Measuring slip depth

[marshcat]

I keep my shallow draft catboat at a friend's dock. I would like to figure out the true low water depth, so I know want kind of draft the slip can actually handle.

I assume it is as simple as sticking a pole in and measuring the depth (in a few different spots) over several low tides. Is there anything else to be aware of, or that I should do to get a good trusworthy reading of depth?

Thanks.

[Canoeyawl]

I found an old engine block on the bottom in a slip once...
and a few batteries etc.

[rbgarr]

A local tide record may show the extreme low and high tide dates and times. IIRC April 8-10 will be when those occur next on the East Coast. Wind conditions before and on those dates can have an effect on whether those heights are met.

There's a business here that has been pushing for a permit to put in a sizable marina. Much of it will be located on a set of flats that has about a foot of water at extreme low tides. It's incomprehensible to me that it will get permitted. I predict that they will be seeking further permits for dredging in the future with the excuse that "'We didn't know!!"

[Ian McColgin]

Yep, look at a tide chart to identify the springs and neaps. Depending on your location, you may have to make time and height corrections off the main station table and you may find that even at that, you should use the closest prediction as a guide for the hours over which you should get out with your dip stick. You'll want to do this through several cycles as many locations have tide much influenced by weather, both local and oceanic.

Remember that the tide changes the least in the hours on either side of the tide, high or low, according (CEGW) to the "Rule of Twelvths." That is between one tide (low or high) and the next (high or low) rounded to about 6 hours or at least the span divided into 6ths, the first hour will see a change of 1/12 the total change, the second hour 2/12, third hour 3/12, fourth hour 3/12, fifth hour 2/12 and last hour 1/12.

G'luck

[TerryLL]

Another thing to consider that you will not find in the tide charts, and you will not learn be measuring at low tide, is the effect of atmospheric pressure on the tide level. An extreme low or high pressure can cause the published tide data to be off by as much as a foot. Extreme low pressure will cause the actual tide to be higher than the published number, and extreme high pressure will cause the actual tide to be lower than the published data.

So if your lowest low tide occurs during an extreme high pressure event, the actual tide will be noticeably lower than expected.

[Woxbox]

Also, sustained winds in wide shallow bays can have a remarkable affect on tides. Two feet either way is not unheard of. But if your boat settles into the mud once in a blue moon, where's the harm?

[S/V Laura Ellen]

There a about a down cresent wrenches and pliers on the bottom under my slip.

[rbgarr]

and sunglasses... and fuel and water tank fill caps....:D

[S/V Laura Ellen]

and sunglasses... and fuel and water tank fill caps....:D

How did you know?
Surely you're not suggesting that I submit a full list?:eek:
This could take a while!:D

[Canoeyawl]

and coffee cups, and wine bottles -
but that darn V-8 Chevy will make an ugly dent in your boat at lower low water