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Thread: efficiency of the sprit rig

  1. #71
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    Default Re: efficiency of the sprit rig

    Quote Originally Posted by johnw View Post

    In small boats kept on a trailer, I've developed a preference for unstayed rigs, which go together much quicker than stayed rigs. The problem with the Bermudian rig in that case is, if you don't have a jib, the mast gets tall pretty quickly as the rig grows. With my bad back, even stepping a 20' stayed aluminum mast is a challenge, never mind hooking up everything and still having time to sail. So, I'm wondering, if I build a small boat with a sprit rig, would I have anything like comparable performance to a Bermudian sloop with no spinnaker? If the efficiency loss is 3%, maybe the tradeoff is worth while. If it's 10%, maybe not.
    What you might want to look at is the freestanding rig developed for the new UFO foiler. No shrouds, no jib, a fat "sprit or gaff" headed sail. Or using expensive carbon tubes to create high aspect ratio lugs like Nigel Irens did with his cruising designs which I copied with even a higher aspect ratio for RANTAN. There I have the convenience and reefability of the lug with a main that approaches the efficiency of a 10sq m sailing canoe.
    Ben Fuller
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  2. #72
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    Default Re: efficiency of the sprit rig

    Quote Originally Posted by johnw View Post
    Here's an example. I designed this for a 135 square foot sloop rig. Here's the hull wearing a 150 sq. ft. sprit rig. I'm wondering, will I really be able to carry more sail with the low-aspect rig, and will the extra area make up for the loss in efficiency?
    The twist in that sail will be pretty horrible negating the advantage of the increased area, unless you add a horizontal sprit. It would both aa challenge to keep the sprit from bending and to setting it up to reef readily.
    Ben Fuller
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  3. #73
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    Default Re: efficiency of the sprit rig

    Fathead sails are on my radar, as is the balanced lug, but carbon spars are not in the budget. The jumper strut wishboom on the UFO looks interesting, but it also looks like stays.

  4. #74
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    Default Re: efficiency of the sprit rig

    Quote Originally Posted by johnw View Post
    Here's an example. I designed this for a 135 square foot sloop rig. Here's the hull wearing a 150 sq. ft. sprit rig. I'm wondering, will I really be able to carry more sail with the low-aspect rig, and will the extra area make up for the loss in efficiency?
    I know it's just a drawing, but I hope you are aware that the panels are laid out wrong. They should be parallel (or perpendicular) to the leach, not the luff.

    /Mats
    Last edited by mohsart; 11-12-2017 at 07:07 AM.
    My blog about my time as a boat building student and as a rigger apprentice http://kaptenmohsart.blogspot.se/ in Swedish only, but there are many pictures :-)

  5. #75
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    Default Re: efficiency of the sprit rig

    Quote Originally Posted by johnw View Post
    Fathead sails are on my radar, as is the balanced lug, but carbon spars are not in the budget. The jumper strut wishboom on the UFO looks interesting, but it also looks like stays.
    What the UFO uses is a really inexpensive windsurfer carbon tube. The mast goes into a glass tube that gives it a couple of feet of bury. What the Clark's did is solve the problem of too much bend in a unstayed windsurfer tube with a diamond whose spreaders go back at an angle to the mast. A combination of jumper strut and spreader angled forward. The tension on the diamond is adjustable to control mast bend.So the rig does have stays but the rig is freestanding. You set up the diamonds then drop the mast into place.
    Ben Fuller
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  6. #76
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    Default Re: efficiency of the sprit rig

    To get firsthand experience with spritrig : Somewhere in may 2018 we will organize in The Netherlands a weekend for oarandsail boats. It will be near Giethoorn, and we will have the use of 5 traditional Dutch Punters, spritrigged boats. So if you come all the way from Seattle or Truro and cannot take your own boat with you in the plane you can still sail. We will provide good honest food (I will be the cook), wine, beer, a nice day-stay, sleeping in tipi's or your own tent, and the costs will be reasonable. Surroundings are beautifull. More information will follow. Frank van Zoest

  7. #77
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    Default Re: efficiency of the sprit rig

    Quote Originally Posted by Ben Fuller View Post
    The twist in that sail will be pretty horrible negating the advantage of the increased area, unless you add a horizontal sprit. It would both aa challenge to keep the sprit from bending and to setting it up to reef readily.
    Perhaps that's why the Optis have taken to locating their sprits much farther up the mast than traditional sprits.

