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Laukejas
03-09-2017, 04:38 PM
Hello,

I am solving a certain engineering challenge. A little background: I plan to make a lateen sail for my boat. Boat is 3m 10cm (10' 7") long. The principal requirement is that the spars must fit inside the boat. That means no spar or spar section can exceed 3m (118"). Mast is exactly that long. Now, to get any reasonable sail area, the lateen yard must be as long as possible, preferably 5m 40cm (212") or even longer. I want to find a solution to make a 2-piece yard that can be assembled for sailing, and disassembled for transportation and storage.

Building that yard from aluminum would make it very easy to make such a joint. However, I would prefer to use wood, for the sake of appearance, but more importantly, to save weight aloft. Aluminum won't permit tapering, and a yard this long must certainly have some tapering. So, if I go with wood, I do not know how to make a reasonably lightweight and strong joint that would be quick to assemble and disassemble.

Several very important notes:
1. The yard will be using a rectangular section, probably about 3x5cm (1 3/16" x 2", tapered towards the ends). I still have to make calculations if this will be enough for a yard that long, but for now, that's my reference number.
2. The sail will be using a luff pocket instead of grommets to improve airflow around the yard. There will be, of course, a short opening in the sleeve to tie the halyard to the yard.

So far, I have came up with following solutions:
1. Make scarf cuts on each end of the yard section, and fix them together with several bolts on each end of the scarf (obviously, using this type (https://ksd-images.lt/display/products/0002/1289/50400898.JPG?h=742&w=816)of threads on the other side). However, I suspect that the loads will be too concentrated, and bolts will split the wood. Using metal plates to distribute the load might help somewhat, but I don't know if would be reliable in the end. Yard twist might also be a factor. Here's a picture of such a joint (dashed lines represent where the bolts will go):

http://i.imgur.com/I36ms98.jpg

2. Same thing, but with aluminum sleeve over the joint, glued to one of the sections. The downside here is that if wood swells or shrinks (and that will happen regardless of how much I waterproof it), the joint might become too tight or too loose, becoming flimsy, or not usable at all.
3. Same thing, but using an aluminum sleeve which has a slot-cut along it's length on one side, so it is possible to "close up" the gap and tighten the joint by using some sort of external tightener on top of the sleeve... Like these (https://ksd-images.lt/display/products/0005/9462/51123746.jpg?h=742&w=816). Obviously, that will make the whole thing protrude a lot, and it might prohibit me from using the luff sleeve.
4. Using the same scarf joint, but without aluminum sleeve and without bolts, only these external tighteners on each end. Just like in the previous picture, but with tighteners on the outside instead of bolts. Simple, but something tells me it won't be strong enough, and it will still protrude.
5. Using a butt joint on each end of the sections. Gluing an aluminum sleeve on one section, and then another, larger aluminum sleeve on the other section, which will go on top of the first one when joint is inserted. Sort of a male-female thingy. This should solve the shrinkage/expansion issue, because aluminum will contact with aluminum, not with wood. One bolt should be enough to keep the joint from sliding out. The downside is, it is a butt joint, not scarf joint, so it might be not as strong - it would all depend on the strength and length of the larger aluminum sleeve. Also, I'll have to find aluminum profiles that can be inserted snugly into one another, which might be a serious challenge. Here's an illustration (scaled down for better view, the joint will actually be longer):

http://i.imgur.com/1iZ6dmg.jpg

So far, the 5th method seems to make most sense. But being an amateur in engineering and boatbuilding, I might have missed some other, more elegant solutions. Can someone give any insight? As I said, I want sections to be no more than 3m (118"), yet the whole spar to be as long as practically possible, while keeping the joint simple and lightweight.

Thank you for your time. Looking forward to any advice you might have.

Peerie Maa
03-09-2017, 05:13 PM
Think fishing rods, go for solution 5. You do not have to use aluminium, brass or stainless will also do and might be easier to source. I suggest that your section is too skinny and a round spar would be easier to find/maker tubes to fit, nearer to 3" diameter for your length. Making the peak and throat lashings to the spar will stop it coming apart at the joint.

