By request, jibing keel reasons...

[Chad]

So as not to muddy the other thread, I'll describe what I think might happen with a jibing keel on an i550.

Basically, boats sail upwind with their underwater foils at some small angle of attack, also described as leeway. Usually it's about 1-3 degrees, depending on boat speed and foil efficiency. When heeled, the chine of the i550 has an angle of attack of around 7 degrees, plus whatever the leeway angle is. If you can get your main lifting foil to rotate a little, the foil will still have about the same leeway/angle of attack, but the BOAT will rotate to better align to the direction of travel. So with a 3 degree jibe angle on the keel, the chine only sees maybe 4 degrees plus the same foil leeway angle. The end result is less lift and less drag from pulling the hull (chine) through the water sideways, and more lift being generated by the feature of the boat specifically designed to provide lift -which is the keel foil.

There is a contrary school of thought that since the hull is much longer (18' in our case, versus the 13-odd inches for the foil) and sees much smaller Reynold's numbers, that the lift from the hull is actually pretty efficient. My guess is the chine might trump that idea, since I just can't see dragging the chine sideways through the water as efficient. Time will tell, I suppose!

Anyway, here's a straight from below fish's view of two hulls, each heeled 12 degrees, one has a jibing keel, and both are sailing straight up the page with their foils at a 3 degree angle of attack. I added some lines every 24" to show the travel direction of the boats. You can see from the knuckle to the transom the chine of one boat is lots more skewed...

Edit: I goofed on one of the angles in the pic I originally attached to this post. See post below for corrected pic with more info, too.

[admin]

makes sense to me!

[M&S]

Wow!

I have been trying to do this in my head for years. Brilliant.

At what angle of heel does the chine present the least curvature to straight line path ?

TR

[Chad]

If you really heel the boat over, the chine near the keel starts to "tuck under" a little and straighten out, by about an inch when comparing the two right hand examples shown below:

fisheye2.jpg

[slowpoke]

How do you plan to close up the opening around the keel, so it doesn't scoop water? Some sort of skirt around the keel? And does the benefits of the jibe keel offset the added drag of the larger keel slot?

[ryderp]

It will be interesting to see this work in practice. It seems to make sense to allign the chines with the direction the boat is going when it is heeled over. Is it establshied that carying a heel is faster in an i550 vs. trying to keep the boat as flat as possible? I know that in an e-scow (another flat bottomed boat) it is definitely faster to allow a bunch of heel and the bilge boards are angeled at 19 deg just for that purpose.

I would assume that one outcome of the jibing keel is that you wouldn't want to trim the sails as tightly since the real direction of the boat would be upwind of the direction that the bow was pointing.

I'm staying with the fixed keel for simplicity, but since I have a rectangular sleeve it would be pretty easy to convert later if it is advantageous.

[micah202]

How do you plan to close up the opening around the keel, so it doesn't scoop water?

...a sponge would deal with that,,but what'll stop the keel from banging around in a bumpy seaway?

[Chad]

Rocky,
I'll have a sort of fairing plate to cover the larger hole in the bottom of the boat- a piece of 1/16" glass with tapered edges held up tight to the hull with elestic, that slides on the outer hull surface. Yes, that is a source of added drag, hopefully not too much.

Phil,
Shazza and his sailmaker started sailing their boat a bit flatter than Tokyo had described until that point, but I don't think there's any conclusive evidence that 12, 15, or 19 degrees is "right". I think everybody agrees something more than 10 is needed though.
Yep to the sail trim changing, part of the reason I used transverse jib tracks.

Micah,
I placd the cg of the bulb a bit further aft than most, so it's aft of the keel pivot axis. With any heel, it will fall to the jibed position. I've got some ideas about adding some tension to help tame any slop and wobble, but I suspect that building the jibing head tight to the case and adding delrin shims etc. as needed will be enough.

[Chad]

I'm out of filler and peel ply, and had to wait a week to order more since some twit in Rancho Cucamonga, CA tried to charge $140 to my credit card at "Bed, Bath, and Beyond". I've been trying to keep busy on the boat, but I needed to do some figerring anyway so I've spent the morning coming up with a plan for the jibing keel bits. Presented here for your amusement, criticism, and even thoughtful input:

JustKeel.jpeg

So here's just the keel (orange, of course) as it is now, with its head poking out about flush with the top of the rectangular opening. I cut away the front and back "shoulders" of the keel blade, and I'll add the jibing shims at the bottom of the keel box so you can't see those in the pic.