  8. #78
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    Default Re: efficiency of the sprit rig

    Quote Originally Posted by mohsart View Post
    I know it's just a drawing, but I hope you are aware that the panels are laid out wrong. They should be parallel (or perpendicular) to the leach, not the luff.

    /Mats
    Those aren't sail panels, they are a continuation of the sections on the lines drawing. It's an artifact of the drafting system in which the boat was designed, which is Delftship.

  9. #79
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    Default Re: efficiency of the sprit rig

    Quote Originally Posted by FF View Post
    To get firsthand experience with spritrig : Somewhere in may 2018 we will organize in The Netherlands a weekend for oarandsail boats. It will be near Giethoorn, and we will have the use of 5 traditional Dutch Punters, spritrigged boats. So if you come all the way from Seattle or Truro and cannot take your own boat with you in the plane you can still sail. We will provide good honest food (I will be the cook), wine, beer, a nice day-stay, sleeping in tipi's or your own tent, and the costs will be reasonable. Surroundings are beautifull. More information will follow. Frank van Zoest
    That's a wonderful invitation! Unfortunately, I own a small bookstore and seldom have the time or the money to take time off and travel.

  10. #80
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    Default Re: efficiency of the sprit rig

    Quote Originally Posted by Ben Fuller View Post
    What the UFO uses is a really inexpensive windsurfer carbon tube. The mast goes into a glass tube that gives it a couple of feet of bury. What the Clark's did is solve the problem of too much bend in a unstayed windsurfer tube with a diamond whose spreaders go back at an angle to the mast. A combination of jumper strut and spreader angled forward. The tension on the diamond is adjustable to control mast bend.So the rig does have stays but the rig is freestanding. You set up the diamonds then drop the mast into place.
    Well, maybe I don't need as stiff a mast anyway. Problem is, 8 meters isn't enough sail area for the proposed boat. Might look at the cost of it for a smaller design.

  11. #81
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    Quote Originally Posted by johnw View Post
    Perhaps that's why the Optis have taken to locating their sprits much farther up the mast than traditional sprits.


    Just in from a weekend in a coach boat with some top Optimist sailors in blustery conditions. The Optimist rig though simple is very controllable and twist is eliminated or are allowed to happen to good effect. Though the sprit is high the controls are lead to a good height for the user.
    Other positives for the Optimist being that possibly up to 1/3 of the sail is in clean air above the mast and the mast rotates, not quite Taser efficiency but it must help a bit with mast turbulence.

    Back to the OP I am in the UK and the level of training, support and information about getting the most out an Optimist is good. It is just a theory but this I feel means the the Optimist sailors are good at sailing up to the handicap which then bolsters the handicap.

    Again back to Sabot (again I only know it from the internet) the relatively small lee board can be no match for the large and deep daggerboard of the Optimist.

    Not my picture but twist looks under control in windy conditions



    Just out of interest and adding to the International 12 Lug Sail debate the Optimist always rig the spirit to starboard, the idea being to be fast off the line on a starboard tack.


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    Default Re: efficiency of the sprit rig

    Quote Originally Posted by johnw View Post
    Sunfish sailors think their boats are closer-winded with the sail against the mast. I wonder if this is also true with the balanced lug.
    I have found this phenomenon to be true with both a standing lug and a balanced lug, but attributed it to the cut of the sail for the particular condition. Lugsails are perhaps not cut to optimise windwird work so the mast may actually "flatten" them a bit, enough in my case so that the "VMG" was better on the "bad tack"!

