Ukraine claims it hit a Russian ship with a 'Sea Baby' drone. Russia is fast running out of space to repair them.

• Ukraine claims to have struck two Russian vessels with "Sea Baby" drones this week. 
• If confirmed, the damage will ramp up pressure on the Black Sea Fleet's strained repair facilities. 
• This is likely to compound Ukraine's advantages in the waters over time, an expert told Insider. 

Ukraine doubled down on claims on Friday that it had damaged a Russian patrol ship near Sevastopol with "Sea Baby" drones.

If confirmed, the strike could add to long-term pressure on Russia's ability to maintain and repair its Black Sea Fleet, experts say.

Amid its bombardments on both ships and port facilities, Ukraine faces a "reinforcing cycle and loop of successes and opportunities" in the Black Sea, Basil Germond, a maritime security expert at the UK's Lancaster University, told Insider.

Russia is already barred from bringing reinforcements to its Black Sea Fleet. The more damage its ships take on, the more they will clog up its drydocks, bringing on a cumulative effect on Russia's naval powers in those waters, he said.

"Consequently, the Black Sea Fleet will have to be increasingly prudent with its remaining assets," he added.

Reports of 'Sea Baby' strikes

Ukraine claimed on Wednesday that it struck the Russian patrol ship Pavel Derzhavin with "Sea Baby" USVs, Ukraine's experimental maritime drone, Ukrinform reported, citing an unnamed source from Ukraine's security service.

Further, on Thursday, it struck the Buyan missile ship, the source said. Neither report has been independently confirmed.

Crimean Telegram group Crimean Wind reported that locals had heard an explosion at around 10 a.m. local time on Wednesday.

But a prominent Russian Telegram group, devoted to following the movements of the Black Sea Fleet, shared an image that same day purporting to show the vessel, undamaged, in port.

Russia's Ministry of Defense has not commented directly on the claims. On Friday, the fleet released a statement saying that the Pavel Derzhavin was involved in an exercise to remove sea mines in the area, with no mention of an attack, state-controlled news outlet TASS reported.

This was rapidly followed by a post from pro-Russian military blog Rybar saying that the Pavel Derzhavin's rudder was damaged that morning. The outlet suggested that the damage came from Ukrainian sea drones.

Images of the same class of ship, trailing black smoke, circulated online on Friday, which open-source naval researcher HI Sutton said were as-yet inconclusive.

Should the reports of either attack — on Wednesday or Friday — prove true, the ship will soon be seeking to squeeze in on an increasingly tight repair schedule.

Russia's bind

In September alone, Ukraine devastated the Black Sea Fleet's headquarters and did significant damage to a KILO-class submarine and a landing craft in one of its drydocks.

Independent naval researcher and former Norwegian Navy officer Thord Are Iverson told Insider that, as of last week, Sevastopol's dry dock space was at full capacity. He earlier told Radio Free Europe that damage to the drydock itself from Ukraine's attacks is likely to have been minimal.

To repair the Pavel Derzhavin space "could probably be freed for more urgent requirements," he said.

Nonetheless, "the impact of reduced dock capacity on maintenance and ship availability is something that will accumulate over time," he said.

The Montreux Convention, a treaty that controls military ships entering the Black Sea, bars Russia from bringing in reinforcements.

Trapped there, its fleet faces both wear and tear and increasingly confident Ukrainian attacks — notably at Sevastopol.

Russia has moved at least a dozen vessels from that port to safer shores on the Russian coast following the September attacks.

Satellite images dated to early October showed that at least a dozen ships were seen heading toward the port of Novorossiysk, more than 300 km away. The move, though not unprecedented and potentially temporary, has led experts to see it as a sign of Russia's waning control over the Black Sea.

"Novorossiysk has much less developed naval infrastructure than Sevastopol," Sidharth Kaushal, a sea power expert at the UK's Royal United Services Institute, told Insider.

According to Radio Free Europe, the port can't do specialized servicing to submarines, for example. And the other ports Russian ships have moved to, such as Feodosia, on the eastern side of Crimea, also can't take on complex repairs, the outlet reported.

"Retrofitting another yard to take over from Sevastopol will take time — time a Black Sea Fleet at war does not have," Iversen told Radio Free Europe.

This squeeze on the Black Sea Fleet ultimately hampers some of its ability to project power over those waters, Germond said.