he may be looking for the CG, to keep it on the trailer....
the CG, if the boat is sitting on the ground on it's keel, will be several feet "under ground"..not sure that it is really an issue for the trailer specs...the weight of the keel, the bunks and tie downs will keep it centered and on the trailer...
the biggest issue for calculating the CG, is how much more stuff do you have on the boat than it came with...each weight and where it is stowed or placed will have an impact on the overall CG...
jomanning, is that your reasoning?