John Welsford's website

John Welsford's design page

A few of John's designs:

Golden Bay/Setnet






From the Drawing Board
(occasional ramblings of a Small Craft Designer)

by JohnWelsford

Mr. Bolger would laugh his socks off...

As a New Zealander with a passionate interest in sailing, I drive through Auckland with one eye on the road and one on the sea, and of late I even make detours and sit on the clifftops of North Shore City where the parks and beaches overlook the Hauraki Gulf where the Americas Cup contenders will be racing in a few weeks time.

Yesterday there were five pairs of the distinctive sails with their attendant fizzboat wakes out there, and when later in the day I pulled into Halsey St. where the challengers bases are, the activity was like an anthill that had been well stirred with a stick. The pressure is on, Team New Zealand has launched the first of their two boats, and will be sailing her very soon. The rumours are flying as to a new breakthrough in design, possibly a new type of rig, odd shapes underwater, strange keels and odd winglets and fins. All top secret, all big bucks, and so far beyond the aspirations of the likes of us that it hardly seems related to reality at all.

But while sitting chatting to one of the senior members in a challenger compound that has to remain nameless ( I'm on good enough terms with the troops to get into some of these places, but the boss had better not know I'm there) I noted that the shapes of most of the boats is actually very simple. The odd bumps and hollows of years past seem to have disappeared in this generation of boats, while the keels, ballast bulbs and rudders are sprouting odd little fins and wings the hulls actually have a very strong resemblance to some of our simple plywood hulls. Mr. Bolger would laugh his socks off and drag out the plans for the old "Black Skimmer".

Many point to the excesses of The Americas Cup and witter on about the "waste" of money ( we have a name for this sort of thing here, we call it a "Woftam" - this means a "Waste Of F (you know the word) Time And Money). But there are some interesting things to be gained from the research and development. Even our simple plywood sharpie shapes are able to be improved, and tank testing is not something most of us have access to so a few minutes spent carefully eyeballing a shape that has cost millions to develop, and half an hour with binoculars watching a boat sailing can give a designer like me a years worth of experiments to do.

Now I don't have a test tank, but do have one of the best tow testing sites I know of. Lake Rotorua about 10 minutes walk from home discharges through a weir about 12 meters wide and a meter deep. The water speed through there is around five knots and the lake bottom for several hundred yards out into the lake shelves very slowly into deeper water and the bottom is almost perfectly smooth giving a waterflow with very little turbulence. I trial hull models in there with a video camera, a big surfcasters fishing rod, a very delicate spring balance and a long rod marked off in tenths of a meter in the same scale as the hull model.

How I go about this is I build a model, some would call it crude, I call it appropriately simple, all is has to do is give me an accurate scale representation of the underwater shape, and it has to have a consistent surface finish so that a series of models will not have their results skewed by one having a surface finish with more drag than another. The model is then fitted with the scale marked rod along the centreline and ballasted to its design waterline.

Next, I get out my fishermans waders and head off down to the lake exit very early in the morning or last thing on a calm night, wander around in thigh deep water with my hand held boat speedo until I find the speed range I want, then go about 20 paces upstream and drive a spike with a fishing rod holder into the lake floor.

The rod is perfectly ordinary, it has 20lb monofilament nylon line on the reel, but I have a very delicate spring balance in between the reel and the first guide. The idea being that by taping the line to the balance I can measure the pull. By undoing the tape and letting out more line I can let the model back into faster water closer to the weir and take another reading.

I puzzled over speed reading for a while, messing about with means of measuring speeds and movement, but came to the conclusion that it was Speed / Length Ratios (S/L) that I wanted, and by putting the marked rod along the centreline of the boat and noting the spacing of the peaks of the wave train in the wake, I could determine the S/L ratio and compare them with the balance readings. An hour or so in the soft light of a summer dawn can give me twenty or more readings over S/L ratios from 0.5 to 1.5 and I can go home to breakfast with enough data to keep me puzzling for a day or two while I run the videos and compare the results with graphs made on other days with other models.

I am also a bit of a petrol head, having raced motorcycles and cars in the past. There is a very true saying that "you can take the boy out of the racer, but not the racer out of the boy" . Throughout the 7 or 8 months of the season I sit up every second Sunday night watching the Formula One racing cars shriek around circuits on the other side of the world.

Now what on earth is this turkey on about I hear the voices say! This emag is about us amateurs building little boats not mega million dollar racecars and even more expensive boats.

I am old enough to remember driving cars with cable brakes, cars that would slide off the road and fall or roll over at the slightest provocation. The car I drive today has four wheel hydraulic disk brakes with an antilock system, fully independent suspension, amazingly grippy radial ply tyres. It uses half the fuel at much faster cruising speeds than I could have achieved with my first car, and is hugely safer in an accident than the old one. Many of these improvements were pioneered in racing cars, cars that at the time seemed to have no relevance to our day to day reality, and so with the boats.

The IACC ( International Americas Cup Class) boats are magnificent, their speed upwind and their ability to manoeuvre, to maintain speed through a tack or gybe, their resistance to pitching, and their use of high tech materials is a testing arena similar in relevance to our pottering about on lakes and bays as the Formula One racing car is to our commuting in to work each day.

As a designer, I have to believe that I can produce something a little better today than yesterday. If not, then I may as well just tell people to go buy a copy of John Gardners Dory Book. So I actively pursue improvements both to the boats and to my knowledge of how they work, and for me one of the many challenges I face is to adapt and to make relevant to "our world" some of the information being generated by the many millions of dollars being spent on those incredible boats now sailing Aucklands outer harbour.

John Welsford Small Craft Design.