A roll your own mouse
Part One - Part Two - Part Three
In one of my more creative moments I was experimenting with half sheet boats and was working on an idea for a squashed hexagonal shape. I had built a few of this sort of thing in cardboard so I went on and looked at seeing how well it would work across two half sheets (or if you prefer a whole sheet). It seemed eminently practical. I had even worked out that an eight inch side piece would give a half hexagon and a 12 inch would give a half square measurements in between would give in between, or 'squashed' shapes further pulling pushing and trimming would of course alter the shape.
A bit of time fiddling with variations made for a surprising amount of difference, ranging from one 'stubby' end to making the boat wedge shaped, thicker at one end than the other by flipping side pieces around. Having done this I was suddenly struck by how much, at first glance, I had stumbled across a slightly enlarged variation of the legendary mouse by Gavin Atkin with tacked on pointy ends, or a close but still no mouse. A closer inspection of the two plans side by side shows the mouse is wider in parts, shallower overall and has full length rocker, where my version is a lot more angular (to start with anyway). In short they are two different boats, that only look similar on a superficial level. I had a few fiddles trying to get at a boat that I knew was hidden in these variations that would have both all of the pointy ended features I had created and more freeboard and an identical waterline to the original mouse. I was sure it was still hiding in there somewhere without me being able to find it but I have come to peace with the notion that I can not find it because it is not there. At the 8 foot core level (4 feet from the centre). The mouse has a wider floor panels at the ends - 9.3 inches at one end and 12.5 inches at the other. Height wise at the end however there is much more height in the end in my draft design than the 1.7 and 2.3 inches in the original mouse.
Then I took a look at the following criteria from the history of mice file on the Yahoo mouse boat group:
General Mouse Design Characteristics:
1. Flat "pram" bow
2. Flat stern
3. Hull panels bent around 2 primary frames. "Sharpie-style"
4. Four (or less) hull panels (not multi-chined, cold molded, strip-planked
5. Vertical sides, no flare.
6. 16' max LOA & 5' max beam
7. Shoal draft (dagger/lee boards yes, Fixed keels no.)
8. Adequately performs in accordance with its intended purpose.
9. Captures the simple "spirit" of the original mouse...
What to do with all that pointy stuff on my ends then? The answer to that conundrum came in the rat cunning of shifting the seams to split across the ends and taking a trick from the the Banana boat which I found on the one sheet wonders yahoo group and also in Hannu's boatyard
gallery (second one down) The slight magic in it is that the offcuts can be reattached to the same sides (attaching 4.5 inch triangle to inch ends & etc) and the middle two pieces are switched.
BUT to create a much more mouse like folding alternative I fiddled with one of the ends a took the two 7.5 inch ended triangles only, using them to square up the ends, like a proper mouse. The bonus is that I lose a problem I was having with finding sufficient space to fold in at the small narrow ends, especially if I was going to add gunwales, plus there is a leftover pair of triangles that look just perfect for making a double ended paddle or a pair of oars.
The measurements can be varied a little bit and still generate a very good and mouse like boat. The angles required to fold vary slightly as the measurements varies. There is also the slight blessing that mouseboats as seen in nature tend also not to have exactly perpendicular sides.
Inherent laziness causes me to note that all one has to do is cut the sheet of plywood in half, clamp the two cut halves together, mark up one side and cut the two pieces together. Given my plan exact halving of the sheet would be a bad thing as I am not going to divide the middle triangles in two but there is sufficient scope in the plan to minimise measuring and cutting and at the same time maintain the symmetry which is inherent in the design of the craft.
