Battle Island game B for Riverrun was an instance of a great plan that worked right up til it failed.
I believed that sea power could dominate on this map, with convoys breaking up the logjams that would inevitably form at the bridges. Conversely, gaining the seas would protect you from having someone else convoy into your backyard.
Towards this, I set up an alliance between myself (Riverrun) and Winterfell. We agreed that fighting ourselves would let the others gain the island so we agreed to focus across the waters and get to Battle Island first. I even gave Winterfell 2 of the 3 SC's that lay between us as I focused on getting to the island and building sea power first.
By Fall'04, Winterfell had gained the western seas, and I had gained the Eastern seas. We both had developed positions on Battle Island and Borderlands single foothold was being cast into the sea.
Fall'04 - The Winterfell/Riverrun alliance is working

By Spring of 05, the taking of Battle Island was almost complete. Winterfell had grown to 10 SC's and was looking at a build of 1 and perhaps 2. I had 8 SC's and looking at a build of 3. I had taken Talkeetna Mountains on Battle Island and was looking at taking Brooks Range. Back at home, I was poised to take the remaining SC between Winterfell and myself.
However, looking forward, there were only 2 more SC's left to take on Battle Island, one Winterfell would take this turn (St Elias), and the other (Romanov) was also going to fall to Winterfell due to an SC sharing plan we had devised back in 03.
This, to me, was the fork in the road. Either I would continue the alliance with Winterfell until the end, or it was time for the ultimate stab...
The benefits of the stab consumed my thinking. I could use Talkeetna to deny Winterfell St Elias, while taking The Eyrie from him back home to force him to disband 1. A swing of +4 with my 3 builds versus his disbanding of 1. Denying him his build, he would be defenseless back home with 5 SC's up for the taking. I could come at him with 3 builds at home, invading his home centers, preventing him from building in the future.
What I did not put enough weight on in the decision was the growth of Midlands, having 3 armies ready to burst forth onto the Island and the relatively weak position I would be in on Battle Island as my builds would be required back home taking out Winterfell's home centers. The proverbial storm on the horizon that goes unnoticed.
Spring'05 - Poised for the stab

Winter'05 - The stab complete

By Fall 07 I had taken 4 SC's from Winterfell including 2 home SC's... but Midlands was flooding onto the Island. Fortunately for me, Borderlands and Aeil were still fighting, ensuring that a third front didn't break out in the east. I was working with Aeil against Borderlands to some degree, trying to keep the battle going there (and away from me). But this did not last long. Borderlands was overpowering what was left of Aeil and I would be his next target. I reached my maximum size at 18 centers in Fall'08, but even in Fall'07 the wheels were getting ready to fall off.
Fall'07 - A hollow dominance

The vulnerabilities post-stab were coming to the fore now. By Fall'11, I had retreated on Battle Island to hold only 3 of the 12 centers (after holding 8 at my zenith). I had consolidated the old Winterfell home centers and the combined Winterfell/Riverrun Island was my defensive perimeter.
Fall'11 - Fall back to the keep!

From this point forward I began working with Borderlands to prevent Midlands from breaking the game open. If both had come at me, I did not have the strength to defend on 3 fronts. The many small choke points were coming into play. Sea areas where you could not bring enough firepower to bear to break the stalemate line. Also many mountain passes where you couldn't bring forces to bear to crack an enemy stronghold. I even brought 4 fleets around to the west and was able to dislodge Midlands from the Southern Sea of Storms. But could go no further as the map only allows 2 fleets to broadcast their power north from there.
Fall'14 - The inevitable draw was growing near.

In hindsight, I should not have stabbed when I did if I wanted any chance of getting to a 2 way draw, or soloing. The vulnerabilities on Battle Island should have signaled me to keep my alliance, which Kerrmit had vowed to continue to the end.
I still do not know if Sea Power would/could decide this game. I did not achieve total superiority on the oceans, particularly, encircling Battle Island. After the stab, Borderlands only had the one fleet, but was still able to build more and challenge me along the eastern front. If not for the stab, perhaps Winterfell and myself could have driven to total superiority on the oceans. We'll never know.
SS
To Kerrmit my old ally... sorry, I went for the 30 pieces of silver and lived to regret it.