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I had naively thought that all 15's would have the same length of shrouds but they don't and therefore when you compare pin settings with your fellow competitors you may not be comparing like with like. So is there an official length for shrouds? and if there is, what pin setting is recommended for various wind conditions.? (probably one for Brian )
A few years ago, when we were debating forestay lengths (Spark, Dart 15, Sprint 15) i did some measuring at our club of 12 boats from 640 to 1978 including Kevin Dutch's 1938.
The shrouds were +/- 8mm on all boats except one and I came to the conclusion that they should be 4300 +/- 5mm measuring inside the eye at each end. In my old manuals it did not give a length for the shrouds.
The holes on the chain plate are 1/2 inch or 13mm apart I believe so there is scope for some small variation in mast angle.
One thing that we did notice was the wear on the mast ball and plate in the mast foot casting makes a big difference. I found the height from the top of the tramp slot to the join between the mast and its foot casting varied between 98 and 104mm (all masts up at the time). We later found that the 98mm one had a hole worn through the plate by the steel pin in the ball. A drop of 6mm on the mast is exacerbated by the shrouds attaching part way up the mast and this can affect the angle of the mast by 10-15mm. If you are getting into serious setting up make sure the mast ball and casting plate are in good condition. If the mast is left up in the same direction to prevailing winds for most of the season the mast foot casting and the ball wear on one side. You can normally hear when the plate and casting are wearing as it is characterised by a 'clonk' from the mast foot when you tack - as the pin in the ball falls in or out of the worn plate hole.
Most boats had one 1.6mm plate riveted in the mast foot casting, once it wears through the ball pin starts to eat into the casting. Some boats had two plates. The new plates are circular, much thicker (3mm I think) and are to be glued in. We have had to change several mast foot castings and quite a few plates over the last few years.
Most of us sail with the shroud plates in either the 3rd or 4th hole down and don't change it. However we do occasionally adjust the rig tension on the forestay according to conditions.
Steve Willis wrote:Most of us sail with the shroud plates in either the 3rd or 4th hole down and don't change it. However we do occasionally adjust the rig tension on the forestay according to conditions.
I've aways set my boat up without the shroud plate hole being the deciding factor. I seek to achieve the maximum mast rake such that I'm block to block on the mainsheet when the wind strength is at a level that I'm just overpowered. So my critical factor is the adjustment of the forestay tie. The shroud plate hole used is then dependant upon how loose you like to have the whole rig. I, personally, like to have it very loose, so that the mast can then rock forwards and be more upright on the downwind legs.
Maximum mast rake gives the best pointing on the upwind legs, and an upright mast gives the best performance downwind.
Hello Chris, it is good to have your advice, especially for a lesser sailor such as myself. Please could I ask you to elaborate a lttle.
Taking your scenario (say force 4, block-to-block, forestay slacker, and just overpwered, as you say). If the wind is stronger at the next race, would you take some of the slack out of the forestay? If you did, would you find you can no longer be able to be block to block?
Moreover, would a tightened forestay (more upright mast) put even more power into the rig, making you even more overpowered?
As you can see, I am just as perplexed as ever!
Fading star of the Thorpe Bay fleet
Former rugby player in the extra-B
Struggling musician
Second best cabbage in the village show...
1 Why is it that the wealth of info in the Tips section of this website seems to get overlooked? Start with Paul Smith's Stay Tooned and work on from there!!
2 I think it is generally agreed that sailing with the mast (close to) upright will generate most power. George Carter (multi-champion in both Unarig and Sport Mode) coped with excess power on the beat and reach (eg wind strengthening while racing) by letting out the traveller while maintaining mainsheet tension - note this means letting out a little main to let the traveller move out before fixing the traveller and retensioning the main. It's what nearly all of us now do. He'd vary batten tension to depower further in stronger winds, but I'm not sure he introduced much mast rake when the wind really strengthened - but Bob will know better. There will be little or no weather helm with an upright mast.
3 I think it is generally agreed that the mast should be able to rotate 90 degrees on the beat and reach, so that the angle and the mast bend maintain close to optimum sailshape and angle relative to wind. In stronger wind conditions the wind will blow the sail and achieve this angle with a rig that is a bit too tight to rotate to 90 degrees using (one) finger pressure that you MIGHT use in light winds.
4 Sailing with a loose rig will allow the mast to lean more to leeward on beat and reach. Some (many?) think this adversely affects beating and reaching.
5 It's always been the case that different good Sprint 15 sailors have favoured different rig set-up, and yet get similar results. Probably most of this is due to consistently good boat handling by the better helms. But some is due to rig set-up and some of this is due to factors like helm weight (and height). So Chris Black (so good to hear from you, Chris) is on the taller/heavier side, with experience of other cats (Dart 18??), and has a tendency to rig in the way that some good D18 sailors rig their D18s - loose rig. Paul Smith was a lightweight, hailing from Beaver where the small pond developed top-notch boat handling skills. Despite the flatter water at Beaver they tend to sail with tight rigs, including ex-champions John Postlethwaite et al who were distinctly heavier!!!
6 Wave action should not be ignored. While a looser rig works ok with light wind conditions, if there is significant wave action left from earlier stronger wind a loose rig will slop around, severely affecting performance if not controlled. Easiest to tighten the rig.....
7 Mast rake is essentially determined by forestay length, BUT
7A if you can't get the mast upright, the shrouds have to be adjusted up a hole (or more)
7B if the rig is too loose the shrouds have to adjusted down a hole (or more)
8 If you introduce more mast rake (aft) then you increase weather helm. With "new" style blocks, this will also mean that when you pull the mainsheet block to block there will still be curve in the leach, so the sail will be less powerful on the beat. Raking aft will also make the boat a bit less prone to capsize (pitchpole) on the run. When (if?) you introduce more mast rake will depend on your weight, and competence in stronger winds.
I agree the Tips link is very good. But they don't explain the paradoxes. The Beaver case is a good example, where tight rigs are the norm irrespective of the weights of helms. The paradox is that Chris Black sails with a loose rig and John Postlewaite with a tight one. Both are unbeatable, for me at any rate. So, which is right? Tight or loose. Are they both right? Does it really matter?
It's a conundrum!
Fading star of the Thorpe Bay fleet
Former rugby player in the extra-B
Struggling musician
Second best cabbage in the village show...
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