Tennyson lived on The Isle of Wight for many years and used the Lymington to Yarmouth ferry as it was the nearest to his home.

Lymington bar has a legend that if you hear the bar moaning it means that you will die soon. The Lymington bar is not a hard one to navigate, being mainly mud and sand and not very large, so few will hear it moaning.

When Tennyson went to Salcombe he may well have heard the bar there moaning and put the sound with the local Lymington story to come up with the idea for the poem.

Just a theory but one that does make some sort of sense.