Bionic Broomstick
My green proa’s steering improved when I reduced the beam from 11’ to 8.5’ and built a new, higher volume ama. I think it’s easy on a small proa that you plan to sail from the tramp or platform to make the beams too long and the ama too small, and then have it dig in a lot and try to turn the boat up to windward.
If you’re going to sail from the big hull then a lot of beam and a tiny ama seems ok, or at least that’s what I see the native boats doing. But if you’re normally going to sit out to windward the ama has to hold you up in the lulls without digging in and yanking you up, so a low immersion rate per pound of load is good.
I don’t believe it is a rudder balance thing. I had enough balance built into design. I light wind, while i was sitting on the main hull and kept outrigger just kissing the water she would go in straight line for minutes. However as soon as i move to the trampoline, pull would show up.
Vlad’s note about the differences between the unloaded ama with a balanced helm versus loaded (him on trampoline, weather helm bad) caught my eye. If rudder states are the same in both conditions, then perhaps excessive aka length, in combination with ama drag should be considered. If I recall correctly, Simba/Pacific Bee’s current owner shortened aka length (after careful deliberation) and the boat performed better.
Seems that the ideal amount of righting moment needed for balanced helm is a moving target dependent on conditions. With a fixed aka length the boat has a narrow optimal set of conditions - and if the wind is higher or lower either the righting moment will be inadequate or the ama drag will be much higher. Controllable water ballast in the ama is one approach to mitigate this.
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Bill in Ottawa
A lot of this is still a mystery to me, I think Crazy Russian will persevere and we’ll know more in time. I know that the boat had a pantographing system to move the ama fore and aft at one time. I tried that once on P52 when it had a swing arm system, was terrifying, I’m a telescoper nowadays.
Reminds me of the steering oar conundrum with P52. A steering oar worked quite well on ACDC and did also on P52 until…. Moving at speed when a little weather helm needed to be straightened out there was a runaway feedback effect where a little force was applied by the oar trailing behind the boat bent the oar a bit which required a little more input which bent the oar a little more ... ad infinitum.
https://www.youtube.com/watch?v=iVoVP5ozj4I&feature=channel_page
P52 is moving right along, no turbulence, spray or other indication that things are unbalanced. Not shown in the video is the white knuckle grip on the oar that’s visibly bent to keep things going in a straight line. Not because things were out of balance but because I couldn’t make an oar stiff enough.
Skip
Finally got Trackmaker to do what I wanted, attached is the GPS track of the first outing along with a couple of other pictures
Skip
PS I was so excited to be back in a canoe I forgot to focus the shots of Kevin sailing
https://www.youtube.com/watch?v=iVoVP5ozj4I&feature=channel_page
P52 is moving right along, no turbulence, spray or other indication that things are unbalanced. Not shown in the video is the white knuckle grip on the oar that’s visibly bent to keep things going in a straight line. Not because things were out of balance but because I couldn’t make an oar stiff enough.
Skip
Skip:
I’ve always really liked that video of P52 - it was one of those things that made me give proas a double take. So little sail and so much performance in the T200. It did look like there were no control issues or effort on your part. Looks like 10 plus knots of speed and you could sit a full cup of coffee on the deck with losing any.
Contrast that with John Harris’ comments about both Mbuli and Madness - the helms were so balanced he indicated there was a lack of “feel” and feedback. Russell Brown’s boats also exude a lack of drama and no histrionics.
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Bill in Ottawa
Contrast that with John Harris’ comments about both Mbuli and Madness - the helms were so balanced he indicated there was a lack of “feel” and feedback. Russell Brown’s boats also exude a lack of drama and no histrionics.
Bill,
Thanks for the comments, regarding helm please note that when P52 went to rudders, it was always two finger steering at most, the white knuckle stuff was simply a runaway feedback endemic to long shafted steering oars.
I miss the boat, which is the primary reason I’m travelling down the current path with the Broomstick. Already there’s been some simplification in the rudders for Nomad, saves maybe a half sheet of ply and 10# +/-.
