Request for IOM Class Rules Interpretation from CAN NCA.

With the emergence of the new high prismatic narrow hulls with chines, the decks are becoming much narrower than traditional IOM designs.

With a narrow deck, the chainplate position moves inboard and the shroud base gets narrower. I have attached a pictures of a narrow IOM (see below) with rounded sides where the chainplate eye has been placed proud on the center of the topsides to widen the shroud base. See diagram F.

My question is does this contravene class rules?

D.2.3.c Fittings shall not project outboard of the hull shell or deck.

This question raises the issue of the location of the sheer and where the deck ends and the topsides of the hull begin. The chainplate eye can project above the deck, but cannot project outboard of the hull shell. So how do we interpret the class rule for the diagram examples B, C, D, E and F?

It also asks the question about the hull shell – is the class rule use of SHELL, referring to the plane of the hull in the area of the chainplate eye, or is it referring to max beam?

In case B, the sheer is a small radius curve and the chainplate eye extends outboard of the hull lines and max beam.

In case C, the sheer is a large radius, and the chainplate eye lies inside max beam. There may be some question as to where to locate the projection lines.

In case D, the hull bottom is round and the chine extends from a vertical tangential extension at max beam. The chainplate eye is outboard of the chine, but inside max beam.

In case E, the hull bottom is a flat section and the chine extends from a wide angle tangential extension at max beam. The chainplate eye is outboard of the chine, but inside max beam.

In case F, the hull is an oval with no discernible sheerline or chines where the chainplate eye is attached. This matches the picture of the IOM (below).

 chainplate

chainplate-2