I need to run power underground from my house to my dock to operate my boat lift. What I was wanting to do was put a 40amp sub panel at the beginning of my dock. I have 400 amp service at the house. It's a 600 feet run fom the house to the dock. Then a 200 feet run from the sub panel to the 20 amp plug. There are 2- 3/4hp 115v motors on the boat lift. I would also like to run a second plug for my boat's battery charger on the same circuit. Lift and charger will not be running at the same time. I was thinking about running 2-2-2-4 urd cable from house to sub panel and 10-2 from sub panel to plugs. Will that work? If not please give suggestions.

Not doing any voltage drops calcs which will be significant, I have a few questions and comments.

Questions:
1. What is the power requirements for the lift? i.e. Breaker size
2. Will both motors operate at the same time

Comments

1. GFCI protection, I believe, is required.
2. Conduit for the doc.
3. THWN, single wires for wet locations are required even if in conduit. Usually THHN may be dual mark THWN, but there are cases that it isn't.
4. 1000' and 2 motor loads are significant.

20amp breaker is required.
I can run each motor together or one at a time they each have there own controls.

For the 200' length, I'd go with #4 copper THWN for a 2.1% drop at 20 A non-continuous at 200'.

For the 600' length, I'd go with 4/0 or 0000 Aluminum for a 2% drop.

Getting below 3% total would be better.

350 kcmil Aluminum wire would give you a 1.3% drop for that segment. Total drop would be below 3%.

For the 600 foot run, the #2 will work fine, allowing the max of 5% V voltage drop, and assuming one motor on each 120 volt leg of the 4 wire 120/240 volt #2 Al URD feeder.

The 200 foot run will need #8 to run only one motor using a 2 wire cable. If you need both, then use a 3 wire cable, again to have both 120 legs, one for each motor.

Go here:

Southwire - Delivers Power

And enter aluminum wire, direct bury, 600 feet, 5% Vd, 120 volts, and 15 amp load for the #2, direct bury, copper wire, 200 feet, 5% Vd, 120 volts, and 15 amp load for the #8 wire.

The charger load is insignificant.