This sounds very promising. I will email you with any info I have. However, David is buried in Athy and did not die in a boating accident but had a brother who was a sailer, Andrew, who died of a heart attack after seeing the shores of England after returning from a long voyage. He is buried (not confirmed as yet) in Hull or Lowestuft.
I have visited David's grave in Athy but I know there would have been only one David Duthie who has lived in Athy at any time so it is very lightly that it is the same family if your information is correct.
David also had a brother Charles.
Unfortunitly, these names were very popular around the time so there are lots of blind trials when trying to track family histories. I pin my hopes on the Athy contection.
I lived in Athy until I was 18. I now live in Aberdeen. Where do you live ?