Laukejas
03-09-2017, 05:30 PM
Think fishing rods, go for solution 5. You do not have to use aluminium, brass or stainless will also do and might be easier to source. I suggest that your section is too skinny and a round spar would be easier to find/maker tubes to fit, nearer to 3" diameter for your length. Making the peak and throat lashings to the spar will stop it coming apart at the joint.

Thank you for the answer. Brass is a lot more difficult to source where I live. As for steel, isn't it too heavy for this type of application?
I wasn't going to ask, but since you mentioned, is there any reliable method to determine the section and tapers for lateen sail? I know how to find moment of inertia, bending amounts and so on, but I have little idea on how the forces work in lateen sail, and what loads should be expected. I might go with round section, but I would prefer rectangular - easier to make, stronger for the same weight (yes, I did the math, rectangular is about 5% stronger for the same section area). I do have a source of rectangular aluminum profiles. But for now, I just want to make sure I select the best type of joint for the job.

jackster
03-09-2017, 05:39 PM
Yes... solution #5...a round spar (wood- 2-part) as Nick suggests... and a sleeve that is situated where the halyard attaches.
I think, anyway.

Peerie Maa
03-09-2017, 05:42 PM
You are not using very much metal in the grand scheme of things. Aluminium might suffer from corrosion, with the corrosion products jamming the joint. You could consider laminating an epoxy glass sleeve which would allow you to include a slight taper.
As to dimensions, I used a lug spar for guidance, it being close to a lateen in the way it supports the sail.
Try to find the spar dimensions for a range of balance lug rigs and reverse engineer the yard to gain an understanding of the safety factors etc.

Laukejas
03-09-2017, 05:50 PM
You are not using very much metal in the grand scheme of things. Aluminium might suffer from corrosion, with the corrosion products jamming the joint. You could consider laminating an epoxy glass sleeve which would allow you to include a slight taper.
As to dimensions, I used a lug spar for guidance, it being close to a lateen in the way it supports the sail.
Try to find the spar dimensions for a range of balance lug rigs and reverse engineer the yard to gain an understanding of the safety factors etc.

Well... If my spar was 5x3cm (and if you're right, I'll need even larger one), then for that size, 1 meter of steel section would weight 1.5 kilos (thinnest wall size available, which is 1.2mm). Considering that I'll be using both inside and outside sleeves with method 5, I might come very close to a meter of steel section in total. That's a lot of weight...

Anyway, if I were to use method 5, how long should the joint be? Any guidelines? Like, 1:10 of total spar length or something? The shorter, the better, but not if the joint will be weaker than the rest of the spar...

P.S. I'm not exactly confident in my ability to make such a sleeve from epoxy... And surely I have no idea how to predict the strength of glass+epoxy combination. Too much guesswork in such a critical part, especially when a lot determines on the quality of the job I would make.

Todd Bradshaw
03-09-2017, 06:06 PM
Just to be sure....... you are planning to put a sail with a yard 17.6' long on a boat that is only 10'7" long????????

Laukejas
03-09-2017, 06:10 PM
Just to be sure....... you are planning to put a sail with a yard 17.6' long on a boat that is only 10'7" long????????

Yes, that's the plan. Here's how it looks now and how it will look with lateen rig:

http://i.imgur.com/omn07Si.jpghttp://i.imgur.com/BppY0nv.jpg

Height is pretty much the same. Sail area is a bit lower, center of effort is a lot lower, center of mass is also way lower. My current rig is just too heavy, and I really love Lateen sails! As for the sail area, I know it looks large, but 95% of the time in my country, this is undersized. We just don't have the kind of winds that you people do...

Peerie Maa
03-09-2017, 06:16 PM
Well... If my spar was 5x3cm (and if you're right, I'll need even larger one), then for that size, 1 meter of steel section would weight 1.5 kilos (thinnest wall size available, which is 1.2mm). Considering that I'll be using both inside and outside sleeves with method 5, I might come very close to a meter of steel section in total. That's a lot of weight...

Anyway, if I were to use method 5, how long should the joint be? Any guidelines? Like, 1:10 of total spar length or something? The shorter, the better, but not if the joint will be weaker than the rest of the spar...

