This may be a serious issue, but in my search for a catamaran
I was advised by a couple of brokers and one well-regarded surveyor that it should be far from a deal breaker, if the boat is solid in all other respects.
We often think brokers tell us what we want to hear to make a sale
; however, I thought both were being forthright about the issue. It first came up in looking at a 2009 Leopard 40
. The second time was a 2010 FP Lipari
41. Both boats had flex similar to that shown in MTF's video. I also saw it on a Lagoon 420
. Each broker gave similar explanations and insisted it's not "that uncommon". I got the same general explanation and opinion that it was normally a minor issue from a well-regarded, Florida-based surveyor who had no connection with either broker. I also got a couple of opinions that differed.
What I did learn is that many boats do have areas of flex in their hulls, it was demonstrated to me several times on cats and monos alike. The owner (for 30 years) of the boatyard I used for over 15 years, thought it to be more than a minor issue and something that definitely needed attention, but again seldom a deal breaker. He said he had seen it often over the years in both high-end and production boats. He said a proper repair was generally straight forward. Of course, he does own a boatyard, what else would he say?
The hull flex issue, be it minor or not, was one of several things that eliminated both boats early on in my search. My wife and I ended up buying
a 2019 Lagoon
42 and our boat doesn't appear to have areas of flex in the hull.