Small Tri Test Platform

Discussion in 'Multihulls' started by P Flados, Sep 30, 2014.

  1. P Flados
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    P Flados Senior Member

    Friday I did some sailing, but the wind never got up enough for much fun. I did figure out a couple of things. Specific adjustments implemented Saturday/Sunday include:
    • I am gaining confidence that my current AOA control line/lever arrangement will do the job. However, as I was slowly increasing AOA on a downwind run (the hull was up 50% out of the water at around 7 kts), it would reach a point where it would go “over center” and suddenly rotate too much. The fix for this is to move the cross beam further behind the pivot point.

    • The Port ama foil horizontal portion was just too close to the surface. I made a shim to change the angled portion to be slightly more vertical and drop the horizontal portion approx 6”. Hopefully this will improve things.
    I also pulled out an old Venture 15 main I had acquired years ago and found that I may be able to use it as long as winds are not too strong. It is only 2' taller than the Hobie jib, but SA goes from 55 sq ft to around 96 sq ft.

    I swapped out my wooden mast tip with with one that is 1' longer and I can live with the sail foot down 1' closer to the boat. I will just have to lift the boom up and over me during tacks. Part of the enabling idea for this was a main sheet re-think. I will get rid of the vang and use the main to pull down on the boom as required. I have been doing this for a while, but my solution took too much effort each tack and I was not happy with it at all. Now I will have my cleat up front just behind the cross beam, the main sheet will go up through a forward pulley, back along the boom to a rear pulley, then down to a tie off point behind me. The key is that I will have the ability to quickly shift the effective tie off point up to 1' to the lee of the boat centerline.

    I am not sure where winds will be too much for this sail and mast combo. The mast is pretty wimpy (made from 1 and 1/3 sunfish spars) but light. I will need to work things out so that I can use either sail depending on wind.
     
  2. Doug Lord
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    Doug Lord Flight Ready

    Test platform-"axis of instability"

    (from post 19)
    ========
    Paul, somehow I missed this earlier. The problem with a lifting ama foil and a rudder foil (only) with the windward ama foil not in the water is what I call the axis of instability: if you look at the sketch below you can see what I mean. The stb foil and rudder t-foil form an axis between them that allows the possibility of the boat rolling about that axis with nothing you can do about it. If it rolls clock wise raising the windward hull higher it can change the angle of attack of the foils resulting in a problem. A more immediate problem occurs if it rolls counter clockwise about the axis.
    That one of the many reasons why I went with a lifting foil on a daggerboard along with the rudder t-foil and ama lifting foils.
     

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  3. P Flados
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    P Flados Senior Member

    I am not sure this is a significant concern.

    On a downwind run with the B ama to Lee, the sail is pushing in line with the red line you have drawn. No reason to become unstable.

    On an upwind run, I loose all power when I head too far upwind, the lack of pressure in the sail means there is no reason to pivot to the side/rear.

    On a reach, the sail force is again not lined up to cause rotation around you red line.

    There have been numerous 3 point foilers. My boat may or may not be a successful foiler. Regardless, I am sure I will learn a lot and have fun while I am at it.

    A single cross beam, light weight main hull tri with minimal amas and foils for RM has lots of potential for those that want to be able to sail where "hand carry" launch is essential due to the lack of decent local boat ramp facilities. If it can provide for full foiling with kick up foils all around, the layout is even more attractive.
     
  4. Doug Lord
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    Doug Lord Flight Ready

    I wasn't talking about a three point foiler-you had mentioned sailing only on the lee foil and rudder foil. A three point foiler would be stable.

    From post 19: "This mode may eventually result in a full fly, only 1 foil + rudder T foil wet, up-tip stable config. ."
     
  5. P Flados
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    P Flados Senior Member

    The post 19 possibility was only in the context of active crew control of heel similar to what it take to fly a hull on a small cat (very high skill index).

    The 12' effective beam would probably help, but on the other hand, I am not sure I would be up to the task.

