The forestay is not designed to carry the load during sailing, it it only there to keep the mast up when the sails are down. The jib is designed to take all the load, and you adjust the mast rake by adjusting the tension on the jib halyard. The forestay will actually go slack when the jib is up, so don't sail without one (it is a dog anyways without the jib). Check around for a used one, most racers replace the jib frequently.