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Thread: Lug Rig Conversion Info?

  1. #1
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    Default Lug Rig Conversion Info?

    I have been tasked with converting my sister's sprit rigged Sid Skiff (14' lapstrake centerboard open boat) to a lug rig. It's a welcome task for many reasons, but most of my library is focussed on gaff rig, so I need to pick your collective minds on a reading list.

    I'm not entirely starting from scratch, in that I need to keep the existing mast (it's already the max that, when lowered and stowed, fits within the boat), and that I have a good idea how the existing rig powers the boat (significant lee helm, but about the right amount of sail area).

    Anyway, I'm looking for information on such details as percentage of the yard forward of the mast, peaking angles, halyard traveller options, etc. What are people's preferred reference works? Anyone have any good detailed photos that you can post for my edification?

    Thanks,
    Alex

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    Default Re: Lug Rig Conversion Info?

    The yard is normally slung at 1/3 length, however the French standing lugs sling alot further forward, which results in higher tack tension.
    Are you thinking standing or balanced lug? Does she have a jib.

    Best thing you can do is calculate the centre of effort of the existing rig, then sketch a new on with its coe adjusted in comparison with the old one to sort the lee helm and see how it looks.
    It really is quite difficult to build an ugly wooden boat.

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    Default Re: Lug Rig Conversion Info?

    The yard is normally slung at 1/3 length, however the French standing lugs sling alot further forward, which results in higher tack tension.
    Ah, good. I thought I remembered hearing the 1/3 part, but doubted my recollection. Thank you for confirmation.

    Very interesting about the French rigs. Do you know if that approach showed any distinct advantages? I expect I won't push that 1/3 rule of thumb too far, as I doubt my sister would appreciate having to fight with higher tensions.

    Are you thinking standing or balanced lug? Does she have a jib.
    I'm thinking standing lug with a boom, no jib. The boat is currently cat rigged with a loose-footed sprit main. Short of towing a bucket astern, my sister has the deck pretty completely stacked against her.

    Best thing you can do is calculate the centre of effort of the existing rig, then sketch a new on with its coe adjusted in comparison with the old one to sort the lee helm and see how it looks.
    That's the current plan --I measured the current sail a couple days ago-- but reading Leather's "Sail and Oar" and Marino's "Sailmaker's Apprentice" I get hints of the importance of peaking angle for lug, which I'll need to consider when drawing out the new plan. I've seen enough photos and drawings that I think I can draw something that "looks right", but I'd like to have at least a passing knowledge of the technical details before I start cutting fabric.
    Alex

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    Default Re: Lug Rig Conversion Info?

    Maybe, since it's a centerboard that's not easy to move around, the place to start is to correct the "significant lee helm".

    Would be good to know where you are before changing things.

    What reasons for changing?


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    Default Re: Lug Rig Conversion Info?

    Last edited by sharpiefan; 07-10-2017 at 12:46 PM.

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    Default Re: Lug Rig Conversion Info?

    Quote Originally Posted by Pitsligo View Post
    That's the current plan --I measured the current sail a couple days ago-- but reading Leather's "Sail and Oar" and Marino's "Sailmaker's Apprentice" I get hints of the importance of peaking angle for lug, which I'll need to consider when drawing out the new plan. I've seen enough photos and drawings that I think I can draw something that "looks right", but I'd like to have at least a passing knowledge of the technical details before I start cutting fabric.
    Alex
    A higher peaked sail has more "luff length" like comparing bermudsn to gaff. The highest peaked lug is a gunter lug
    It really is quite difficult to build an ugly wooden boat.

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    Default Re: Lug Rig Conversion Info?

    I would have thought you need to find out the area of your centreboard and its position in relation to your new proposed rig. I have a 96sq ft balanced lug on a Michalak family skiff. How big is the existing mast and rig area?

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    Default Re: Lug Rig Conversion Info?

    Just as a test, put some grommets on the head of your sprit sail, and find a bit of timber, closet pole or something to which to lace the head. Then set the spritsail as a standing lug, without a boom if you don't have one. I've had a reasonable amount of luck using one of my sprits as a lug for one boat and sprit for the other. It is a cheap simple experiment that does not spoil your sprit.
    Ben Fuller
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    Default Re: Lug Rig Conversion Info?

    Sharpiefan: Wow. Thank you. I'll go read my homework.

    A higher peaked sail has more "luff length" like comparing bermudan to gaff.
    Hmm. Makes sense, and I had guessed that was part of it, but not having worked much with lug, I wondered if there was more to it; specifically, something to do with luff tension and leech twist off the wind. So your sense is that establishing the correct peaking angle is mostly about "luff length"?

