feet) and half in metres ( and decimetres ).

[MicHughV]

In a 35 year career of sailing, I have had some pretty impressive groundings.....bottom terrain in shallow water changes due to strong currents, silts up, etc..the chart might say one thing, but the reality is often different.....the USA east coast ICW is classic......

What I found interesting, was that when I first started sailing, I did not have a depth sounder, so I never knew with any accuracy what the water depth was. In a way, this was quite blissful. I never worried about it. I would, off course, run aground from time to time, but I did mostly worry free sailing. I never knew if there was 6" of water under my keel or 6'.

Fast forward a few years, and a digital depth sounder appeared at the helm. I would find my eyes glued to this device, in essence it became my guiding light. It became addictive, and whereas I was at one time, a mostly carefree sailor, I found I had become a worrywart....

Sometimes, ignorance is bliss....'jes sayin'....

[Mike OReilly]

Originally Posted by MicHughV

Fast forward a few years, and a digital depth sounder appeared at the helm. I would find my eyes glued to this device, in essence it became my guiding light. It became addictive, and whereas I was at one time, a mostly carefree sailor, I found I had become a worrywart....

I use the sounder as an essential part of basic navigation. It's a great way to determine your location or work your way into small harbours and little nooks. Find a contour and follow it in.

I have sailed without digital sounder though. Our sounder died at the start of one season. Instead of hauling out, and spending valuable cruising time replacing the transducer, we just learned to rely on the old lead-line. We both got really good at taking quick soundings as we entered harbours to anchor.

I've continued the practice, and always have the lead-line ready for use.

[Phyrcooler]

Originally Posted by Adelie

I think you are misreading the tide tables. NOAA says the lowest tide recently was about -1 on 7/10. I believe the lowest slows are about -2 and tats only every several years.

https://tidesandcurrents.noaa.gov/no...ion=dailychart

Good eye! And not so much reading wrong as much as playing with my phone the day before and stupidly left the App setting on MSL which gave that reading I had referenced. I actually caught it this afternoon, but it was too late to edit my post to clarify. Regardless, underlying lesson I was trying to get across is that you can and will have depths less than chart depths in the bay.

[Letterkenny]

Looks like the Navionics Boating app can adjust the depth on the charts live for the current tide. I’ll likely double check that when going into that area. When posing this question, I am mainly just looking at this area which is better documented (but always go past the shoal first!) as I’d likely be a lot more hesitant in unknown or less documented waters.