P.S. I'm not exactly confident in my ability to make such a sleeve from epoxy... And surely I have no idea how to predict the strength of glass+epoxy combination. Too much guesswork in such a critical part, especially when a lot determines on the quality of the job I would make.

Again, think fishing rod. I doubt that you need more than 6 inches, 8 at the most 4 inch bury and 4 inch attached to the spar.
A search on Google brings up the Dyer Dhow, which uses a scarf joint secured by a short sleeve on each end of the scarf.
http://sailboatdata.com/imagehelper.asp?file_id=6040

Garret
03-09-2017, 06:24 PM
I was going to suggest the Dyer method. I'll see if I can get a pic from mine.

Laukejas
03-09-2017, 06:26 PM
If I were to choose the Dyer method, how do I make sure that the wood swelling/shrinking won't make it loose or un-insertable into these sleeves?

Garret
03-09-2017, 06:31 PM
Good varnish! That's all my mast has ever had & it's 20+ years old.

Laukejas
03-09-2017, 06:36 PM
Good varnish! That's all my mast has ever had & it's 20+ years old.

Well, yeah, but the problem is, it's very difficult to determine what the dimensions of my spar will be once it is epoxied, varnished, etc. If it's wrong, there won't be much to do to fix it, except for removing varnish, shaving off the some wood, and then varnishing all over again...

Anyway, which method would be better? My 5th method (fishing rod, as you called it), or the Dyer joint?

Peerie Maa
03-09-2017, 06:46 PM
The Dyer method is tried and tested, and probably easier to source the metal work, as you only need one size of sleeve, not two with a sliding fit.

Laukejas
03-09-2017, 06:53 PM
The Dyer method is tried and tested, and probably easier to source the metal work, as you only need one size of sleeve, not two with a sliding fit.

All right, I see. What about manufacturing the wooden part of the joint so that it fits perfectly snug inside the sleeves? How do I achieve that kind of precision when the wood has to be finished, and the finish makes dimensions grow?
Also, is 1:10 (based on diameter) good enough for this kind of scarf joint?

Garret
03-09-2017, 07:02 PM
Here's a (not great) pic. Details below:

http://i1194.photobucket.com/albums/aa372/garretmott/Dyer_zps42letges.png

The sleeves are split because of a groove for the sail in the mast. They are tacked to the mast with 4 copper tacks each. The sleeves are resin (epoxy? dunno) & cloth.

The fit is tight for sure & also remember that this is a mast, so the sections are held together by the main halyard putting downwards pressure on the mast. I can get accurate dimensions on the mast cross-section, but it's roughly 2 1/4 x 3 inches.

The Dhow was originally sold in 1934 (wood) & continues in production (switched to glass hulls) today.

Let me know if you have more questions!

Garret
03-09-2017, 07:06 PM
If I were making something similar, I'd build the spar, cut the joint, varnish everything, stick it back together & wrap each end in the metal (thinner copper so you can to sever wraps maybe?) & tack it down.

Peerie Maa
03-09-2017, 07:08 PM
1:10 is good.
The varnish will be measure in microns. I doubt that anyone can shape wood that accurately. Make it fit without varnish, then use a mallet to gently tap the sleeves into place lubricated with wet varnish and secure with a couple of screws. The taper of the scarf will tighten the joint in use.

Laukejas
03-09-2017, 07:11 PM
Here's a (not great) pic. Details below:

The sleeves are split because of a groove for the sail in the mast. They are tacked to the mast with 4 copper tacks each. The sleeves are resin (epoxy? dunno) & cloth.

The fit is tight for sure & also remember that this is a mast, so the sections are held together by the main halyard putting downwards pressure on the mast. I can get accurate dimensions on the mast cross-section, but it's roughly 2 1/4 x 3 inches.

The Dhow was originally sold in 1934 (wood) & continues in production (switched to glass hulls) today.

Let me know if you have more questions!

Wow... Thank you! It's really surprising, I thought these sleeves would have to be much larger and stronger built. If they only can be this small, then I'll definitely go with steel. Or maybe I could also build them up layer by layer with epoxy and cloth. I'm just not too confident in my ability to make such sleeves strong enough. Do you think I should glue my sleeves to each section, or have them removable like in this example you showed?