    Maybe, since it's a centerboard that's not easy to move around, the place to start is to correct the "significant lee helm".
    I would have thought you need to find out the area of your centreboard and its position in relation to your new proposed rig.
    By starting with the known sail and finding its CE, I can work backward from its known luff (laced to the mast) and adjust the new CE aft without actually knowing the precise shape or placement of the CB. Yes, the CB can be adjusted and, thereby, the entire CLP be changed --but so can the entire CLP be adjusted just by changing where my sister sits, or by her shifting around the half dozen 4# lead "piglets" I cast for her (and which did help). Since she hasn't managed to get satisfactory performance by either of those measures, I can assume that the variables within the *hull* can be "maxed out" in favor of inducing weather helm, and yet not actually bring about weather helm. So if I shift the CE aft on the new sail plan, all those hull variables will now be more effective in inducing a weather helm, and could --if the new CE is adequate on its own-- be neutralized for a satisfactory helm balance, or even reversed to *mitigate* any new weather helm should I goober my guess and bring about too much weather helm. That's not absolute, of course --there's a limit to how one can play a CB before it becomes ineffective-- but I think it's a fair working premise.

    I have a 96sq ft balanced lug on a Michalak family skiff. How big is the existing mast and rig area?
    On paper, the sail is about 70 sqft, which is about all she needs. I can give her a bit more, since she's a summer boat and south Puget Sound has typically very light winds, but I don't want to turn her into a sandbagger. (More accurately, my sister doesn't want me to turn her into a sandbagger.) The mast is just *barely* short enough to fit inside the boat, diagonally, when lowered, so about 13' 6"(?). The halyard "sheave" is a beehole a couple inches down from the truck, and the current luff is 10' 8" long: it's two-blocked when set, with the taper of the eyesplice affixing the halyard to the throat swallowed by the beehole. I'll need to shorten that luff in order to allow enough working room for the yard, traveler, the hitch to bend on the yard, etc. --maybe by a foot? The tack can't go down any further if I'm to allow both headroom under the boom and room for a tack pendant.

    What reasons for changing?
    The big reason is that the boat doesn't handle well under her current rig: she won't point (typical sprit, in my experience), has some alarming bad habits off the wind (loose-footed main), and hangs in stays (lee helm). Additionally and importantly, while a sprit rig brails up brilliantly --that's why fishermen loved it-- at this scale (and with this sail's details) it's inconvenient to reef and no sprit rig can be fully doused in a squall. Brailed up, all that sail area still forms a nice big bag up high, giving optimum leverage for the squall to knock the boat down. Those are faults that can and have been mitigated in different hull forms, such as the Woods Hole boats (which I have sailed), but the Sid Skiff is a tiddly thing by comparison to a Woods Hole boat, and in her the faults are tedious at best and very dangerous at worst. It is my hope that shifting to a boomed, standing lug rig, I can mitigate some or all of those faults.

    Alex
    Last edited by Pitsligo; 07-10-2017 at 06:45 PM.

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    Default Re: Lug Rig Conversion Info?

    Just as a test, put some grommets on the head of your sprit sail, and find a bit of timber, closet pole or something to which to lace the head. Then set the spritsail as a standing lug, without a boom if you don't have one. I've had a reasonable amount of luck using one of my sprits as a lug for one boat and sprit for the other. It is a cheap simple experiment that does not spoil your sprit.
    Well hey. That's an interesting idea. I might play with that.

    Thanks!

    Alex

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    Default Re: Lug Rig Conversion Info?

    You're welcome. Time for a bucket of strong coffee, hmmmm?

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    Default Re: Lug Rig Conversion Info?

    This is a good start. But it would be even better if you can increase the rake on the mast.

    Quote Originally Posted by Ben Fuller View Post
    Just as a test, put some grommets on the head of your sprit sail, and find a bit of timber, closet pole or something to which to lace the head. Then set the spritsail as a standing lug, without a boom if you don't have one. I've had a reasonable amount of luck using one of my sprits as a lug for one boat and sprit for the other. It is a cheap simple experiment that does not spoil your sprit.

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    Default Re: Lug Rig Conversion Info?

    Time for a bucket of strong coffee, hmmmm?
    Oh yeah...!

    This is a good start. But it would be even better if you can increase the rake on the mast.
    I had just gotten there myself. I need to eyeball the mast step and see what can be done. I'll be in town tomorrow and will have a look at the boat then.

    Alex

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    Default Re: Lug Rig Conversion Info?