  13. #83
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    Default Re: efficiency of the sprit rig

    Quote Originally Posted by Canoeyawl View Post
    I have found this phenomenon to be true with both a standing lug and a balanced lug, but attributed it to the cut of the sail for the particular condition. Lugsails are perhaps not cut to optimise windwird work so the mast may actually "flatten" them a bit, enough in my case so that the "VMG" was better on the "bad tack"!
    I wonder if the "bad" tack doesn't also have differences in twist.

  14. #84
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    Default Re: efficiency of the sprit rig

    Quote Originally Posted by tink View Post
    Just in from a weekend in a coach boat with some top Optimist sailors in blustery conditions. The Optimist rig though simple is very controllable and twist is eliminated or are allowed to happen to good effect. Though the sprit is high the controls are lead to a good height for the user.
    Other positives for the Optimist being that possibly up to 1/3 of the sail is in clean air above the mast and the mast rotates, not quite Taser efficiency but it must help a bit with mast turbulence.

    Back to the OP I am in the UK and the level of training, support and information about getting the most out an Optimist is good. It is just a theory but this I feel means the the Optimist sailors are good at sailing up to the handicap which then bolsters the handicap.

    Again back to Sabot (again I only know it from the internet) the relatively small lee board can be no match for the large and deep daggerboard of the Optimist.

    Not my picture but twist looks under control in windy conditions



    Just out of interest and adding to the International 12 Lug Sail debate the Optimist always rig the spirit to starboard, the idea being to be fast off the line on a starboard tack.


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    Thank you. This might justify a shorter mast, and less weight aloft.

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    Default Re: efficiency of the sprit rig

    Quote Originally Posted by johnw View Post
    Thank you. This might justify a shorter mast, and less weight aloft.
    It is a fascinating issue, my daughter has sailed for 4 years, loves her Optimist and not corrupted by thoughts of the superiority of the Bermudan rig. It has been said many times before but are we just being played to get a half knot by using a highly stressed and expensive rig.

  16. #86
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    Default Re: efficiency of the sprit rig

    Quote Originally Posted by tink View Post
    It is a fascinating issue, my daughter has sailed for 4 years, loves her Optimist and not corrupted by thoughts of the superiority of the Bermudan rig. It has been said many times before but are we just being played to get a half knot by using a highly stressed and expensive rig.
    Among the cheaper ways to make a boat faster are to add length or to add sail. The more expensive ways typically crop up when those things are limited.

  17. #87
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    Default Re: efficiency of the sprit rig

    Sunfish sailors think their boats are closer-winded with the sail against the mast. I wonder if this is also true with the balanced lug.
    FWIW, Bucephalus points higher and moves faster on port tack, when her yard topsail is pressed against the peak halyard. Part of that is because since the yard stands to port the gaff twisting off to leeward effectively slacks the topsail sheet on starboard tack, just the way a jibboom fixed aft of the jib tack will slack the jib foot, but some experimentation has shown that isn't the entire story (ignore the tack/peak crease, please; I had her peaked up for better wind outside):



    Photo credit: Goldrock.

    How much of bermudian's theoretical advantage is due more to hull form than rig? Were those races with gaff and bermudian racing together, thus needing handicap formulae, at a time at the cusp of different hull designs, and thus handicapping the "rig" was a shorthand for handicapping the hull form?

    Further, how much of the disadvantage of gaff / sprit / lug is due not to sail shape, but to the added weight of the spar aloft *and outboard*? I don't see many gunter rig fans chiming in on this thread, but how do they compare to a bermudian for performance? After all, NGH's Alerion was originally gunter rigged, and I doubt he'd have been too hung up on tradition or dogma to give away performance. Isn't a gunter yard (arguably) just an extention of the mast, thus making weight aloft a bit difficult to differentiate --but there is more weight aloft, with sometimes considerable doubling of the yard and mast.

    I'm not sure how the intrinsic mechanical challenges of a gaff's jaws or saddle could be translated to modern materials, but it might be interesting to see how a carbon-fiber gaff and lightweight "jaws" (of some lightweight configuration), or sprit, or lug yard performed on a modern hull. Just to curl people's toes, what would an Open 60 look like not bermudian / fathead, but gaff or sprit or lug rigged?

