Crossbow fl

Discussion in 'Sailboats' started by Doug Lord, Jun 21, 2012.

  1. ancient kayaker
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    ancient kayaker aka Terry Haines

    Since the trapwing and the DSS are both technological add-ons it makes a lot of sense to me to try out the system starting without using them both at once. That will separate problems resulting from one or the other and also establish their individual contributions to performance. It will give you an opportunity to learn how to handle the subsystems one at a time - you may find you have enough work in the early test stages just setting up and learning to drive the basic sailboat . . .
     
  2. Doug Lord
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    Doug Lord Flight Ready

    ========
    Thanks, Terry. The biggest problem I see is that, overall, the "one at a time" process will be substantially more expensive requiring two complete rigs. Of course, only one at a time! It may still be the best way for now....
     
  3. ancient kayaker
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    ancient kayaker aka Terry Haines

    The sticks for the test rig can be the same; if the sail has eyelets where reefs would normally be (I assume the rig is not reefable as designed) it can be lashed for testing. Not sure if that's practical in this case but it may be an option. The eyelets would not affect normal sailing.
     
  4. Doug Lord
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    Doug Lord Flight Ready

    Well, the mast section is $90+ a foot and the "non-turbo" version is 15' long vs the turbo version at 18'..... And Matt has a 15 foot section available.
     
  5. Doug Lord
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    Doug Lord Flight Ready




    If I decide to go without the Trapwing to start with, these are the revised specifications:

    =================
    Non Trapwing version--

    Specifications: (changes are to be expected)
    LOA-14.6'
    Beam- 4.75'
    ---at waterline-3.75'
    Sail Area-(boat will use a carbon A Class wing mast from Matt McDonald/ Falcon Marine LLC, laid up specifically for this boat).
    --upwind- 92.5 sq.ft.
    -- downwind- 192.5 sq.ft.
    Weight-sailing weight w/o crew- 170lb which includes:
    --a. hull, rig, foils-123lb
    --b. ballast bulb 47lb.
    --c. Max Crew weight: 250lb
    All up sailing weight including crew-420lb
    DSS Foils: each 1.63 sq.ft.( 6" X 39") 6.5/1 aspect ratio, Welbourn section.
    -------
    Ratios-
    DLR=(smaller better)
    a.Windmill-93.95
    b. Crossbow-60.25
    SA/D=(higher better)
    --upwind-
    a. Windmill- 28.68
    b. Crossbow-26.37
    --downwind
    a.Windmill- 28.68
    b. Crossbow- 54.89
    SA/ton(2240) : ( Note: rule of thumb says 500 sq.ft. per long ton required to plane. It is well known that the Windmill planes-and early compared to many boats)
    a. Windmill- SA/ton=493.85
    b. Crossbow-
    --Main +jib- SA/ton=493.3
    --M+J+asy spin-SA/ton= 1023.36

    This is very encouraging because I raced Windmills for years and it was a great boat to sail. It was also quite fast for its time-(especially in light air against Flying Dutchmen!).
    The upwind SA/D is very close but Crossbow is much better off the wind. The Crossbow DLR is substantially better. I wanted to try to tweak the non-turbo(minus the Trapwing) version of Crossbow to get as close to a Windmill as possible while still retaining it's self-righting capability which I think I have done. The Crossbow will carry 47lb of lead at the bottom of the daggerboard and should be self-righting with the crew in place. It should recover from a knockdown with little to no effort from the crew. A block and tackle on the boom(maybe the vang?) would be used to mostly retract the board allowing the boat to still be sailed off a beach.
    I'm pretty well convinced after doing the design work yesterday and today that going with the "simple" version to start with is better for me-all things considered.

    Pix-model and side to side comparison of working sketches of turbo and non turbo(1st draft) sailplan:

    click on image for best detail-
     

    Attached Files:

    Last edited: Aug 1, 2012
  6. sharpii2
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    sharpii2 Senior Member

    It's good to see you trying some of your ideas.

    I think you are wise to compromise, for the time being, by going with just the DSS foils.

    I wish you the best of luck and congratulate you for going through with this.
     
  7. Doug Lord
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    Doug Lord Flight Ready

    Thanks, Sharpii-appreciate you checking in!
     
  8. CutOnce

    CutOnce Previous Member

    Doug:

    You have lost absolutely nothing by opting to defer feature implementation - as long as the critical structure for future integration remains. I really think your odds of getting a great boat on the water just went up a huge amount. Not because you've "given up" on ideas, rather because you now can deal with these ideas on a carefully staged basis.

    Since this is a technology testbed, one thing to put on the list of little structural supports is a couple T-nuts and backing plates on boom end, mast top and bowsprit for mounting your GoPro. Much lighter and more reliable than huge wraps of duct tape.

    On the "testing" design, I'd also consider a strong hollow keel bulb, with a strong threaded cap. That way you could adjust the bulb weight with lead shot without having to re-fabricate the keel if you wish to tune your RM/recovery aid.

    I'd also put some thought into failsafe systems concepts. Since this is going to be designed for limited mobility and centreline seating, perhaps incorporating a "safety leash" (like a PWC) that pulls pins on the mainsheet blocks if the crew leaves the seat. If you capsize and recovery doesn't pop you back up, the last thing you want is to bail and the boat to self rescue and sail off without you. I'd also put some thought into aids to getting back into the boat if you do bail. Righting lines, handlholds and stirrups for feet. Basically, plan for worst case trouble and incorporate features to help you when it happens. Try these systems in shallow water with a beach crew to help. Make sure you can operate the asym kite recovery line from the seat while capsized, and with a wet kite.

