Desperate to sail 2015

The physics of lug are becoming more clear, but I still can't figure out how to make it work.

If halyard is attached to the middle of the yard (center of gravity), then it's obviously the pivoting point for the yard. With some friction between mast and yard (and lashing to keep them together), the peak of the yard goes up, and the forward end goes down. And then it gets stuck in that position.

So how does one raise the lugsail yard without these problems? Especially high-peaked yard, to which halyard cannot be attached to the middle?

For example, here http://3.bp.blogspot.com/-TplyERYW_5Y/UBfLwnNUd-I/AAAAAAAABDw/OejC2MhWA1w/s1600/Aber+Sailing+Ricoh+029.jpg

This is pretty close to my design. Can someone explain how can I raise the yard without these complications with a single halyard?

 

Laukejas,

I have been away from my computer and did not see your trials until now. for the yard to hold up the sail on a lug you have to attach the halyard near the center of the yard, and you have to have a portion of the sail ahead of the mast to blance it out.

I have not found the lug rig that user friendly when hastily made, perhaps others have made it work, but I did not spend the time to work it out. I have made simple modified junk rigs work will well. cut flat, with just three full length battens, and the plan form was roughly ellipitcal. no boom, just used the bottom batten (though a boom held in place with a snotter might be helpful to allow better adjustment). we have won a number of local "build and race" type contests with this simple rig without any testing or adjustment. it just takes three flexible full length battens, and duct tape and some string. No sewing required at all! I put some small triangular pieces of plywood in the folded over sail at top and bottom where the halyard attaches, and the down haul, and drill a hole through it to tie to. this spreads the load out over more fabric to make strong attachment point. I also but caulk or adhesive between the plywood and trap cloth, but mostly it is the several layers of duck tape that spread the load over the fabric and make the attach point strong.



you can get some camber in it by folding a hem around the perimeter and running a string around it, pull the string tight and it kind of "cups" the sail to give it camber. but I have not found this extra work necessary, using it flat seems to work just fine. far better than all the other improvised sails in the races we entered with it.

 

Thank you for coming to help, Petros. Problem is, I tried every possible combination I could think of, and none of them raised the yard properly. Either the peak stays down, or the throat goes down after raising the peak. Even if I attach halyard to the middle of the yard.

Any idea how to fix that?

If it's too difficult, what rig would you suggest with following spars: 245cm mast, 230cm boom, 330cm yard? I need maximum possible sail area with maximum reaching ability. Something like 6m^2 and above would be preferable. I'd do lug, but as I said, I cannot raise the yard that high up as in the screenshot before. I tried sprit before, but it only gives 4.3m^2, and that is too small for the light winds I got here. What would you do if you had what I have?

P.S. I will add battens if I manage to find something that could work for them, but right now I need to decide on how to squeeze maximum sail area from these yards...

 

If you are going to go this route, use the smaller spar as the yard. You'll have less area, but it will set much better.

With what you've drawn, there will be so much tension on the luff that the aft portion of the sail will sag, and, if it has a bolt rope or edge tape on it, it will bag.

Not only that, but how are you going to cut and tape this thing together without a good flat surface to work on?

High aspect ratio wins races, where slight improvements in performance make a huge difference.

Not so high aspect ratio sails work more than well enough.

The dinghy I race up wind with my raft had a higher aspect ratio sail than I did. I beat him anyway.

Now that I think about it, a balanced lug may work best for you.

I'd use what was the sprit as the boom. and what was the boom as the yard. That way you have less uncontrolled sparage swinging about.

Maximizing sail area does no good, if the sail becomes a useless lump when set.

I designed and built the Asthetc No when I was 18. I was painfully aware of what my skill limits were, so I designed around them.

You could make a sette sail, with the sprit as the yard.

Due to your very short mast. the end of the yard will come quite close to touching the front end of the boom, making it look almost like lateen.

But this is good as you can have more spar length in front of the mast, without having a lot of sail area in front of it too. This will put less bending strain on the bits of spars behind the mast, making for a sail that will probably set better and will be a lot easier to control.

 

Sharpii2, you suggest switching yard and boom? That creates very odd looking sail, and small too. It will be as long as the whole boat! Somehow that doesn't look good... Here, see for yourself:

http://static.dyp.im/LLfjcbmxTm/82f8e9afb9549864fce1cd8654f11394.JPG

I realize area and aspect ratio are nothing if you can't handle it, but remember, the boat's hull isn't designed for sailing. The daggerboard is also in question. There is no proper rudder. All these things don't contribute to weatherliness. I need at least one component that would compensate for these shortcomings. That's why I wanted higher aspect, since these sails are said to work better when reaching.

I don't know, but my gut feeling says that I shouldn't switch spars... But how do I make sail most weatherly with what I have?

P.S. I mentioned earlier - I now have flat space to work on

P.P.S. What about this? It seems much more like lug sail. Area is only 4.14m^2, though. Will it set better than the sprit rig?

 

Using a spreadsheet I designed for this purpose, I tried using first the the sprit and then the boom as the yard.

I allowed 0.3 m for head clearance, which whittled the useable mast length down to 1.7 m. Then I allowed about 0.2 m for the halyard pendant, which seems about right.

With the sprit as yard, I ended up with 3.84 sm.

with the boom as yard, I ended up with 4.38 sm.

With the boom as yard version, the butt of the yard ended up just 0.69 m above the end of the boom. The yard is set at a 1:1 pitch (45 deg. angle), which nets the maximum sail area per mast length.

Though 4.38 sm in sail area is not generous, it is quite sufficient to move a 175 kg boat around. It gives an S/D of 14.

