Abstract: A pivoting keel guide for boat trailers which can be used with most boats, can be easily field added to existing trailers, and which will provide excellent centering action for crosswinds when the trailer is submerged. A base plate attaches to a cross-member of the trailer. Pivotally attached to the base plate is a U-channel guide arm, with a pair of guide rollers supported on roller arms mounted on the end of the guide arm opposite the pivot. The guide arm is biased into a raised position using resilient elements such as springs, so that the guide rollers can contact the bottom of the boat while the trailer is submerged. The guide arm pivots along the length of the trailer as the boat settles onto the trailer, exerting a constant centering force.