Jib Physics & "the slot effect"

Yea Tony I think you are correct, the more I think about it. Even if the stay line is not tied (or up against a knot) at the top, the excess force is still directed downward on the mast vs forward, (like the center bar on a playground teeter totter works). Hobies spinnaker system appears to protect the mast from damage (too much forward force) but still allows the mast and mainsail to operate like normal un-impeded in it's normal bendy/floppy fashion, clever setup.
FE

Have any of you tried doing this with 2 sails? Looks like you could create a better upwind sail. http://www.elvstromsails.com/images/zoo ... eDec15.pdf

Thats pretty much what I have
FE

But with your jib, right Bob? Not the main.

Bob I am thinking you can make this work and show me how to do it.

Bob, I respectfully beg to differ. The major aspect of the sail design mentioned in the link is that EACH SIDE of the wingsail surface can largely be controlled independently, by having twin tracks on the mast, rotating the mast counter-intuitively, and varying outhaul tension (plus of course the conventional controls such as mainsheet, halyard tension, boom vang, traveller etc).

You can immediately see that the wingsail they are describing is vastly different from yours.

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Tony Stott
2012 Tandem Island "SIC EM" with Hobie spinnaker

Tony:
You are correct, I didn't read the article, I just looked at the pictures and saw it was a soft double sided sail (like mine) vs one of those giant rigid wing sails that everyone pictures in their mind when the word wing sail is mentioned.
Mines just a jib, I don't need all that extra stuff because my sails are not my primary propulsion source (the are just power amplifiers).
As you know on a real sailboat with the sail as the primary propulsion source, you need all those adjustments to suit all the different conditions required.
My setup uses completely different physics from anything else in existance. I figured after 3000 yrs of sailing with pretty much no changes, I thought I would just come up something new.
My boat is a peddle boat not a sailboat (works on different principles).
FE
Edit: basically my boat works like a piper cub, if the engine quit you fall out of the sky, with my setup if I stop peddling, the boat stalls and stops.

Tony I think the tracks are served to raise and lower along with keep the sails 180 apart. Then I would guess there are some other control lines. It seems that this could be possible with an Island. The inside sail would have to be mounted at 180 and have some perforations to inflate the area between. It would also have its own main line although you might be able to adjust by just adding adjustment points along the other sail. Anyway it is an interesting thought and it would appear it would be a better upwind sail. That could still be furlable.

Bob,. the way I understood it, the tracks have a distance between them. If the mast is rotated AWAY from the wind direction (eg in the opposite direction compared to conventional rotating masts, where the leading edge of the mast points towards the wind direction), the actual airfoil shape of the wingsail can be adjusted for conditions.

Rotating the mast the "wrong" way tightens the windward sail panels while simultaneously adding depth to the leeward panels. So the airfoil created by the two sailss gains a deeper chord, developing more lift. As wind strength increases, rotating the mast slightly will change this airfoil to a lower profile.

This ability is a serious advance on even "conventionasl" wingsails

_________________
Tony Stott
2012 Tandem Island "SIC EM" with Hobie spinnaker

Tony:
I read the article, finally, you are correct, their wing is nothing close to either my furlable wing jib design or my furlable main wing design (two distinctly different designs). Both mine work more like a parafoil wing (fills with air like a baloon thru slits in the leading edges), and forms an assymetric Eppler 420 airfoil shape.
Different concepts all together.
FE

very interesting subject though it started concerning the "slot-effect" and turned into the wider "fore sail systems" subject.
It seems that many of us wonders about adding or not a fore sail to hour island, and which one. The new hobie kit is a ready solution but maybe not the best for all of us.
What makes the difference is that have different initial requirements. Some have the need to make very long trips to reach some destination, some sail in places where the downwind sailing is more rare than the upwind (this is my case), some sail in big lakes, other along the coast, some of us really like the speed and taking the boat to the limits, some others just would like to have improvements just in the "slow wind" situations when moving at 2/3 knots could be too boring and this is my case. Another difference is also on how much we want to "modify" our boats, drill holes, add ugly aluminium bowsprits and so on.
A solution that is good for my requirements maybe is not the best for others. The best way to make a good choice is to know all the issues and understand what is best for us. reading all your interesting comments filled my brain with informations but I didnt yet undesrtood what is best for me.
Maybe you can give me some suggestion.