Garret
03-09-2017, 07:24 PM
Wow... Thank you! It's really surprising, I thought these sleeves would have to be much larger and stronger built. If they only can be this small, then I'll definitely go with steel. Or maybe I could also build them up layer by layer with epoxy and cloth. I'm just not too confident in my ability to make such sleeves strong enough. Do you think I should glue my sleeves to each section, or have them removable like in this example you showed?

I took 'em off to varnish the mast - which is handy. Haven't tried putting it back together yet :)

Here are some more measurements for scale. Done in 20 F/ -7C - so done fairly quickly...

The approx 12" in the pic is exactly 12" (good to see my eye is still pretty good)

The mast is oval (or rectangular with the corners shaved way down) - 2.5" x 1.75"

The taper is from 1.5" at the thick end to 1" at the thinner (outer) end.

I shoulda measured the sleeves - but didn't - I'd say 4" long max - maybe a bit less. I'd guess 3 layers of cloth?

Finally - remember that this is a mast - so possibly less lateral pressure than a lateen sprit? Maybe not - but I've never sailed a lateen rig.

Laukejas
03-09-2017, 07:45 PM
I took 'em off to varnish the mast - which is handy. Haven't tried putting it back together yet :)

Here are some more measurements for scale. Done in 20 F/ -7C - so done fairly quickly...

The approx 12" in the pic is exactly 12" (good to see my eye is still pretty good)

The mast is oval (or rectangular with the corners shaved way down) - 2.5" x 1.75"

The taper is from 1.5" at the thick end to 1" at the thinner (outer) end.

I shoulda measured the sleeves - but didn't - I'd say 4" long max - maybe a bit less. I'd guess 3 layers of cloth?

Finally - remember that this is a mast - so possibly less lateral pressure than a lateen sprit? Maybe not - but I've never sailed a lateen rig.

Thank you very much for taking these measurements! Hope you didn't catch any cold. So if the joint is 12", and diameter is 2.5" (long edge), isn't that like 1:4.8 ratio (or 1:6.85 for the short edge)? I thought you advised me to do 1:10. In my case, since I'm limited by the final length of sections, the longer the scarf, the shorter my yard will be!

Laukejas
03-09-2017, 07:53 PM
If I were making something similar, I'd build the spar, cut the joint, varnish everything, stick it back together & wrap each end in the metal (thinner copper so you can to sever wraps maybe?) & tack it down.

Garret, could you please elaborate on the copper wrap part? You mean, layering metal, wrapping it around like cloth? How exactly will these layers be held together?

Garret
03-09-2017, 08:34 PM
Garret, could you please elaborate on the copper wrap part? You mean, layering metal, wrapping it around like cloth? How exactly will these layers be held together?

I wasn't the one saying 1 to 12 scarf ;) I can only say what mine is. But - 1/2" in 12" = 1-24, no?

re: copper wrap - Just a thought, but take some fairly thin copper (22 ga?) & wrap it around the mast say 2 times, While holding it tight (tape) - drill a couple of holes & put in screws.. Maybe varnish the copper after trimming the end to protect it?

No cold - I should be used to it - but was away at a client's in warmer climes for a few weeks & lost my cold conditioning!

Laukejas
03-09-2017, 08:58 PM
I wasn't the one saying 1 to 12 scarf ;) I can only say what mine is. But - 1/2" in 12" = 1-24, no?

re: copper wrap - Just a thought, but take some fairly thin copper (22 ga?) & wrap it around the mast say 2 times, While holding it tight (tape) - drill a couple of holes & put in screws.. Maybe varnish the copper after trimming the end to protect it?

No cold - I should be used to it - but was away at a client's in warmer climes for a few weeks & lost my cold conditioning!

Oh, forgive me. I got confused on who said what :D Anyway, epoxy + fiberglass tape seems to work out fine for you, so I guess I'll stick to it too. Copper would probably work too, but... I don't know, I trust cloth and epoxy more. Provided I can make it with adequate quality.

Thank you very much for all the advice and patience with my questions. Peerie, thank you very much too. You both helped me decide on how to do this, and I'm glad the solution is so simple, lightweight and elegant.

