aye aye there
I should imagine any standard servo, such as Futaba or HiTec would do the job. This is because the Sea Queen isnt a really exceptionally large model with huge rudders.
The yacht lads might use them in their big yachts - cos some of the rudders on the yachts can be about 6 - 8 inches long - 3 - 4 inches wide.
Also, the power boat lads would use the metal - geared servos for their reliability - plus the amount of vibration which the servo in the power boats would encounter.
If if it was me - I would go for the bog standard servo - plastic gears, but, I would ensure that the servo is mounted correctly and there is no restriction in any movement such as 'tight spots' between the rudder linkage and servo.
I have had trouble with a servo which was my own doing, and this was cos I was converting the electric plug so that it would run on the old Sanwa set. Then, after conversion the said same servo I plugged into a standard Futaba RX - needless to say it 'fried;
aye
john