Counting occurence of multiple cells containing data

I have a worksheet that has rows of data, that are made up of blank cells or cells containing a single letter (see screenshot example). The cells I'm interested in are groups of 6 or 7 cells that contain the letters "d", "a" or "n".

I need to count how many of these groups of 6 and how many groups of 7 cells exist in a row. Note that often such a group is followed by cell containing a letter "U", these should be considered as a blank cell (and not counted).

There are also groups of cells containing the letter "v", these should not be counted as well.

Hope this makes sense