Thanks Carl-Henry. I am delighted someone more knowledgeable than me about DNA is having a look at my Blennerhassett DNA project. Please don't go away.
Well first of all I am delighted Paulo is interested. I did not know he had a post here until today.
It is indeed an interesting hunt. So let me explain. As Paulo said, I spent a lot of time on a "Plan A" theory, namely that my family descends from Letitia Blennerhassett of Tarbert (born 1780). I did no less than 295 one-to-one DNA comparisons on Gedmatch and the best I got of all of them was 8.4 cM. And there was no pattern either.
So I finally dumped Plan A and tried to find a Plan B theory.
The obvious Plan B theory was the Baronets branch, since there was some evidence we are connected to their seat, Churchtown House, Co.Kerry, plus some other clues, explained here:
Then on my very first Baronets sample, I got a 15 cM match with a George Cashel descendant.
The Baronets line person (Chute) is in the UK. Known ancestry is heavily Anglo-Irish Munster:
The Cashel person (Niemi) is in the US. Known ancestry is mostly Scandinavian and Russian. The only Irish Munster line is Cashel (ancestors born 1807 and 1840). There is one line to Co.Derry (Porter, ancestor born 1752).
Niemi could hardly be less likely, of all the people in my tree, to match Chute.
So you can see why it looks good to me.
There are then further 9 cM matches to the Baronet's wife's family, and this combined with the clues in the documents.
And then last week, I discovered the baptism of a daughter of Sir Rowland, previously unknown to any of the printed histories.
The baptism of Melisent Blennerhassett in 1768 is here:
When the RCB library re-opens, I will go there and photograph the original.
So I think I'm getting somewhere.
However, I like your scepticism, so I need to keep going.
On triangulation, no luck so far.
I have 11 George Cashel descendants on Gedmatch.
None of the other 10 have a matching segment (over 3 cM) in that region on Chromosome 11 that Niemi matches.
In reply to the other issues, no, I only have DNA of a single descendant of Sir Rowland so far. I am working on more.
And then on the Bayly matches, yes that person is only on Ancestry. I am trying to get them onto Gedmatch.
I tried using Gedmatch Triangulation tool but it never seems to terminate.
Is there anything else I could do with the material I have right now?
Carl-Henry, if you drop me an email I could send you the Gedmatch kit IDs and maybe you could have a look yourself?