What do you think about the Nautilus Lifeline for both diving and sailing?

[Cadence]

For diving or man overboard it seem cheap. if it is only a couple of miles.

[Steadman Uhlich]

I am in the market for a handheld radio for my personal use on a boat. So, I have been looking at the different makes, models, and specs.

I was curious about the range of a handheld VHF radio if it was used by a MOB (in the water and at water level, like a SCUBA diver would be at the surface) and IF trying to communicate with another VHF handheld radio being used by a person in a small boat (such as a RIB, dinghy, or small sailboat).

Here is some information I found. Again, I am not a radio expert, but this is from a site devoted to radios. I saved this to my notes on radios, and am simply posting it here to illustrate the issue. You are encouraged to do your own research too, but I am satisfied with this info.
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"The higher your antenna, the farther the horizon. For any given antenna height use this formula: Horizon at Ground Level (in kilometers) = 3.569 multiply by the square root of the Antenna Height (in meters). So if the antenna height is at 6 feet tall (1.82880 meters), times the horizon (3.569), equals 4.83 kilometers, or 2.99 miles away.

Antenna Height 1.82880 meters (6 feet off the ground)
Horizon at Ground Level x 3.569 kilometers
Antenna Horizon 4.83 kilometers (or 2.99 miles) away

However, the example above assumes the receiving antenna is on the ground. Raising the receiving antenna's height would extend the line-of-site even more. So if the receiving antenna were also 6 feet off the ground you should be able to communicate almost 6 miles without obstructions (2.99 miles + 2.99 miles).

Thus, two people carrying a handheld two-way radio, the maximum communication distance on flat ground with no obstructions is approximately 6 miles.

(STEADY NOTE! That is if both the users are 6 feet tall and standing on ground or on a "flat" surface, and NOT if one is in the water at surface level, with the radio at the surface of the ground or water.)

So if the antenna height is at 6 feet tall (1.82880 meters), times the horizon (3.569), equals 4.83 kilometers, or 2.99 miles away."
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In sum, if you are a diver or MOB, the most you might expect for range if trying to communicate with a person also using a handheld VHF in a small boat (not a base radio or a radio with an antenna up a high mast), is about 2.99 miles MAXIMUM (in perfect conditions).

Note! The radio site also makes clear elsewhere that the MAXIMUM range is under perfect conditions and the actual range may be much less, depending upon factors such as radio power in watts (1-5), battery condition (strong or weak), environment, weather (rain), obstructions (metal, walls, trees, etc.) AND the type of antenna used (a long whip or a short stubby). That site recommends using a longer "whip" antenna (which is about 6" long) rather than the shortest stubby type on a handheld if you want maximum range.