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 Post subject: Re: Spinnaker kit needed
PostPosted: Sat Dec 10, 2011 11:01 am 
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Joined: Sun Apr 20, 2008 6:18 am
Posts: 1317
Location: Sarasota,Key West FL
Louis:
Awesome setup.
Is that an H16 jib you have on there. It looks a little large, I had problems keeping helm control when I had a larger jib, but that was with the old rudder system, I imagine the new rudder system can support a larger jib (120% Genoa in this case). And I suppose you can just furl it in a little if you are overpowering.
I also like your jib furler design (tube within a tube), much cleaner than my setup.

Bob


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 Post subject: Re: Spinnaker kit needed
PostPosted: Sat Dec 10, 2011 7:37 pm 
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Joined: Thu Jun 26, 2008 7:20 pm
Posts: 27
Location: Marietta Ga.
Bob,
I do not know what boat the sail was off of, I will ask the sail loft if they know. I was lucky to find it in great condition and a workable size. I probably would have ended up with a different rig if I had found a sail short enough to use the attachment point Hobie has sewn on the sail. Although, I don't think that a rig that attaches to anywhere other than the top of the mast would be as easy to use.

on certain points of sail and wind conditions I do have to furl the jib to a smaller size to maintain control, even with the larger rudder. I feel that even if I sailed around with the jenny completely furled when close hauled in higher winds, the dramatic speed boost off the wind would make it worthwhile. The boat reaches planing speeds at much lower wind velocity with this rig vs. stock. I can only imagine how your spinnaker performs.

I find that if I furl the jenny to working jib proportions it points highest into the wind.

Have you seen any pictures posted of the collapsed hull Matt spoke of in another thread? I have an idea on how to prevent a compression break, but would want to be sure the break occurred where and how I think it happened before fabricating a retrofit solution.

Louis

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Louis
Marietta Ga.


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 Post subject: Re: Spinnaker kit needed
PostPosted: Sun Dec 11, 2011 7:29 pm 
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Joined: Tue May 18, 2010 2:31 pm
Posts: 2712
Location: Kailua 96734
Awesome mods Louis. Looks like she will fly.

The sail tube you added to the trailer was a great idea too.

_________________
"THE WIND IS YOUR FRIEND,.."


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 Post subject: Re: Spinnaker kit needed
PostPosted: Sun Dec 11, 2011 9:57 pm 
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Joined: Sun Apr 20, 2008 6:18 am
Posts: 1317
Location: Sarasota,Key West FL
Louis:
I also feel the jib really helps when pointing up wind.

I only know what I have read on the forum about the problems Hobie had with the jib kit.

I believe I know the biggest problem with the TI design (speculation on my part) that makes the jib option not likely to be released. If you open the front hatch and look inside you will see the big triangle brace inside that works like a bridge truss, I think it's sufficient for the typical side to side forces created by the sail (as long as everything is tight). However there really is nothing to obsorb and distribute the front to back stress's from the mast except that small pad at the base of the hull. This normally would not be a problem but, unfortunatly the force is multiplied on that joint because the actual fulcrum point of the mast is 10 inch up from the bottom. This is like taking a long 2x4 and putting a brick under one end, you can then lift a car by pressing down on the long end with your finger. Same is occuring on the AI/TI sail mast. The sail control line (block) tied to the rear of the boat helps relieve some of that forward stress on the mast. However if you were to go down wind with your rig you would naturally try to create a batwing (jib to one side and main to the other, both pulled out with barbour haulers or whatever), when set like this the sail control line is no longer holding the top of the mast back and all the forward force is on that tiny nut and pad in the bottom of the hull (a little whoops in the basic design), worse yet the force is amplified by the fulcrum effect, this can easily be many hundreds of lbs of force on the little tiny spot in the bottom of the hull, because the force is amplified by the fulcrum. As an example to illustrate ... applying 200 lbs forward force at the top of the mast is amplified to 3600 lbs of rearward force at the critical joint 'in theory', (in reality the actual force is distributed down the length by the sail so it skews the calculation, real world it's likely 4 to 1, or about 800-1000 lbs on that joint).

