We are proud to finally be able to publish details about the Celeste 34 Sport project. In all its simplicity, this design is one of the most intriguing we have developed.
The first test sail of the prototype will be later this summer.
In this first post, we will focus on her hull and general parameters and some of the design considerations she has raised.
WHAT SORT OF A BOAT IS SHE?
A ‘fast’ sailboat can be just anything.
The client for the first boat, Mr Torbjörn Hurtig, is a passionate racing helmsman. His previous boat was a J/80. In our first meeting he made it clear that he wanted a boat with focus on speed and excitement. And without regard to any rating rules. Just fast.
Mr Hurtig’s only problem with the J/80, by the way, was that it is not usable for family cruising. The new boat should offer some basic comfort and also had to be well mannered enough for more laid-back family cruising.
But in order to offer both downwind speed and great entertainment, Mr Hurtig was adamant that the displacement must not exceed 3 tons. He had looked at every boat on the market and found nothing to suit his demands. This boat had to be faster.
ONE FAST BOAT, COMPARED TO ANOTHER
It was clear to Mr Hurtig that he was not interested in an empty carbon shell with a canting keel, exotic foils, outriggers or wing masts.
He wanted a ‘normal’ kind of sailboat, in the sense that her better speed potential should be compared to other normal 34′ cruiser-racers with a cabin, a galley, some comfort inside, an engine, a fixed keel and a rudder.
For us, we were thrilled when asked to design a boat which was plainly meant to be faster, within the constraints of her size and type. Indeed, this is a wonderful challenge – to try to improve on the hundreds of racing boats or cruiser–racers on the market.
So how will we achieve this? It is about 7 different aspects – or, talking about sail boat performance, let’s call it the Seven Pillars of Design:
1. The Best Hull Shape for High Speeds on a Reach
2. The Ultimate Hull Shape for Speed to Windward
3. Limiting All Unnecessary Weight
4. As Much Stiffness as You Can Get
5. As Big Sail Area as Possible
6. Sail Handling and Control
7. Steering and Course Stability
To make things more interesting, there are a number of conflicts and contradictions here… between almost all of these 7 aspects.
Raise one pillar, and another one falls over.
And they don’t easily support the same roof.
This is what makes yacht design such an interesting challenge. It is easy to make the wrong assumptions.
1 – THE BEST HULL SHAPE FOR REACHING AT HIGH SPEEDS
A hull needs to have very straight lines forward-and-aft or, in yacht design parlance, as little rocker as possible. This is much the same as to say the hull needs to have as low displacement as possible.
The hull bottom also needs to be relatively flat, seen from the bow or stern. It may be an advantage to have a sharp transition or ‘chine’ between the bottom and hull sides.
On the other hand, consider the fact that the hull is not always level. You will want to be able to maintain planing speeds also when heeled over. This requires that the heeled underwater shape is just as straight as when upright and the chine can just as well turn into a disturbance.
In addition, it is an advantage to have the transom dip a little down into the water when the boat is resting at a dock. This only works well at high speeds and does not go together with other demands, though.
Regardless of how deep the transom goes, the bottom corner of the transom should have a sharp angle towards the hull bottom. But just cutting the hull at an angle will make the boat shorter on deck. To overcome this, most performance boats these days will just have a vertical transom.
This is the reason for the unusual shape of the transom in the Celeste 34 Sport. The backwards angle higher up is there to extend the deck, in order to get the backstays and gennaker sheets as far aft as possible. Another view of the transom:Heyman 34′ hull, appendages & transom
2 – THE BEST HULL SHAPE FOR GOING TO WINDWARD
Upwind speed will be at below ‘hull speed’ – in the case of the Celeste 34 Sport, somewhere below 8 knots, usually around 7+. This requires some major departures from what would be the best hull shapes for downwind planing speeds:
First, the waterlines may well be straight, but the transom should lift out of the water. Not by much, but it should not drag too obviously, neither upright, nor heeled.
Secondly, the heeled ‘footprint’, the part of the hull which rests in the water when heeled, should ideally be as far away from the centreline as possible. This makes for a stiffer boat.
Third, the part of the hull surface which is under water, the wetted surface, should be as slight as possible. Hull friction will slow the boat regardless of speed, but the effect of friction is proportionately more noticeable at lower speeds.
And finally, the bow shape should be the best possible in order to go through waves, without stopping the boat too much and without inducing too much pitching. This last one is a particularly tricky requirement and one which has been neglected over decades of research and development.
Yacht designers can use many methods for arriving at the best proportions:
* Experience from sailing different boats is valuable.
* Mentally deconstructing a problem and solving it intuitively can be a powerful tool.
* But designers looking for scientific guidance have had to base their knowledge on the assumption that water is flat.
* Now, add in the factor that otherwise sensible people tend to trust science more than their own perception – even when science goes wrong. It feels better to use a handhold than wiggling along on your own.
So, wrong assumptions, how?
The problem, until recently, is that a sailboat’s motion in waves has not been possible to research adequately. In tank testing, it usually looks like this – a yacht model cutting through a mirror-like water surface at good speed. Most scientific research on sailboat hulls have been based on tests like these.
During the past 4 years, together with Chalmers University of Technology and SSPA, the consulting specialists which run the 260 m test tank in Gothenburg, we have had the privilege to perform a number of tests on different sailboat hulls in different sea states, and at a range of speeds. More reading here
Our studies at Chalmers and SSPA were performed on 3 scale models of 41′ boats, but the lessons learned apply also for a 34′ hull.
The Celeste 34 Sport is the first design to come in production, based entirely on what has been learnt in our research.
This article will be continued.
27 February, 2019 / Gabriel Heyman