This is one of those niggling details that really don't affect the time travel problems, but is a problem related to the time travel that does not seem to have an explanation. Somehow an equipment tower broke off the ship and fell through the vortex into the future. The issue is, how did this happen?
This is a United States Navy vessel in active service. It is built to withstand the worst conditions of wind and waves, plus a fair amount of shock damage from enemy attacks. The turbulence of the transit alone would not seem able to do that kind of damage to the ship. Further, there is no evidence in the scenes we see that there was significant turbulence--Dave and Jim are not thrown off their feet, we do not see the decks pitching and yawing, and while this is a terrifying situation completely off the books, it is not tossing the ship in a way that would exceed tolerances.
Thus it must be an effect of the field. It does appear that the field is causing parts of the ship to phase between being material and immaterial, and so we might suppose that somehow the lower part of the pole became immaterial and the weight of the upper part caused it to fall. However, we are stuck with a dilemma at that point. If the upper part of the pole was within the field, then this same effect ought to have happened all over the ship, as bulkheads and beams and joints became immaterial and failed to hold their surrounding parts. The ship would within a few minutes rip itself apart. Perhaps, then, the tower was cut, part of it becoming immaterial releasing the part above it outside the field. In that case, though, the tower was outside the field and ought to have plunged into the harbor (and been seen to have done so). To be within the vortex at all at that point, it would have had to have fallen on the deck of the Eldridge--and once there, there is no reason for it to have become separated from the ship (again, there is not sufficient turbulence that any sailors were thrown overboard, so why should a heavy piece of ship's equipment do so?).
Further, immediately upon opening, the vortex began drawing matter into itself. This matter does not seem to be going out the other end; it is filling the vacuum that is hyperspace. The suction increases as the vortex enlarges, but from the beginning there would have to have been negative pressure at the future end, and thus a tendency for objects to be drawn into it, not ejected from it. However, we can accept that the pressure is still not high enough to prevent the momentum of two persons and one tower from overcoming it and exiting in the future.
C. S. Lewis somewhere wrote that the reason Ophelia drowned is that Shakespeare drowned her, and that principle applies here: Doctor Longstreet needed to find something that could clearly tie back to the Eldridge, and the tower looked fragile enough and specific enough to be that object. That we cannot figure out how it got separated from the ship is a separate issue, and again not one that impacts the time travel analysis other than that it makes us wonder about how the field itself worked. The tower got separated from the U. S. S. Eldridge somehow, fell through the vortex, and was ejected in the future. It is necessary for Longstreet to find the answer to his problem, so it happens.