    Regardless of theoretical discussions, the boat is no where near demonstrating anything even close to the above at the moment. My biggest concern is that I do not think I can get enough Overturning Moment to fly the windward foil. My current mast is very iffy at best. It is made from 1.5" OD aluminum tube and is now 21' long.

    My other readily available mast choice is my Hobie 14 aluminum mast. However, it is very heavy (30 lbs). If I use it, I would need to do some serious structural re-configuration efforts and it would completely change my setup routine (my current mast I just stand up by hand and slip into a plastic tube). Also, weight up high tends to change boat dynamic response for the worse and getting the boat back upright on the water after a capsize would be much more of a challenge.
     
  6. P Flados
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    P Flados Senior Member

    Friday I did some sailing at the local pond. Wind was across the narrow side and this really messed the wind up. It had plenty of puffs, but was never steady and was very shifty. It was also cold, around 42 °F.

    I was also trying out the bigger sail (95 sq ft Venture 15 main, photos attached). I was not happy with this configuration.

    • I am no pro at getting a good sail shape, and I was hopeless with this one.
    • I would get a sudden puff, and instead of accelerating, the load would overwhelm the foils and they would tend to stall.
    I may try to add an extension to the bottom of the 55 sq ft Hobie 16 jib to get up to 65 to 70 sq ft.

    I have made a few improvements, but I am not sure if I will get any more good days sailing days this year.

    Water will start cooling off.

    I will need a day with enough wind but temperatures of 50°F or so if soon or above 60 °F after the water gets cold.
     

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  7. P Flados
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    P Flados Senior Member

    Went for a sail today.

    Now that it is off season, parking on Wrightsville Beach is free and there are plenty of spaces. It is quick & easy unload directly onto the Banks Channel beach and sail what is probably one of the better dinghy venues in the area. Here is a Google map street view of where I launched from
    https://www.google.com/maps/@34.1945654,-77.8069395,3a,75y,288.03h,54.76t/data=!3m4!1e1!3m2!1s6baoxRDx4TUP-BK-BmEIlg!2e0

    Wind was from the East and strong. Pretty much across the channel. Kind of shifty in spots due to buildings. I used the small sail (55 sq ft Hobie 16 jib) and had lots of fun. I did a lot of reaching, but never really had a chance to do much of anything more downwind. I let it load up and just build speed more than a few times.

    The foils were great for RM but I never got to a steady fast speed with the sail loaded where I could dial in more foil AOA to try to get the hulls up more than 50% out of the water.

    My GPS tracking app shut down recording shortly after I got on the water. Really frustrated at the lack of data.

    As I was pushing things, I did find a couple of problems with the boat that need fixing. The biggest item was the cross beam. Drag from the lee foil was shifting the cross beam to be at an angle instead of directly across. That put the boat angling though the water and causing lots of drag.

    The Port ama planing surface also need adjustment so that it skims better. When loaded today it would tilt up with too much AOA and cause lots of drag.

    Wednesday looks like another potential sailing day at the beach.
     
  8. Doug Lord
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    Doug Lord Flight Ready

    Test Platform

    Paul, thanks for the update-keep at it and good luck! Hope you can find a way to take some pictures and video- I read about this one on SA-seems pretty good:
    Mobius-$79: https://www.mobius-actioncam.com/
     
  9. Gary Baigent
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    Gary Baigent Senior Member

    Doug me old cobra, I have to disagree with you here. My foilers are the two foils working set up: leeward lifting main foil and T rudder, the windward main foil flying clear the majority of the time (to reduce loathsome drag) - this works perfectly. There is absolutely no pivoting or rolling about a diagonal axis line from T rudder to lee foil, platform is steady. IF there is a roll to windward due to wave motion, then the windward foil once it touches down, lifts you back up again.
    Paul, you'll only need a range of AoI from 1 to maximuim of 5 degrees, anything more is just drag and turbulence.
    Also, if you're serious about beating high to windward, your angled lee foil is not going to do the job, will slip sideways; you'll need a vertical main hull dagger for this ... so in the end there are actually three foils immersed, two lifting and one countering leeway.
     