    Alex

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    Default Re: efficiency of the sprit rig

    Quote Originally Posted by Pitsligo View Post
    FWIW, Bucephalus points higher and moves faster on port tack, when her yard topsail is pressed against the peak halyard. Part of that is because since the yard stands to port the gaff twisting off to leeward effectively slacks the topsail sheet on starboard tack, just the way a jibboom fixed aft of the jib tack will slack the jib foot, but some experimentation has shown that isn't the entire story (ignore the tack/peak crease, please; I had her peaked up for better wind outside):



    Photo credit: Goldrock.

    How much of bermudian's theoretical advantage is due more to hull form than rig?

    None at all, in the many hundreds of cases where the two rigs were used on identical one-design hulls.

    Were those races with gaff and bermudian racing together, thus needing handicap formulae, at a time at the cusp of different hull designs, and thus handicapping the "rig" was a shorthand for handicapping the hull form?

    Not really, because many sisterships used different rigs, and many boats changed from one to the other, as did many classes.

    Further, how much of the disadvantage of gaff / sprit / lug is due not to sail shape, but to the added weight of the spar aloft *and outboard*? I don't see many gunter rig fans chiming in on this thread, but how do they compare to a bermudian for performance? After all, NGH's Alerion was originally gunter rigged, and I doubt he'd have been too hung up on tradition or dogma to give away performance. Isn't a gunter yard (arguably) just an extention of the mast, thus making weight aloft a bit difficult to differentiate --but there is more weight aloft, with sometimes considerable doubling of the yard and mast.

    The Stars had effectively a gunter rig and they changed to the "short bermudan" rig without doing anything but changing the mast. They even normally kept the same mainsail, and found it to be faster and more convenient. In recent years the Mirror and Heron class dinghies have done much the same thing, although whether they have found a difference in speed is an open question.

    I'm not sure how the intrinsic mechanical challenges of a gaff's jaws or saddle could be translated to modern materials, but it might be interesting to see how a carbon-fiber gaff and lightweight "jaws" (of some lightweight configuration), or sprit, or lug yard performed on a modern hull. Just to curl people's toes, what would an Open 60 look like not bermudian / fathead, but gaff or sprit or lug rigged?

    Alex
    An Open 60 would have major problems because they run a lot of their headsails from the masthead, and you couldn't run that sort of stay tensions off a gaff or gunter yard.

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    Default Re: efficiency of the sprit rig

    Quote Originally Posted by johnw View Post
    I've not said the gaff rig is less work than the Bermudian, although Taylor indicated that in that particular race it was. I think fractional rigs, especially in small boats, are less work than masthead rigs because they depower better. This thread is actually about the sprit rig, or was before it started drifting.

    When I started racing, we used up to 170% overlap, and had to change the jib often on our masthead rigs. Under IOR, 150% overlap became common, and spinnakers became more specialized. Are cruiser-racers now using 105% in light air these days, or do you not have light air?

    In small boats kept on a trailer, I've developed a preference for unstayed rigs, which go together much quicker than stayed rigs. The problem with the Bermudian rig in that case is, if you don't have a jib, the mast gets tall pretty quickly as the rig grows. With my bad back, even stepping a 20' stayed aluminum mast is a challenge, never mind hooking up everything and still having time to sail. So, I'm wondering, if I build a small boat with a sprit rig, would I have anything like comparable performance to a Bermudian sloop with no spinnaker? If the efficiency loss is 3%, maybe the tradeoff is worth while. If it's 10%, maybe not.
    Like many boats these days, I'm using 105% overlap for a slight loss in light airs in exchange for outstanding ease of sailing.

    For the little it's worth, gut feeling says 3-5% performance loss with a sprit.

    Can you use old carbon windsurfer masts, perhaps with stays and reinforcements? That way a 20ft mast is coming in at about 2.5kg tube weight or something.