Now, all I have to do is figure out the exact dimensions of my yard. Todd seemed a bit shocked with the length of the yard I chose... Bad sign! :D

Garret
03-09-2017, 10:12 PM
Oh, forgive me. I got confused on who said what :D Anyway, epoxy + fiberglass tape seems to work out fine for you, so I guess I'll stick to it too. Copper would probably work too, but... I don't know, I trust cloth and epoxy more. Provided I can make it with adequate quality.

Thank you very much for all the advice and patience with my questions. Peerie, thank you very much too. You both helped me decide on how to do this, and I'm glad the solution is so simple, lightweight and elegant.

Now, all I have to do is figure out the exact dimensions of my yard. Todd seemed a bit shocked with the length of the yard I chose... Bad sign! :D

You are very welcome. I've just returned .001% of the help I've gotten here! Just to be clear: I did not make the sleeves - they came with my boat - so they were "factory" made. I use quotes because Dyer does a lot of hand work. If you don't want the sleeves to stick to the mast, make sure to use some vaseline or some such so they'll slide off after curing.

If I can offer more info - just post back.

Todd Bradshaw
03-09-2017, 10:52 PM
Todd seemed a bit shocked with the length of the yard I chose... Bad sign!

Not shocked. I just wanted to be sure we were talking about a traditional lateen sail, not one of the Sunfish-style modern recreational lateens (which would be huge with a yard that long) and that you figured that the boat could stand up to all that potential heeling lever in the type of conditions you plan to sail in. You will likely need to build a very generous spar bend allowance into the sail's luff - a situation where you might be adding an inch or two to produce the draft, but need another half foot of round or more to compensate for bend. I would certainly build the mast first and even bridge it, weight it and measure it for bend just to try to get some idea of how much bend allowance to build into the sail. Measuring spars for bend tends to be rather inaccurate as a preview of what to expect in actual use, but sometimes it's better than nothing.

Testing the formulas that I normally use for determining diameters and tapers on yards and booms I get the impression that this will be a pretty massive spar. The "standard" weight yard of that length came out 3.3" maximum diameter, tapering to about 2.7" at the heel and 2" at the peak. The "lightweight" version was 2.65" maximum diameter, tapering to 2.1 at the heel and 1.65" at the peak. I don't know how much thinner you could get without the yard becoming so whippy that you can't maintain consistent sail shape. In any case, the thought of building a hollow yard to reduce weight aloft looks better and better.

Laukejas
03-09-2017, 11:11 PM
Not shocked. I just wanted to be sure we were talking about a traditional lateen sail, not one of the Sunfish-style modern recreational lateens (which would be huge with a yard that long) and that you figured that the boat could stand up to all that potential heeling lever in the type of conditions you plan to sail in. You will likely need to build a very generous spar bend allowance into the sail's luff - a situation where you might be adding an inch or two to produce the draft, but need another half foot of round or more to compensate for bend. I would certainly build the mast first and even bridge it, weight it and measure it for bend just to try to get some idea of how much bend allowance to build into the sail. Measuring spars for bend tends to be rather inaccurate as a preview of what to expect in actual use, but sometimes it's better than nothing.

Testing the formulas that I normally use for determining diameters and tapers on yards and booms I get the impression that this will be a pretty massive spar. The "standard" weight yard of that length came out 3.3" maximum diameter, tapering to about 2.7" at the heel and 2" at the peak. The "lightweight" version was 2.65" maximum diameter, tapering to 2.1 at the heel and 1.65" at the peak. I don't know how much thinner you could get without the yard becoming so whippy that you can't maintain consistent sail shape. In any case, the thought of building a hollow yard to reduce weight aloft looks better and better.

Thank you for your input, Todd. I will make sure to build in plenty of bend allowance. I'll see if I can make some tests as you suggested before sewing the sail.

When you quoted these diameters, you had a round spar in mind, correct? I am planning to go with rectangular section, with a lot more depth than width. I will translate the diameter from round to hollow rectangular by aiming for the same moment of inertia. Just wanted to make sure you really were talking about round spar. 3.3" sounds massive. I mean, my current mast is 2.5", square hollow box with 9/16" walls... And I thought that's big!

