Jib Physics & "the slot effect"

Hello
I also think that PVC is not a good material for a mast top. Blasius' prototype should be transformed into metal.
Speaking about the several mounting solutions I have seen I dont like the ones with the jub furled together with the mainsail. I understand that it solves a lot of problems but we'd loose the independance of the two sails and I think I would not renounce to furl and open only the jib when I want.
I like the rotofurling jib solutions. What is not clear to me is how to manage the jib stay and the rigging.

I will make a small video to show you how the jib setup allows for the jib to be quickly removed or raised while sailing. You do not need to get out of you seat to do this although you do slide forward slightly.. What I loose with this arraingment is the ability to sail the jib alone while the main remains furled. That is all thats lost and although I would like to try it, I don't think the boat would be balanced and I can't imagine sailing that way very often.

I do also loose the ablity reduce the size of the jib while showing a full main as well. I can furl the main about 1/2 way before the jib begins to get furled with the main.

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Greg

2016 AI - Spinn & Jib

“Out of sight of land the sailor feels safe. It is the beach that worries him.”
– Charles G. Davis

Just curious, why all this talk about jibs when a big downwind sail might be more fun and more useful? You could fly either an asymmetric from the bow or a symmetric from the fwd akas. With the asym you could set it up to roller furl (although, since you CAN move around on the boat-you could just raise it when you need it and stuff it in a bag when you don't). With the symspin you could either snuff and deploy from a snuffer OR you could just raise it when needed and stuff in a bag when you don't. Granted, I like spinnakers--separates the weekend warriors from the sailors.

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R/Thom
SeaRail 19
Triak
BMW C600
Formerly Getaway with Custom Spinnakers
Formerly raced F24 Mk II

I can't speak for Blasius but for me, I see value in both. Hobie has the reacher in the works so I'll let them take care of that while I focus on the jib. If I were forced to pick from a jib or a reacher, I'll take the jib every time. For me, the jib is more versatile helping you upwind but to some degree downwind as well. The reacher is going to be downwind only and will offer nothing upwind (I suspect). I can also fly the jib in a wider range of winds.

That doesn't mean I haven't been drooling for a reacher ever since Hobie confirmed one may be on the way. I'm sure I will be ready with checkbook in hand the day they are available.

All this jib talk is carry over from the Adventure Island Jib & Lee Helm thread. When I have the video to post I will post it there rather than this thread. I look forward to see what Blasius puts together.

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Greg

2016 AI - Spinn & Jib

“Out of sight of land the sailor feels safe. It is the beach that worries him.”
– Charles G. Davis

My opinion regarding the reacher and the jib is very similar to the Vetgam one.
When I go out sailing with my AI, I always sail upwind until it is time to go back.
I think that a reacher is more inportant for races or for long trip, but not for what is my usual way to sail.

Today I tried a new prototype of the top mast, it is much stronger than the previous one.

In the test you can see in the video it is hanging around 30 Kgs ...

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Biagio

Hi Vetgam
the jib with the mainsail furled is a configuration used in other boats with very strong winds, when they dont want to expose too much sail. I dont know if these "added" jibs could be trusted in 20+ knots winds. What, IMHO, is more useful is to furl immediately the jub as the wind get stronger, for example 12+ knots and we understand that the mainsail alone is enough. If the jib is furled with the mainsail i think u must start furling both. How is the behaviour with 12 or 15 knots winward?

tpdavis473 I think that the interest in the jib comes also from the fact that you cannot use the reacher when u sail winward and this is the situation when you usually need more power also because you have wind and often current against u. If i sail qith 12 knows downind i am already a rocket with the mainsail and i start sumbarining, for sure I woudnt open the reacher. The reacher will be good with winds weaker that 10 knots.

OK, I can see where you folks are coming from. I suspect Hobie is designing the reacher to be similar to what is used on windriders. It is useful for upwind work to about 8 kts true wind. Useful downwind to about 30 kts if you are brave enough.

