Thread: GIS handling characteristics

Hi Brian

What you've just written were my thoughts exactly. Here is a pic just prior to launching our GIS roughly 3 weeks ago, which shows the throat lashing. However, I think I had the head too tight, because this became apparent when sailing that the head was luffing before the luff.

Also, I thought the sail where it is lashed to the yard was too flat. So what I need to do is ease the head lashing a bit, and this should also provide a bit more fullness there?
Attachment 141195

Hi Bruce, nice picture!

Where you have the throat lashed to the yard - can it slide under downhaul tension? If it cannot slide, then you can adjust the yard tension on its own. If it moves under heavy downhaul load then you cannot control the head tension on its own. For me it's a bit easier because the sail slides in a luff groove and just the head clew can be adjusted to the end of the spar.

Lashing along the yard it is harder to get things correct as I found last year. I think I ended up with a small loop at each grommet and then just the head lashing to adjust.

Guess head fullness is about sail rounding, if there is any broadseaming and yard bend. As youease the sail foot out the sail will become fuller. Does that help the head as well?

Lug rigs - hah........

Brian

Originally Posted by callsign222

Woodeneye, I lost a batten, but pulled the other one out since it had been mentioned maybe the battens were making the sail too flat, I was trying to get some camber into it. What does the collective think? I can add them again, I'd be happy too if this will improve things.

Another quick moment - I suggested trying with the battens out as Biting Midge and Joost had found that worked better for their sails, but I might have been completely wrong regarding your sail. People have talked about full length battens flattening the profile, but batten tension is key. With full length battens, the tension you put in them adjusts the camber in that part of the sail to a large extent. More batten tension = more camber, less batten tension = less camber. On a cat with full length battens you spend a lot of time with the rig on it's side getting the tension right in all the battens so the camber is right all the way up. (Especially if you've got a dozy old sailing school cat with half of them broken or replaced with whatever was lying around)

Rigging in the car-park: Can tell you a lot, look at the rig upright with lots of tell-tails on it, see what happens as you let the sail catch the wind, adjust something, evaluate if it's an improvement...

Also can be worthwhile with the boat on it's side and camber induced only by gravity. Sight along the sail, see where and how much the profile is, is it twisted too much or too little... Get someone good to help you - if you can, buy a good sailmaker lots of beer to look at it with you (before he drinks the beer). Remember Lug rig or not, what you are trying to achieve is the same - a good airfoil and good airflow over it. It's just that for a Lugsail some of the adjustments to get there are unique (as detailed by Brian above).

Get lots of pictures, including close ups of all the corners in case there is something else you/we're missing.

All the best,

Ian

On the batten thing. The sail for RAID41 was flat cut with only yard round. I figured there was nothing holding the sail shape in place lower down the sail. If it had been broad seamed then fine.

So, I dug out my Neil Pryde windsurfing sails and had a look at the battens. They are extruded in a crusiform shape. The front of the batten has the top and bottom profiles sanded off so the batten is flat. Load one of these battens against the wall and it takes up the most wonderful sail shape.

I went to local sailmaker and they stock the same battening. Only £6 for enough to do two full length battens. I profiled the batten the same and they worked great. Slightly odd on port with the batten against the mast but ok.

So this sail was a success. When I made another smaller one for a sail and oar boat without battens it was very poor and very unstable.

Brian

Hello Callsign,

Thanks. Hopefully on Sunday the Netherlands will be victorious again in South-Africa!

I have the same Duckworks sail as you, but rigged on the standard spars made exactly to MIK's specifics in the plans. On my spars, the sail sets nicely without any strange wrinkles.

Because there is no broadseeming in the Duckworks sail, the draft needs to come fully from the rounding of the foot and head. My sail does set flattish as the bending of the yard and the boom induced by the downhaul and force of the wind allow the boom and yard to take the same shape as the rounded foot and head.

I believe your spars are a lot stiffer than mine (the boom especially), and I think that the sail should set rather nicely when properly rigged as the spars don't bend as much and the sail is forced in a nice draft.

I fully agree with the comments made above and espcially Brian's concerning the throat being well fixed to the yard to ensure that the forces induced by the downhaul, more or less stop there.

The battens cause an awkward sailshape in my sail when the sail is on the wrong end of the mast and I therefore don't use them.

Not sure whether you have seen this rigging guide for the GIS on MIK's site:

Goat Island Skiff (GIS) - systems for lug sails and rigs - Michael Storer Wooden Boat Plans

This shows you exactly what needs to be done:
1. What helps to put tension on the sail is to take the outhauls through the eylet and holes in the yard/boom a couple of times to have a nice purchase on it (pulley system!). Seperate pieces of line for putting tension on the sail and for keeping the sail next to the boom/yard.
2. Lacing system of the boot and head according to MIK's instructions.

Best wishes,

Joost

Originally Posted by keyhavenpotter

Hi Bruce, nice picture!

Where you have the throat lashed to the yard - can it slide under downhaul tension? If it cannot slide, then you can adjust the yard tension on its own. If it moves under heavy downhaul load then you cannot control the head tension on its own. For me it's a bit easier because the sail slides in a luff groove and just the head clew can be adjusted to the end of the spar.

Lashing along the yard it is harder to get things correct as I found last year. I think I ended up with a small loop at each grommet and then just the head lashing to adjust.

