Hi there Hagar
To calculate the position of the rudders and prop shafts on this plan we have to use the side profile drawing of the actual vessel. On the line drawings there are no prop shaft/rudder positions shown. What you need to do is use the very edge of the transom as a reference point; where the transom meets the keel of the vessel. Take all measurements for your centre rudder and prop shaft from this point.
Then, transfer them to your line drawing if you wish; or, transfer them to the keel drawing on your piece of chosen plywood. The distance between the two outer propeller shafts and rudders come from the stern elevation of the vessel; this again, you may transfer to your bottom profile line drawing. What I would strongly recommend is you mark your centre prop shaft on your keel because this needs to be cut and cheek pieces added prior to any part of the building of the hull.
Complete the build of the hull, without worrying about the location of the two outer prop shafts; once the hull has been completed, you can then calculate from the drawing onto the actual hull the position of your two outer prop shafts - using your centre prop shaft as a guide.
As far as engine mounts are concerned, as you have suggested, for those who are unfamiliar with building from line drawings; and have the ability to calculate frame positions for motor mounts; (which knowledge you will gain through experience
) is do as you suggest by putting flat-beds in to support your motors.
Now .... for a confession - and this has no reflection on this particular plan
- I redrew this plan and added an extra rib in at the stern and altered the width of the hull and the flare of the bow. This was because I had received adequate photographs and information to correct very slight imperfections; now, before anyone thinks that this plan will not build a very true to lifelike hull, do not worry AS IT DOES because I have built a hull directly from this plan, with no modifications.
The only problem I found with the original scale and hull was at the time I built it, we did not have brushless motors or the associated electronics to go with them. To get the best performance from this scale hull it may be better to go to the 'brushless set-up'.
Hope this is of some help.