I have posted this in another thread and I think it would be of interest to post it here with some modifications. The subject is:
What happens to stability when we charge a modern boat?
Modern boats are not like old boats where the ballast was intern and the load was part of the ballast and indispensable to have stability.
On a modern keel ballasted boat the ballast is kept under the boat, on the keel, sometimes more than a meter under and because the boats displace very litte water and the hull is not deeply immersed, loading the boat, even with a good load distribution, has a negative effect on the GZ curve (arm's length curve) and therefore on the boat AVS and on the final stability.
But as we know what really measures the boat stability is not the GZ curve but the RM curve (moments curve) that is obtained multiplying the arm by the mass of the boat. So what we get is this:
If the GZ curve is worse, Why, on what regards most of the positive part of the curve, the RM curve is better? Simply because the added mass more than compensates the slight decrease of GZ in all points of the curve except in what regards the final stability and the AVS
The Max righting moment will go up but in what regards the final stability, it will go down, as well as the AVS. On this case the AVS passes from 122 to 120.
Will the boat will be faster with a Max load than with a minimum load since he has more RM and can carry more sail? Every racer will tell you no. The added power cannot compensate the drag that the bigger weight will imply.
Will the boat be safer loaded than with no charge? That is debatable and it will depend on the boat and its B/D ratio but I will say that in most cases a boat with a half to 2/3 load will be safer. With this load the AVS and the final stability will not be yet much compromised and the boat would have a bigger positive stability and a bigger max righting moment.
But take care, when you approach the max load the final stability starts to be compromised and will be compromised if you go further than what the NA stated as a max load to the boat.
On the jeanneau boat manual (as in any other boat manual) they advise specifically on the safety precautions:
The boat shall not be loaded more with than the maximum load recommended by the builder, in particular the total weight of the food supplies, of the different equipment that are not supplied by the builder and of the persons on board.
If you will pass the Max load, that in this boat should be of about 5000 lb over the unloaded weight , the value of the AVS will decrease rapidly as the one from the final stability and you will have a boat with a compromised stability and not a safe boat to sail.