A Stretched Big Zen boat

The above images are of the Proa Big Zen. So what is Big Zen you ask. Big Zen is a 15ft proa that appeared on the Duckworks magazine website around 2005. It has intrigued me for a long time. I have to admit to being bugged by this boat. It is very unusual. It seems to meet its objective of being a simple camp cruiser for a young family very well. As a sailing boat perhaps less so. Lets look at the plusses and minuses

    Positives of Big Zen
  • Easy to build
  • Very spacious
  • Very stable
  • Cheap to make
  • Good sitting headroom
  • Good fuel economy under motor
  • Nice large sundeck for lounging about
  • Shoal draught
  • Very easy to trailer due to low weight and flat bottom (no keel)
  • The craft is most obviously heavily biased towards comfort over speed
    Possible negatives of Big Zen
  • A difficult rig to manage
  • Short waterline length
  • Cargo space is small (crew accommodation is good)
  • Flat bottom, prone to pounding in a short steep chop
  • Rudder needs to be physically moved from one end to the other on each shunt
  • A short clunky hull resulting in fairly low speeds
  • High cabin windage

So lets do a hypothetical, lets do a design for a stretched Big Zen proa, a bigger more capable boat.

Big Zen is small at 15.5ft and as such it is limited to the places it can go. If it was a bit longer then there would be more storage space, and a longer waterline length. Additionally a simpler to use rig could be utilised. It is my understanding that the builder was not happy with the rig, as it was not as easy as simple to use as hoped. Originally electric power was tried, but this was discarded in favour of a small outboard (4hp)

We have to be careful when stretching the boat not to make it too big. Making it too large would increase the unladen weight making it very hard to get onto a trailer and to manhandle. Making the boat too large would also increase the cost. For these reasons the boat is increased solely in length by 2.5ft, Heights, cabin width and overall width remains unchanged. We can also try a rudder system that does not require the rudder to be physically moved from one end to the other. The result is shown below. We can also adjust the bottom profile a little for smoother lines and to let the boat sink a little more, so reducing hull windage

Now at this point we have a more capable boat, with a simpler rig, at only a modest increase in overall weight and cost. So how does it stand. The two obvious downsides are  (1) the complicated dual rudder set-up,  (2) and the rig which keeps the center of effort aft of the ideal position. Yes we could add jibs at each end, but then the complexity starts to add up, having four sails instead of two. So lets try and simplify the craft overall without increasing its dimensions.

If we make the craft a tacking craft, instead of shunting, we only need one rudder, and we can apply a much simpler rig. I think the original craft had the outrigger to windward (as a counterweight) though I am not certain. The outrigger is also large in volume, so it could work very well to leeward, as a float without modification. Now if the craft is to tack not shunt, there is no requirement that the craft be symmetrical fore and aft. So we can move the cabin back a little to a place that will have less motion. Additionally we can deepen the forefoot a little for better wave piercing. The result is shown below.

So you ask, why the mizzen sail. That is there because of use of a leeboard. Now the leeboard is to be at maximum beam width, which is fraction aft of the center. Now adding a mizzen takes the C of E aft a little. The use of deep forefoot moves the CLR a bit forward. The exact placement of the masts has not been determined. Maths would be needed to get the placement correct. It is worth noting that this boat in profile has a lot of resemblance to Matt Ladens Paradox micro-cruiser. However compared to that craft, this one will be more stable, be faster due to longer length, less beam and more sail area. Additionally this craft can have more sitting headroom as topweight is less of an issue

The canoe stern is not all bad. It must be remembered that this is a craft heavily optimised towards comfort and family cruising as opposed to performance. The canoe stern should have low drag at low speeds and when trim is poor. In terms of overall size the craft is only 2.5ft longer than the original, and widths and heights are unchanged. The topsides remain vertical to assist in speed of construction. An 18ft canoe stern boat equates to a 17ft boat with a transom in terms o size. So this can be seen as being 2ft smaller than the TO19. Now I think when I did the TO19 I made it too big. When all I needed to do was increase the size of the original Big Zen only modestly

This craft has a lot of potential as a low cost, simple fun family cruiser. The size is small, keeping weight and costs down. The rig is simple and low cost. It should point to windward reasonably well but use of a 4hp outboard would be used a lot of the time. The outrigger needs some weight to give the craft stability. For simplicity sake this may as well be left inside for the duration of the trip.