    Another area that may prove worthwhile at a small drag penalty is providing for a leash on the removeable DSS foils. I can see the necessity of pulling the foils at the beach, and a little leash could save the loss of one inadvertently. I have retainers on daggerboard and rudder foils to prevent loss. Maybe a DSS foil "ejector" line is a good idea as well - for unseating the foil from the seat if approaching a dock or pilings. It could be as simple as a line that wraps around the fully seated end of the foil and exits the trunk to the cockpit and be combined into the leash as well.. I can't see a limited mobility helm reaching down under the water to pull a foil out.

    --
    CutOnce
     
  9. Doug Lord
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    Doug Lord Flight Ready

    Good comments, Bill-thanks. The go pro will be mounted with a long carbon tube at the transom and a short one near the DSS foil. The DSS foils(at this point) are bolted in place with a single bolt.
     
  10. tspeer
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    tspeer Senior Member

    I wouldn't shorten the mast.

    All the changes you mention would optimize the boat without the movable ballast, but will cost more when you put the movable ballast on. Instead of optimizing the boat for not having the movable ballast, I think it's better if you try to stay as close to the intended configuration as possible.

    The objective for the boat at this point should be to establish a baseline against which you can compare the difference in performance between the movable ballast of the trapwing and the fixed ballast of the bulb.

    1) Reduce your sail area by reefing the main and stick with the original size. That way you only have to buy one mainsail. You may want to have a smaller jib made, but it can be your heavy air jib when you go to full sail area. If the wind is light enough, you can still sail with the full main.

    2) Leave off the assy spin for now. You can do a lot of useful work upwind and reaching without it. Or, have the smaller spin made with the intent to use is as your heavy air spin later. A screecher that can be used upwind in light air or as a reacher/heavy air spin would be another possibility for a sail that is useful now and later.

    3) Keep the total weight the same so you have a more useful baseline. You will then be able to compare the difference between sailing with two different ballast configurations at the same displacement.

    4) Keep the same mast length. Otherwise, you'll have to purchase a new mast when you want to put on the movable ballast and go to the full sail area.

    For each major feature of the final design, you should ask, "What is the technical risk that this feature won't work properly?" Then you can plan for attacking that risk in the buildup to the final configuration. For example, there will be issues with DSS bearing design, board handling controls, board incidence setting, handling the board when launching and recovering, etc. These can all be worked out with the bulb keel before you have to deal with moving the ballast.

    And then there's the question, "What does each feature add to the performance of the boat?" You'll want to test with and without each one. This is the time to test without the trapwing. Then when you add it later, you'll be able to document just what the difference in performance was. This information is invaluable when you start considering the MKII version.
     
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  11. Doug Lord
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    Doug Lord Flight Ready

    ==================
    Thank you very much ,Tom. I have the option now of getting a 15' section of the A-Class wing mast at a good price since it is from a section that got screwed up during layup. Matt says he thinks he can get 15' undamaged but it will have been laid up with the A Class laminate. Originally, we were going to use a different lay up for my 18' mast. So I think I'll take the good deal and go with the short rig. In considering everything, going this way with the small sails saves a bunch of money which I have to do to get this thing in the water. It saves money NOW when I need to save money. A year or two down the line I may be able to avoid the higher costs of new sails and mast better than I can now.
    I'm making a lot of sacrifice here to get going but cutting out the asy spin is one step too far because,in my opinion, it is essential to properly evaluate the foils and the boats' offwind potential w/o movable ballast.
    Thanks very much for your suggestions-I really appreciate it and will stick close to them in evaluating the boat.

    PS-I have a go pro camera and speed puck to help see what's going on and will send video to Hugh and Eric(and you if you would take a look?) as well as posting some of it here to help understand if the foil is working well. The DSS foils are probably too long but they are "plug-in" foils secured with a single bolt. They can be adjusted as required for incidence,length and fore and aft placement. This mounting option is a tradeoff since most DSS foils are retractable but the logic with this particular boat is that I would probably not sail in conditions where the foil doesn't work or, at least if I do, I won't worry about it.
     
  12. Doug Lord
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    Doug Lord Flight Ready

    Updated sketches of the tall rig DSS+Trapwing and short rig/DSS only:

    click for best detail-
     

    Attached Files:

  13. Doug Lord
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    Doug Lord Flight Ready

    Crossbow fl-testing

    Because of my concern over the skin temperature of the boat getting too hot, I just bought an Extech 42511 Dual Laser Infrared Thermometer
    with adjustable emissivity. Many of these instruments have fixed emissivity which is ideal for dark objects but this boat may be white silver or? I want to monitor this carefully so I don't melt the EPS foam!
    I'm also looking for "high solar reflectance" high gloss two part polyurethane that might allow me to paint the hull a shade of red. The center portion of the deck may be clear(with a uv filter) carbon if it is built of 1/8th in Okume instead of foam.

    Features:
    •Manufactured by Extech
    •Dual laser for accurate target spot
    •White backlit dual LCD display
    •Fast 150 msec response time with Max display
    •Adjustable emissivity increases measurement accuracy for different surfaces
    •Adjustable High/Low set points with audible alarm alerts
    •1% accuracy
    •Lock function for continuous readings
    •Double molded housing
    •Ships complete with carrying case and 9V battery
     

    Attached Files:

  14. P Flados
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    P Flados Senior Member

    Doug,

    At work, we have guys that monitor stuff with infrared all the time. One of them told me to use black electrical tape. He just sticks a small tab on surfaces, waits a few minutes & takes his readings. He compared this to direct reading contact instruments & said it was real realiable.
     

  15. Doug Lord
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    Doug Lord Flight Ready

    Thanks, Paul.
     
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