BB33
Wow Skip, that seems almost too good!
There’s gotta be a down side to a solution that simple.
Let me see if i got that straight; when we shunt, the head-sail becomes the new main-sail and vice-versa by putting tension on the leech turning it into the new luff, while loosening the luff turning it into the new leech, and doing the same with the main-sail turning it into the new head-sail.
Thus eliminating any need to rotate or tilt or slide the mast or sails during a shunt.
That’s great.
Has it been tried - does it work well?
Wow Skip, that seems almost too good!
There’s gotta be a down side to a solution that simple.Let me see if i got that straight; when we shunt, the head-sail becomes the new main-sail and vice-versa by putting tension on the leech turning it into the new luff, while loosening the luff turning it into the new leech, and doing the same with the main-sail turning it into the new head-sail.
Thus eliminating any need to rotate or tilt or slide the mast or sails during a shunt.
That’s great.
Has it been tried - does it work well?
As a schooner rig, 2 identical sails, that is more or less correct, the balanced club staysail has a lot going for it, powerful see https://www.youtube.com/watch?v=iVoVP5ozj4I&feature=channel_page , easy to shunt, etc. The ease of shunting involves rotating the rig 180 degrees, pivoting on the axis of the head and bridle attachment on the boat. Powerful disadvantage is the almost infinite tension to make the thing work upwind in a breeze. My trials with the Broomstick were to see if going to a cambered panel type sail would lower the tension required. Jury is still out, the test are on hold while I try out the wingsail. The cambered panel staysail has already won out over the rig I’d played with for years variously known as the Bolger, AYRS, Biaxial…....
Cheers,
Skip
Skip, i think i’m missing something here - why the need to rotate at all?
If the head-sail and the main-sail are identical, roachless, mast-head triangles, both rising vertically mid-ships and both angling down to either end, why can’t they just trade functions after each shunt without rotating at all?
Why can’t we just release the high tension on the tack and use it as the new clew with the sheet ready and waiting in place - while pulling high tension onto the clew making it the new tack?
Skip, i think i’m missing something here - why the need to rotate at all?
If the head-sail and the main-sail are identical, roachless, mast-head triangles, both rising vertically mid-ships and both angling down to either end, why can’t they just trade functions after each shunt without rotating at all?
Why can’t we just release the high tension on the tack and use it as the new clew with the sheet ready and waiting in place - while pulling high tension onto the clew making it the new tack?
What you are talking about comes close to the Bolger, AYRS type sail and it’s a seductive idea, but.
What can go wrong will go wrong and sooner or later, both ends are going to get loose (believe me it ain’t pretty).
Until you’ve broken the top out of a well stayed mast you don’t really understand the forces involved.
Speaking of forces, sheeting what is essentially a jib is going to require a winch or two to handle the smaller forces in the clew(s). Twice on every shunt plus hardening down the tack(s).
All courses not hard on the wind are going to require some sort of whisker pole to get any real effectiveness out of the sails.
There’s a lot of stuff about biaxial sails buried in the forum, look at Nomad for what I played around with for some time. Bottom line still, if I had to pick a soft sail today it’d be a balanced club staysail, period.
Skip
Hey Skip,
Could you tell us more about testing your keel/ama? How much lift are you getting, do you think? Any idea how it might compare to a high aspect foil? Any bad manners?
Pretty much, I’d love to hear all about your design assumptions (foil shape, lateral area calculation, etc.) and what you’ve learned from prototypes (bad manners in specific conditions, optimization, leeway angles, performance compared to conventional amas, etc.)
Thanks, as always for sharing, Skip.
Chris
Hey Skip,
Could you tell us more about testing your keel/ama? How much lift are you getting, do you think? Any idea how it might compare to a high aspect foil? Any bad manners?
Pretty much, I’d love to hear all about your design assumptions (foil shape, lateral area calculation, etc.) and what you’ve learned from prototypes (bad manners in specific conditions, optimization, leeway angles, performance compared to conventional amas, etc.)
Thanks, as always for sharing, Skip.
Chris
Well let’s see…....
Started out with ACDC, the $50 proa, most of the lateral resistance was in the main hull and one of my major hassles was getting back winded with float to lee.
When noodling up P52 the thought was to put most of the leeway resistance in the float (seemed to work, P52 got back winded a total of one time and that under unusual adverse conditions).
