New types of ships

Faster and safer mail and passenger transport accelerate the unification of the empire of CHARIS(m) and allows faster political decisions

https://www.youtube.com/watch?v=EuKf0TqjPNc
shows a boat with an airscrew powered hydrofoil

with a boat-like hull, small wheels and pontoon skis it could be used for amphibious landings

A rigid inflatable boat (RIB) with motorized, retractable and steerable wheels, powering the boat on land
https://oceancraftmarine.com/amphibious/military/

a steam powered, armoured amphibious Landing Vehicle with tracks
https://en.wikipedia.org/wiki/Landing_Vehicle_Tracked

Powered catamaran passenger/RO/RO ferries

A traction kite increases the distance a steam powered ship can reach without coaling stations.
https://en.wikipedia.org/wiki/SkySails

As a kite pulls a boat, it does not also heel the boat over or pitch it forward as a sail does.
https://project.kiteboat.com/design/

I think that this has already been flogged to death several times.

As of the end of ATSoT the only form of steam engine is the coal fired reciprocating engine. Those with their attending pumps, bunkers and whatever tend to be fairly heavy and so have to be placed deep in the ship to keep balance under control. This probably precludes any hull type except a displacement hull (no planing for you!). As for LVTs, hydrofoils and multihull/SWATH types, weight issues, power to weight ratios and balance issues will probably keep them from being practical. You should be able to put together a steam-powered LCM (IIRC ATSoT has some) but even then cargo load will be a lot less than our IRL versions.

Kites might be useful, but having ones winched by a donkey engine might not be. Doesn't a donkey engine have to be available anytime the sail is up? If so it effectively has to keep steam up all the time which costs fuel.

Personally I think that a steam courier type (for mail and VVIPs) and a few cargo or mixed cargo/passenger types in displacements from 1000 to 10,000 tons should already do a lot to make the empire (and Safehold) a much smaller place. Steam power allows for much tighter schedule keeping, so I would imagine scheduled (passengers and freight) liner traffic starting up pretty much as soon as the first civilian ocean steamers started coming out of the yards. Experiments with railroads, canal barge tugs, steam traction engines (road train haulers) and steam powered mail/stage buses should IMO only help this.

Maybe there is room somewhere for an (amusing) story about some charisians or dohlarans trying to introduce steam haulers and mail buses to the sodarans. I get the idea that they and the northern harchongians could be a lot richer if they had a working logistics network to import/export things in quantity. Railroads could follow once the haulers were established, before that the locals might steal the rails. Similarly a truck/rail story set in western Siddarmark IMO has opportunities for drama, comedy, tragedy and profit.

Modern Catamarans require small volume jet turbine or high performance Deisel to power them (I am ruling the hybrid electric drives out by definition on safehold).

You don't use a traditional steam plant as you don't want to be piping live steam further than strictly necessary and you sure as hell don't want to have any kind of bend or bootleg in the driveshaft. There is a thread in the archives about using steam in outside the hull drive pods where this was argued extensivly.

These along with the afore mentioned weight issues pretty much rule out anything but a displacement hull. Also the design issues in a Catamaran hull are much much more difficult to design than a displacement hull.

Finally you really need welding to make the hull for a Catamaran as riviting will result in a much greater drag.