My requirements are: more power in light winds but not in average or strong wind, I am absolutely ready to furl/remove the fore sail when the wind reaches 10/12 knots cause then i am very happy with the mainsail in those conditions both upwind or downwind. The use of the sail only in light winds should also reduce the risks cause the pressure should be lower, right? this makes the "easy to furl" another requirement.
I am not ready to make incredible modifications or drilling to many holes, especially not to mount an aluminium bowsprit that transforms the boat into "robocop". Therefore I dont need to have both a jib and the spi. since i would get only one sail and since i suffer more in the upwind i would prefer a jib/genoa to a spinnaker. Moreover i think that a genoa not only works upwind but can help also downwind. For all these reasons I am more attracted by a genoa. I know that the genoa could overpower the boat but, as i said, I am ready to furl it as the wind gets to 10 knots. Fot the tacking issue i dont think this is a problem cause as somebody else already wrote, when u tack and u are towards the wind the sail is "soft" and should just "caress" the mast when passing on the other side. this is what happen when i sail with the dinghy.

Now the question is. what is the best rigging or which rigging would u choose if u would install just genoa/jib and no spinnaker? is the same hobie-kit circuit still the best solution? thanx

I got my mast top swivel. It looks almost nice enough keep it in my wife’s jewelry box, though she might notice it as it is a bit bigger than what she has now. As far as strength is concerned, it is a 'bombshell', but it swivels nicely on greased bearings. But, in testing the contraption with my jib, it didn’t work quite as I had expected. I may be doing something wrong, or not understanding something, or have wrong expectations. I am not sure.

Problem with ‘plan A’ (I am not using pulleys, but surfaces that have minimal friction):
In order to tighten the jib enough to furl it, I tighten the one line (halyard, back-stay) only to have the mast pulled back by the tightening. The mainsail at this point is still furled up and no control line is attached. With the mast pulled back and therefore bent, it is much more difficult to furl. Not only that, I don't know if I like the idea of the mast bending back just because I tighten (and not very tightly) the leading edge of the jib. Even pulling forward (jerking it forward with my hands), the mast doesn't move back to straight. I think it bends because the mast wants to have equal pressure on both sides and has to move aft to be in the comfortable center spot. Confused, I tried 'plan B'.

‘Plan B’:
When I designed the mast topper I included a cross bar, just in case I might want to run a support line down to the amas. There is a eye strap just in front of the handle on each ama. Watching Penguin Man’s 2011 EC Youtube videos it looked like he used them with his jib setup instead of a back-stay. The location of the eye strap is a little aft of the mast. I adjusted the side lines to be just barely snug with a straight mast. So with more forward pull from jib (when tightening the luff with the halyard), the mast moves forward a little more, but not much.

I ran a halyard from almost directly below where the head connects to the mast topper. If I pull the halyard tight, and the mainsail is loose, the mast bends forward just a little but not nearly as much as it bent back in ‘plan A’. By adjusting the tension of the jib halyard, and the control line of the mainsail, I have full control of the bend of the mast and tension of the sails. One limitation is that both sails are tight or both are loose. But the same is true under ‘plan A’, and I am guessing that in real life it is not a limitation since I probably want the mainsail loose when I want the jib loose.

Using ‘plan B’ the jib furls very nicely and the mainsail also furls without any difficulty (though currently in opposite direction). So, as I need to, I can easily adjust the size of both sails.

Questions:
- Using ‘plan B’ Are there likely points where I might get into trouble or be at a disadvantage?
- Is there an advantage or disadvantage to both sails furling in the same or opposite directions.
- From what I have written under ‘plan A’, is there something that I may be doing wrong or differently than others of you using the one line (back-stay, fore-stay, halyard) system?

I am still waiting on some hardware to get the lines set up the way I think I might want them. They should be here any day. When I get the hardware installed I will shoot some pictures or video so you can better visualize what I am talking about.

For now, here are some pictures of the 'jewel'. It weighs in at 1.75lb, and not as difficult to put up the mast as I was anticipating. If I do end up using a back-stay ('plan A'), I may add a piece of square aluminum tubing, supported by the existing support, to the top to extend it beyond the longest batten. I do need to furl it to the batten, or close) for a jibe.