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    Default Re: efficiency of the sprit rig

    Quote Originally Posted by Chris249 View Post
    Like many boats these days, I'm using 105% overlap for a slight loss in light airs in exchange for outstanding ease of sailing.

    For the little it's worth, gut feeling says 3-5% performance loss with a sprit.

    Can you use old carbon windsurfer masts, perhaps with stays and reinforcements? That way a 20ft mast is coming in at about 2.5kg tube weight or something.
    Might be better for the sprit.

    Weight is an issue with the mast, as well, because a sprit-rigged catboat has the mast way forward.

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    Default Re: efficiency of the sprit rig

    Srit rigged Adept 11-11-2017 6-54-00 PM 877x845.bmp.jpg

    This should be a better size for viewing the rig as designed.

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    Default Re: efficiency of the sprit rig

    Fix your panel seaming/warp yarn orientation. That one just hurts to look at and would make an absolutely horrible sail. And while you're there, bring the heel of the sprit forward so that it overlaps this side of the mast. Probably want an extra 6" or so at the sprit's peak and the aft end of the boom.

  23. #93
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    Default Re: efficiency of the sprit rig

    It's been my experience that you want to bisect the peak angle with your sprit so you might want to drop it a touch. I've found that on larger sprits need to be pretty stiff. For my larger sprit which is about 76 sq ft I have a sprit made with a double taper.
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  24. #94
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    Default Re: efficiency of the sprit rig

    This one shows a boom and there is no sheeting angle possible for sailing boomless so it wouldn't be able to be brailed, but on those spritsails which can, it works better with the heel of the sprit down a bit lower on the mast. Then the whole thing just "hinges" better and brails up more of the sail area. As to sprit stiffness, spritsails are usually cut with a dead straight head edge and no round added for making upper sail draft. An inch or two of sag, which is going to be there whether you like it or not, is generally all you need to create plenty of draft unless the sail is huge. Obviously there are various rewards to be had by keeping your sprit as light as possible but at the same time, a sprit which is too flexible is a real sailshape liability. If it is flexing or pumping as you're sailing along, your sail's shape and draft will be constantly changing at random, which is extremely inefficient for sails of any type.

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    Default Re: efficiency of the sprit rig

    Quote Originally Posted by Todd Bradshaw View Post
    Fix your panel seaming/warp yarn orientation. That one just hurts to look at and would make an absolutely horrible sail. And while you're there, bring the heel of the sprit forward so that it overlaps this side of the mast. Probably want an extra 6" or so at the sprit's peak and the aft end of the boom.
    As stated in #78:

    Quote Originally Posted by johnw View Post
    Those aren't sail panels, they are a continuation of the sections on the lines drawing. It's an artifact of the drafting system in which the boat was designed, which is Delftship.
    The plan shows the heel of the sprit even with the bow, overlapping the mast. I think I'm not understanding what you're saying. Are you saying the sprit needs to be longer and the snotter set lower?

    I could probably draw a more precise rig on paper. The sprit is difficult to show and move, and things like the tapered end that attaches to the sail are beyond my skill in Delftship. I'd love more input into how the sail should be shaped.

    I've noticed that the Optis have moved the heel of their sprit higher as the class has developed, maybe that helps with sail shape? Honestly, I'd rather have it lower, to make the boat easier to rig. What about the planform of the sail? Is the corner above the mast really useful, as Tink thinks?

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    Default Re: efficiency of the sprit rig

    Quote Originally Posted by Ben Fuller View Post
    It's been my experience that you want to bisect the peak angle with your sprit so you might want to drop it a touch. I've found that on larger sprits need to be pretty stiff. For my larger sprit which is about 76 sq ft I have a sprit made with a double taper.
    Thank you, that effectively eliminates using a Windsurfer mast as a sprit.

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    Default Re: efficiency of the sprit rig

    Bring the sprit forward toward the viewer. No biggie, I'm just giving you a hard time. It's just that in the drawing the sprit is on top of the sail (to starboard of it) and then the mast is on top of the sprit, which wouldn't actually happen in real life. Making sure that I had properly overlapping drawing elements was always really tedious when I did almost 300 computer drawings for my book. Back in those days, finding something similar which needed fixing was often a royal pain on my old Mac drawing program. Sometimes it would take fifteen minutes just to pan across the drawing to get to something.

