I must say I've thought about this often.
It seems to me propwash is a very uncontrolled method that would also blow lighter materials like glass and ceramics all around and likely cover them with sand again.
A metal detector won't pick them up so... it seems a bit chaotic and potentially wasteful to me.
A sluce box set up with a hand held dredge would definitely be on my boat.
You can vary the speed of water in the sluce to capture materials of different densities.
I have wondered the same thing. How many holes have been blown where in the process artifacts have been uncovered and recovered beyond md range during the process? My rookie thought is a dredge in the surf zone, screening the material. Anyone ever specifically focused on finding jewels or just metal? Could the deep sands along the beach be riddled with gems?
Salvor6 is correct. propwash excavation is done via a dredge permit through ALL the Govt entities and yes the state of FL doesn't allow dredging without the proper permits from ALL those entities.
Part of the expertise knowledge one gains with experience using propwash excavation is how to excavate efficiently and effectively. I would lean towards saying it is often a slight error of inexperience that has one "blowing the heck" out of a hole.
With that said, with the heavier, more dense artifacts they will fall, slide to the bottom if they weren't there to begin with.
My first ever Spanish shipwreck cob coin was a half reale up out of the hole on the berm. Possibly from aggressive RPM, I will admit these days excavations for me go a little slower and slightly longer. There are various factors that lend to artifacts not making it to the bottom, density/weight, I believe being a couple of them. We find pot sherds all over the different parts of the hole.
I may be wrong but I do believe "gems" would be blown around too much with propwash, hence why they dredge them on the Atocha and why not many are found on the 1715 fleet.
Generally speaking propwash is much more effective and efficient than "dredging". That's why it became the methodology of modern shipwreck artifact recovery when one wants to uncover large areas of ocean bottom. Once a specific target area is found then the dredge would be better as in emerald city on the Atocha. But the dredge could also be used too aggressively without enough experience.
Days of calm enough seas to be in the "surf" are few and far between but as history proves, any day can be the day. I've said for years, you can't find it if you don't look!