...mark...

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...mark...

Enjoying a 2012 TI
w/ hakas, a stainless steel
mast topper & furling jib

Mark:
Nice looking mast topper.
If you go to the ultimate Tandem island (spinnakers, jibs, etc) thread you can read all about my escapades, and my mast topper (warning it a really long thread).
If you look at the bottom of your mast, you will see a pin at the bottom that sticks into the mast at the bottom. This is called a pin bearing. It is similar in concept to the jeweled movements on a watch. Pin bearing designs provide the least friction of any bearing type. I guess you could call my mast topper a 1 jewel movement (lol).

I suspect any mast topper design is going to have a little more friction than nothing at all. I can still unfurl my main ok, but I typically need to help it along the last couple turns by reaching up an spinning the mast by hand to get the sail all the way out.
I just accept it. It does help if you point into the wind so the sails are unloaded when furling and unfurling (most all sailboats do this).

If you are just running a small jib, there may not be a great need for a rear stay line, unless you using that line as your halyard. The rear stay only really becomes neccessary with big spinnakers because of the tremendous forward force on the mast base. If you look at the base of the mast holder on the hull, the only thing preventing forward and aft movement of the mast base is that tine 1/4" threaded stud, which will sheer off if too much forward force is applied to the sail system.

Since I have both jibs and spinnakers on my, I have two separate halyard systems, one for the jib and the other for the spinnaker. I also prefer to run everything on rotofurlers, and sometimes bring along different types of sails that I can switch out as needed. Very seldom do you ever run the jib and the spin at the same time, (jibs and spinnakers are different types of sails for different purposes).

I have run side stays before, I'm not sure they are worth the effort, one thing they do is prevent the mast from bending around too much, the jury is still out if that is a good thing or a bad thing.

My jib halyard runs off a pulley mounted about 2-3 inches in front of the main mast. The halyard line runs thru some 3/8" dia PVC water pipe so it can't fowl and wrap around the main when furling the main in and out. The pvc also helps keep all the misc lines from getting all tangled. I mounted a harkin cleat on the front AKA cross bar (near the outside end on the left side of the boat, after pulling up the jib, the harkin cleat holds the halyard line tight.
My spinnaker halyard is similar in design to Hobies setup on their new reacher kit. The only difference is I always run spinnakers on masts with rotofurlers (my spinnaker mast is 1/2" dia PVC tubing, with a PVC rotofurler at the bottom).

The reason I always furl around masts has to do with the fact that the main mast is unsupported and unstayed, and waves all over the place. Most all furling jibs, and furling code zero spins are assuming to be used on rigid stayed masts, so they are difficult to retrofit to Islands.
FE

Erm Bob, sorry to be picky, but I don't believe that is a pin bearing at all, as a pin bearing takes the load on its pointed top, minimising friction. That flat-topped pin at the base of the mast has zero vertical load on it, and its sole purpose is to locate the bottom of the mast laterally.

Or I could be blowing smoke outta MY mast base!

_________________
Tony Stott
2012 Tandem Island "SIC EM" with Hobie spinnaker

Tony:
Study Hobies design again, 100% of the weight of the mast and all downward force is on the top of that pin. With rotational force the smaller diameter/surface area you have the easier it is to turn. The two materials stainless steel up against delrin (acetal) is self lubricating and offers the least frictional resistance so they can actually get away with a little larger flat surface (lasts much longer than a pin point would). The white ball bearings are there to give the least amount of friction on rotational side forces (the design is actually brilliant). The design also has great resistance to sand and fouling ( a problem with most thrust type bearings).
On my mast topper I just tried to duplicate Hobies design on my mast topper less the plastic ball bearings ( I couldn't find any), the compromise design is a 1 3/8 OD plastic pipe spinning in a 1 1/2 inch dia brass tube (pretty resistant to sand and fouling and self lubricating). Down here sand gets into everything, so you kinda need to design around that. Plus I'm kind of working on a budget, if it had cost more than $15 bucks to make, or more than a couple hrs labor to make it I wouldn't have bothered. I've been using it for 6 yrs now every weekend, most of all the components are the same original components (never been replaced), I have no idea how many spins that works out to, but I would guess 30,000 spins of the mast with no issues or problems, just sayin.
FE