>>14637933
That's not the only or even the biggest issues with boats, though. The problem isn't even the boats, it's the area they operate in that's fundamentally worthless to fight for.
You don't have bases on water, so every ocean bit of the map is entirely optional. Making a fleet of boats to contest it is fundamentally pointless since you'll still need to make ground forces anyway and due to popcaps, every boat you make is a few soldiers you don't have on land contesting actual important territory.
Only way this ever changes is in Island maps, and even then you're better off shipping a few Builders\Villagers, setting up some barracks on the other island and reinforce by that.
There are a few games that try to solve this on their own. Supreme Commander for instance gives very large range to naval units and a T1 naval unit is as strong as a T2 land unit. They end up serving as support and long range artillery but they still require your oponent to being near their base.
Age of Mythology has trade routes by sea and fishing boats, both performing better than land trade routes and farms for their respective resources. This means having maritime superiority enables you to have a much better economy. Which is still a moot point since the pop cap is what ends up controlling your army, not your economy, and the extra popcap you get from not having to make as many villagers, you lose far more than it in your fleet to protect your boats.
The actual reason naval combat is so important is twofold: transport and economy, the second being a followup on the first.
Troops traveling by ground can take a fuckload of time to get anywhere. Put them in boats instead and they'll only take a fraction of the time, even if they still have to walk a bit after disembarking.
Towns and Cities do not share resources in a global pool like most RTS do, but instead they constantly trade what they produce with what they lack and since transportation is so much more efficient with boats than caravans (bigger and faster loads) the sea trade routes are the backbone of the economy for any large, sprawling empire.
So the only way to make boats actually usefull in RTS is to make incredibly huge maps that encourage using transports for fast transportation if you want to have a mobile army. Optionnaly, your troops come from population you recruit in towns, so you can't pop a Barrack in another island and crank infantry out of thin air. Instead, you have to train them in your base and reinforce the front by transports.
Additionnaly, towns should have local resources that they use locally and trade with simple automatic routes. The second a dock is available, maritime routes are created that you must protect. The more a town trades, the more prosperous it grows and the bigger it becomes, giving large empires an achilles heel that smaller players can exploit for comebacks in guerrilla warfares.
>>14637995
Give fuel to planes. Optionaly to every vehicle. Planes burn fuel a lot faster and thus have to return to base for a refill more often. They excell at surgical strikes in specific targets or to assist troops. Boats however last a lot longer out in the sea and therefore are the sustaining force of your army out there.
In terms of transports, boats should carry 5 times as many people as planes can, so they are used for mass transportation while planes are used to transport specialist units.