As the bottom stringers are generally installed first it is a good idea to include the engine stringers and beds at this time.   The location of the engine stringers, if called for, especially if there is a twin engine installation,  will govern the spacing of the other bottom stringers.   Engine bed stringers can be all foam and glass construction or they can have timber or steel inserts.   You plans should specify the recommended method(s) for building the engine beds for your particular boat.   Size of the engines, both physical and by horsepower ratings will be important factors in deciding just how you build the beds.   There are special high density cores available for this purpose - check with your supplier for details.   Overkill in this area is recommended.

   Usually engine beds have a laminate that consists of alternate layers of mat and roving with extra layers on the top of the beds.   A required system of athwartships webs is installed to support the engine beds.   These webs will be cut away below the engine to allow room for the sump.   If you are using a foam and glass, or a foam glass with timber or steel inserts, it is best to build the basic core structure and then laminate the complete structure as one unit.   This avoids as much secondary bonding as possible.   The area under and around the engine will need to be particularly well covered with interior gelcoat.  On smaller boats, engine beds can be made from plywood on edge, heavily glassed and with angle iron bolted to the tops to support the engine. This is a well proven system.