This

[placid summit]

local PrimaryPart = script.Parent
local Ship = PrimaryPart.Parent

local SUBMERGED_VOLUME_REQUIRED = 70
local DAMPING_FACTOR = 1.0

local WATER_LEVEL = 5.0
local GRAVITY = game.Workspace.Gravity

if not PrimaryPart:IsA("BasePart") or not Ship:IsA("Model") then
warn("Struktur kapal salah.")
return
end

local TotalMass = 0
for _, part in ipairs(Ship:GetDescendants()) do
if part:IsA("BasePart") and part.Mass > 0 and not part.Massless then
TotalMass = TotalMass + part:GetMass()
end
end

local RequiredBuoyancyForce = TotalMass * GRAVITY

if TotalMass == 0 then
warn("Kapal tidak memiliki massa! Pastikan Massless=false.")
return
end

game:GetService("RunService").Stepped:Connect(function(time, dt)
local CurrentY = PrimaryPart.Position.Y
local Depth = WATER_LEVEL - CurrentY

if Depth > 0 then

    local BuoyancyMagnitude = RequiredBuoyancyForce * (Depth / SUBMERGED_VOLUME_REQUIRED)

    local BuoyancyForce = Vector3.new(0, BuoyancyMagnitude, 0)
    PrimaryPart:ApplyImpulse(BuoyancyForce)

    local LinearVelocity = PrimaryPart.AssemblyLinearVelocity
    local AngularVelocity = PrimaryPart.AssemblyAngularVelocity

    local DragForce = -LinearVelocity * TotalMass * DAMPING_FACTOR * dt
    PrimaryPart:ApplyImpulse(DragForce)

    local RotationalDrag = -AngularVelocity * TotalMass * DAMPING_FACTOR * dt
    PrimaryPart:ApplyAngularImpulse(RotationalDrag)
end

end)

@dark rock

[dark rock]

ok

[dark rock]

increasing the mass could work like the other person said but the buotancy would increase with the mass
you could just add a rotation damping variable as well
but i think the main thing you should change is not only applying the impuse on the primary part

you could make it spread out more around the ship

[placid summit]

I use 4 attachments. So by widening the distance until it goes outside the ship?