Original float on P52 was an symmetrical ogive section, designed to have about 4% of sail area (160s.f.) immersed at nominal static conditions. Seemed to work fairly well, boat would shunt thru almost 90% in light conditions per a friends gps. One thing that didn’t work that well in original iteration was trimming the float fore and aft to trim the boat (float was attached to pod with parallel swinging arms).
After using the boat that way for a couple of years, I added a layer of 1/2” extruded foam covered with a layer of glass to increase the bouyancy of the float and get closer to Speer bidirectional section, part of the reasoning was that less profile area was required since the boat was never going to sail again with 160 s.f.
Revised float, now telescoping with slats in lieu of trampoline was much better, mainly just in utilization but I believe it was better hydro dynamically also but that’s just a gut feeling.
I’ll set down and diddle some numbers to get estimated lift coefficient and such but the basic idea plugs into Tom Speers admonition that it’s not the aspect ratio but the span (draft in this case). I’m shooting for the best I can be in knee deep water.
Cheers,
Skip
Looking back at some posts, it seems that this is not the first time I’ve asked about the efficacy of the tapered/extruded foil ama. Sorry for the redundancy. I keep looking at it and thinking “wow, if that works its a pretty sweet solution” and then assuming it does not work. I’m still coming to grips with it.
And somehow I had never seen the almost Marshallese underbody shape of the P52 ama.
Having said that your explanation above is the best so far. Thanks for that!
Here are more, hopefully less redundant questions.
Broomstick is the first boat built with the tapered/extruded foil ama, yes? I know you’ve only had a couple outings, but how would you say it compares to the P52 ama? In terms of leeway prevention? In terms of handling? How does it do off the wind, when the foil is not supposed to be working too hard?
That’s one of my concerns about using a Speer for a tapered/extruded foil ama..that it’ll be pulling when I don’t want it to.
I love the winglet, buy the way. Of course you put yours on the low pressure side, like a 747, rather than the high pressure, chine runner side. Any thoughts on the design parameters for the winglet (area? Span? chord?)?
Oh one more thing for the Proafile community. Anyone have a DXF or other vector format speer proa foil section they’d like to share?
Yes, I’m full of questions today.
Thanks for your patience and wisdom.
Broomstick is the first boat built with the tapered/extruded foil ama, yes? I know you’ve only had a couple outings, but how would you say it compares to the P52 ama? In terms of leeway prevention? In terms of handling? How does it do off the wind, when the foil is not supposed to be working too hard?
That’s one of my concerns about using a Speer for a tapered/extruded foil ama..that it’ll be pulling when I don’t want it to.
I love the winglet, buy the way. Of course you put yours on the low pressure side, like a 747, rather than the high pressure, chine runner side. Any thoughts on the design parameters for the winglet (area? Span? chord?)?
Oh one more thing for the Proafile community. Anyone have a DXF or other vector format speer proa foil section they’d like to share?
Thanks for your patience and wisdom.
Broomstick has actually been in the water once, Handling was non eventful, keep in mind it was in very benign conditions. Based on experience with P52 I expect general handling to be pretty straight forward, never had an issue in any direction once I went to rudders.
Keep in mind everything to date has been symmetrical foilwise. Everything works towards simple low stress solutions and a little leeway angle is all the force you need (I think).
Winglet is a shot in the dark and as much a step back onto craft as much as anything, plus a little abrasion resistance.
I have Speers’ P30012 section in dwg (Acad 14) format. It’s a bit of heresy particularly since I’ve followed everything Tom has published but am currently using plain old ellipses for float profiles. This is based on some well reasoned arguments for a 75 series section that Rick Willoughby spoke of. When I plotted it twas close enough to an ellipse that it’s what I’ve been using since. Part of the rationale has to do with buoyancy. Speers’ section(s) have a form factor (Pc) of about 0.72 ellipse is 0.7854.
Cheers,
Skip
Oh one more thing for the Proafile community. Anyone have a DXF or other vector format speer proa foil section they’d like to share?
You have access to the actual offsets on Tom’s page, right? http://www.basiliscus.com/ProaSections/AppendixC/AppendixC.pdf
One last time
Here’s what BB33 has morphed into after thinking about deploying anchors and the like.
Can’t say it’s good looking but it does look right, my take on what’s “just big enough”.
The slightly more detailed build also leads me to believe it could be done stitch and glue.
Cheers,
Skip