This in-water experimental study deals with the effects of the after-body on the FIV response of round and sharp edge cylinders. Different circular, square, diamond, and right-angle isosceles triangular cross-sections are investigated. The triangular cylinder is examined in four different symmetrical and unsymmetrical configurations with respect to the incident flow. The current towing tank experiments form a basis for the feasibility study of the isosceles triangular cylinders for FIV energy converters. The results indicate that the cylinders with a flat side perpendicular to the flow have a galloping type of response. In contrast, the cylinders with a sharp vertex pointing the flow show a VIV type of response. The galloping amplitude in the triangular cylinder with similar after-body and separation points to a diamond cylinder is significantly higher than that in the square cylinder. This right isosceles triangular cylinder also displays considerably greater hydroelastic efficiency than other sharp edge oscillators. © 2018, © 2018 Informa UK Limited, trading as Taylor & Francis Group.