There are codes for small boat wiring. Ring terminals with shank insulation are recommended and meet code. Shrink tubing is not recommended. While the thought of protecting the joint from flexing is noble. The shrink tubing moves the flexing further up the wire (further from the connection) and when the wire breaks you won't be able to see it under the insulation. You can see a broken connection at the ring terminal.
Same principle applies to soldered connections. The solder may reduce flexibility, however you need that flexibility to protect the connections. The wire WILL break where the solder ends almost every time.
Repairing broken wiring in your driveway is one thing. However that wiring won't break in your driveway. It will break as your boat is being bounced around by rough seas and more than likely when you need that circuit the most. Making a field repair in rough seas is tough at best, however if you can't find the break you're never going to get it fixed. And that could be the difference between life and death...
ISO10133-2000 Small craft electrical wiring.
10 Wiring connections and terminals
10.1 Conductor connections shall be in locations protected from the weather or in IP 55 enclosures, in accordance
with IEC 60529 as a minimum. Connections above deck exposed to intermittent immersion shall be in IP 67
enclosures, in accordance with IEC 60529 as a minimum.
10.2 Metals used for terminal studs, nuts and washers shall be corrosion resistant and galvanically compatible
with the conductor and terminal. Aluminium and unplated steel shall not be used for studs, nuts or washers in
electrical circuits.
10.3 All conductors shall have suitable terminals installed, i.e. no bare wires attached to stud or screw
connections.
10.4 Screw-clamp or screwless terminal blocks shall conform to IEC 60947-7-1. Other terminals shall be of the
ring or self-locking captive-spade type, not dependent on screw or nut tightness alone for retention on the stud or
screw.
An exception is that friction-type connectors may be used in circuits not exceeding 20 A if the connection does not
separate when subjected to a force of 20 N.
10.5 Twist-on connectors (wire nuts) shall not be used.
10.6 Exposed shanks of terminals shall be protected against accidental shorting by the use of insulating barriers
or sleeves, except for those in the grounding system.
10.7 Solderless crimp-on terminals and connectors shall be attached with the type of crimping tool designed for
the termination used and for a connection meeting the following requirements.
Each conductor-to-connector and conductor-to-terminal connection shall be capable of withstanding a tensile force
equal to at least the value shown in Table 1 for the smallest conductor in the connection, without separating...