I just bought a used 10 ft Avon Rib and am a little confused with the ballast setup. On the stern of the boat there is a drain hull on the engine mount and a hole underneath that which I'm assuming is to fill the bottom chamber of the rib with water as ballast. The boat didnt come with a plug for that so I launched it with it open. I'm running a 4hp tahatsu and it was very slow going. Felt like dragging along. My question is do I need to plug that hole or regulate the amount of water I let in so I can get the boat going a little quicker. Thanks for any insight.