IMAGINE LIVING DIFFERENTLY,
LEARNING, CREATING, GROWING ....
WITHOUT SCHOOLING.


Wednesday, 10 September 2014

Model Boat Building Develops Imagination

A Guest Post by Grandpa following ongoing project work with the boys this year

Our experience of Model Boat building is that it develops the imagination, it builds skill in project planning, in drawing, in measurement/arithmetic, in mechanics/physics and in construction techniques. It also provides a platform for looking at the science of flotation, and at history. It develops manual dexterity and instructs on the effective/safe use of power tools.

We used a powered jig saw, a power drill and a powered sanding machine. We also used a sewing machine. The boys had to be taught how to safely use these but then trusted to operate them solo.

We first discussed what sort of boat we were to build. As a result, we have built five different designs:
A pirate ship
A sailing boat
A bigger sailing boat
A big fast racing sailing boat
A warship from the Second World War.

We used three techniques:
A Horizontal sandwich
A vertical sandwich
Solid wood

The Horizontal sandwich: On a piece of 5-ply wood, we made a series of 10 drawings of horizontal sections through the hull. Straight lines were OK at this stage so careful measurements, and reducing or increasing the same point in successive sections by a centimeter produced the desired result.

The Vertical Sandwich: We decided that we wanted to sail the second boat we made. It followed that it had to have a keel. The keel had to be integrated into the hull. So we used a mix of 5-ply and timber in vertical sections, the first section featuring the keel and then four to six sections each side. Into each vertical slice we needed to cut a central flotation chamber – that is, the hull is not solid but hollow.

In our “sandwich”, we needed reference points at a position common to each section to give correct alignment as we glued.

When we had drawn, we cut everything out with the electric jig saw. The sections were then glued and their alignment carefully checked before clamping and leaving for the glue to set. In all three of our sailing boats we used an “exterior” waterproof wood adhesive. Applied generously it gives a wonderful seal.

The hull was then sanded to shape. This required some hours of work and produced a great deal of sawdust.

We then varnished the hull, building up 8+ coats over a period of days, sanding down in preparation for each. A pleasing feature of the horizontal 5-ply design was that the exterior of the hull features “planking”: use the 5-ply vertically and the planking appears on the deck.

We then drilled holes into our hull for the masts. These were commercially produced dowel, cut appropriately, and then glued into their sockets.

We prepared for the installation of the rigging by fixing brass eyes, for which a small hole had to be drilled at strategic stress points in hull and masts. We identified those stress points by discussion of the forces that would act upon them.

“The Crocodile”
For the pirate ship, our decision was that it would be a model from the waterline up. Waterproofing was not specified. The hull sandwich drawing took some imagination : an old ship was wider above than at the waterline, and there needed to be an authentic tumblehome. This lends itself to the horizontal sandwich. Our hull is 60 x 20cm. It has two hatches in it, and these were drawn in at the earliest stage. The yards were dowel, cut and fixed to the mast by hook and eye. The requirement for the sails was assessed and measured, and run up on a sewing machine. We put a tunnel on the top edge of each sail which then completely enclosed the yard, so the yard was fixed to the mast after the sail was hung. Other details, a figurehead and stairways were fashioned from “Milliput”. The choice of figurehead gave her name. A 1/72 scale plastic crew was purchased before she set sail for the Caribbean.

On reflection, I wished that she had been waterproof. The picture also shows a pirate puzzle, drawn and then made with a jig saw and housed in a specially designed box.



“Galadriel”
Our first sail boat was named after the Tolkein character. As originally built, Galadriel was inspired by something seen in my brother’s house. She carried a rudder cut from biscuit tin metal, then folded round a shaft and soldered. And to the keel we fitted a lead weight (which we cast ourselves). However, we then found she was not a good sailor. So we discarded the lead, and the rudder, reshaped the keel, gave her a bowsprit, and re-rigged her Bermuda-style, adding a bowsprit. In her radically different new style she sails well. She was made from 11 vertical slices of 5-ply and measures 44 cms in length and 54 cms from keel to masthead.



“Galadriel II”
We had then wanted something really impressively big, so our second boat was planned at one metre in length and over a metre from keel to mast head. Following the vertical sandwich technique we used 5-ply for the centre section with an integral keel, then we used on each side two layers of two-inch timber. The result was a sleek hull. However, she was actually laterally unstable, too narrow, too heavy and sailed poorly. She was at first ketch-rigged but we concluded she could not spill wind and must be allowed to do so. So we radically rebuilt her, power drilling into her hull with a big bit to make floatation chambers, and then added extra width by adding two extra sandwich layers. The result was wider but lighter. Now Bermuda rigged, she sails well. As finally configured, she is 98 cms long and 91 cms from keel to mast head.



“Arwen”

These experiences led to “Arwen”. She is a metre long and 95 cms from keel to masthead. From the beginning she was constructed using a hollow hull, and again 5-ply for the central section with integral keel, and four wooden sections on either side. From the start she sailed beautifully, so our learning curve had peaked satisfactorily. Arwen was Bermuda rigged from the start. Note her rudder.



A feature of our sailing designs was “the bath test” at an early stage to check sailing characteristics, and to make changes as problems were detected. We also looked at bouyancy in a crude Archimedes experiment - assessing how much water was displaced by the boat and what that weighed in comparison with the weight of our model.

As suggested above, experience led to complete redesign of our first two sailing boats, and in finding success, we were guided by a “pond boat” which we bought on the internet.

We kept the rigging very simple, following the example of the commercially produced pond yacht. Our rigging is nylon twine which has slight elasticity, but needs the ends glued when cut (as it rapidly unravels). It is fed through small brass eyes, and tension is maintained by small wood “blocks”.

We added the ensigns by painting (in duplicate) a piece of paper in enamel paint and folding and gluing this around twine (so that we can raise and lower the flag).

The solid wood model

This brought much quicker results, but not a sailing model. Following a drawing obtained from a library book, we produced a waterline model of the hull by drawing on a piece of wood and then shaping this with the electric sander. The bow section being higher we had to add and treat similarly a second piece of wood. Details were added using cardboard, wood blocks, balsa wood, and wire from clothes hangers. The funnels were steel tubing. We prime painted and then used grey undercoat, which effectively hid all the blemishes. The gun turrets and torpedo tubes were screwed in place, so they traverse.



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