40mm prop on that motor is a good load.
For what it is worth. I found this
https://www.greathobbies.com/shipmodels/about_msw.phppay attention to the R/C gear section.
Yorkshireman I believe is equipped with 45mm props..
And speaking from experience ,having a trawler with a 40mm prop and a Mabuchi motor. 12v is a reasonable start . just bare in mind that a lot of full throttle action will heat the motor up substantially , that was with 9.6 volt.
12v would load it up a little more ,
The advantage would be better bottom end slow speed, and a little more grunt at the top end. All of this would depend on the batteries,the condition ,discharge rates ,and amp hour rating.
It would be wise to tread lightly at first with frequent checks of the battery and motor temp. Generally speaking ,if your motor isn't getting beyond 80Celcius , its doing fine, If the batteries are feeling more than luke warm , its cause for concern.
The jest is ..start slow and easy and work your way into it , anything that gets hot , never hurts to ask , MHO 80C isn't that bad for for a motor or ESC.
the SLA batteries ...hot ... shut it off...
Please bare in mind lead acid batteries don't like to be left in a discharged state , charge them after every run . And never run them down to the point where your ship is struggling. They don't always like to be deeply discharged.