Clare: About the gratings: The basic question is how the internal arrangement of fluits was worked out. Basically the type was designed as a freighter. Taking many guns aboard diminished the loading capacity, for which reasons most fluits (if armed at all) carried no more than 4 guns. The lower deck, in men-of-war a real living space, was in the fluit just a low compartment to store goods that had to stay dry. Gratings were useless there. Of course often times the type was adapted to the purpose it was used for. An example is the heavily armed fluit we see in my illustration in post #39. probably the drawing was made because of the exceptional ordnance of the ship. Looking at the Schwarze Rabe I don't see much logic in the spreading of guns. But enough is said about the reliability of the kit.
Bob: as usual I base my comments on the available literature and on original models. To the left the only drawn example of a chesstree we have, made by Witsen (1671). This is an illustration from my book, with my 'modern' interpretation to the right.
You are right about the obvious lack of practical use without a sheave, but hey, the same thing we can say about the absence of an engine. Not very practical, hm? :-).
The subject becomes even more mysterious if we look at the rope, the tack itself. It was made in a way that the thickest end was at the sail and the thinnest end entered the ship. Don't know how they made such a rope or why it was done that way, but we have sufficient proof for the correctness of this observation.
Modelbuilding will always bring up questions. That's why it's such an interesting hobby.