The ThunderTiger Neptune SB-1 is a great boat to mod. But as you do, you'll notice the fixed ballast in the keel section needs to be adjusted. On top of that, as you put it in different waters and with different loads (camera, side tanks,....) it will tilt forward or backward depending on a number of factors such as water temperature. Adjusting the ballast in the SB-1 is a hassle, you have to take of 1 front diveplane, remove 12 screws, remove the side panel, loosen the lockingrings. Only to find out that you over compensated, after having it put back together again and seeing it float in the water. This adjustable ballast sled should ease that hassle: it makes the ballast front-back adjustable with a knob located in the cavity just in front of the ballast, right behind the ON/OFF switches. After taking it for a few dives... i noticed the ballbearings became rusted and the ballast wouldn't move anymore. Replaced it wit a couple washers soaked in industrial lubricant (grease)... works even better. The knob does come loose from time to time. Don't have a solution for it yet.You should now be able to move the ballast back/forth by turning the knob. I have not printed and tried it myself, so mind the 'work in progress' sign. As soon as i do i'll post pictures and maybe need to upload an updated .stl