Yes, because you have a fairly deep area around your dock I would recommend using at least 2 thruster type deicers, 3/4 HP each, placed at the end of the dock angled towards the shore to create enough movement to keep the entire structure free from ice damage. This would be an inexpensive option and you could use the dock mount system if you wanted to add a permanent mount for the units.
Here is a commercial De-Icer unit:
This is a commercial Ice Eater® that is suspended by mooring ropes below a dock or boathouse or slips. The propellor spins creating a strong thrust that is directed via the cowling towards the surface at an angle that best ensures a proper ice opening.
A 3/4 HP Ice Eater can keep an area free from ice from 30 to 60 feet in diameter. It uses only 4.7 AMPS at 115V or 2.35 AMPS at 230V making it an efficient and low cost method of de-icing. Ice Eater prices and more information is here
A bubbler type of system with air pump and weighted die-slit diffuser tubing placed around the dock would also work.
No trouble to have so many questions. I understand when associations or homeowner groups are involved that it is best to fully understand the purchase of group equipment. I will responded to your questions in bold:
Just to clarify this dock system is 80 feet in total length West to East. Are you saying the 2 thrusters will circulate the warm water that distance ? Yes...I would use two 3/4 HP thrusters like the Kasco or Powerhouse Ice Eaters.
I assume you are suggesting to mount the trusters at the very Western end of the dock system, one midway between the main gang way and the northern finger and the other mid way between the main gangway and the southern finger. So the trusters would be in a max of 6 to 8 feet of water if they were on the bottom? I would place the units at the outermost end of the dock. Aiming the units towrads the shore slightly will create an ample ice free zone over the entire dock.
My thoughts were to run one extension cord from our boat house down the main gang way so we would not need two 100 foot cords. You may need to run one extension cord per unit. The amp draw of each unit may cause a single extension cord to trip the GFI. Ideally you would use a thruster with a 100' cord which may add to initial cost but would ensure correct operation.
How would the "dock mount system" attach to the dock ? How deep should the "dock mount system" be set so to position the trusters down below the surface at the optimum depth ? In other words what is the optimum depth of the thruster for 6 feet of water and what is the optimum depth for 9 feet of water? The dock mount kit uses a hinge-like mount that screws to your dock. A 10 foot 1" steel pole fits in the dock mount and attaches to a brace secured to the thruster. The kit allows a precise aiming of the thrust, in your case you would position the unit about 12" from the pond/lake bottom and aim it towards the surface angled towards the shore. Always locate the unit as close to the bottom as possible (12" to 18" is best)
I assume the thermostats measure the surface water temperature ? Do they mount in the same proximity of the "dock system mounts"? The thermostat units measure air temperature and are plugged in to the main power source. The unit is plugged into the thermostat power outlet. The thermostat turns on the unit only when the air temperature is below freezing thus saving energy.
Why would the thruster system work better than a bubbler system. I assume a bubbler system would be more cost effective ? A bubbler system would cost a bit more initially but the power consumption would be less with a bubbler. But because you have a fairly deep area surrounding your dock the thruster would do the jopb and be easier to install and service.
Please contact us by email if you would like a quote for each system to show to your group so they can make the decision that best works for the marina and the caretakers.