Slitherine

Is there a rule about which units under what circumstances can load onto watercraft?

I landed a Marine Engineering unit and a 105 howitzer unit on the same small island (strip of land about seven hexes long and one hex wide) just southeast of the airfield you have to take in the New Georgia battle. The howitzer can come and go as it pleases on a boat but the engineering unit is stuck there. They also have their own supply ship so that isn't an issue.

I also have a Marine 43 unit on the mainland on a coastal hex in the same battle. It is not a core unit. It is in supply and 10 for efficiency but it cannot load onto a watercraft. but a Marine 43 core unit can load onto a watercraft right next to the non-core unit?

So what is the criteria for boarding boats?

To board a transport, you either have to be in a port, or adjacent to a coastal warship.

So to extract units where you have no port, move a warship to the coast, and you can board your units into transports there.

Myrddraal wrote:To board a transport, you either have to be in a port, or adjacent to a coastal warship.

So to extract units where you have no port, move a warship to the coast, and you can board your units into transports there.

Supply ships are considered warships to apply this feature?

Only Destroyers, Cruisers & Battleships IIRC.

Boarding seem to work for all but adjacent carriers, supply ships and submarines, so it works even with tiny PT boats or the support ships (mines/repair) according to my test.

I think it is a bit too easy to get units on transports using an adjacent warship.
During beta I proposed to add a small resource and/or 1 naval command point cost each time you debarked outside a port.