Fishing tool and method

1. A fishing tool comprising:

a grapple;

an exciter having:

a housing in vibration transmissive communication with the grapple; and

a rod having an axis, the rod mounted in the housing with the axis of the rod transverse to an axis of the housing, the rod having a cross sectional shape that produces vortex shedding upon fluid flow thereacross.

2. A fishing tool as claimed in claim 1 wherein the exciter is fluid flow based.

3. A fishing tool as claimed in claim 1 wherein the rod extends at right angles to a longitudinal axis of the housing.

4. A fishing tool as claimed in claim 1 wherein the rod extends at an angle to an axis of the housing.

5. A fishing tool as claimed in claim 1 wherein the rod has a circular cross sectional geometry.

6. A fishing tool as claimed in claim 1 wherein the rod has a square cross sectional geometry.

7. A fishing tool as claimed in claim 1 wherein the rod comprises a relatively high modulus material.

8. A fishing tool as claimed in claim 1 wherein the rod comprises ceramic material.

9. A fishing tool as claimed in claim 1 wherein the rod has a cross sectional area of about 10 percent to about 80 percent of a cross sectional area of a flow channel in which the rod is disposed.

10. A method for retrieving a stuck fish in a borehole comprising:

running the tool as claimed in claim 1 into a borehole having a stuck fish;

engaging the fish with the grapple;

actuating the exciter;

vibrating the fish.

11. A method as claimed in claim 10 wherein the actuating of the exciter comprises flowing a fluid through the exciter.

12. A method as claimed in claim 11 wherein the flowing of the fluid causes a periodic oscillation in a rod of the exciter thereby generating vibrations having an orientation.

13. A method as claimed in claim 12 wherein the flowing is over more than one rod.

14. A method as claimed in claim 13 wherein the more than one rod is oriented differently than another rod.

15. A method as claimed in claim 10 wherein the method further comprises retrieving the fish.