Back in April I wrote two posts about flat-bottomed sailing and rowing boats (see Discussion About Flat-Bottomed Boats and Sharpie Hulls and Fine Sections ).
Things have been pretty hectic at our place since the disasterous flash-flooding which hit our area on January 10, 2011, but over the last few weeks Ive been getting back to work on some over-due jobs, one of which is a nice flat-bottomed skiff for a customer in Brisbane. She is a Jim Michalak-designed Mayfly 14 and is a good example of a well-designed flat-bottomed hull. The point to note is the relationship between the curve (or rocker) of the bottom when viewed in profile, and the curve of the topsides when viewed in plan-view. These two shapes, in combination, determine the chine-line, and the the flow of water around that chine. The aim is to reduce cross-flow to a minimum in order to minimise eddying.
A nice, simple boat, showing the pivoting leeboard, centreline hatches, and external chine log.
Many people find external chine logs difficult to accept, but they have some advantages. They are much easier to install on a boat which isnt built on a strongback, avoiding compound bevels and determination of length. In addition, they provide good protection to the chine, which is somewhat vulnerable on a flat-bottomed boat. Phil Bolger had a theory that if the hull was properly shaped, an external chine log may reduce drag, by delaying the point at which cross-flow occurred. In addition, I guess that they provide a bit of extra lateral resistance, which is good in a sailing boat.
Brutally simple pivoting rudder design which requires only one rudder cheek. The key is the amount of blade above the pivot point, as it provides support to the blade regardless of which tack the boat is on. The patch at the bottom of the blade is where Ive cast in a block of lead to sink the blade. It is covered with a small patch of 200gsm/6oz glass to prevent cracking between the lead and the plywood. The white is epoxy and sanding filler.
Very simple, but rugged, mast step and mast partner, well braced by framing on the other side of the bulkhead.
Close-up of the mast step showing the very necessary drain hole to get rid of water in the step. This is all a bit rough at this stage, still waiting for some clean-up and fairing work.
Close-up of the external chine log, rounded over on both edges, and showing how Ive brought the epoxy/glass bottom sheathing around the bottom edge and up over the chine log. This is to protect the vulnerable edge grain of the 1/2" plywood bottom.
Outer stem made from a superb piece of Celery Top Pine from Tasmania. Hard, dense, and strong. Still waiting for finishing work and fairing.
Close-up of the external gunwale/sheer clamp, laminated from two beautiful pieces of Silver Quandong. Note how in a simple boat like this, there are plenty of places where the edge grain of plywood planking is vulnerable - this needs to be considered, with action taken to protect the edge. The edge of this plywood will be treated with three or four soaking coats of epoxy prior to being painted, but even then it will have to be watched in service.
Detail of the corner joints in the hatch framing. Once again, Silver Quandong
The single-sided pivoting leeboard allows for a clean and open interior. Although simple in concept, the leeboard design requires great attention from the builder when fabricating the leeboard upper and lower guards, so that the board is absolutely parallel to the centreline of the boat. Trickier than it looks!
A nice, simple, rugged boat. The external stem cap is yet to be trimmed, and at this stage Im planning on finishing it off with a Jonesport Cleat.
So, there you have a nice little boat. But you dont get something for nothing. These boats might be easy to build, but they consume large numbers of silicon bronze screws, and the structure is quite heavy. However, she should give long and trouble-free service, given that she is painted properly (she will be) and stored properly
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