DaviD - I know you are a careful an serious operator, so I will try and line up some statements by Alexandre and especially by Denis - LE JAG - as to the performance of Manta prototypes.
The below quotes are, as far as I know, from the only forum posts Alexandre has ever made on the subject of the Manta. I will draft another post with LE JAG’s reports.
Alexandre’s first post was on the Geotec forum in May 2016, under the Forum name Asgar. In this thread he made several posts, below are quotes from them.
“All ferrous on all depth, mute or multitone.
Palladium ring 3 grs surrounded by iron + volcanic sand up to 13 " Very quiet !
Palladium ring 3 grs in the volcanic sand without iron up to 17 " Very quiet !
Recovery speed iron/gold/iron -> 0" !!!!”
So a 3 gram Pallaium ring at 13” with iron ID enable and 17” without....and then
“Normally on a 18k gold ring of 3 grams, I detected 10 to 15 cm below the goldscan 5c latest version at the beach on normal wet sand.”
So his Manta beat the Goldscan 5c (which is more powerful than the TDI) by 4 - 6 inches...and then...
“We do better than GPZ 7000”
And then...
“17 Pouces on US nickel with slow sat speed (12 pouces coil at 6us delay)
15.5 Pouces on US nickel with fast sat speed (12 pouces coil at 6us delay)
13 Pouces on square foil aluminium 1" (medium sat speed, 12 pouces coil at 6us delay)
16 pouces on square foil aluminium 1.5" (medium sat speed, 12 pouces coil at 6us delay)”
Of course “Pouces” is inches!...and then, because he is concerned that his results might be compared to sir tests, he states...
“the results are on wet sand for me, in air, I have a result most important but not real, ordinarily the small sound disappear on the beach because too ground effect near water and wet sand....”
So the Manta achieved even greater air test depth...He goes on to qualify the results...
“In France we have no 9ct, we had 18ct and 22ct (but rare), It is obvious that the 18k target is much harder to take than 9ct, we can not achieve depth of 20 "on the big rings and in some wet sand conditions (harsh downhole)”