Thread: GIS handling characteristics

This has some relevance too ...
https://www.woodworkforums.com/f169/f...4/#post1171871

MIK

Good with the toe straps. The plates to hold them down can be epoxy screwed into the framing at the base of the bulkheads.

One important factor is to keep them off the floor to make sure you can get your feet under after a tack. The normal way is to use a shockcord loop that goes higher up the bulkhead and passes under the toestrap to hold it up off the floor.

MIK

Originally Posted by Boatmik

Good with the toe straps. The plates to hold them down can be epoxy screwed into the framing at the base of the bulkheads.

One important factor is to keep them off the floor to make sure you can get your feet under after a tack. The normal way is to use a shockcord loop that goes higher up the bulkhead and passes under the toestrap to hold it up off the floor.

MIK

I did find that being round that it was quite easy to get the feet under and kick it up, but shock cord that can be unhooked easily would be good so that it lies flat when not needed.

And yes, the screws are set in poxy

In the past I would have specified bolts only ... but the screws, or better metalthreads, set in epoxy seem to be at least as effective and don't require access to the other side.

MIK

Originally Posted by callsign222

I think I'm carrying forward about 15cm more than I should. 40cm is the rule, I'm probably around 55cm. I will change that too.

Yes, 55cm is an awful lot of sail ahead of the mast. Even 40cm is a lot to me. 16". Our normal amount is around 10"/12" or 25cm/30cm. My current setting is 0 cm. I have the downhaul actually fixed at the front of the boom and use the kicker (vang) tension to pull the boom forward. By playing with the two I can set the boom exactly as far forward or back as I wish.

Brian

In a sense, on the scows it moves to something more like a standing lug, but doesn't suffer the disadvantage of losing the vanging effect of the downhaul because of the effective separate vang/kicker.

I would be guessing that modern sailcloths keep the centre of effort much further forward than the original sails so that moving the rig back helps bring the boat back into balance too.

I started windsurfing during the era of dacron sails. With every gust in stronger winds you could feel the centre of effort move back a foot or more because of sail distortion. In medium winds you could sail with your hands about a foot apart all nicely balanced. In the strong stuff you had to put your back hand a foot or maybe further back so that when the centre of effort went back in a gust you still had the back hand aligning with it pretty well. When better sail cloths came into windsurfers it was very different and you could keep your hands in one position much more.

So I would be guessing the centre of effort of the scow sails has moved a long way further forward compared to when they were designed.

MIK

Originally Posted by Boatmik

so that moving the rig back helps bring the boat back into balance too.
So I would be guessing the centre of effort of the scow sails has moved a long way further forward compared to when they were designed.

MIK

It must be true that the centre of effort has moved forward. As is usual with life though, we spend all our time trying to get the rig as far forward as possible to balance the boat! My mast is well past vertical.

The reason I think is that the old Scows had heavy metal plates, controlled by a horrible metal handle with teeth cut into it so the plate could be set at different depths. Frightening thing. I guess the plate never went lower than 45 degree, whereas our new foiled boards are only a little short of vertical. So the centre of effort of the foil is now further forward.

Brian

Bruce,

Thanks for the suggestion of the windvane, but I'm a "feel the wind on my face and back of the neck" kind of sailor--- for better or worse!

Originally Posted by callsign222

Up goes the sail and I start taking off again, but a huge gust comes along and slams me. I swing the bow into the wind and dump the sail but I can't stop the boat from going over, it just goes. It's like watching a train wreck and you're powerless to stop it.

Hope you don’t mind me continuing to make suggestions, I’m keen to see you try them all out and report which are worthwhile before I get my GIS on the water!

Your comments about the train wreck happening remind me of my experience sailing Hobie 16 cats on a mountainous lake in Germany. (I sailed and taught sailing there 6 days a week for about 4 summers). Segelschule Rehbach Edersee

What follows might be old hat, but might be helpful.

What gets you when you’re sailing a light, fast boat in gusty conditions isn’t so much the increased wind strength when you’re in the gust, but the rapid change in apparent wind angle as you hit the gust. What follows is from my experience with a Hobie 16, but maybe applies to the GIS. I’ll talk about sheeting in and out, leave aside the arguments as to whether you should be doing so with the mainsheet or traveller on a cat as that doesn’t apply to the Goat. I’ll also say boat, when I’m meaning cat or fast light monohull.