    Most of the stuff you would actually do when designing and building the sail won't show up, or even be on the sail plan. It's generally more of a perimeter and CE balance drawing than anything else. You can show panel orientation if you want and add a bit of foot round on loose-footed sails, maybe indicate and a little bit of leech hollow, but most of the important details won't be included. They're left up to the sailmaker. Even so, you can fairly easily yield a decently realistic impression of what you intend to build. Personally, I like that just to motivate me and get me excited about the job, and it doesn't take much.
    Attached Images Attached Images

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    Default Re: efficiency of the sprit rig

    That's beautiful! However, part of the logic is to have the mast as far forward as possible to open up the cockpit. The idea is to have room for three adults without sinking the transom. The actual purpose of the boat is to teach people to sail with a traditional rig, so we need to accommodate two students and an instructor. I was going to wait until the project was further along than the dreaming stage before I started a thread on it, but we seem to have drifted in this direction.

    By the way, I drew the rig so that the sprit actually goes through the mast and the sail. I've learned to draw hulls much better than I've learned to draw rigs. It's just a cartoon.

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    Default Re: efficiency of the sprit rig

    Quote Originally Posted by Ben Fuller View Post
    ....
    The only real way to measure efficiency is measure sail area strictly but put no limits on sail and rig shape. The purest manifestation of this is seen in the wings of class C catamarans: anything goes but you only get 300 sq ft and everything is measured. The evolved rig is 3 element stacked 3 high. Camber, twist and angle of attack completely controlled.
    Why define efficiency in terms of sail area? Sail area makes sense for racing rules - its a relatively simple direct measurement if the sail rig is to be restricted.

    But for maximizing speed with a given hull the heeling moment from the rig is the limiting factor, not sail area. It is conceivable that a lower rig with a larger area and the same heeling moment may be faster.

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    Default Re: efficiency of the sprit rig

    Quote Originally Posted by johnw View Post
    When I was trying to understand the IOR, I tried designing a gaff rig to fit the rule. Gaff peaked no higher than 70 degrees, when real gaffers are more likely to be peaked at 45, no compensation for an aspect ratio less than 2:1 when most gaffers have at best 1:1. I'm thinking the low aspect ratio wasn't really compensated in most rules.

    That said, there were real advantages to the Bermudian rig, like a longer luff, taller mast that would carry a larger spinnaker, ease of handling with fixed backstays. I'm not nostalgic about the rigs, I'm just curious, now that so many rigs have gone with a square head, like the Merlin Rockets and I-14s.

    There are other factors. Yes, a high-aspect rig gives you a better lift-drag ratio close-winded, but it has a higher CE. Maybe you can carry a bigger rig with the old low-aspect rigs and not have to carry light kites to go fast on a reach. If the goal is not efficiency per square foot, but efficiency for effort, are there possibilities for the sprit rig?
    I think that "efficiency for heeling moment" would be a good way to compare rigs, with that criteria the low aspect ratio lugsails and gaffers do gain somewhat off the wind, but the conventional sloop gains upwind, its a case of horses for courses. On racers, given a rule that allows such I draw a fat head fully battened main of around 80% of the total working sail area, a 3/4 jib to clean up the airflow around the lower part of the main, and the biggest spinnaker or gennaker on the longest pole that the rules allow. Thats very hard to beat on any point of sail with any rig.
    But for other uses, I define "performance " as "suitability for purpose, and if the purpose is getting somewhere with as little fuss and bother as possible, in good order and condition, then sprit or lugsails, or gaff rigs can very much have a place.
    I've been working on high performance gaff rigs for a while now, and they more and more resemble the fat head mains, short gaffs with a flat angle, not pretty, but they work really well.
    Spritsails are not something that i've played with but I note that there are some very well performing Scandinavian small boats that use them, and I'd love to have a chance to compare other rigs with them.