BTW, you may be submarine-ing because you don't have any lift at the bows which would be alleviated with a big headsail...just sayin'. Mainsail only with cat-rigged boats is more of a problem than with sloop rig because the COE of the sailplan adds a vertical moment toward the bow/water instead of what would be preferable - vertical moment toward the sky (especially with square top mainsails). You can fix that by letting out more mainsheet and driving deeper (and moving your weight aft).

The swivel on top in the new video looks robust enough. What/how are you rigging the jib halyard/forestay from that? Bridle through the T to a furling swivel for the jib/forestay?

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R/Thom
SeaRail 19
Triak
BMW C600
Formerly Getaway with Custom Spinnakers
Formerly raced F24 Mk II

Hello SI. I agree that It's best to use the main alone in higher winds. When the winds get over 17 mph, it's time for me to drop this jib and put it away. At that point I'm beginning to worry about the large forces on the sails and especially the mast. It is at these wind speeds that I quit having fun and can't stop stop thinking capsize. This is with TI amas on an AI. I haven't tried the jib with the original AI amas yet. I'm guessing that would drop my tolerance for winds down to 14-15 mph or so.

I think the jib arraignment I have is the simplest one I have seen for dropping or raising a jib quickly. It just also has the ability to furl partially or fully with the main. I fish and I need to quickly be able to furl both sails to bring in the fish. I don't want a roller furled jib preventing me from bringing my fishing rod around the bow of the boat. With the big fish we catch in the Gulf of Mexico that poses a real problem/danger. This setup allows me to deal with a sudden bite on the line (furl) as well as increases in the winds (drop the jib). I hope I can demonstrate this in video. I will try to make it this weekend.

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Greg

2016 AI - Spinn & Jib

“Out of sight of land the sailor feels safe. It is the beach that worries him.”
– Charles G. Davis

Well, a couple multihull experts (e.g. Ian Farrier) prefers to drop mainsail and jib and fly spinnaker alone. I have used this technique in big breeze on my Triak. It truly is safe.

This video that shows me with just spin up in a big breeze.



Here's why. If you are driving deep (and you will with 30 kt breeze), the spin collapses if you head too high--so you can't capsize going over sideways. If you have the spin working, you get lift at the bows so you don't bury--unless you are going so fast that you pitchpole by hitting the back side of the wave in front of you. You only have one control line to release, and when you do so, the spin is completely depowered.

Granted, in a boat with no boom such as the AI/TI, you can certainly be as safe by furling until you feel comfortable..

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R/Thom
SeaRail 19
Triak
BMW C600
Formerly Getaway with Custom Spinnakers
Formerly raced F24 Mk II

If this will be, I will think about a Reacher usage too
Let's wait then ......



To be honest, I have only some ideas about the jib rigging to use with the mast top I just made.
It's uneasy to describe the way I would connect the jib to the mast and to the bow, I will try to make a drawing later today and maybe it will explain it better than lots of words.
Anyway I am proceeding in a try and improve process, doing a step by step designing. So it could be that I will completely change my ideas or maybe I will just try to copy the Vetgam rigging ....the time will let us know that

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Biagio

The only function of that top swivel is so you can furl and unfurl the mainsail while still having the forestay stay pointing at the bow. On my boat, there is a bracket instead of that T and the bracket is bent at the end to point at the bow; there's a hole at the end of the bracket to hold halyard blocks. Be advised, sometimes it takes lots of tension to keep that bracket pointing toward the bow for furling and unfurling the mainsail. Also, the bracket serves a secondary function, it moves the forestay away from the mast so nothing gets hung up when furling and unfurling the mainsail (there is an eyestrap near the top of my mast that could (does) catch on something).

Have fun with your project. Trial and error is the better way to improve IMO.

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R/Thom
SeaRail 19
Triak
BMW C600
Formerly Getaway with Custom Spinnakers
Formerly raced F24 Mk II

Here are two hand drawings that show my initial idea regarding the jib rigging.
It is just in my mind and maybe it doesn't work.
Unfortunately, because of the weather forecast, for upcoming weekend (rain), I am not planning any sail ride, so I cannot do any test with the real AI. Maybe I will do some test simulating the mast with something else in my garage.

https://goo.gl/photos/kr4en1iMDPhDqe7s7
https://goo.gl/photos/MF6Yx1t6JW5CDhUs6


Any suggestion is welcome.

