Remember that when you turn on the cold water faucet, the water goes right from the tank through the pump to the faucet. With the hot water side, there is the water tank inside the heater and that has to fill up first, before it can further reach your hot water faucet. So, be patient. Also, NEVER TURN ON THE HOT WATER SWITCH on the electrical panel until you are sure that the water tank is full of water and water is coming out on the hot side of the faucet. Turning on the switch without water will burn out the heating element and until that is replaced, you will never get hot water. Sometimes also in the winterizing process the pressure valve is opened to drain the HW tank and if not closed off, then it will just piss out water as you try to fill up the heaters tank. You should notice that your bilge is filling up though, or see the stream of water coming from your hot water heater. Some people are mentioning that you installed a new water heater, but I don't read that in your post. Maybe i missed something. If you did, then sometimes you have to make sure all the air is out of the system in including the heat exchanger. Usually an indication of this would be your engine over heating because there are hoses from the heat exchanger also entering the hot water engine side of the twin tank in the heater.