How many chines?

Chines are the angled edges where planks meet in hulls. The pros and cons depend much on the usage of the boat.

For example, a runabout:

… and a racing powerboat:

… often use a single hard chine and ribbing because chines give you stability – they stop the sideways rocking. They also present a flat surface to the water which enables the boat to “plane” or go up on top of the water, thereby reducing overall wetted area, therefore reducing drag.

Anyone who’s been in a power boatknows the downside – the bang, bang, bang wave slap which jars the teeth out of their sockets after a while.    In sailing boats, single hard chines [misusing the term a bit here to mean two longitudinal panels each side of the keel] are usually the preserve of the dinghy:

Most keelboats [especially racers] tend to go for a round bottom:

… and modern cats certainly do.   The reason is that, for a given hull section size, round gives less wetted area and therefore less drag.

In a keelboat, you get away with it through the heavy weighted keel holding the boat up but in a sea, you still get that slewing around of a round object in the water.   In a cat, the problem is not slewing around but sideslip and you need ways to stop that.   A chined boat tends to stop that to an extent but it depends on the number of chines.

Some boats use multiple chines to approximate a rounded shape:

… and there’d be two reasons:

1.  Cost and materials – the chined hull is easier to build and cheaper;

2.  It does give stability, at the cost of speed to an extent.

The more chines, the closer to round you get but the greater the complexity of building.   The fewer chines, the less sideslip and greater initial stability but there is the waveslap factor – and do you really want that every second on a trip – and then there is the lower stiffness in a chined panel rather than a rounded – roundness adds stiffness, which means speed.

If you take chines to their logical extent – that is, overlapping planks – you have lapstrake or clinker:

… one of the strongest construction methods known and a traditional one.   And there is the question of beauty.   Tastes differ but I don’t particularly like rounded, though they suggest cutting edge and professional looks to many people.   Chines and clinker mean traditional to others, including me.

So a compromise is necessary – will you go for one chine either side, multiple chines:

… clinker or rounded?

Again, usage is vital.   In a cat, cost-saving is one of the few reasons you’d use a single chine either side and many of the earlier cats had those.   Clinker is perhaps overkill in a cat so multiple seems the way.   How many either side?

Two or three.   Chines also prevent rise and dip to an extent, which includes preventing hobbyhorsing.   In narrower rather than wider hulls, two would be fine.   For a more rounded design, you’d need three because chines at rightangles maximize internal space, whereas those on an angle cut internal space.

Oh, another thing – a deep V allows rise and fall with comfort but shallow V allows spray to shoot out the side, rather than rise up the sides of the boat and into it.

Decisions, decisions.   Here’s a nice article on the question.

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