Or do what I do, when the model is complete, I put it in the bath then add weights to get it down to its waterline. That way I have a model with a similar stability and handling to the real thing, though not completely the same as most of the weight goes in the bottom making the models stability stiff to the original. But they do look better than model tugs only half down to thier working waterlines and the model bounces every where and rolls badly. The weights being lead sheeting cut up to small strips, strategically placed and then glued in the hull afterwards.