Guess head fullness is about sail rounding, if there is any broadseaming and yard bend. As youease the sail foot out the sail will become fuller. Does that help the head as well?

Lug rigs - hah........

Brian

My problem is that I don't have many opportunities to sail at this time of year. It is mid winter here and bitterly cold. I have only been out once, so I'm really keen for some more action on the water, which is looking quite good for this weekend. The venue this time will be fresh water, with flat water and nice even winds and temps are forecast for the mid teens. My eldest daughter is keen and has this w/e free, so I'd really like 20 - 25 knots. I don't want much do I?!

OK, I'll make sure there is no sliding of the throat under downhaul tension. I was so over the moon with sailing her for the first time that I did not notice if this was happening. I have a loose footed sail, which is adjusted via a sheave set into the end of the boom, so the curvature is easy to adjust. However, I thought that the top third of the sail looked rather flat. With lots of downhaul, it is as flat as a piece of paper with the yard bend. I know this is desired, but I still think some curvature would be good. I think this is also a feature of Christophe's sail.

I have a spare yard and boom which I did not take any further beyond shaping to Mick's dims because they were too bendy. A little ways down the track I'd like to experiment with adding a small diamond stay brace to the spare yard to see the effect that yard bend has on my sail. Theoretically, I should be able to induce fullness through negative yard bend right through to a flat sail from positive bend.

Here is a sketch of what I have in mind. Do you think this could work? Note that the brace has been exaggerated in the drawing for clarity.
Attachment 141218

I'll go take a look, thanks Ian. You're talking about the head tiedown and the tension thing, right? The marlin-lacing for the head was removed for this picture just for clarity and show the meat and potatoes.

EDIT EDIT EDIT

I Just replied to Ian's post, didn't see the below discussion! SORRY off to read now, thanks guys you are all awesome!

OK

You are all correct. The head-clew tie down can slide up and down. The downhaul tension was running up the luff and then into the head. I now understand that I must stop the downhaul tension at all costs at the throat. I might have to figure this one out with the materials at my disposal, give me the day.

Brian, there is no cleat on the yard.

I have marlin laced the head and the foot to the sails per Mik's system, though I was thinking of going back to just tying on the individual grommets along the boom to aid in outhaul tension/release if need be.

I will use the little block on my yard for outhaul purchase, and this way I'll draw the yard in a little closer to the mast.

If this fixes 80% of my problems, I will be forever in gratitude to the amount of wisdom that is on this board. Thank you all so much!

Howdy,

With the batten question .. I would simply recommend trying the sail with and without the batten and see what you think.

With the BETH sail I get way more power with the battens out. It is quite a remarkable difference.

It does make the boat a little bit more tricky to handle as after a tack there is
no power
no power
then you hit the right angle and there is
POWER.

But try both and see what you think. Even if it doesn't work the same as for me you will have learned something about your boats.

MIK

yes ... the pic at the top of the page with the throat some distance away from the surface of the yard will mean the sail is excessively flat.

Like the GIS rigging page shows

Left method is wrong. Right method is correct. The reason the right is correct is that the sail cannot pull away from the surface of the yard or boom.

Both lashings at each end of the boom and yard MUST be like this so the corners of the sail cannot move away from the surface of the spar. This is recommended for those who just want to go sailing in a properly set up boat.

For those who want to try and find the BEST way of doing it then they might want to adjust the tension at the back end of each spar.

The FRONT lashing is as above. But the back one could be adjustable.

If the back is adjustable then there still needs to be a separate rope around the spar so the sail cannot move away from the surface of the spar when the tension is eased. if it does The sail will get flatter and it will put more load on the other eyelets and the sail will twist more than it should.

BTW .. good discussion!

MIK

Hi MIK, would you consider that it might help if your drawing of the lashing method included an added section of how to lash the throat clew to the front of the yard.

It's the most important lashing and easy to get wrong. Could it show how the clew needs fixing to the hole in the yard closely, with line over the top of the yard to take the strain. As you say, keeping it close also allows the fullness to take shape.

Most builders may be new to lug rig and since it's taken me years to learn all this stuff, it might be nice to save your builders some time in what has to be an already steep leaning curve.

Back to the Tour de France - yesterday was one of the most amazing days I have ever watched.

Brian

Thanks Mik for chiming in, good points all around, batten wise too. I will work on it this afternoon. Unfortunately I am limited with line, decent line is well over an hour away, and I have what I have. I will make something work in the meantime and post pictures later.

Mik, you drawing is good, and "technically" that's what I did. Maybe there wasn't enough emphasis about no-motion and tightness of the sail, especially at the throat area. I got things as tight as I could, but the downhaul overpowered and stretched the tie-downs. Once I get some more spectra/dyneema we should be good! I'm excited.

Chalk it up to me having never using a lugged rig, but I appreciate the clarification. A little breeze if we get one and I'll take some good pics in my driveway.

WOAH simultaneous suggestions! Great minds, great minds!

Ok, going to rig her up right now.

Its tough, I can't find low-stretch stuff around here, I just have my limited supply for my halyard and downhaul. I'm using some crap polypro stuff I found, I know I know a temporary solution at best, but it's thin enough to get many wraps around the head clew tiedown. Everything else is low-stretch nylon, but not the good stuff. Here goes nothing. I'm taking her into the street so I can get different angles in the breeze up here on the hill.