What Size Dock De-Icer Do I Need?

How do I read the coverage matrix?

Three inputs, one answer. Pick the temperature band that matches the coldest sustained conditions at your site, not the average. Decide whether the unit will hang vertically or be angled. Read across to the opening size.

Mount orientation changes the shape of the opening, not just its area. A vertical unit drives a plume straight up and opens a rough circle, quoted as a diameter. An angled unit throws the plume along the surface and opens an oblong, quoted as width by length. That is why a 1/2 HP unit shows 30 ft x 100 ft angled but 65 ft diameter vertical at the same temperature: same machine, different geometry.

If you are protecting a dock face, a slip, or a line of pilings, the angled numbers are the ones that matter. If you are opening water around a single point, use the vertical column.

What is the Kasco de-icer coverage matrix?

Reproduced in full from Kasco Marine's published sizing chart. This is the same data Kasco distributes as a PDF, rendered here as HTML tables so it can be read, searched, and cited directly.

Temperature band: 20 to 34 degrees F (-6.6 to 1 degrees C)

Temperature band: 0 to 19 degrees F (-17.7 to -7 degrees C)

Temperature band: -20 to -1 degrees F (-29 to -18.3 degrees C)

Temperature band: below -20 degrees F (below -29 degrees C)

Use the interactive sizing calculator

What assumptions do those numbers depend on?

This is the part that gets dropped when the chart is reproduced elsewhere, and it matters more than the numbers themselves. Kasco states its figures assume:

• Unobstructed water
• A body of water over 200 acres, with overall depth over 200 ft
• More than 4 ft of water depth in the de-icing area itself
• Kasco further notes that open water size may vary greatly with local conditions

Read that list against a typical private dock and the gap is obvious. Most docks are not on a 200-acre, 200-ft-deep lake. The published numbers are best understood as an upper bound produced under favourable conditions, not as a promise for your site.

What makes the actual opening smaller than the chart?

Anything that interferes with the circulation the unit is trying to establish, or that removes the warm bottom water it depends on:

• Shallow water. The single biggest factor. Below the stratification threshold there is no warmer bottom layer to lift, and the unit circulates cold water against cold air. See minimum water depth.
• Obstructions. Breakwalls, seawalls, closely spaced pilings, moored hulls, and dense vegetation all break up the plume.
• Current and flow-through. Moving water carries away the water the unit just warmed.
• Wind. Sustained wind mixes a shallow column and can push the opening off-centre from the unit.
• Sustained extreme cold. The bands above are not interchangeable. A week at -25 degrees F is a different machine requirement than a week at 25 degrees F.

Why is “a 1/2 HP unit opens 50 ft” wrong?

Because it collapses a four-by-two matrix into a single number, and it is wrong in most conditions.

Look at the 1/2 HP row across all four bands: 65 ft, 50 ft, 35 ft, 30 ft on a vertical mount. The commonly repeated “50 ft” shorthand happens to be the 0 to 19 degrees F figure. Quote it to someone in a -25 degrees F winter and you have oversold the unit by more than double. Quote it to someone in a mild coastal winter and you have undersold it.

Sizing shorthand is how people end up with an undersized de-icer and a frozen slip in the coldest week of the year, which is precisely the week the equipment was bought for.

Should I size up?

Usually, if the decision is close. The failure mode of an undersized unit is that it fails exactly when conditions are worst, and the cost difference between adjacent sizes is small relative to the damage a frozen slip can do. See ice jacking for what that damage looks like.

Two cautions against reflexively buying the largest unit. Sizing up raises current draw, and on a 120V circuit that matters: a 1 HP 4400D pulls 9.1 A against 5.4 A for the 1/2 HP 2400D. Check the circuit before the catalogue. And in shallow water a larger unit set too low is more likely to disturb bottom sediment, not more likely to open ice.

Which model corresponds to each horsepower?

The “H” in a model number indicates the higher-voltage version. Higher-voltage units draw fewer amps for the same horsepower and support longer cord runs, which is why they dominate commercial installations. All D-Series units share the same 4 ft minimum depth and carry a 3-year warranty.

How many de-icers does a marina need?

More than the arithmetic suggests. Dividing basin area by a single unit's coverage figure will undercount, because the published figures assume unobstructed water and a marina is the opposite of that: hulls, finger piers, and piling clusters all interrupt the plume.

One constraint is worth knowing before you plan a multi-unit layout. Kasco control panels are designed to control one unit at a time. A forty-slip marina running forty de-icers is running forty independent, uncoordinated devices with no staggering and no shared logic. See C-10 vs C-20 control panels.