Its mostly only single seaters that have full carbon roll over protection and it has to be heavily crash tested to meet FIA rules.

However with the correct load spreading plates, a bolt in roll cage is perfectly ok. Plenty of the supercar type cars with monococque chassis have bolt in cages for GT series and the like.

Done a bit of research and a lot of monococque tubs are using a fairly simple skin based around either a 10mm foam core panel or 10mm honeycomb increasing to 15mm in some areas. Obciously the higher the level of motorsport, generally the more technical the core - ie slightly stiffer but lighter yet twice the cost!!

Some of the bigger sports cars use double skins formed into a box type section.

Also in a lot of the carbon cars they make use of honeycomb to form crash structures for frontal impact.

So with a bit of discussion with work colleagues ive come up with a sketch of my sill structure:


The outersill is original body panels remade in carbon with the void filled with honeycomb as a crash structure. It is not part of the monococque but represents the bodywork and in effect a replacement crash structure for minor accidents.

Ive chosen to use foam core. Its cheaper than alloy honeycomb and easier to produce a consistant strong panel (consistancy is important when you consider how much panel i will need!) and the only penalty being a 20% weight increase over honeycomb cores.

Plus its much easier and cheaper to make. The core isnt massively more expensive if you use honeycomb, however the specialist glue film sheeting, which needs oven curing, IS expensive and could easily add a couple of grand to the cost of a monococque.

I also intend to fill the monococque side panel voiding with honeycomb. It will add some stiffness plus add further crash protection with the honeycomb absorbing energy as it crushes.

Should give me a good strong side profile.