Pgitug
Guru
I have referenced Bob Taylor in past discussions for his extensive scientific anchoring knowledge that he acquired during 45+ years with the US Navy and offshore industry.
Our late company founder kept a small library of his US Navy work and here's a download to a report that Bob did on multiple anchor use:
NCEL Tech Data Sheet 83-05.pdf
On page 4 ( image below) of this report is a brief summary of different anchoring set ups. When I questioned him recently on using our anchor in a tandem (or piggyback) combination, his comment was:
"The best way to use Fortress and most other anchors with this configuration in tandem is to use option 4 in table 2 of the Tech data Sheet. This allows each anchor to function properly. In reality the rear-most anchor will eventually move into the trough created by the front anchor and dig deeper than it normally could resulting in more than twice single anchor capacity."
gif uploader
Looks like my method is option #3.