NavList:

I am looking for help in understanding something about Thomas Sumner’s event during which he discovered his line of position.  Space does not permit recounting the details of his situation, nor a drawing of the navigational plot of his attempt to find Small’s light.  However, this is covered in detail in Bowditch and many other navigational books.  At the very end of the recount it says” The DR position was found to be in error by 8 min too far south, giving a longitude of 31 min, 30 sec too far west.  The result to the ship might have been disasterous had this wrong position been adopted”. My question is howso?

Can anyone tell me from historical insight of navigational procedures what course Sumner would have set had he not questioned his first position?  In other words would he have turned to go straight through St. George’s Channel, or would he have turned to acquire Small’s Light first? I can see that the latter choice might have been more dangerous because he would have gone south of Small’s light, and his eta would have been upwards of 2 hours late, catching him off-guard when land (or rocks) appeared. But there were the Saltees Rocks light and the Tusker Rock light off the coast of Ireland which would have given him some protection had he opted to go straight for the Channel.

This is not just a pedantic question I have.  I talk about this situation in my seminars to show how his line of position was discovered, but thankfully no one has questioned me about exactly how a disaster was averted.  Any comments are welcomed.