Step one is to make or find a suitable ship. First it heeds to have a flat under side. and second it you made it out of wood such as this one its best to spray it with a thick coat of clear lacquer of finishing spray to seal the surface so nothing will soak in and it will slide out of the mold more easily. On another note it fills the uneven splinters and wood grain on wooden ships such as this one.
Step two is to glew the ship to a piece of paper (hints the flat under side) this keeps the ship from floating to the top of the rubber solution.
Step three build a barrier around the ship to create the edges of the mold. legos work well as seen above.
Step four mix the rubber and catalyst then slowly pour over the model. Make sure you fill the rubber a few millimeters above the highest part of the model. Let sit for about five hours to harden completely.
Step five after waiting a few hours test to see if it is hardened. It should be solid and dry but somewhat flexible. If so remove the legos or other casing.
Step six tear off the paper and test under side for hardness.
Step seven carefully remove model from mold by flexing the mold until model pops out. The first time is often tricky, and if the rubber tears slightly that is fine, but be careful. Now you have a mold that should be good for about 100 castings. In time it will wear and likely break so hang onto the master if you are planning on making a lots. Good luck and God speed.