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Biagio

If you put rigging in front of the mast for the jib furler swivel, then attach two additional lines rigged behind the mast, you may force that swivel to bump up against the mast-that means you won't be able to furl (reef) or unfurl the mainsail. If you move those two lines to or forward of the front aka, it might work better.

An alternative would be to forego the side stays. If you swap your T for a 90 degree elbow and attach a 45 degree elbow to the end, you have a bracket that keeps the furling swivel away from the mast and points toward the bow.

There are other options, as well. The Hobie Getaway (and Windrider) hoist the furled jib/forestay when the mast is stepped; so the jib is always there when needed and furled when not needed.

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R/Thom
SeaRail 19
Triak
BMW C600
Formerly Getaway with Custom Spinnakers
Formerly raced F24 Mk II

Biagio:
My advise would be to forgo the side stays on an AI/TI, I tried it years ago and it screwed up the performance of the main badly (it's designed to bend). I highly recommend a rear stay though on any AI/TI with additional big sails. The little 1/4-20 stud at the bottom of the mast holder cannot withstand much forward/backward force (very little actually), and what makes matters worse is the leverage 17 to 1 on the bottom of the mast from the sail control line, if you don't believe me just pull your main tight, then give the sail control line a swift tug, it will snap that little stud like it wasn't even there.
Also with a big spinnaker especially in higher winds you have to be a little careful how you deploy the spin, if the sail pops open suddenly in 20mph winds without the boat moving, it simply snaps that stud. I have my big 135 sq ft spin on a rotofurler, where I get going downwind batwing style with my jib and main, get up to around 10-12 mph then I furl the jib then unfurl the spinnaker carefully (it only takes a second or so to furl or unfurl any of the sails). I almost never run the jib and spin at the same time, and often pull the main straight back (for additional mast support) while running hard downwind with the spinnaker, you can also furl the main if you like (the spinnaker is doing all the work anyway). Now when it's time to slow down, you have to release the power on the spinnaker, then furl it in (you can't furl it under power very easily). I have the control lines for my spin on pulleys on the rear outer AKA bars as far back on the boat as I can get them ( mine is a single line running from the sail back around the right rear AKA, across the boat, then thru the pulley on the left side, then back forward around the front of the spin, then attach to the same point as the other end of the rope. This allows you to go left tack or right tack easily. Though I could probably switch tacks without furling the spin in, it's way easier to furl it in do the gibe, then furl it back out the other side.
I know nothing about the AI, but on my TI if I'm running downwind hard with 200 plus sq ft of sail showing without a bowsprit or my hydrofoils, the bow dives badly. I found I had to add a 2 ft bowsprit to the front of my TI so all the foresails are angled enough to create enough lift to the bow to keep it from diving. Currently when pushing very hard downwind in higher winds and chop (over 15-20 mph) the front of the bow needs to be at least 6 inches out of the water. Anything lower than that is a for sure pitchpole first time you hit a boat wake (I've pitch poled many times with my spinnaker, ( 20 to zero in about 2 seconds (lol))). Another word of advise (based on my own stupid experience's) your boat had better be just as capable upwind as it is downwind in the same conditions especially if you live on a tiny Island dot like Key West (lol), you have to go home eventually.
Instead of side stays you can always add a trap and harness to the top of the mast, this helps with the super bendy mast on the TI (when not using it you just leave it slack). I still highly recommend the back stay though with big sails sets (no need with a tiny jib, mostly just with big giant spins).
My opinion there is nothing more fun in sailing than flying a giant spinnaker. I'm really happy Hobie is finally doing it.
Hope this helps
FE

FE, can you elaborate on the "trap and harness"? Not sure I understand what you have in mind. Any pictures?

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Greg

2016 AI - Spinn & Jib

“Out of sight of land the sailor feels safe. It is the beach that worries him.”
– Charles G. Davis