Might I inquire into what formulas you mentioned that you used to come up with these numbers?

Todd Bradshaw
03-10-2017, 02:56 AM
Yes, round. I use a sometimes slightly modified version of some of the spar diameter formulas from Iain Oughtred, which have always worked pretty well for my customers' sails. For lateens, we can usually go a bit narrower for the yard than we would for a lugsail's or gaff sail's yard, but we do want to limit bend as much as possible and at the same time reduce weight aloft as much as we can.

Laukejas
03-10-2017, 07:18 AM
Yes, round. I use a sometimes slightly modified version of some of the spar diameter formulas from Iain Oughtred, which have always worked pretty well for my customers' sails. For lateens, we can usually go a bit narrower for the yard than we would for a lugsail's or gaff sail's yard, but we do want to limit bend as much as possible and at the same time reduce weight aloft as much as we can.

Okay, I see... I did my calculations, and the numbers are not inspiring. If I go with the "light" version you described, converting it to square hollow spar gives a diameter of 2.5" with 0.4" walls. With the tapering, end caps and filling at the joint the whole thing will likely weight nearly 9 pounds. Maybe I can bring the number down a little by doing yard rectangular instead of square, but it's still very heavy. Compared to my current rig, the total center of mass will only move down by 1.1" (in an empty boat)... Which isn't much of an improvement. My boat will still be top-heavy.

EDIT: I made some calculations, and here's what I've got. If I make this yard rectangular hollow section, 0.4" walls, 2.75" x 1.73" at the middle, 2.45" x 0.8" at heel, 1.77" x 0.8 at peak, this yard will have the same moments of inertia as the round spar you quoted. Theoretically, it will weight 7.5 pounds, and the center of mass of the boat will be 1.25" lower than in my current rig (considering no crew). A little better than purely square section, but still very heavy...

Damn. That's a rain on my parade. I somehow expected that the yard could be a lot slimmer. I guess I'll have to consider some another rig, then. This is the third season for the little boat, and I'm still failing to make a rig that would provide a massive sail area without bringing a lot of weight aloft. My current lug is 83 square feet. That kind of area is just barely enough for our conditions. The lateen would have been 73 square feet. A lot less, but I thought I could sacrifice it for stability and convenience of transportation. Now, I'm back at square one.

BOI
03-10-2017, 11:02 AM
I've only sailed once in person on my brother's yacht, and everything I know about sailing is from the internet, so take my words with a grain of salt. Maybe my comment will inspire a bit of discussion.

Sounds like you do your sailing in light winds. How does your sailing and your boat's performance compare to the one in the video: https://www.youtube.com/watch?v=Cz9lMLKmQuY&feature=youtu.be It is a Brooks DragonFlyer 3.2, a planing dinghy almost the same length as yours with even less sail area. It comes with either a 59 square foot or a 70 square foot sailplan, and I don't know which one is in the video.

Maybe if the winds are really light, the yard won't bend so much and you could use the lateen with a thinner yard after all. Have you considered bamboo poles? They are hollow and if you can pick through a pile you can sometimes find some straight and light ones without splits. They are not ultra permanent but are used in the Pacific for masts and yards. I've gotten some just under 7' long with a diameter of ~1" to 1.25" and they are stiff enough to make serviceable oars with a fairly small blade. Once my boat is finished I plan to use similar poles as mast and yard for my first solo sailing experiments.

But maybe going back to square one could mean a different boat altogether.What are other people sailing in your area, and are they moving any faster?

Looking at the picture of your boat and the existing sail, it looks pretty maxed out with sail area. I can totally see the advantage of storing, launching and transporting a 10' boat, but unless it is ultra wide, it strikes me as a one person boat. With two people, is the transom immersed at the stern? That would create drag and if it is a pram and the bow transom is also in the water that would make it much worse.

Laukejas
03-10-2017, 11:38 AM
I've only sailed once in person on my brother's yacht, and everything I know about sailing is from the internet, so take my words with a grain of salt. Maybe my comment will inspire a bit of discussion.

