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The ultimate Tandem Island (hydrofoils, Spinnaker, jib, etc)
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Author:  fusioneng [ Thu Aug 09, 2018 3:08 pm ]
Post subject:  Re: The ultimate Tandem Island (hydrofoils, Spinnaker, jib,

One thing you will find out is upwind in light winds the main by itself luffs too easy and has almost no power, (just flops in the wind). With the jib upwind I could direct some wind over the mainsail, kind of forcing the mainsail to do work in lower winds, better than with just the main, and the ability to point higher. Which was pretty much my main reason for using jibs.
I had several streamer ribbons on my jibs, (near top, middle, and near bottom), making it easier to see exactly what it’s doing with the air.
Your jib looks pretty stretched out.
I like your 2/1 jib control lines, I also had two control lines, makes self tacking very easy, ( usually no need to adjust anything between tacks when working upwind.
Pretty cool setup

Author:  prettig [ Sun Aug 12, 2018 12:41 am ]
Post subject:  Re: The ultimate Tandem Island (hydrofoils, Spinnaker, jib,

Yes you are correct the jib "helps" the mainsail upwind.
Directing wind is one factor, the other it pushes the boat to one side, main catches the wind better that way (mainsail only: point and hike out leeward, does the same).

Thanks to all the info here I could get this setup done fairly easy. Basically I only used a carbon pole instead of PVC, hobie topper and used a different control lines setup.
Now i can buy a new jib (but even with this old streched out jib it works fine).

- Tandem mainsail (I just swap the mast holder, with jib it will be even better balanced)
Speed ..... not sure it will go faster (hull limit), so rudder foil or planing hull otherwise it does not make sense.
- Rudder foil (but winter job, need to reinforce the back and rudder setup, so need it in the garage for some time).
So this will be a combi project.

- Spinnaker (just need to find a smaller bag, want to mount it on the nose), not sure i really need the spin (small lake)

Author:  fusioneng [ Sun Aug 12, 2018 3:03 pm ]
Post subject:  Re: The ultimate Tandem Island (hydrofoils, Spinnaker, jib,

The hullspeed on the TI is 8.6mph, (sqrt(18.5)x 2.0= about 8.6mph). However that’s a soft number because of the 8/1 length to width ratio of the hull. The AMA’s have no hull speed limit, but it’s better to to try to keep AMA’s completely out of the water, (less drag).
The horsepower requirements start to go up exponentially at anything over 9-10 mph, so it’s hardly worthwhile shooting for higher cruise speeds on all points of sail. Obviously downwind is a different story with a huge spinnaker, with enough wind the boat holds pretty well to 1=1 to the wind, in over 20mph winds we have had ours over 20mph speeds many times, but we have a long bowsprit that angles the foresails so they create quite a bit of lift to the boat, when pushing very hard the bow is a good foot or two above the water. Basically the sail is dragging the boat, so the hullform means very little, what we call crappy planing, (only works downwind).
To get true planing upwind, you have to modify the hullform.
Without a bowsprit you have great risk of pitchpole downwind, ( just be careful).

Author:  prettig [ Mon Sep 10, 2018 3:30 am ]
Post subject:  Re: The ultimate Tandem Island (hydrofoils, Spinnaker, jib,

Small update on the JIB.

It works really good up to 3 bft (up to 10 knots).
Above: furl (21/22 knots, furl 75% and use as tacking help). Furl early is the advice (you loose to much speed, rudder and nose).

The Jib puts extra force on the mast, bending it more then normal.
Yesterday I had full jib/mail (10 knots), but suddenly I got over 16 knots on a beam/close reach.

And almost all the wind spilled over the mainsail (looked like it folded !), jib pulling to much on the mast (side but also front).
Speed gone, quickly recovered, no damage.
Will start testing with stay lines that stretch a bit and then are fixed, to prevent this.

- if you look at the mast under sailing conditions: surf sail position (a bend mast, and spilling over the top, same setup).
- Thinking of adding an extra line to keep it bend always (tension a surf sail and it bends the mast), I will try some of my windsurf tensioners and see what happens.
- Then the jib can pull as hard as it wants (in fact it will counteract the bending forces on the mast, so less force on the mast) and with streching side stays the mast can handle higher forces.
- Jib and main pulling means the pin below will hold much easier and not snap.

