How do I stop my boat from going up on land?

So my boat in my game it can fly up the beach (a wedge) and then it doesn't go back down

here's the movement script found within the Vehicle Seat

local bv = script.Parent.BodyVelocity

local bav = script.Parent.BodyAngularVelocity

local seat = script.Parent

local speed = 0
local maxSpeed = 40
local rotSpeed = 0
local maxRotSpeed = 2

--Start the constant movement calculator
delay(0, function()
	while true do
		bv.velocity = seat.CFrame.lookVector * speed
		bav.angularvelocity = Vector3.new(0, rotSpeed, 0)
		wait()
	end
end)

seat.Changed:connect(function(prop)
	if prop == "Throttle" then
		if seat.Throttle == 1 or seat.Throttle == -1 then

			speed = maxSpeed * seat.Throttle

		elseif seat.Throttle == 0 then

			speed = 0

		end
	elseif prop == "Steer" then
		if seat.Steer == -1 or seat.Steer == 1 then

			rotSpeed = maxRotSpeed * -seat.Steer

		elseif seat.Steer == 0 then

			rotSpeed = 0

		end
	end
end)

Explorer (Boat Model)

Body Velocity

BodyGyro

BodyAngularVelocity