    So your sense is that establishing the correct peaking angle is mostly about "luff length"?
    uhhh.............no, that isn't it. In order to keep a lugsail's luff tight (which is critical) the yard needs to be pretty tail-heavy. The more you peak it up, the less tail-heavy and resistant to the heel flopping around and messing with your luff tension it will be. You don't want the yard dipping and trying to stand vertical every time you ease the sheet and prepare to tack. On the other side of the coin, a head angle which is very shallow won't perform as well, since it does have less "luff length" (even though some of it isn't really on the luff). Like everything else in sailing, the best angle will need to be some sort of compromise between these two, and unfortunately, there really isn't any formula for it. It's up to the designer or sailmaker and his lugsail experience.

    Increasing mast rake on a sprit-to-lug (balanced or standing) conversion is usually helpful if possible. It can help switch rigs without making drastic changes in the CE/CLP relationship. The best rule of thumb, unless you actually know otherwise, is to pretty much maintain the original fore and aft CE position and the original sail area as you design the new rig.
    (example: http://webpages.charter.net/tbradsha...s/!SKERRYL.PDF Ignore the pricing, it's 15 years old and I'm retired and lazy)

    Trying the sprit as a lug for testing isn't a bad idea. You may not need to do any more to the head (like grommets) than just stretch it tight between the throat and peak. Usually spritsails are cut with a straight head, which should pull pretty tight, where lugs would have head round. In use, the sprit-as-lugsail is likely to be pretty flat up top as a result, but it isn't a big deal just for testing.

    If you can fight through all the pop-up crap and ads that Photobucket has these days, there is a photo series on lugsail making here. Balanced and standing lugs will likely have slightly different perimeter shapes, but most of the design and construction work is basically the same.

    http://s1303.photobucket.com/user/To...?sort=9&page=1

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    Default Re: Lug Rig Conversion Info?

    uhhh.............no, that isn't it.
    Yep, that's *exactly* what I was wondering about! Your explanation makes perfect sense, too --though I do wish there were a formula I could follow to be sure I got it right. (Don't we all...)

    Increasing mast rake on a sprit-to-lug (balanced or standing) conversion is usually helpful if possible.
    What I drew this evening locates the lug's CE almost exactly (an inch or so aft and a few inches lower) atop the sprit's CE --which is a bit of a nuisance, since I'd hoped to shift the CE aft a bit. It does come at an increase of sail area: from 69sqft to 77sqft, which I expect would be acceptible given the much greater ease of reefing a lug. However, with the variability of where the yard will actually set, despite my drawing it crossing the mast at 1/3 its length (using the luff edge as the datum), I expect that CE is a bit of a guess.

    It's only when I rake the mast aft 5° that I get a significant change in lead, so I suspect that modifying the mast step will be equally important to the performance change I'm hoping for.

    Ignore the pricing, it's 15 years old and I'm retired and lazy.
    What a pity. I half hoped I might give you the job! The illustrations are great, though. And from them I think I might do well to drop my rig's peak. I'll compare them in the morning.

    Trying the sprit as a lug for testing isn't a bad idea.
    That was sort of what I was thinking, with not bothering about intermediate grommets for a test run. Glue up a Q&D yard and give it a whirl.

    Photobucket isn't even letting me look at the photos: it just tells me "Please update your account to enable 3rd party hosting." (Bastids.)

    Thank you, Todd; after reading what you've had to say on other lug rig threads, I was rather hoping you'd chime in here.

    I'll see if I can figure out how to photograph and post what I drew, to get people's general impression of my line of thought.

    Alex

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    Default Re: Lug Rig Conversion Info?

    Here's a thread on switching to a balance lug rig on a boat of similar size, using one of Todd's sails. Zero theory, 100% practice.

    http://forum.woodenboat.com/showthre...psy&highlight=
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    Default Re: Lug Rig Conversion Info?

    I used my balanced fam skiff rig on my Vattern snipa mast that is sprit rigged. The way the mast is fitted through a thwart and fixed at the bottom meant no changes to rake was possible, but being able to shift the rig fore n aft certainly helps. Boat was transformed as a sailing boat with the balanced lug, have only used the sprit rig when racing the other snipas.
    Michalaks Mayfly has a 10ft 6in mast and a 75ft sq rig, if those dimensions are better for you?

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    Default Re: Lug Rig Conversion Info?

    Here's a thread on switching to a balance lug rig on a boat of similar size, using one of Todd's sails. Zero theory, 100% practice.
    Very good! Thank you. I especially like your details for the parrel lines.

