Low Water & Safety Margins.

[lw395]

Under keel Clearance minimum safety margin 20% of draft is a common recommendation. For my boat at over 6ft draft or approximately 2m. 20% would be 40cm or 16 inches.
I'v a feeling I'd want at least twice that. Probably a meter would make me happier

Never heard that before.
sounds less than useful to me.
The issue is mostly the uncertainty in actual height of tide, uncertainty in charted depths, and an allowance for waves.
None of those are proportional to the draft of the boat.
The first two factors can be contained by using a local real time tide gauge and local knowledge.
The third is a matter of judgement, but you might hope that a wind that made the entrance a lee shore might make the water a little deeper....

The other issue is knowing that your track will be in the deepest water at the key time... can you trust the helm to keep the boat exactly on the transit etc?
I once motored very slowly into the Yealm, in a boat drawing 2.4m. The smaller boat 'following' me ran aground, I didn't.
At least nobody has mentioned the immutable rule of twelfths yet....

 

[alahol2]

Just to add to the uncertainty, the tide times/heights that are being quoted relate to Buckler's Hard, about 3.5NM up a river.

 

[Ian_Rob]

That's correct and another factor that I was pondering the consequences of. Having spoken with the harbour master, he is quoting from the same tide table so I assume that that is the best available data. Interestingly, he also says that the lowest depth on the transit is rather more than 0.8m. The tide gauge at Gins Farm (as pointed out by ChrisE) will be helpful.

 

[Sailfree]

I have always been cautious at Bealieu but often wondered what the bottom is. Can anyone advise?

Going into Parkstone YC I have often scraped the bottom of the keel but always going slowly. I have ploughed my way out of Wotten Creek when we found ourself sinking into the silt and mud and the water clearly going out 1hr before HW!! If the bottom is hard or even gravel and a swell possible then I leave lots of clearance. I would speak to the Harbourmaster ref any changes in entrance depth and profile/position of deepest chanel.

 

[ChrisE]

I don't know for certain, but according to the chart sand.