Cheers,
Skip
Update on the wingsail for the Broomstick, pieces are going together. Assembly at this point is using 96 clamps, all joints with foam involved done with Gorilla glue, wood to wood with titebond. The wood strips are cypress left over from Laurents proa.
It’s really good to be back building something again. Building anything is better than nothing, building boats is best, building proas the very best.
Cheers,
Skip
Glad to see that my excess bold cypress is still useful!!
I am really impatient to see that wing in use…
What tube will you use as the main beam for the wing? Aluminum? Carbon fiber? Do you intend to make it retrievable?
If not, I would have thought that it would help to use that actual tube as the backbone for the construction itself. Slide in all the foam ribs, set the tube on sawhorses and then you can place and align and glue all the ribs to the tube…
Maybe the tube is not going all the way to the top?...
I want more pictures!!!
Cheers,
Laurent
Glad to see that my excess bold cypress is still useful!!
I am really impatient to see that wing in use…
What tube will you use as the main beam for the wing? Aluminum? Carbon fiber? Do you intend to make it retrievable?
If not, I would have thought that it would help to use that actual tube as the backbone for the construction itself. Slide in all the foam ribs, set the tube on sawhorses and then you can place and align and glue all the ribs to the tube…Maybe the tube is not going all the way to the top?...
I want more pictures!!!
Cheers,
Laurent
Hang on, I’m slowing down in my old age 😉
The wing pivots on a stub mast of 2” OD alum tube of questionable quality (HF flagpole piece), projects 30” into the wing. Wing pivots on the tube, tube fastened to the broomstick via 3 pvc struts. General approach of having a stub mast seems the most structurally efficient, the thickness of the wing (21%) lends itself to having a deep spar to carry the loads. And it’s much easier to (I hope) to slide the wing over a 30” long stub than a 150” piece.
FWIW Kevin convinced me that for the next iteration (Nomad) it should be easy to roll the boat on its’ side to insert the wings, makes it much easier to contemplate.
I’ll post some more pictures in a few days.
Cheers,
Skip
Looks like a serious effort Skip. Can’t wait to see it in action. What are you going to use for the outer skin?
Looks like a serious effort Skip. Can’t wait to see it in action. What are you going to use for the outer skin?
Thanks Mal, the leading edge gets wrapped with Dollar Store foam (3/16” xps) then the whole thing is skinned with heat shrink window film about 2 mils thick. I built a skin on frame sit on top kayak using the film many years ago, this time I’ll put some UV protection on the finished product.
It’s premature but I’ve mulled over what to use for the next generation and am seriously considering hot wired foam skinned with 5-7 mil mylar. Should be weight and cost effective.
Skip
I meant to ask, how is the weight going so far? I think that weight is the big challenge!
I meant to ask, how is the weight going so far? I think that weight is the big challenge!
Won’t know for a few days until the thing comes off the strongback. Bionic Broomstick weighs about 80# at the moment, will weigh about the same with the wingsail, current cambered panel sail has some very heavy battens. Only things that’s been weighed is tailplane ~ 10 Oz.
Biggest weight issue is actually with the operator 😉
FWIW prelim thoughts for Nomads slightly larger more robust wing sails are at about 20# each.
Skip
FWIW prelim thoughts for Nomads slightly larger more robust wing sails are at about 20# each.
Skip
Is this going to be a flapped two-element wing or a single, like SailDrone?
Dave
Is this going to be a flapped two-element wing or a single, like SailDrone?
Dave
Flapped, a direct clone of Elkaims’ Atlantis. You can see the thick trailing edge in one of the pictures along with the alum. tube sockets for the tail booms.
Skip
Wing update, things have progressed to where wing is off the strongback, weighs 6.5# as shown. Probably will come in at about 10# total plus maybe 3-5# for the counterweight.
Right now the wing is terribly fragile in torsion (expected) and fore and aft stability (not quite so expected). Stiff as heck in the plane of the main spar. Everything should settle down with the foam D tube in front of the spar and the heatshrunk skin. The thing wasn’t done to withstand a gale but to investigate slow speed characteristics.
Work’s going to come to a standstill for a couple of weeks while some family stuff is done.
Skip