reading depth levels on charts

[guiltypleasure]

The depth levels on charts indicate an average depth but how do I accommodate for the tide shift? I remember learning this a few years ago but it obviously didn't stick. Any tips on how to adjust my depth reading based on tide shift?

 

[tommays]

Re: reading depth levels on charts

The depths are at LOW tide BUT they do NOT redo the surveys very offen so in many places there a guideline as to were there may be shallow water

 

[Chris1956]

Re: reading depth levels on charts

Aren't the charts marked as Mean Low Water?

One of the things that would be important is how much the tide changes from high to low. For example, on the Bay on which I boat, low and high tide are about a foot or 1-1/2 feet. So the mean low water markings on the chart will be within inches of accurate dispite moon tides, blowout tides and the like.

 

[guiltypleasure]

Re: reading depth levels on charts

The waters where I boat have a tide variation of anywhere from 2.5 - 4 feet. A very low tide means I'm not getting home that day, hence my interest in reading the chart depth and knowing what that number is based on.

If I understand chris1956 correctly, the Mean Low Tide would indicate that if the chart says 1, then that's what I should expect at low (of course accommodating for shift of the bottom over time and variations in the moon). Is that correct?

 

[donnymac]

Re: reading depth levels on charts

Yep, the depths are for mean low. I live where the tide changes 8-12'. Great for fishing, not so good at the boat launch. Timimg is everything.

 

[INJUN]

Re: reading depth levels on charts

Yep, soundings at mean low, but heights are above mean high water.

 

[Intuition Gloucester]

Re: reading depth levels on charts

And some of those lows can be 'mean' indeed. Watch the traffic and the bottom. I've strayed too close to the side of the channel, well within the markers" and bumped along.

 

[dingbat]

Re: reading depth levels on charts

On a lot of bodies of water the tides can get trumped by the wind. I've seen water piled up in parking lots at what was supposedly low tide and I've seen boats sitting in the mud at what was supposedly high tide.

As someone else already alluded to a lot of the shallow water soundings on charts are useless. They are either too old to be of any use or change so often that you can't count on the depths you ran in just a year earlier. Nothing can take the place of knowing your local waters.

 

[Billdc]

Re: reading depth levels on charts

When I'm reading tide charts and they give low tide and a ( 0.8 ). Does this mean that I add 0.8 feet to the chart reading?

 

[Blue Crabber]

Re: reading depth levels on charts

That is my understanding of it. Since the chart depths are mean low tide. When you pull up chart tables online of current tide levels and they give you a reading in feet it would be in addition to mean low water time. Add the readings together and you should have the current water depth.

Hopefully someone else can verify that this is right or correct me if i am wrong as this was the method i have been using.

(I also don't normally go anywhere that would be to low in my boat at mean low tide even while boating at high tide)

 

[Home Cookin']

Re: reading depth levels on charts

Yes and there should be a corresponding (3.4) or whatever to show the height of the high tide above MLW. But as said above, these are printed based on moons and not weather.

Saturday I was running in the intracoastal waterway, low tide, in the channel and about 20' from a channel marker when I ran slam aground, drawing about a foot. From there, there were no more channel markers across the bay (about a half mile) but we poked over to shore, using the tops of crab pots as a guide. We found a winding creek through the marsh and picked up channel markers about a mile away. The Army Corp simply abandoned a section of channel. This was not a surprise to us, but would be to a boater who followed charts and channel markers, especially at low tide, and could have been very dangerous to such a boater.