Sounds like you do your sailing in light winds. How does your sailing and your boat's performance compare to the one in the video: https://www.youtube.com/watch?v=Cz9lMLKmQuY&feature=youtu.be It is a Brooks DragonFlyer 3.2, a planing dinghy almost the same length as yours with even less sail area. It comes with either a 59 square foot or a 70 square foot sailplan, and I don't know which one is in the video.

Maybe if the winds are really light, the yard won't bend so much and you could use the lateen with a thinner yard after all. Have you considered bamboo poles? They are hollow and if you can pick through a pile you can sometimes find some straight and light ones without splits. They are not ultra permanent but are used in the Pacific for masts and yards. I've gotten some just under 7' long with a diameter of ~1" to 1.25" and they are stiff enough to make serviceable oars with a fairly small blade. Once my boat is finished I plan to use similar poles as mast and yard for my first solo sailing experiments.

But maybe going back to square one could mean a different boat altogether.What are other people sailing in your area, and are they moving any faster?

Looking at the picture of your boat and the existing sail, it looks pretty maxed out with sail area. I can totally see the advantage of storing, launching and transporting a 10' boat, but unless it is ultra wide, it strikes me as a one person boat. With two people, is the transom immersed at the stern? That would create drag and if it is a pram and the bow transom is also in the water that would make it much worse.

Looking at that video, I'd say my boat performs worse. I optimized the hull for extremely low speeds, so that I can beat the fleet in these 0.1-0.5 knot winds. Other boats struggle just as mine does in these winds. Last regatta I sailed in, I finished 3 races with 5th, 4th and 6th positions in a mixed 30 boat fleet - Lasers, Cadets, 420s, 470s, catamarans, cruising and racing yachts, etc. So I think my boat performance is very decent in these super-light winds, but if I shave down my spars to save weight, I might break something once the wind picks up. I already broke a boom on the previous summer.

No, at this point, I do not have finances, nor the time to make a new boat. I'm pretty happy with my current one. I just want to make a competitive rig that wouldn't weight so much... I mean, with my current lug, the boat won't stay upright even on the shore, even with no wind. All it takes for a boom to pivot to one side, and the whole thing comes crashing down. It's as stable as a sailboard... And when the boat capsizes, it's barely possible to lift the mast out of the water by stepping on the daggerboard - there's just not enough leverage, the rig is way too heavy. Which is one of the many reasons why I want to cut the weight while preserving as much of the sail area as I can.

The boat was designed for two people by displacement - the transom is not submerged. But for any real performance, I have to sail alone.

Zuri
03-10-2017, 02:36 PM
I'm probably too late in this discussion, but for joining spars or shafts:

How about using the finished spar as a mandrel to form a sleeved collar made from epoxy and a few windings of fiberglass tape (or carbon fiber fabric). It can be permanently attached to one spar. Use a release agent on the other.
After it sets, it can be further shaped, sanded for a smooth profile and a locking pin added.

Travis.

Laukejas
03-12-2017, 10:47 AM
Todd, if I may ask, where can I find these spar formulas by Iain Oughtred? Some book of his? I want to educate myself so that I wouldn't need to take other people's time every time I need to dimension my spars. I know the Skene's formula for sizing masts, but I can't find anything about other spars, especially in traditional rigs, but what you said sounds promising.

Todd Bradshaw
03-12-2017, 12:19 PM
They're in his book "The Clinker Plywood Boatbuilding Manual". He seems to be one of the few who give formulas for small-ish boats and have real world examples out there sailing around successfully. I've been suggesting them to my customers building spars for better than a decade and they seem to work pretty well. This makes my job more predictable, since sails have to compensate for spar bend and that's a lot easier if you have some reasonably consistent idea of how much they will bend.

He doesn't give figures for lateens, so I'll generally suggest something a little bit lighter than something like a lug yard or boom would be to reduce weight aloft. A lateen yard always has to be a pretty big compromise. If you allow for all the bend that can happen when sheeted hard in a high wind you could easily be adding a foot of excess luff round as a bend allowance, even on a rather small lateen. Unfortunately, all that extra round would make for a super baggy sail when in lighter air, so you have to split the difference based on your best hunch.

