My most popular design is the Goat Island Skiff a light plywood planing sailing dinghy that is devastatingly fast in most conditions – not so surprising when you realise a lot of the development was because of racing dinghy advances but intended to avoid the skyrocketing costs of sailing participation.
It was an experiment on how far we could go with a simplified hullshape towards modern dinghy performance.
Note the small tiller movements needed. If you can see the horizon, then the boat is quite heeled – but helm remains neutral. Very unlike a Laser or many other conventional sailing dinghies which are tricky if heeled at speed. See the reason below.
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Lug and boat handling experience from 3 years racing and cruising sailing canoes
The Goat Island Skiff was my first sailboat design after BETH, the sailing canoe (1989). BETH gave me a lot of experience with lug rigs and I knew I could make them sail fast when fitted to hulls of modern dinghy weight. Photo below
From BETH I loved the speed downwind in particular, and some experiments with centreboard length allowed me to find good upwind performance too. Other assumptions were that modern ropes (at that time Kevlar core) would allow me to carry modern sail tensions and mast/sail interaction of a racing dinghy would allow much larger sails to be carried than was usual on light boats.
It all worked rather well and the boat did extremely well in open regattas and even joined some club racing and being competitive with conventional racing dinghies.
First Thoughts when I was designing the Goat Island Skiff.
So where did the Goat Island Skiff (GIS) come from?
The dinghy class I have spent the most time in is a development class with a relatively small sail area. The Australian NS14 has 9.3sqm of sail but is expected to carry two adults – hull 4.3 x 1.8m and hullweight of 63kg – so the design pushes towards the lowest drag possible. There literally is no sound from the bow or stern – the loudest sound is the water moving across the surface of the boat.
This is my second NS14 from 1979. Photos are the present owner (boat is 40 years old next year)
So my thought was to hit the same target points. And some of the styling. Most of our restricted classes have an overall length restriction so have the plumb stem that is so familiar on the Australian Skiff classes.
The NS14’s 63kg is right for two adults to lift and move without extra help when building or on the beach. The question was could I achieve that with a longer boat. So my intention was to remove every piece of ply or wood from the boat as far as possible. Even the faux traditional inwale and gunwale is to provide massive stiffness for the structure, with the ply body of the boat hanging from the upper construct.
In Australia our plywood racing boats are typically 4mm and come in at 8 to 10lbs/ft of length. Thus the 63kg for the NS14. Apologies for the mixed dimensions!
So I was really pushing a longer boat hard to come to the same weight. I was so surprised when the second GIS weighed in at 127lbs (58kg). More surprised to see it sailing very well with 4 people aboard on launch day. Exact photo right from almost 30 years ago.
The GIS sail at 105sq ft is 5% more than the NS14 to make up for some of the inefficiencies of the lug rig.
The hull was designed to be a very small 4.8m (16ft) boat. Minimal rocker (fore and aft curve of bottom) consistent with two crew and the boat is all bow with the widest point of the bottom panel behind 70% back. This is a big risk for most boats, but from the Scow moths and development catamarans in the ’80s there were strong hints of another way to prevent handling problems from a fine bow.
For the history of sailing we had been trying to fix bad behaviour from a fine bow by adjusting the bow. The scow moths, 18ft skiffs and development catamarans – not to mention performance sailboards – demonstrated that the circumstance at the bow is controlled by the circumstance at the stern.
There was some hint of this with double ended boats – but the explanation was cloudy that “the pointy stern parts (splits) the waves”.
This is wrong. When heeling the overcanvassed BETH in very strong wind gusts she doesn’t want to veer off course. Just keeps going straight.
Try that in a Laser!
Note the centralised rudder.
What really happens is that if the volume at the boat is balanced by the volume in the stern then several things happen at once.
- Boat will go straight when heeled and respond to helm almost regardless of heel angle
- Sailing downwind boat will not veer if the nose digs into a wave as the balanced volume in the stern allows the bow to rise.
Here the Viola Sailing canoe gets a gust – boat goes faster, bow rises without crew having to move.
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So fat stern – have a fat bow – scows are good in this regard.
Narrow bow, squeeze the stern in.
Sailing canoes … you can almost do no wrong!
The Paradigm that kept sailing dinghies planing slow for 5 decades
The old style sailing dinghies of the 1960s in Australia were often designed under an assumption of “long flat run to the stern” to get speed. Particularly downwind speed.
