Chine width

[Boysie]

Hi Folks,
I have the plans of a 19 ft monohedron planing hull that is 5ft 0ins across the chines midships reducing to 4ft 10ins at the transom, beam 7ft 6ins (so there was quite a lot of flare in the sides) that I built in 1963 for pulling rock lobster pots. The boat was very successful, handling rough water particlularly well.
I have moved to a location where we have to cross a shallow bar and have decided to build a boat to the same plan but increasing the width across the chines at the transom to 5ft 0ins. A friend (not a designer) tells me that if I do this then the boat will be hard to steer in a following sea. He says that in his experience some narrowing across the chines at the stern (albeit small) is essential. Is he right?
Regards, Boysie.

[Nojjan]

Your friend is correct to some extent. Making such a change to an existing hull will make it slightly more resistant to directional change no matter what course and slightly more sensitive in following seas (more bow steering). Looking at many modern hulls this old rule is forgotten but the directional thrust of an outboard or sterndrive is sufficient to yaw the boat for good steering and maintaining good course stability.

At the end though I wonder if your 2" change will provide the other benefit your are looking for. /N

[Pericles]

Boysie,

Tom Lathrop posts here and his site address your questions.

http://www.bluejacketboats.com/

In addition, Jacques Mertens has designed craft which work well. See DE 23, DE 25, LB 26 and others, such as Classic 19 Express and Pilot 19. Explore the site.

http://www.bateau.com/categories.php?cat=29

Welcome to the forum.

Pericles

[Boysie]

Thanks for the information Nojjan and .Pericles. I'll revert to the original chine. Propulsion was a locally manufactured primitive jet drive no longer in production, powered by an automobile engine. Presumably the weight of the inboard engine placed at approx the centre of buoyancy would have assisted with stability. Although a bit lively at anchor (but not unpleasantly so) the boat performed very well in head and following seas.
Regards, Boysie.