About half the yard is going to end up in front of the mast, as well as about 0.81 m of the boom.

 

I know it may look odd, but it gives you the maximum amount of sail in a rig I'm pretty sure will work.

Your other picture is somewhat close to what I came up with. It will work as well, but yield less area.

Attached below is a sketch of what I had in mind, with the 2.3 m boom being the yard.

Yeah, it still looks dorky, but I bet it will set better and furl better than the sprit being yard alternative.

 

I modeled what you wrote, sharpii2.

Here it is:

http://static.dyp.im/RVith7Cv2I/b415fcfc9f33cee0eea48cc348ae162a.JPG

By my calculations, sail area is 4.08m^2. Are you really, really sure about your spreadsheet on this?

The clearance in the screenshot might not be correct, the boat is crudely modeled there.

But what worries me is the size of the sail, and the shape. It definitely doesn't look like anything I've seen. Maybe a dipping lug, but not balanced... The mast will cut off airflow for a lot of sail on the bad tack here.
Did you really had this in mind?

P.S. Displacement is more towards 250kg figure - I will take a passenger in 3 days.

 

Yeah, I have thought of that. But its low aspect ratio will help when it comes to that. This is because there will be time for the airflow to reattach, once it's disturbed by the mast, on the bad tack.

Also, a slit can be cut in the way of the mast, and the new luff behind it can be laced to the mast. This makes the bad tack less bad, but it also makes the good tack less good. I would only do it for chafe reasons.

A thing to understand about high aspect ratio surfaces is that they stall at a lot lower angle of attack and are far more sensitive to irregularities in the air foil. IMHO, it takes far more skill to make a workable high aspect ratio sail than a workable low aspect ratio one.

Also, The aspect ratio ((S^2)/A) of this sail is 1.22, which isn't to bad considering.

The discrepancy of sail area between my calculations and yours may be due to two things:

1.) Your drawing has the butt of the boom further aft than the but of the Yard, and, more likely
2.) you subtracted 5 cm from the boom and the yard for the purpose of allowing for an out haul. I didn't think this necessary for a flat cut sail, so I had the sail cloth come to the very ends of the yard and boom.

My spreadsheet divides the sail profile into all right triangles and rectangles. It also assumes that the front of the boom is going to be right below the front of the yard.

 

Okay, I see. Tomorrow I will try out both options on the boat with measured ropes acting as edges of the sail, and will see if lug raising works, as well as what are hull clearances.

Of course, I can go back to the sprit rig - it would provide more area compared to lug, now that I know that I can't really peak up the yard that much.

If anyone has any comment, please share... I must start work on sail tomorrow.

P.S. How does this lugger keep the yard so high peaked with halyard being attached so forward (not middle) of the yard?

 

The yard is actually held up by the halyard.

Since the lower, forward corner of the sail is held down at the bow, and the yard crosses the halyard, the yard acts as a lever. It would do the same if the lower corner of the sail were attached to the mast, as long as there is some yard that is past the halyard. This would be true even if all the sail were behind the mast.

The halyard attachment is the fulcrum. Some gaff rigs (usually with very short gaffs) have just one halyard and peak up just fine. (see attachment)

As you can probably guess, the amount of yard in front of the halyard, being much shorter than that behind it, puts terrific tension on the leading edge of the sail. this is good, as it keeps the leading edge straighter.

But the sail cloth and re enforcements must be strong enough to stand the load. The halyard too is under the same load. If this leading edge stretches too much, the sail will lose its profile shape.

Usually good windward ability with sails with long, clean leading edges, require a great deal of tension.

This is why lug sails made of poorer materials (like the one I sketched for you) usually have much shorter leading edges and have much more of the yard in front of the halyard. It's a design trade off.

 

I prefer this one that you have drawn: http://static.dyp.im/Ct36zfxGnR/4994993023da4b4d714ffa6742f98d47.JPG

Just try to tweak it to give the maximum area.

You certainly don't need that much space above the yard though! You can pretty much tie the yard straight to the mast, especially if the mast rotates.

For your rope testing: remember that a sail is a 2 dimensional shape, not a set of 1 dimensional ropes. To model the sail more accurately using ropes, try putting a cross of rope across the sail as well. (from the tack to the peak, and head to clew). I'll bet now all your rope sails will set.

I think I just had a good idea. I'll get back to you soon.

 

Well, my good idea was to extend the mast using the boom (permanently, scarf joint), and have a massive boomless balanced lug. You would need to put a traveller or something on the back of the boat to get a better sheeting angle. You could even add a boom if you found another stick.

Looking at the pictures again though... it would be very unstable if the wind pick up!

The other advantage of a boomless sail is it should help with your downwind steering problems. Upwind it should make little difference if you design it right.

Maybe you have time to make a nice rudder ??

 

Tdem, extending the mast doesn't seem like a good idea here... I tried it before, and it was a huge failure. Very unsafe in high winds, at least it seems to me. Thank you for your idea, but I'm a bit afraid to do that.

Sharpii2, thank you for explanation. But could you (or someone else) explain me how this works (it's Goat Island Skiff). I tried re-creating it just now, and what happens is that the yard slides all the way forward until the pulley on the yard reaches the pulley on the mast top. I see no more additional lines that would prevent yard going forward...

P.S. And in this design I see no lashing between yard and mast at all! What prevents yard moving around?

 

The yard will find its own equilibrium when the wind pushes the sail. On the goat island skiff, remember that there is also a downhaul which prevents the sail going all the way up. Also, the yard is supposed to go forward! Put the pulley about where you want the halliard to "attach" It is rigged that way so when you release the halliard the yard comes down easily.