The LOS is clear, Since it is a Sea.
Dont forget that due to how the wireless radiation happens even through its clear line of sight you might still have some issues due to how the transmission separates into Fresnel zones and the reflections on the water etc.
going to the main questions I it will be hard to say since your configuration is not posted so please do so in your next response (make sure you take out all sensitive)
To be honest this is just a simple config, all you need to do is make sure your AP is set up as ap-bridge and the clients to station bridge then connect them all wirelessly, using the access and connect lists is handy when wanting to specify different wireless clients by mac but its hit or miss for me on this one i.e dont see any real benefit or negative applications if set up right other than setting up access lists etc is more effort than the blanket rules.
From there you just have to bridge all the wireless interfaces to their respective ports and you are done, after this you will need to set up security etc
https://wiki.mikrotik.com/wiki/Manual:S ... our_Router
One thing to note about setting it up this way is that there is a limitation with the layer 2 headers when going over the wireless interface, to forward layer 2 packets correctly there needs to be 4 mac addresses involved, one for the ultimate source, one for last source, one for ultimate destination and next destination i believe.
So when we go over the wireless interface the ultimate source gets cut off, so when the traffic returns it has no clue on where it actual came from.
Each vendor has their own way around this but mikrotiks was to hold a translation table on the client side as well as the ap side.
This is not 100% transparent layer two connections but it is pretty damn close, the only other way to get around this/if you 100% all the layer two information un-touched what you can do is create eoip interfaces between them as it will actually encapsulate the layer 2 packet in a layer 3 so that way the outside layer 3 packet will be the one edited and the layer 2 packet inside will not be changed until it gets to the other side of the EoIP tunnel where is gets decapsulated