In a boat which can travel at or faster than the wind speed, the apparent wind moves well forward as you accelerate and so you sheet in for the apparent wind direction. You’re humming along, power is just right for the boat, windward hull is just about flying/ the boat is planing.

Now you hit a gust, the true wind is stronger, so the apparent wind angle moves aft of where it was. At that moment, the sail is still sheeted in, so the flow over the sail stalls, and the increased force of the wind is all sideways. That’s not good, but it gets worse. Because flow over the sail is stalled and there is no forward drive, the boat slows with the increased wind strength. This causes the apparent wind to move even further back, it’s full in the side of the sail now and you’re going over. You can let out the sheet all you like as the boat heels, the apparent wind angle is moving back quicker than you can get the sail out if you react to what is happening. “Watching a train wreck” is a good metaphor for what’s going on.

Now let’s get the boat back upright and try that again:

As you hit the edge of the squall, you sheet out exactly in time with the changing apparent wind angle. The wind is stronger, but as the sail goes out, the direction of the force in the sail moves forward. There’s more force, but more of it is pushing you forward, less is pushing you sideways. The boat accellerates, and the apparent wind angle moves forward again, so you can get some sheet back in and hold the speed through the gust. Timing is critical in a fast, light cat in a mountain lake gust – the wind increases 50% or more in less than the length of the boat, so you can’t react to what’s happening. If you time it right, you only have to sheet out maybe 20cm, then you can pull it in over the next couple of seconds as the boat speeds up. Half a second too late and the sail is stalling, it’s all over. It doesn’t help to anticipate too much, as if you ease the sheet too early, the boat is slowing as you hit the gust and that’s bad for all the reasons above.

All the above is most relevant in cats/other boats that are light, and able to go fast relative to the wind speed, and in mountain lake conditions where the gusts have a “hard edge”. It’s not so much how much the wind increases, but how quickly. In a gust on the ocean where wind speed increases over several boat lengths and/or in a slower, heavier boat you mostly have time to react to what’s going on and sheet out and/or steer closer to the wind as you feel the gust make the boat heel.

All the best,

Ian

Ian, that was really good. Well written. Thank you.

I will report back tomorrow.

OK, so I'm having a quiet morning at work...

Originally Posted by callsign222

My yard has some nice medium flex to it... not too much, not too little. I don't have exact numbers but I could get some. It's rectangular too. It's a smooth even flex throughout the spar. Its not tapered, though... ?

I wonder if there is room to take a leaf out of the 18ft skiff book. If you order a mast for one of those things, they ask you for your all up crew weight, then they vary the layup so the stiffness matches the crew weight - stiffer for a heavier crew, softer for a light crew. Maybe it's worth doing the same for the yard on the Goat - especially if your most likely crew weight / main use is different from normal.

A square section is 70% stiffer than a round section so if your yard is square at 40mm, it's probably at least 70% stiffer than anyone elses, more so as it's not tapered. It's probably exactly right for 2 up sailing, but maybe if your main use is single handed and you're about 70kg/150lb, it's worth having a much softer yard that bends more/depowers the sail in the gusts.

Edit: Christophe has just posted the dimensions and stiffness measurements for his yard below, his 35mm x 35 mm square section yard has almost the same stiffness as the standard 40mm dia round section specified in the plans, so the above paragraph doesn't apply to his rig.
Ian


Joost wanted a stiffer yard sailing 2 up hiking hard and trying to keep up with a Ness Yawl to windward on Loch Ness, but apart from that sort of sailing you might be better taking a plane to your yard than lugging 100lb of sand around.

I have another alternative to carrying around lots of sand, you could try a serious training program involving consumption of lots of these:



Let me know how you get on with this one!

Ian

I'm not interested in a heart attack, just a fast boat.

My spar, while squarish, is still kind of bendy. I will go bend test it right now. What do you say, 25lbs/12k at mid-point, is that what people were doing?

Originally Posted by callsign222

I'm not interested in a heart attack, just a fast boat.

My spar, while squarish, is still kind of bendy. I will go bend test it right now. What do you say, 25lbs/12k at mid-point, is that what people were doing?

It doesn't matter too much how much you put on it, as long as you record how much weight you put on it and how much it bends as it can always be converted to cm bend per kg or similar. 10 or 12 kg /25lbs seems about right.

Ian

OK, in my very un-scientific bending experiment I get the following results:

Approx. 25lbs bends my 35mm x 35mm spar:

2" (5mm) if suspended from the head to the peak of the sail

2.5" (63mm) if suspended from end of spar to end of spar.