Helicopter pilot questions whether approach minimums to Runway 4 at OTH take into account the possibility of large ships in the channel.

Narrative

During practice approaches at OTH (North Bend Regional Airport) I realized that the proximity of the Coos Bay ship channel is a safety hazard to the IAP structure at the airport. The channel is directly under 'short-final' to Runway 4. It seems apparent that the possibility of a large ship being an obstruction to an aircraft executing a instrument approach is not taken into account in the TERPS and MDA/DA of the Runway 4 approaches. Coos Bay is not a large shipping port; but the port does have transits of large log and wood-chip ships several times a month; at all times of day and night. These ships have superstructure and cranes that extend well over 100' from the waterline. There is the distinct possibility that if a ship was in the channel on the extended centerline of RWY 4 while a aircraft was approaching DA for the ILS 4 approach (and others) sufficient clearance would not exist and an aircraft could strike the ship. I have seen where TERPS have been adjusted and MDAs/DAs adjusted at other airports when this same situation was investigated. Departures on RWY 22; circling approahes; landings to 13 and departures to RWY 31 should be similarly investigated. The 'Port of Coos Bay' could be contacted for specific vessel characteristics.