A weapon that does not penetrate the deck still needs a deck strong enough to carry it. Electrical supplies and supporting sensors must also be installed. Non-penetrating systems can concentrate substantial weight high in the ship. A deck-penetrating mount distributes more of its weight down into the hull, helping stability. Tens of tons placed on deck matter much more to a vessel of a few hundred tons than to a very large ship, especially when the equipment is in use. Those engineering questions take time to resolve before a proposed installation can be treated as a practical conversion.
Notable Point · 37:23-38:23
Deck-mounted weapons still need structural and stability work
Avoiding deck penetration does not remove the need for reinforcement, power, sensors, and stability calculations on a small patrol hull.