This is actually counterproductive. A flat area has to be at a positive angle of incidence to the water surface to develop lifting forces. This plate is travelling to the right.
If it is horizontal – no lift. If negative incidents … it sucks down.
So the incorrect paradigm for many years was to produce boats with a “fine bow to cut the waves” and a “long flat run” to produce higher speeds downwind and reaching.
But the flat part of the boat was at the wrong angle to produce lift.
The result was the boats would have insufficient area at the right angle to produce lift, so they would start making big waves around hullspeed and find it hard to “get over the hump”.
Once “over the hump they can be very fast indeed, but the bow up trim looks very weird compared to truly modern dinghies and yachts. No disrespect to the awesome FD – from memory the caption was “FD in full flight helmed by silver medallist Helmar Pederson”
How modern boats plane differently
The Goat Island Skiff was intended to behave like the development dinghies that started appearing in the late ’70s and early to mid ’80s.
Mike McNamara, sailmaker at McNamara sails and one of Britain’s very best dinghy sailors with more than 60 National sailing titles wrote this on sailing the Goat Island Skiff. Note his comments about “planing”.
I had a nice long sail in Richard`s Goat Island Skiff today and had a lovely sail.
He has made a great job of the boat and it went like a dream.
I was very impressed with how simple the controls were and how quickly the boat went. It was also beautifully balanced.
As you could expect the boat felt better when it was slightly heeled when beating. Off wind it felt fast but didn’t create a planning sort of wash…it just went faster and faster.
When tacking I found that I had to be quite forceful in pushing it into the wind and it was definitely better to “roll” it coming out of the tack.
Instead of thinking that lift is something that you get above “hull speed” they worked on the idea that lift is something that happens when the boat starts moving.
So it may as well have some lifting area forward. The classes I knew that were working on this were the NS14 and Moth Classes in Australia, The National 12s and the Merlins in the UK.
These boats all have one thing in common – a very modest sailplan for the crew weight. So drag reduction is the driver of design.
The NS14s – instead of being veed in the bow became finer but a prominent flat area from bow and through the centrecase area.
This starts lifting from the moment the boat starts moving.
The results are:
- The boat transitions through the hulls speed “forced mode” zone quickly and smoothly. Bethwaite calls this “dynamically humpless hull”.
- The crew doesn’t have to move aft in the boat to get the planing surfaces at the back of the boat to the right angle.
- The bow doesn’t rise, the crew doesn’t need to move aft, the boat just accelerates with any extra wind speed.
The Goat Island Skiff can’t go to the same extremes of shape, but I pushed it as far as I dared while still allowing it to be easily built.
And as Mike Mac says above … it is in the same ballpark of dynamics.
Sail size and configuration was cost based
The single sail was a 70% a cost control decision but I didn’t feel too bad because single sails are more efficient upwind and down except for a narrow range of reaching angles.
And I was so familiar with the difference in rig cost. I’d spent a few years doing rig quotes to set up differently rigged boats of similar size.
There has been an enormous amount of feedback from the users of the GIS that allowed us to work out ways of making the boat better. Primarily rigging setups for the lug. Also learning a lot about reef sizes for the sail.
Other work we did at the time which also informed the Goat Island Skiff
At that same time we did some other craft. A Raceboard class sailboard in plywood. It cost $400 at the same time that a Mistral Raceboard was $4000. And the ply board was competitive for much of a decade – where the Mistral would have foot dents in the deck after the first few month. Oh .. the ply Raceboard was built Australian Scow moth style and was 2kg lighter than the class minimum.
Structurally we knew we wanted the minimum number of pieces to do the work. We removed everything from the Goat that we could.
So our big theme was lightness and performance and using traditional rigs with modern dinghy thinking. And all of that contributed to low/reasonable cost. Everything achieved in sticks and string. Minimum of fittings.
Our idea there was to take the same materials as existing plywood dinghies but be true to our antipodean heritage of doing it much lighter and consistent with racing dinghy style. It is not carbon fibre that makes modern boats so fast and easy to handle.
It is mast/sail interaction, good foils in the water, light hulls and new sailing methods that make modern boats fast.
The carbon in modern racing dinghies is worth much much less than 10% in performance compared to the plywood restricted class boats of the mid 1980s.
But has pushed the price of participation sky high. That is why most weekly sailing happens in classes intended to be self built like the Vaurien, Sabre or Mirror with modern boats like the Moth and 49er only able to generate small weekly fleets.