I still have this crazy idea:
- pull the surfsail over the hobie mast, tension it, use the boom, connect end of the boom to the standard mainsail line........ up to 100 sqft sail (high power stiff sail....) on an adventure... :o
- If that works it will be better then a jib. Better balanced boat, pointing upwind..... windsurf sails does that better by design, downwind.....just flap out the full sail (it has a boom)....
- I will test it with 65 sqft first (got one lying around), just for fun.
- And maybe it turns out to be a not so crazy idea......

Author:  fusioneng [ Mon Sep 10, 2018 4:51 am ]
Post subject:  Re: The ultimate Tandem Island (hydrofoils, Spinnaker, jib,

Where I always launch there are a bunch of windsurfer people typically there setting up, some of those guys have 5-6 different sails and boards that they use dependent on the conditions that day. We usually chat a lot. Some of their masts are near identical to our Hobie mast, and some of their sails are bigger than my main sail.
If I had one of those sails I definately would have thrown it on my boat to see what I could do with it, ya never know until you try.
Actually on another thread, (about booms) I thru out a furlable windsurfer type boom design that would probably work. The furler part would only be relevent for ease of boom setup/breakdown, (not while underway).
Always wanted to try stuff like that out, just for fun.

Author:  prettig [ Mon Sep 10, 2018 10:38 am ]
Post subject:  Re: The ultimate Tandem Island (hydrofoils, Spinnaker, jib,

Almost sure it will work (idea in my head already, have surf sails lying around) and then i ran into this thing:


You gone love love the design fusioneng......it is a fusion (cat, moth and surf) with a self leveling foiling system.
And a very clever lines setup for mast stiffness.

If he can put a surf like sail (84 sqft) on that small thing it will work on an island.
I just need to figure out a good tensioning point on the base of the island mast without breaking something......a lot off force on a surf sail tensioning system).

Author:  John Lunn [ Fri Nov 30, 2018 11:18 am ]
Post subject:  Re: The ultimate Tandem Island (hydrofoils, Spinnaker, jib,

UFO Foiling....I know this is a Hobie Forum.....
However, you have to hand it to Steve (the dad) and Dave (the son) Clark, they have conceived and built an amazing foiling cat.
I've been in a regatta with them (different class) and I was lucky to drive the camera boat for the demo afterwards.
The engineering is so simple and elegant, especially the foil trim tab.

Go to the gym to upgrade your hip flexors, and try one.

Author:  fusioneng [ Fri Nov 30, 2018 12:30 pm ]
Post subject:  Re: The ultimate Tandem Island (hydrofoils, Spinnaker, jib,

The sail on that boat is a wicked nice design, (way more powerful than an island sail). We never got our island to foil upwind without motor assist. The fun for me was all the design and construction, and working out issues, then testing every weekend....fun memories.

Author:  bluelaser2 [ Tue Dec 04, 2018 8:53 am ]
Post subject:  Re: The ultimate Tandem Island (hydrofoils, Spinnaker, jib,

An Australian called Frank Bethwaite literally wrote the book on planing dinghies. He empirically tested all the key ratios etc. to come up with some rules of thumb for weight to righting moment, weight to wetted surface area, etc. needed to sustain upwind and downwind planing. he did it mostly in the '70's via direct measurement. The foiling era was just starting has he aged out. His son is an accomplished skiff racer and designer too. I have a Laser2 dinghy he designed, but modified with a TI style rig and Hoyt boom. It's an ageless thoroughbred of fast sailing fun. You won't get that kind of experience on a TI- different purposes. A TI won't ever truly plane, but it will get you from point A to point B faster than many 'high-performance' craft because its own ratios are pretty extreme. Esp. with a haka for righting moment and pedals for light air / high point, pretty hard to beat. OTH in four foot waves, downwind in 20kts of air? A pure dinghy is almost like seated Hawaiian surfing with beer in hand. Also hard to beat :D

https://www.amazon.com/High-Performance ... 4806&psc=1

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