Marine and automotive electrical systems using a 12V battery operate at up to 14.2 - 14.4V when the engine is running, as this is the voltage required to charge the battery, Components such as motors are made to withstand this voltage. Conversely, when the engine is stopped and the battery partially discharged, giving say 11.5V, devices must still be able to operate even allowing for some voltage drop in the wiring. So most will still function, although not perhaps at nameplate performance, at 10-10.5V.
Lastly, could running the pumps at the lower voltage damage them?
Because the mechanical power absorbed by a centrifugal pump varies dramatically with speed, as the voltage (and hence speed) is reduced, the load on the motor reduces so much that the motor can continue to rotate down to quite a low voltage at which point the pump will deliver hardly any head or flow. The motor will not be harmed by this, so long as it keeps rotating.
There is a slight possibility of damage if the voltage is just low enough that the motor stalls. Then, the current (albeit much reduced) will flow through one spot on the commutator and one coil, and if the brush contact isn't ideal at that exact spot, might erode the commutator segment by arcing. Unlikely, because the current will be low, but outside the intended operation conditions of any normal small brush motor.
Note that the above is not true of all types of motor and load. There are situations in which reduced voltage can lead to overheating even while the motor is still doing its job.
Looking at the motors, they are 12V 2.1A. So it needs 25.2 watts at max flow. It also supposed to be fused at 4A. Does this means it could draw 48W at times?
Momentarily when starting from a standstill, if connected to a source of constant voltage and negligible resistance. A stationary motor generates no back-EMF, so the starting current will be the supply voltage divided by the winding resistance, usually many times higher than rated current. A large industrial DC motor cannot simply be switched on to the supply, it must be started through a resistance. A tiny motor like this has enough resistance of its own to be switched directly on to full voltage, but it will take a surge of current hence the need to provide a larger fuse. In fact the starting current is probably more than 4A but very brief. The manufacturer has probably proven through extensive testing that the specified 4A fuse represents a good compromise, being small enough to blow and prevent the motor catching fire if mechanically jammed, but large enough to avoid nuisance failures through repeated thermal cycling each time the pump starts.
With the solar panel, the maximum current will be limited so the motor will never achieve that sudden peak power consumption. Again thanks to the minimal power extracted by a centrifugal pump at low speed, it will still start on the panel's limited output, but just take a second longer to spin up. The same is not true of say an elevator motor, that must start from standstill with a deadweight torque that it must overcome before it can begin to accelerate, so it cannot ramp up from zero current.
To fully understand the behaviour, one needs to see the pump's torque/speed curves for various heads, and the solar panel's output curves, and crank them through some relatively complex mathematics. You would do that for a large solar-powered irrigation scheme but it's a bit far-fetched for a 360GPH bilge pump.
