spoil the ship for a ha'p'orth of tar
do not spoil the ship for a ha'porth of tar
Do not ruin something for an avoidable reason. "Ship" is thought to be a dialectical pronunciation of "sheep," and a "ha'porth" is a "halfpennyworth." Tar was used to protect sheep skin from flies (and thereby illness and death), so not having enough tar would contribute to the death of the sheep. You know your mom is going to be offended, so please call her before the dinner party—do not spoil the ship for a ha'porth of tar.
spoil the ship for a ha'p'orth of tarrisk the failure of a large enterprise by trying to economize on trivial things.
The expression originally referred to the use of tar to keep flies off sores on sheep (ship represented a dialectal pronunciation of sheep ). Ha'p'orth is a contraction of halfpennyworth .