[...] with only having two levels there would be no need to reload between inland vessels and sea-going vessels. For a route from let's say Cologne to London a player would use only inland vessels which do a direct job.
Not necissarily. As already mentioned, both types of ships (inland vessel, sea-going vessel) could be made to use different max speeds
with regards to canals/rivers resp. ocean.
In this way, it wouldn´t be attractive to use sea-going vessels in rivers/canals (or near coast if the water is shallow), or to use onland vessels or coasters on oceans.
Indeed, how to use ships best would depend on the special topography of the map and the depth of water, incl transshipping.
The idea is to have a level which is deep enough for sea-going vessels, but prevent inland vessels from going overseas.
Yes, I understand, but IMO, this could be achieved even better by setting properties 14 and 15 to a certain speed fraction. This would allow both types of ships to operate in "foreign regions", but only with a certain handicap. It would allow sea-going vessels to pass canals (Panama, Suez, Corinth, ..), inland vessels to travel the coasts, and coasters to travel the ocean, but there would be no use to do so on a regular base.
In addition, it might be difficult to introduce three different depths, especially with regards to their graphical representation.
Hehe. As you mentioned you're sailing: Have you ever get stuck in the wadden sea and fallen dry? Reminds me much of that...
But that´s always fun.
[Suez, Panama canals]
Yes, but these big canals only have locks at the entrances, AFAIK. All the way is on the same level. For such canals digging is a good way for simulation.
Well, the Suez canal doesn´t have any locks, but the Panama canal has 46 of them. We recently had the pleasure
to visit them in our "guess the train" game", see also http://www.canalmuseum.com/canalphotos/ ... hotos.html
, very interesting photos!