I'd think that fitting 2 rudders, "line astern" would only create drag turbulence, as the rearmost rudder "bites" in to the wash of the first.

if you wanted to fit a twin setup, its much better to fit them "side by side" equidistant from prop line.

HI John
A rudder acts as a pivot about which the boat turns. Adding another creates two pivots. I have never seen or heard of this combination and it may well work. if it were me I would try just one rudder towards the stern and see how that works. Please keep us posted on your progress as new ideas and methods are always welcome. 😀

HI Dave and thanks for your further response,
I have just had a idea and wondered what you think about fitting 2 rudders, one as close to the prop as pos and one as far astern as pos or am I just being daft.
Regards John

HI John
Nice sleek looking model. Can't see any further aids to straight running but the prop is almost in the middle of the boat so the turning balance will be well out of optimum and even with a large rudder the forces on the rear of the boat will tend to neutralise the effects of the rudder. Had a similar problem with my Aerokits Solent Lifeboat. it would start to turn then suddenly snap back to straight - all due to the large keel fitted. I solved this by reversing one prop on the turn, but this is no use to you.
I believe you may have to move the prop towards the rear, but initially I would just remove the back keel, fit a rudder and see how it goes. if it works ok for you fine, if not you will have to move the prop.
Good luck - please keep us posted
😀

HI Dave
Thanks for responding. I have just uploaded some more photos
if you would like to take another look, you may wish to add further comments. Thank You

HI John
Straight runners were designed for just that. To convert you will need to remove all of the straight keel bits behind the prop and fit a rudder in its place. You have not shown the whole keel but I suspect it is long and narrow so your rudder will need to be close to prop to have maximum effect. The prop is probably too far forward but again this was to help the straight running. You may find it difficult to make the model turn but some trial and error should give you the best result. I suspect the rudder will need to be much longer horizontally than what you would normally see. if there are any further extended keels at the front they will also need removing.
Good luck, please do keep us posted. Why not start a build blog. 😀