masts on a sailing ship are there and ten frames later they go away for a frame or 2 and then come back wrecking everything. could you point out some direction? many thanks.
Sounds very much like you're rendering in 'Fast Preview' mode.
In your render options, make sure that option is not checked, or that the little ball directly to the left of the big render ball (down left hand side set of icons, at the bottom) is green and not grey.