That's why my boat has a back stay (always has), this controls the forward force at the easiest place to control it (at the easy end of the fulcrum). A light line works just fine, and there is actually very little stress on the rear lifting cleat (no more than the regular sail clew creates) I also have side stays, but seldom put them on (don't feel they are needed unless you plan to do some hard sailing). Of course you don't have this problem on regular Hobie Cats (stepped and stayed mast).

The Bravo has a very similar un-stayed roto furling sail to the TI but doesn't have the same problems as the AI/TI because of the very strong mast braces at least a couple feet up the mast right up close to the bottom of the sail so the fulcrum effect on the mast is much less than on the AI and TI designs.

This is of course is all just speculation on my part. When I got my TI in spring 2010 I realized pretty quickly where I live the typical 4-8 mph winds around here really suck. I needed more sail area and got tired of waiting for Hobies jib option to come so I just made my own stuff.
Good luck
Bob


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 Post subject: Re: Spinnaker kit needed
PostPosted: Mon Dec 12, 2011 8:05 am 
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Joined: Sun Apr 20, 2008 6:18 am
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Location: Sarasota,Key West FL
Louis:
If you want to do the work to fix the mast problem I came up with a solution that should work if you don't want to put on front and back mast stays. What I would do is take a 1/4 thick bar of aluminum maybe 3/4 to 1 inch wide (depending on what you can find at Lowes). You will need a piece 6 or 7 ft long. What I would do then is carefully bend one end so it follows the bow contour on the inside of the hull right up to the top so the top edge is touching the inside of the hull at the top. Then run the metal up the center bottom inside the hull so it is pinched between the mast holder base and the bow tightly.
There are a couple ways to add the epoxy, one is just lay in epoxy clay and the other way is make a small dam with kids modeling clay (or playdough), and pour in liquid epoxy (be careful with the heat though). Basically what you want to do is put in a 1/2 to 1 inch thick by about 4 inches wide piece of epoxy between the back of the mast holder and the front edge of the mirage drive pocket. I would spray the mast pocket with silicone before you start so the epoxy doesn't stick to it. What this does is takes the extreme force generated by the fulcrum effect on the mast and distributes it to a much larger area harmlessly. With the left over epoxy you can form a little mound over the aluminum just in front of the mast holder make sure you can still access the nut. In the front of the mast holder you only have to mound up a strip around 6 inches away from the mast holder over and around the aluminum. If your using the epoxy clay (recommended), you could also press in a wad at the tip of the bow on the inside to kind of re-enforce the bow, and hold the aluminum rigid in place. This is quite a bit of work but I think to be nessessary if you want to put extra sails on the boat. If you ever sell the boat it's all easily removed (epoxy doesn't stick to the polyethylene hull).
Also because the bow is kind of weak around the front hatch, it would probably be a good idea to make braces in a V shape between the bow tip and the ends of the front AKA brace (strongest point on the boat). If you look at the pics of my bow sprit you can see them, there also might be some pics floating around of Hobies design that was used in this years 2011 EC challenge.
The mast on the TI is mounted very far forward, and if you are thinking of adding a spinnaker eventually, while your at it making the bow brace you might as well design it so you can convert it into a bow sprit later on ( I know you want to LOL). In my opinion running a huge spinnaker is the ultimate experience and for sure the most fun part of sailing on any boat, there's just something about it thats compelling, especially if it's brightly colored. It's even more fun if you can furl it in and out so it can be launched and snuffed in a couple seconds single handed, you will definately use it all the time ( I know I do) now I have mine on a furler.
Even with the structural re-enforcements below deck, I'm still thinking a back stay (with 1/4" stretchy nylon) would still be a good idea. It equalizes the force of the jib which acts as a front stay to keep the mast straight up. If your side stays can keep the mast straight you might be ok with just them, but looking at your pic, they appear to be mounted too far forward to be able to counter any forward force. I have my side stays hooked on a 1/2 inch dia stainless bar about 12 inches forward of the mast top, they clear the mainsail a little better, and allows the mainsail to go side to side to spill air when needed, but the jib is held tight on center. I didn't use rigid line on anything, this allows the mast top to tip and bend some, but as the force increases the tension on the stays increases protecting the weakness in the mast base design.
Hope this helps
Bob


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