  10. Doug Halsey
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    Doug Halsey Senior Member

    Using the main hull's dagger to counter the leeway isn't always the best solution. It will give you a big increase in wetted area & that's usually very slow.

    If the angled lee foil has enough dihedral (45 degrees or more), there will be a larger projected area for resisting leeway than for providing vertical lift. In a lot of conditions, the sideforce is smaller than the vertical lift, so if the boat can fly OK, then it should be able to resist the leeway too.

    The times that I've use the daggerboard, in addition to the foils, on Broomstick the boat's performance was seriously degraded. Also, I'm much happier with the boat since I cut the vertical fins off the bottoms of the V foils.

    Because I sail Broomstick on a small lake with few other boats around, there are no good yardsticks for comparison, so I have no objective data to back me up (other than top speeds recorded on reaches). But my subjective feelings are in agreement with my objective arguments in this regard.
     
  11. P Flados
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    P Flados Senior Member

    The windward performance is currently pretty bad.

    I was not really trying to get good windward performance at this point, but at times (especially when fighting narrow channel, current & headwind) the poor performance has burned up a lot of valuable time.

    I think three things hurt the ama foil windward performance

    • The narrow chord and small vertical projection (4.5" x around 16.5" per foil or close to 150 sq in) down into the water
    • The angled portion of windward foil operates at a lower AOA and the foil sections are not symmetric. Just looking at the water as I am beating indicates that the windward foil is doing much less leeway resistance than the lee foil.
    • I just am not getting enough velocity to overcome the above.
    I pulled out an old Sunfish daggerboard I once made from 3/4" ply. I re-shaped the lower portion into something close to a foil and I think I have worked out how to hang it over the side to act as a leeboard. The effective area will be close to 9" x 28" or 250 sq in.

    Since I can rotate one or both of the ama foils out of the water, I have some options to try if I want to go for better upwind VMG. Unfortunately, there are "end use complications" to re-configuring (i.e. PITA). Still I want to experiment some and see if a more permanent improvements (swing up leeboard and better provision for rotating ama foils up & down) would be worth the effort.

    I just really wish I had a better venue for this experiment. Currently I typically sail at one location with nasty tidal currents or another location with terrible shifty winds. Hard to really judge VMG improvements in these settings. There is a third potential location (power plant cooling pond known as Sutton Lake). My reluctance to sail there might have something to do with the big alligator warning sign at the boat ramp. I am not so sure this place is a great choice for my style of solo sailing in an experimental craft subject to sudden catastrophic failure.

    Even though in some ways I (the engineer Me) am frustrated with my poor progress in achieving desired boat speeds, I have to remind myself that this is just a "test platform" and that I (the regular guy Me) need to just relish having some "fun on the water". My sail yesterday ended up much more effective at meeting this last criteria :D
     
  12. P Flados
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    P Flados Senior Member

    I actually have acquired an option I will try sooner or later for at least some handheld "from the cockpit" video. When I lost my old cell phone, I made a point to get a water resistant smart phone (an older model - it only cost me $50). I do need to work out some way of attaching a secure tether. Then there comes the challenge of trying to go fast and control the boat with only one hand (not going to happen without really steady wind & generally optimum conditions).
     
  13. Doug Lord
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    Doug Lord Flight Ready

    Paul, just the "coolness" of trying the things you are should make you feel good
    and energize your creativity to solve some of the problems-just be patient and enjoy. Taking video that you can watch later could be a big help as well. The video of my test model has been the single most important tool in getting it foiling. Keep at it.....
     
  14. Doug Lord
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    Doug Lord Flight Ready

    =================
    Could you try rigging a long carbon tube(removably) off the stern or off the crossarm to catch most of the boat? Maybe use duct tape to hold the camera in position on the tube. Or even fix it in position to just watch the lee foil.....
     

  15. P Flados
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    P Flados Senior Member

    If I can get reliable performance worth a video, I would consider such a thing.

    I have used a cell phone for some video at slower speeds. I can actually get some interesting shots of the foils, the hull going through the water, etc with just holding the camera.

    Right now, it is just not high enough on my priorities. Again, I really do have some much more pressing issues that I need to fix.
     
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