I suggest a 10 seconds immunity on respawn to prevent harassment on spawn kill.
Also, to prevent cheating, the immunity should go off as soon as player quits the boat so it cannot work on opponent's boat.
Cosmetically, i suggest the player under immunity to be a skeleton slowly rebuilding it's skin.
Furthermore, default handheld when respawning should be slot 1, but while the character is rebuilding skin, it should have claw attacks as the only action, just like skeletons with no weapon. Once regenerated, slot 1 should be selected because it's inconvenient to chose the right weapon with the stress, using keyboard. Ending up with banana for a PVP is nowhere fun.