Sweet Chariot - a National 12 design for home construction
by Colin Cumming 27 Mar 2015 18:38 GMT
27 March 2015
Sweet Chariot is designed for home construction using a 'one plank per side' approach which importantly can be rapidly as well as easily built.
The development of Sweet Chariot represented unfinished business from the 1970's and my previous N12 design N2882 Hustler (see N12 Newsletter No. 29 January 1976)
As a 4-planker Hustler was also conceived for home construction involving a central 't-beam' utilising the centre board box as part of the web to which a long tapering flat floor plank was attached. Around this spine the rest of the hull was constructed using sub-frames.
This design however coincided with a 'step-change' in N12 development during the transition to round bilge moulded hulls. Consequently the 'idea' of a hull for ease of home construction was not further pursued by me until some 35 years later.
The reasons for further pursuing this idea were essentially:
- My recent work on a 'one plank per side' construction approach.
- Improved cost 'gearing' between home build in plywood v production moulded.
It was my teenage daughter who encouraged me to take up my drawing pens again to help design a simple boat that she could build at school as part of her Design Technology 'O-Level'. This brought me into the world of 'one plank per side' construction using darts and stitch and tape to form the hull shape.
Initially for simplicity I investigated double-ended craft and identified a generic configuration involving two contra-curving 'darts' based on two types of bow. In one the chine intersects the stem and in the other the chine intersects the gunwale (e.g. Seafly/ Mirror 16). When these were married in the same double-ended design, the chines thus formed did not intersect and instead created the 'z' outline within each side panel. The closing of these 'darts' formed a strong frameless hull-shell.
Using this approach (now patented) I further developed the idea into a template for transom craft (illustrated below). Initially this formed the basis for a lightweight 15 foot racing dinghy able to be constructed from four sheets of plywood and weighing less than 95kg,
The photograph below illustrates the unusual chine configuration which created a powerful hull aft and a fine entry forward. Panther as she was known proved to be competitive in club competition in two sail format gaining a PY of 1056 (faster than her peer group). Despite this initial success, Panther proved a bit too large for ease of home construction in a typical household garage (15 foot long & 7 foot wide). Fyne boats of Kendal conducted an evaluation and concluded that although Panther was a very effective craft, the curved bow tended to give the design a somewhat dated look.
The development issue now became that of the formation of a vertical bow. Without a garboard plank this can prove hard to construct without significant torturing of the 'one plank a side' configuration.
The 'light-bulb' moment came when I remembered my earlier approach to the construction of Hustler. The introduction of the 't-beam' spine and arranging for the forward chine to intersect the foot of the stem enabled a vertical bow to be easily formed without inducing double curvature. Thus Sweet Chariot was born.
From the outset Sweet Chariot looked good on the water, with its severe chine lines in stark contrast to the rounded lines of the modern production hull.
Sweet Chariot has been tried by a number of helms in a variety of situations and has proved to be an effective and forgiving club racer. Like Hustler however this design was also developed at a time of a step change in the class with the advent of foiling rudders.
The lift produced by foiling rudders allows for more vee'd rear sections and in the case of Sweet Chariot would if adopted lead to a narrowing of the central plank in order to optimise performance.
Although Sweet Chariot's construction is based on a 'one plank a side' concept, it is technically a late 4-planker (3 planks form bow section, four planks form mid-section and 3 planks form stern section but one of which is not the same as the bow). In this context I would not adapt the design for a foiling rudder but instead tend to dispense with the double floor which would further simplify her construction. But what would be her allocated rating in this format?
The reasoning behind Sweet Chariot has been driven by cost considerations. A scratch build hull can be built for significantly less than £2,000 incl. finishes (Fyne Boat Kits offer a kit for around £2,300 excl. finishes). To this has to be added the cost of rigging, sails and foils at around £2,000 (depending on specification). This brings the entire project to around £4,000 (taking account of ancillaries), a gearing of about 1:2.5 over production craft.
This however still represents a significant investment as compared to purchasing a good second hand craft. Availability then becomes the issue and this in turn is related to popularity. At the current rate of increase in new registered numbers I am under no illusion as to worth of this idea. The real question perhaps being.....'Is there any real interest in home construction as a means to create value, based on the inputs of the individual?'
The precision of the kit from Fyne Boat Kits makes building Sweet Chariot more about assembly rather than boat building. The kit is aimed at the amateur level or novice builder with little experience. Fyne Boat Kits also back up their kits with telephone and email technical support, so should the need arise help is at hand.