Laukejas
03-12-2017, 12:30 PM
They're in his book "The Clinker Plywood Boatbuilding Manual". He seems to be one of the few who give formulas for small-ish boats and have real world examples out there sailing around successfully. I've been suggesting them to my customers building spars for better than a decade and they seem to work pretty well. This makes my job more predictable, since sails have to compensate for spar bend and that's a lot easier if you have some reasonably consistent idea of how much they will bend.

He doesn't give figures for lateens, so I'll generally suggest something a little bit lighter than something like a lug yard or boom would be to reduce weight aloft. A lateen yard always has to be a pretty big compromise. If you allow for all the bend that can happen when sheeted hard in a high wind you could easily be adding a foot of excess luff round as a bend allowance, even on a rather small lateen. Unfortunately, all that extra round would make for a super baggy sail when in lighter air, so you have to split the difference based on your best hunch.

Thank you, I'll try to find if I can get that book all the way to Lithuania.

I guess I have no choice but to scrape my lateen sail idea. With a yard that heavy, it doesn't justify the loss in sail area and loss in performance (especially since the sail is boomless). Sunfish-type lateen won't work on this boat, the mast is too far aft, and the required head clearance will eat up sail area even more. So I decided that I will stick with my current balanced lug, but I will re-build the yard, making it a rectangular box section. My current yard is 300cm (118") long, 50x40mm (2x1.57") rectangular solid. If I make something like 56x30mm hollow with 9mm (0.35") walls, I will save almost two pounds of weight while retaining the same stiffness. But maybe my yard is too stiff already. It doesn't seem to bend too much, even when I pull down hard on my 4:1 downhaul system. I probably overbuilt it - I just eyeballed it to be on the safe side, since I didn't know what kind of stiffness is needed here, exactly. I'll try to get that book, check the formulas, and see if I can save even more weight aloft. Thank you very much.

Chip Chester
03-12-2017, 06:37 PM
Thoughts from a non-sailor, who has to look up half the vocabulary of this thread...
If you put two taper-style joints nearer the ends, leaving the middle section one solid piece (of your designated length), would that help with strength in the middle where I presume the most stress would be at the connection to the mast? And if you do a basic sleeve joint, or a tapered socket affair, you could hold the joint together with a steel cable thru the middle, with tensioning nuts at the end. Making the whole thing hollow would be easiest for internal cable, but it's still doable if not by pinning the cable in the non-hollow segment.

What are carbon fiber sailboard masts tapered?

Chip

Peerie Maa
03-12-2017, 06:48 PM
Thoughts from a non-sailor, who has to look up half the vocabulary of this thread...
If you put two taper-style joints nearer the ends, leaving the middle section one solid piece (of your designated length), would that help with strength in the middle where I presume the most stress would be at the connection to the mast? And if you do a basic sleeve joint, or a tapered socket affair, you could hold the joint together with a steel cable thru the middle, with tensioning nuts at the end. Making the whole thing hollow would be easiest for internal cable, but it's still doable if not by pinning the cable in the non-hollow segment.

What are carbon fiber sailboard masts tapered?

Chip

You are over thinking it. The throat and peak lashings tensioning the head of the sail will hold the joint/s together.

Rumars
03-12-2017, 07:45 PM
Laukejas I think that to get the weight lower you need to go to carbon fiber. Unfortunately a 100% carbon windsurfer mast in the required lenght is expensive, but it weighs only 2-2,4kg. One possible option would be to look for broken masts and join two top halfs toghether to make the antenna (the yard). In traditional wood construction the two halfs are simply overlapped and tied with ropes.
You also do not need to have the mast vertical. Most latin sails have canted masts to bring CLR and CE in the propper relation. On small boats the hailyard doubles as a running backstay to support the mast.

Train
03-12-2017, 08:25 PM
It seems you've already decided on the joint, so I'm a bit late here, but I'm surprised no one has suggested making the scarf joint in a sleeve (has been said), but soaking the ends in penetrating epoxy to ensure there's no swell. If you stood both parts of the spar on end, with the joints literally soaking in a container of penetrating epoxy (tall and narrow), it would soak in enough to not swell or shrink. And it would be super easy. At that point, it almost ceases to be wood, and becomes ... whatever it is. It's thin as water, so you wouldn't have to worry about build up.