    John Welsford
    An expert is but a beginner with experience.

  31. #101
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    Default Re: efficiency of the sprit rig

    Quote Originally Posted by john welsford View Post
    I think that "efficiency for heeling moment" would be a good way to compare rigs, with that criteria the low aspect ratio lugsails and gaffers do gain somewhat off the wind, but the conventional sloop gains upwind, its a case of horses for courses. On racers, given a rule that allows such I draw a fat head fully battened main of around 80% of the total working sail area, a 3/4 jib to clean up the airflow around the lower part of the main, and the biggest spinnaker or gennaker on the longest pole that the rules allow. Thats very hard to beat on any point of sail with any rig.
    But for other uses, I define "performance " as "suitability for purpose, and if the purpose is getting somewhere with as little fuss and bother as possible, in good order and condition, then sprit or lugsails, or gaff rigs can very much have a place.
    I've been working on high performance gaff rigs for a while now, and they more and more resemble the fat head mains, short gaffs with a flat angle, not pretty, but they work really well.
    Spritsails are not something that i've played with but I note that there are some very well performing Scandinavian small boats that use them, and I'd love to have a chance to compare other rigs with them.

    John Welsford
    I think that might resemble the "Swedish rig" or the sort of short-gaffed sail LFH used to advocate.

    As this picture of the EZ Sloat demonstrates, you can go too far with the "efficiency for heeling moment" standard.



    Some sandbaggers were more than three times as long in sparred length as in molded length.

  32. #102
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    Default Re: efficiency of the sprit rig

    Okay, I've moved the peak forward and the heel of the sprit down, and cleaned up the presentation a bit. How does it look now?

    Adept with sprit rig 11-15-2017 5-47-52 PM 632x789.bmp.jpg

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    Default Re: efficiency of the sprit rig

    Quote Originally Posted by johnw View Post
    Okay, I've moved the peak forward and the heel of the sprit down, and cleaned up the presentation a bit. How does it look now?

    Adept with sprit rig 11-15-2017 5-47-52 PM 632x789.bmp.jpg
    Very impressive if you have done all this in Delftship, I have only ever managed to do hulls.

    If it was me I would be making a model. All you need are a sheet of wood as planform of the hull, dowels for the mast, boom, sprit and cheap nylon for the sail. If you mount the mast horizontally gravity will behave like the wind. The spars won’t bend correctly but you will learn a lot about sprit position, twist etc and test multiple sails in a very short time. I would go for a mast about 1foot.

  34. #104
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    Default Re: efficiency of the sprit rig

    Though it will look like that when you're actually sailing and the boom is lifting a bit, you might want to lower the aft end of the foot a little. Tack corner angles (luff vs. foot) less than 90 degrees will often bind as you try to raise the sail. This is a function of the clew to mast horizontal (level) distance being a bit less than the clew corner to tack corner distance along the boom. This can be dealt with by installing a jack line system which will allow the luff to temporarily move back away from the mast as you raise or lower the sail, but it does complicate the issue a bit, and usually without any real benefit unless the boat for some reason has a raked mast and level boom. You wouldn't believe how badly a simple sail can bind going up (or down) if the angles are wrong.

    If the sail is to be loose-footed, you can add maybe 3" or so of round to the foot edge (deepest round about 45% aft of the tack and a fairly flat run out toward the round's aft end) which keeps the foot from looking funky, and your leech edge will need maybe 1" of hollowing for every 6' of leech length - deepest hollow mid-leech. This keeps the leech from flapping in use. The head will be straight on both the plan and in real life. The luff will be drawn straight on the sailplan, but actually have round for draft when the real sail is made. Round would generally be 2%-3% of chord width added in a smooth curve from throat to tack with maximum round about 45% of the luff length above the tack corner.

  35. #105
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    Default Re: efficiency of the sprit rig

    The plan is to use lacing, rather than hoops. Would that solve the problem with raising such a sail? If not, might raise the height of the tack rather than lowering the clew, don't want to hit people in the head.

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