The restrictions in your question are not clear. It sounds like there are 4 LEDs already existing in the boat, and you want them to perform the same function. With the new sensor, that **can not** happen without additional components. They can be purchased modules, or a circuit you whip up from scratch, but somehow you have to synthesize electronically four voltage comparisons and LED drives.
To start: Can you verify that in the old system, each LED was wired directly to a switch and the 12 V boat power? Any sign of external resistors, like current limiting resistors for the LEDs? If not, then the LEDs are 12 V industrial indicator types.
Next, can you measure the LED current?
Next, do you still want a moving dot display (only one LED on at a time), or can you live with a bar graph display. A discrete bar graph display circuit takes considerably fewer parts. With the LM3914 you can select between bar and dot modes with no parts count penalty.
ak