    I used my balanced fam skiff rig on my Vattern snipa mast that is sprit rigged.
    I believe I came across your account of that on another thread, during my "homework" session. I found it especially encouraging, since the Sid Skiff has the same inflexibility in her mast step: fixed at the heel and using a thwart as partners, so impossible to rake without major modifications.

    I'm very curious about any changes you noticed in your snipa's helm balance, with the change in rig. I'm getting the sense that changing the rigs straight across, sprit or LOM to lug (typically balanced lug), the CE moves forward, reducing any weather helm. Chip-skiff made a note of this in his thread. What did you find? With the sprit rig, had your snipa carried a weather helm?

    Michalaks Mayfly has a 10ft 6in mast and a 75ft sq rig, if those dimensions are better for you?
    Yes, that's much closer to the Sid Skiff. I'll check it out. Much depends on that CE/CLP balance.

    Alex

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    Default Re: Lug Rig Conversion Info?

    Quote Originally Posted by Pitsligo View Post
    Very good! Thank you. I especially like your details for the parrel lines. I believe I came across your account of that on another thread, during my "homework" session. I found it especially encouraging, since the Sid Skiff has the same inflexibility in her mast step: fixed at the heel and using a thwart as partners, so impossible to rake without major modifications.
    Actually, the rake of the mast on Gypsy can be changed. The step is mounted on rails above the sole. I didn't build her (I'd have done a better job) and I suspect that the step is epoxied to the rails. But it would be fairly simple to route the space between the rails on either side to admit the head of a large carriage bolt which would poke up through the step and be set with wingnuts, or the like.



    The original mast was square, so I squared the foot of the new round mast. There were stress cracks at the join of the thwart to the hull, so I added vertical crossmembers to brace it and also built a sort-of box (white) to stabilise it fore-to-aft. I also cut away most of the bulkhead, to give my dog some room. I use wood wedges where the round mast goes through the square hole in the thwart.



    Here's another view. The box thingie gives a handy mounting for various fiddles I use to rig a double-ended mainsheet for the leg-of-mutton sail. The lug sail doesn't need dthem.

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    Default Re: Lug Rig Conversion Info?

    Alex, the snipas balance under the sprit was ok, she carries a jib. I think it was just a lucky fluke that the balanced lug from the Michalak boat worked so well, but it has to be said, being able to adjust the position of the boom and yard gives a whole lot of tuning options when it comes to balance. Obviously the snipa does not have a dagger/centre board to pivot on, only a plank keel, i expect that actually helps.

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    Default Re: Lug Rig Conversion Info?

    Actually, the rake of the mast on Gypsy can be changed.
    That looks like a system worth considering, should I find it worthwhile to modify the Sid Skiff. Or, more accurately, should *my sister* find it worthwhile for me to modify her Sid Skiff. I can see how wedging it forward or aft could be pretty easily accomplished, even without that clever idea of carriage bolts. I do know there's a lot less room in the Sid Skiff; the step is very far forward, and as fine as her entry is, it's quite tight quarters in there. So not an identical system, but perhaps one that takes some inspiration from yours.

    That's a good cautioning about the stress fractures, too. I need to take a second look at the Sid Skiff's surrounding structure, to make sure it's up to adding a little sail area. I don't want to tear the boat apart in the process of improving her performance.

    ...the snipas balance under the sprit was ok, she carries a jib.
    I can see how that would work, with the portion of the balanced lug's sail forward of the mast filling in for the jib, as regards helm balance. As you say, a lucky fluke. As I mentioned, the Sid Skiff's mast is very far forward, and she carries no jib, so whatever portion of the standing lug extends forward of the mast (where no portion of the sprit rig currently does) would need to be balanced by some additional sail added (or relocated) aft of the CE.

    ...being able to adjust the position of the boom and yard gives a whole lot of tuning options when it comes to balance.
    I find this especially interesting. I'm reluctant to rely on it too much --"oh, I'll just hang something generally okay up there and correct the helm balance as I go"-- but it is reassuring to hear of that flexibility. Working with a standing lug, as I intend to do, I won't have the boom to adjust, but the yard should give me some of that tuning you speak of. I'll need to be sure her clew starts out high enough not to be problematic if I shift the halyard forward on the yard to tighten the luff, too.

    ...a plank keel, i expect that actually helps.
    Yes, I'm almost certain you're right about that. I changed the underwater profile of my own boat, a 19' deep-keel sloop, adding 1" of depth to the salient keel, and have been shocked by what an improvement that small change brought to her, both in helm balance and directional stability. (She can now heave-to! It's wonderful!!) I expect the difference between a plank keel and a daggerboard --or the Sid Skiff's centerboard-- would be considerable.

    Alex

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