| 13. The Finn - What Makes this Slow Boat So Fast? |
by Jack Knights |
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May I ask you to be patient whilst I attempt to explain that what is puzzling in practise is explicable in theory. First to dispose of the less important contributory factors. Most Finns are sailed by Olympic aspirants and are, accordingly, well sailed. Their helmsmen are fairly heavy, fairly fit and anxious to do as well as possible.
Second, the Finn hull is a good shape for windward sailing. It has none of that exaggerated pigeon-chestedness, which makes so many British dinghies such a handful in heavy weather. It has a noticeably fine entry, yet with no hollows and a fine exit. The stability-giving sections are where they belong - abreast of where the helmsman sits. Third, and getting warmer, the Finn-cat rig, for all that the mast looks as it it has just been felled in the forest, and the sail similar to the old 'leg o' mutton', is extremely efficient. All the published findings of those who study these matters scientifically, whether in theory or practise, bear this out.
It has been proved that any rigging increases the drag and hence the heeling moment of a rig. Also a revolving mast is demonstrably better than a fixed one because it brings the luff slot down to leeward and enables the all important wind, which blows over the lee side of the sail, to journey more smoothly around the mast and on to the sail. Now the Finn has no rigging and the mast revolves, if only a short way. This is why they seem so stiff and sail so upright when they are jammed hard up against the wind
Fourth, and most important of all - in fact, the raison d'etre for this article - is the cut of the sail, the lead of the sheet and the flexibility of mast and boom. These are grouped together because, as I shall show, they are interrelated. I used to think that the effectiveness of the bending mast for certain boats had never been proved in racing. Now I am willing to admit that the Finn has changed this view, for, without a doubt, any Finn with a stiff mast is at a disadvantage against the others.
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The sheet of a Finn is arranged in such a way that it exerts a purely downward pull on the sail when on the wind. There is no inward pull at all. This fetches the head of the sail aft and with it the mast track. This, in turn, throws a deep bow into the whole mast and of course, flattens the sail. In this it is abetted by the behaviour of the boom. The mainsheet is led to the centre of the boom so that its pull tends to put a downward bend in the middle, so pulling out the fullness in the foot of the sail. As the boom is much deeper than it is wide, having the sheet in the middle means that the after-most end is allowed to fall off to leeward. Naturally it takes the clew and the leach of the sail with it. Now if you can visualise this sail in plan for a moment you will understand that this tendency has the effect of flattening the sail still further and feathering it more into the eye of the wind.
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The Finn sail is fuller than any other made for any other boat, particularly at the foot, where it forms a deep pocket just above the boom and so helps to prevent that efficiency sapping escape of wind from one side to the other. Yet, although it is so full, its sheet and spars enable it to be flattened so much that, eventually, it resembles almost completely, a flat plane.
Incidentally, it is worth mentioning in passing that it has been found that the most successful Finn sails are those which are very full at the bottom, but quite flat from mid-height upwards. There is a logical reason for this, which makes me feel that other dinghy classes could profit from it, particularly heavily canvassed classes. If one makes the top flat and the bottom full, the power of the sail is concentrated low down, where it is easiest to use. The boat is all the stiffer for it and the sail can be used in a much wider range of wind speeds.
Because of the sheet arrangement described, now universal in Finns, with a midships horse running the full width of the cockpit, the sail can be allowed to go much further out than is is normal in other craft when on the wind, without having to ease the sheet at all. This means that mast and boom stay bent and the sail flat, and in almost one plane This is the perfect set-up for controlled sailing to windward because it means that the sail can be set at a very fine angle to the apparent wind. It can be feathered, so to speak, so that in heavy weather the wind slips past it with a minimum of resistance and, hence, without causing very much heeling. Because the Finn is not forced over on her ear in these conditions, can retain a good grip of the water and preserve a fair underwater hull shape. Thus she foots fast and goes where she points, in spite of a small and inefficiently shaped centreplate.
Several things follow obviously from these observations. If one eases the sheet at any time when sailing to windward - and this becomes more important as the wind blows the harder - the whole system is spoilt. The boom is able to lift, the top of the mast is released and springs forward, and the fullness is thrown back into the sail. Thus a jamb cleat of some sort for the sheet is a great help, one by which one can really force down the boom until it is only just above the deck. It should only be necessary to release the sheet from its clutches when going about, and then only for safety and to enable the traveller to slide across and one's head to get under the boom.
Paul Elvstrom, it is true, did not use a cleat of any description, but he was exceptionally strong in hand and wrist, and anyway he said that the only reason he dispenses with one is in case his toestraps should break and he should be precipitated overboard. If this happens when the sheet is cleated, a capsize naturally follows. Few, however, would be prepared to put up with so much extra labour for the sake of a contingency so remote.
Naturally, a sharp look out has to be kept ahead for freeing puffs, so that the boat can be pointed into them and weaved away as they pass. This is why one seems to waggle the tiller so much in a Finn. Another point is that the mast should be able to begin bending from as low down as possible. This is because the fullness is mainly in the lower half of the sail. |
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