AddTiller.jpeg

Then a tiller gets added to the keel head. A U-shape over the top, and a simple plate extending aft.

UpperPivotAndBolt.jpeg

Next a G10 disc gets added on top, and little segments to fill to fill the circle next to the keel arm. All bolted down to the top of the keel with a big 5/8" piece of all-thread glued about a foot into the top of the keel blade. With a pinned castlellated nut just for good measure. So all these parts stay with the keel, whether it is up or down.

DelrinPivotGuides.jpeg

These are the delrin guides. They get shaped to the radius of the G10 discs above, and have enough clearance to the tiller to allow about 3 degrees of pivot each way. They also get a notch cut out for the next item...

Slider.jpeg

This slider serves two purposes. By sliding it over the disc and engaging the delrin notches, it keeps the keel from falling out of the boat if inverted. And, it has a couple of little ramps at the back (black in the pic) that center the tiller if the slider is pulled forward. So downwind, the idea is to pull the slider forward and keep the keel from jibing.

Oops, just five pics per post.
See next post for rigged pic and explanation.

[Chad]

...continued.

Rigged.jpeg

So, I want to make this fairly automatic. I'm going to try to use the tension in the leeward/active jib sheet to pull the keel tiller down. My jib sheet (not shown, sorry) will go through the little ring up on the deck, in between the fairlead at the track, and the turning block a little ways aft. Going through a tack, just pull on the new jib sheet and toward the end maybe give it a little extra grunt to get the keel over. Once the keel is set, the ring adds a little friction for the trimmer. I'm showing the keel line 2:1'd to minimize the effect on the sheet, which I don't think will be much anyway. If the keel is stubborn or it's a light day with really light sheet tension, the back of the tiller can probably just get kicked over.

The forward-lead strings are for centering the keel. Pull either end (there'll be stopper knots in the tails and probably an endless loop) and the slider is pulled forward and the little ramps/stops engage the angled sides of the tiller. The slider can also be pulled part way forward to limit the jibe angle, if 3 degrees turns out to be the wrong number for the day. There will be a bungie providing aft tension.

I suppose if I was really clever I could figure out a way to make the kite halyard pull the centering lines like the I14 did a few years back, but I'm not sure where the kite halyard is going to be, yet. Always room to improve...

[jray]

Awesome Chad, I understand what you are doing and why but will have to study everything you've posted to figure out how it all works. Changing the keel angles up wind a definite plus. If it moves when on a fast reach or run maybe not so good. Sweet idea, I look forward to seeing it some day. Keep going with your ideas, they sound great!

[slowpoke]

Thanks for explaining all this Chad. I don't know if I'll go for it or not, I'm not at that point yet, but I ran across a reference to it on SA, and I knew you were thinking of making one. This really helps to understand how they work, and how they function mechanically!

[Chad]

Hopefully I'll have mine together and sailing before too long, and you'll be able to see for yourself whether it works, or it crashes and burns. I suppose I have a few items on the boat that that would apply to...

[Chad]

Some of the parts made...

KeelTiller.jpg

[Chad]

... a little more progress, about as far as I can go until the boat is upright again:

IMG_0404.JPG

[admin]

exciting stuff. at some point, we'll need to know about the fabrication process does it mainly involve some CF sheet layups and a band saw?

[Chad]

Yeah, all pretty simple. Jigsaw, since I don't have a bandsaw. Print the patterns, spray-mount to 1/4" ply, carefully cut and sand to shape, use as router patterns for the flat parts. The patterns all have 1/4" holes where the fasteners will go, so I can bolt the patterns to the parts, repeatedly as needed, and run them past the router's flush cutter.

Flat parts just a stack of carbon cloth, biax, uni, e-glass biax (acts like a core, or thickener), uni, biax, cloth, symmetrical top to bottom, and about 1/4" thick. Lay them out on mylar, put peel ply and absorber on top, then flat piece of wood as a clamping caul on top.

The U-saddle that grips the top of the keel is just a stack of fabric, mostly clearing out the bin of odd scraps with some unis where I think it counts, wrapped over the top of the keel (previously wrapped in packing tape), wrapped with peel ply and absorber, and clamped with some pieces of 1/4" ply so they can sorta follow the foil shaped curve.

The slider is formed around a 7/16" thick by 6" wide board, all wrapped in packing tape. Then a 4mm piece of foam added on top to stiffen the "bridge", topped with a wrap of carbon biax, uni, and cloth with mylar for the gloss bling.