Hull Chines

A recent IBEX conference included an informative seminar addressing construction, location and hydrodynamic aspects of stakes, steps and chines.

Chines are sharp corners in the cross sections of a hull.  They are typically a feature of higher-speed craft and used in combination with relatively flat bottoms they produce higher dynamic lift at planing and semi-planing speeds.  They also make it easier to build a hull from flat panels.

Chines introduce structural problems at the chine itself and in the side & bottom panels because they are flatter than a round bilge hull.  This is a concern in FRP construction, particularly in vessels with cored structure.

Due to their prominent nature, chines can be damaged by impact, blocking, and sling loads.  To ensure sufficient strength and stiffness in the chine area the bottom laminates should be carried up past the chine into the side panels (see Figure 1 – click on figure to enlarge).

To achieve better longitudinal strength the sides of the hull can be effectively made into a truss structure.  The chine and gunwhales form the bottom and top members, the bulkheads / webs form the pillars and the side shell and 0/45 degree fabric forms the diagonal braces (see Figure 2 – click on figure to enlarge).

In case of cored structures, particular care is required.  It is not good practice to have cored sections of a structure joined together (e.g. side & bottom, or transom & side) in such a way that water could enter the core if one section is damaged.  At the chine, the core should be tapered sufficiently far back from the corner to allow the inner laminate to pass smoothly up into the side.  Extra layers of glass in this area are also a good idea since the cored panels will be stiff and ‘hinging’ in the corner should be avoided.  Builders should make it clear to buyers of lightweight cored hulls that blocking or jackstands should be not located in way of the core as the compressive strength of the core may not be sufficient for concentrated loads.

Click on drawing to enlarge

For more information contact the NSBA office at 902.423.2378 or email nsbaexec@eastlink.ca.

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