Access Liberty dinghy

[kmcfast]

I came across this boat designed for physically challenged sailors.http://www.accessclass.org/default.asp?Page=18383&MenuID=Classes/13153/0/
The Liberty's distinctive look is due to the inclusion of two unstayed masts. "The boat had to be self-tacking, and the jib had to have just one sheet which could be led to a winch," Mitchell explains. "The foremast is unstayed and set up with a strut, which looks like a wishbone but is really only half. The outcome is technically a schooner."

These boats are said to point as well as conventional sloops?
Any thoughts on the aerodynamics of this rig?

Thanks

 

[Doug Lord]

Access

Well, I'm not sure of the aerodynamics: a jib in a normal configuration might work better because the slot could be controlled a bit better. I think it is a very interesting solution but if the idea was to have a single jib sheet or even a single sheet for both sails it is not the only solution. The Swift Solo has a sheet system designed by Bram Dally that uses just one sheet for both sails and would be ideal for a disabled crew-or any crew for that matter.

Click on image for best detail( left=sheeting diagram; right=Swift Solo) :

 

[kmcfast]

View attachment Access%20Liberty%20Spec%20Sheet.pdfThe s solo sheeting system is great. My thought was to have thwartship jib travelers with 2 sheets, ditch the wishbone & use carbon tubes. I'm guessing that this setup would have less turbulance/drag than a conventional forestay intersection at the hounds. The slot between the top of the foremast & the mainmast looks open even with the poor sheeting system. I think Mr. Mitchell is on to something.

 

[Doug Lord]

Access

Could be. A concern of mine would be the greater thickness of the tube for the jib luff and the fact that if you're relying on the jib slot that the independent movement of the two rigs might mess that up. A great boat to do a definitive real world experiment with-maybe they've already tested two rigs? Interesting to ponder- thanks for bringing it up!

 

[tabman]

My daughter and I sailed a smaller version for Special Olympics a few years ago. I think it was the 303.

It had the same "Jib Spar" although without the wishbone. I was skeptical when I first saw it but was actually quite impressed how well it worked in practice. Although we were sailing against the same boats, so it was difficult to gauge, it seemed to point well, given all the other attributes of the boat.

Interestingly in a puff the top of the Jib Spar would bend off to leeward and de-power the jib, not a bad feature considering the boat's intended use.

The cool part was how simple it was to rig. Drop the spar into the hole in the foredeck, run the sheets and furling line aft and you're good to go. Great for people with limited abilities.

I wish the boat we sailed on had the wishbone on the jib and not the dual sheets, as it would have made it possible for my daughter to control the whole boat.

The picture shows us in the boat with the jib furled coming into the dock. Looking at the picture you would not know its not a conventional jib furrled around a forestay.

Tom

 

[kmcfast]

Access Dinghy

Great pic, Tab I'm sure you Daughter will cherish it someday. so the top of foremast falls off to leeward in the puffs like a laser mast?
I think the separation top of the foremast from the hounds might solve the problem below see pic. Finding 2 masts with appropiate upper bending moments would do the trick.

From WB Sailmakers http://www.wb-sails.fi/news/Ad_aerodynamics/index2.htm
Jib head vortex on the main

As always at the tips of airfoils, there is a vortex forming behind the leech of the jib towards the head. When this vortex travels behind the leeward side of the main, it bends streamlines above itself away from the surface of the main, effectively "ripping off" the flow from the main surface at the hounds level and a little above it. This can be seen on the simulation as a triangular, disturbed air area. Above this area, closer to the top the flow can still be attached.Lower fractional rigs (7/8-rigs) suffer more from this than masthead or high fractional rigs. This could be one reason that 9/10-rigs have grown in popularity lately.

 

[tabman]

Yes somewhat like a Laser. I raced Lasers extensively in the '70s and it did remind me of the way their mast behaves in a puff,

As I mentioned I was quite impressed by the rig (and the boat). Apart from being really well suited for disabled sailors the boat was just plain fun to sail.

In the "everything old is new again" category have you ever seen an Eastern Shore Stickup Sharpie?

Tom

 

[kmcfast]

Lol

So nothing is really new...