At the risk of increasing my reputation for laziness I decided to use the 7.5 inch end pieces as the definition for my bottom angle. This gives me a definition for my angles and lets me do some trigonometry so I can work out what all my angles and widths are at the top so I can look intelligent and pretend it was anything other than a sheer fluke that I finished up with anything remotely usable. If I keep the sides vertical (at the front) with a 10 degree (actually 9.46 degrees but who's counting) addition to a regular 90 degree square at either end = 100 degrees (based on my 160 degree bottom V adding 10 degrees to each side). Dividing by 2 gives us a 50 degree angle to cut to make the end and side pieces from the wide triangles and have a symmetrical fold. The side triangles can be created with the required 50 degree angle by measuring around 5 and 3/8 inches along one edge and 4 ½ inches along the other for your right angled triangle. The width across the top of the bow and stern then works out to be roughly 14.8 inches.
Cut the above rough diagram along the red lines and rearrange into final configuration thusly:
However, mathematics and a neat solution may not be your cup of warm beverage and you may not have a saw protractor like I do and you may not trust my trigonometry. Never mind a bit of trial and error steps into the breach. All you need is a bit of paper or cardboard the same angle as your outer edge and fold it flat to see how it will go. This is a slightly modified plan as I initially forgot to allow for the fact that the folding joins have thickness and in my prototype I finished up with a transom that looks like this:
The other end which is 3.5 inches high (use a 4 inch to allow for joint width) can be worked out using trigonometry like the above, or do what I did and just fold over a bit of paper.
Cut your panels accordingly and Robert is your avuncular relation. Of course you might also decide that a waterproof fabric end would suit your needs rather than all this fiddling about, in which case the ends can indeed be wider because you now no longer need the offcuts but that would be a different plan.
All of the bottom vertices should be smoothed (or faired) using a spline, rounding across as much distance as possible but taking no more than an inch or two off the curve.
I initially favoured frames which have the rough dimensions of 30 inches across the top, 9 inches down and 15 inches along either side of the bottom (depending on how severe you have been with your fairing.) I do believe though that the top could be flared out to 33 inches, or reduced to as little as 28 inches without harming the essential mouseness of the design by too much and of course because they are removable can be made in multiple sets for the one boat in a wider or narrower configuration, though there will not be much difference. However on my prototype I used a lump of 2 by 4 as a thwart 23 ¾ inches from the ends (for true mouseness). My end pieces finished up about 75 cm long (29.5inches). They were supposed to give me a solid base for building my frames from but they appeared to be doing the job intended for the frames just fine so I have not bothered filling the frames in.
After measuring out one side and the central V we cut out the central Vs and then the mid line.
Then (because I am lazy) we stack the two sides and make all our mistakes at once.
Here are all the pieces cut to size and laid out on the ground.
If I was making a modified canoe type version here is a quick layout. As you may be able to see it would be relatively easy to make something with pointy ends from this step in the process.
A quick look at the middle triangles shows that with a short join in the middle a transom and bow can be put together in short order.
Here is how I laid out the spline using a flexible bit of Masonite I had lying around. You may not be able to see it but the clamp and holding block are being used together to keep the Masonite parallel
(tangential if you prefer fancy words) to the edge. This smoothing was done over what I felt at the time was a a fairly long area, leaving 3 inches straight at the end and the end of the spline was 2 feet in from the corner. Making that last point closer to the middle of the boat would have made bending more even and reduced some of the stress levels in parts of the boat.
Again everything was stacked and clamped to ensure mistakes were all made at once.
After cutting, a plane was used for smoothing the cuts and fine tuning the curve to make it look just right.
Now I measure out the end folding pieces - remember here I should have added an extra half inch or so to allow for the join width.
To make things simpler I have used the simplicated paper method rather than the trigonometric. Any flat piece of paper with a square corner will do. First of all line the top of the paper with the top of the board, and the side with the outside corner. Drag your thumb along the bottom edge to crease the paper where it should fold.
Fold your piece of paper under to get the profile of the end
Then fold the top outside corner of the piece of paper to the bottom edge to get the angle you need to cut for everything to fold flat.
Now take the first offcut and make the rest of the end piece.
And here it is:
Now line up all your pieces and mark out where everything needs to go. I used a bit of masking tape to mark the side I wanted to be the inside.
Continues next month...