Related to the ticket I just created for the Marid. This seems to affect all amphibious vehicles sooner or later. #9769

This also affects the OPFOR MSE-3 Marid in the same way. So the title needs editing to include the MSE-3 & AMV-7 (add & MSE-3 in place of "Marshall")

edit:
title changed, found how

edit:
and also the Strider

Seems to be fixed for all vehicles in latest dev build

Well I have just updated to the latest 5mins ago and it is still exactly the same, though now in addition as soon as the wheels are in land/water interface, the vehicles will lose their brakes and will roll into the water,

or if you transvers the shoreline with the wheels just in the water, so you not floating but driving on the wheels you also have no/much reduced braking effect, so at beaches where there can be stretches of shallow water (beneath hull height) that just the wheels are in, not only dose it become imposable to brake but also to change from forward/reverse, as then you fall foul of the first original problem.

edit:
Added “Amphibious_test.Stratis.zip” which puts all the amphibious vehicles (empty) on a beach where there is shallow water, added some signs and arrows to show the shallow part.

Enter the shallow part and try braking, changing direction etc and generally testing around the area.

Okay you are right, i tested your map and had the same problems.
Before the last dev build i was able to reproduce the "getting stuck" problem even in the airbase area where the water isnt as shallow as in your example. But at least in this area the problem seems to be fixed now as i cant reproduce it there anymore.

This problem is especially apparent when trying to reverse any APC out of the water (perpendicular to the beach). The thrusters keep spinning when high out of the water while the APC sits on it's wheels

Have observed that vehicle wheels continue to turn in water, although on occasion some wheels are turning counter to others. Landing gently on these wheels seems to increase the likelihood of becoming trapped, even with the rotors still turning in the water.
Drive into water until the vehicle is fully swimming and note the direction and speed of spinning wheels. They will rarely be consistent so some number of trials may be needed. Try to land gently on wheels turning opposite your direction of motion.
Front wheels tend to want to spin in reverse. Rear wheels almost always spin forwards. I find it more likely to become stuck slowly backing out of water. Wheels do not respond to control inputs. Sound of screeching breaks sometimes audible as vehicle becomes stuck, unstuck, or exits the water. Even on a successful landing some wheels resist vehicle motion until it transitions to land mode.

I've also noticed if you hit a rock under the water line, you are pretty much stuck - the wheels don't work and the props lack the drive to move you past it. Also on a side not, the AI seems to struggle in transitioning this vehicle from Sea to Land.

Interestingly, I managed to sink an AMV to the bottom of the sea--with the wheels touching the sea floor (setVelocity is fun). You get the exact same issue: the wheels won't turn and the rotors won't turn (and you stay sunk).

On the Marshall at least we could see the props turning, but the wheels seemed to be touching the ground and causing too much friction for the props to overcome.

A manual transition option from water to land would most likely solve the issue.

it still happen on last dev; 28 august

yesterday,my squad have to leave amv-7 behind after get stuck,during cross a small water bay,we stop touching the floor wile wait for others on the boat,and get stucked.

Its been an age since this ticket got assigned and its still not fixed yet

It is still not fixed. Another way to reproduce this issue is by taking the AMV-7 for a drive in the Limni marsh. If you stop in half a foot of water, you will not be able to move, due to only the propellers being active, but not in the water.

Issue still exists on latest Arma 3 stable release.