Mud is a tricky problem to deal with when installing a boat lift. It really depends on how soft the mud is and the skill and equipment the installer brings to the situation. I have installed these lifts into areas where the mud was 4′ deep with no evidence of a bottom and at this point extra steps must be taken to ensure a safe and stable lift. We take 2′ x 12′ treated lumber and cut it into four separate 2′ lengths. Having cut our boards we then take 2 and lay them side by side and take the remaining 2 and place them on top of the first two in a perpendicular fashion. Then using galvanized or stainless screws (depending on the salinity of the water) we screw the boards together tightly. This gives us a 2′ x 2′ square pad that we can place beneath the foot of the lift.
Try to get them as centered as possible under each foot pad and once they are in place you can drill a small hole through the middle of the front and back of the lift’s base pads and screw the pad down onto the 2′ x 2′ wood pad for extra security. If you do not do this you risk the wood shooting out from under the lift as you try to lower it. You may have to readjust the legs at this point to make it perfectly level, but the pads should keep the lift from sinking. If this still does not keep your lift from sinking it may be time to look into a floating lift and go in a different direction.