Glad you got it worked out with the usb -> com adapter. Yes indeed there are issues because the regular com may transmit more data then the usb. There is a ton of different adapters. Some work, some dont.
In regards to the antenna...
A tunes backstay kind of antenna is honestly really a ****-tenna. Yes, it may tunes in many diffent bands and frequencies but it has a efficiancy which is really really poor compared to an antenna which is actually resonant where you are going to use it.
If you transmit 100w into a resonant antenna all that power will be transmitted over the air. Using a non-resonant tunes backstay may in some worst cases leave less then 5w to be converted to "air power". The rest is tunes away in your tuner and becomes ground or heat.
This in turn will let you use alot more power from your batteries to get your traffic transmittet and recieved ok.
A good option is to select a few stations you are going to listen/connect to and make resonant dipole antennas for those bands. Raise it high and make it look like a inverted-V. That is actually what they are called, an inverted-Vee dipole. And you can make several of them on the same feedpoint.
Raise feedpoint high and connect the ends via non-conductive lines to the front and rear corners of the cat. Starbord or port as fits.
Another option if you have a davit or some kind of place to mount an vertical antenna in the aft.
There are several companies who make an antenna whith a insulated tubing. On the bottom there is a motor
and it will let out enough antenna in the tube to become resonant where you are transmitting. Works wonders and is very effective on long distances as if your in salt water
you have a great take-off using a vertical antenna as it will use the salt water
as a ground conductor.
You can control the antenna resonance from a controlbox inside at your helm
station. They are usually rated for 3Kw so there is no way your little Icom M107 is going to blow any coils or overheat it.
One such antenna manufacturer is Stepp-IR and the make 2 verticals. BigIR which is 10m tall and covers 6,9-54MHz and LittleIR which is 5,5m tall and cover 13,9-54MHz.
Now these are the frequencies to use for long distance communication, it is possible and lower frequencies although it is a tough one from a boat
with the conditions in mind.
I would go for one of these verticals and then make 2-3 dipoles for lower frequencies for more closer communication.
PS. I agree with earlier advice. Get a ham license
........ It is quite easy, the morse code requirement is also removed so you can get the highest licence class with just a little knowledge of electronics
and studying frequency charts
some about propagation, antenna theory, the alpha bravo charlie talk and what bands is useable when and where and how. Easy........