Alternative Motorsailer Rig

Discussion in 'Motorsailers' started by Yobarnacle, Dec 4, 2011.

  1. Yobarnacle
    Joined: Nov 2011
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    Yobarnacle Senior Member

    I have enjoyed and learned a lot in this Forumn. Read with interest A frame mast posts, but don't want one. I have a 40 year old Albin 25 Motorsailer with rig. I have made serious modifications to the hull including lengthening to 30ft by adding bow cut off an Oday Daysailer II as a canoe stern.

    My current problem when I stored the boat, was working on mast location. I'm trying to introduce a wee bit of weather helm so she will point.

    My idea is to use a radar arch over center cockpit and step mast and attach shrouds to this arch. With some pinned base mounts on the arch, the whole rig could be tipped aft to clear under bridges similar to an A-frame mast.

    Advantages to me are, no mast compression on roof, Can include pinrails or cleats for halyards on arch frame. Of course it lends itself to underslung installation of a radar dome. And, i already have the rig. I'm just considering a really fancy tabernacle design.

    Attached is a concept drawing of what I'm trying to accomplish. Drawing is missing some cabin hatches and the boat is currently twin screw instead of one as drawn.

    Any and all comments welcome. If you want to bash the design, that's fine too. Please include reasons.
     

    Attached Files:

  2. Boston

    Boston Previous Member

    Thats a lot of modifications. You might want to evaluate things like stability and righting moment. Once you start changing one around to much you kinda open up a can of worms. Only way you'll know what all those modifications are doing is to either run a pile of numbers or get out and sail the thing. Seems the former is a lot safer.

    anyway it looks good

    cheers
    B
     
  3. daiquiri
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    daiquiri Engineering and Design

    I like your idea. Make sure that hull-to-deck joint is strong enough to withstand the tension (winwards side) and compression (leeward side) loads from the mast-carrying arch when boat is running under sails.
     
  4. Yobarnacle
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    Yobarnacle Senior Member

    Presently I and IntrepiDos are 1500 miles apart. When I loaded her on the trailer and stashed in the storage yard, she had an ugly contraption of 2x4s in the center cockpit to serve as the radar arch tabernacle. I was hunting how far aft I needed to, could move the mast. I think I found the sweet spot. Next time I work on the boat I'll install a radar arch like in the drawing with beefed up gunls to absorb the stresses. Still lots to do. Haven't even started on interior. Stripped her out and put some exterior plywood mockup interior in her. We use that when we are test running. When design is perfect I'll spring for nice wood. But operational is more important than creature comfort right now.
     
  5. Yobarnacle
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    Yobarnacle Senior Member

    Thankyou both for your comments. Here is a picture of an Albin 25 sailing for comparison. It's not mine and I don't know whose or whose photo, found on internet, and my apologies using without permission. Neither do I know if she has a modified underbody. Lots of owners retrofit bilge keels to improve sail performance.

    I considered lots of options. Pers Brohall said the rudder was too small to perform well under sail. I consider him an expert on the design, since he designed her. So I wanted a larger rudder, also more lateral area without increasing draft. Shoal draft lets you explore areas others can't and easier to trailer. My distrust of thru-hulls eliminated centerboards ect as option. I wanted the rudder to remain tucked under for protection.

    Lengthening her was obvious solution. Also at 8.5 ft beam and 25 ft LOA, she was too tubby. Whales and dolphins have a beam length ratio of 4 to 1. Again I consider the designer THE EXPERT. Changing beam was not an option. Present ratio at 8.5 ft to 30 ft is still less than 4 to 1 but it's an improvement.

    All this required shifting center of effort of sails aft. Hence the tabernacle arch.
     

    Attached Files:

  6. Boston

    Boston Previous Member

    center of buoyancy vs center of mass and righting moment are going to be critical. lengthening the boat moves the center of one but not the other, its also going to effect initial stability and ultimate stability. Also center of lateral resistance is moved so she might be a bit hard on the tiller. Lots of considerations when major modifications are being made.

    you might want to make a drawing and try and determine what you've changed and how that effects stability.

    otherwise its hard to know just what effects all these changes are going to have. Although you do have the designer handy so thats going to be a huge help.
     
  7. Yobarnacle
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    Yobarnacle Senior Member

    Thankyou for your interest and comments.
    Unfortunately Pers Brohall passed. All the modifications I have done are things that improve an already excellent design stability. An older design principle seemingly abandoned by modern architects is the metacentric shelf. A symetrical or nearly so metacentric shelf is a result of vessel ends being of similar heeled imersed areas. Double enders are naturals. A crossed shelf results in the stern rising and bow rooting when heeling. Lots of modern sailyachts do exactly that.
    The new stern I installed is strong yet light. Foam filled, self bailing. All thru-hulls (4 including cockpit drains) are in this section. The old tramsom still exists, a bulkhead between new stern and rest of hull, which now has no thru-hulls below water line.

    The boom is same height as before, just above wheelhouse roof. I installed a sliding gooseneck. The spar stands a little taller. A bit more weight aloft. But I have a bunch of batteries in this boat way down low.

    The radar arch is increased tophamper as is the light weight roof I extended over the center cockpit. What weight will the radar arch have is unknown at this time. I'll have one as light as permisable for strength requirements. If I need more ballast, I'll buy more batteries.

    I have had the boat out sailing with a heavy adjustable fore and aft 2x4 post and beam arrangement in the cockpit supporting mast.
    I found sweet spot by trial and error, though I knew by theory and calculations it should be CE 3% to 5% lead in front of CLR.
     

    Attached Files:

  8. Boston

    Boston Previous Member

    What about righting moment ? or ultimate stability ? CLR and CE. All that balance must be considered. I'm all for ya don't get me wrong, first thing I do whenever I see a design is consider how'd I'd customize it. But making changes opens up a major can of worms.
     
  9. Yobarnacle
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    Yobarnacle Senior Member

    I do appreciate your comments and concerns. I'm not being defensive, I'm attempting to re-assure you I covered the calculations before and during modifications. I did nothing to adversly affect athwartship/ heeling stability.

    Attached is the designers schematic for a cradle including lifting points. The stern I added I lifted in my arms. I'm 63 years old, 6'1 and 210 lbs.

    Lengthening the hull moved the center of gravity a small % aft but it remained on the centerline.

    Center of bouyancy moved very slightly aft,a %, again along centerline.

    Center of Lateral Resistance moved a greater % aft because I filled in prop aperture and old rudder space as keel and added a larger rudder further aft. But not all at once.

    I dramatically moved Center of Effort of sails aft quite a substantial amount, not a % of.
    I didn't enlarge mainsail or lengthen foot, like I did for keel. I moved the whole rig 6 feet astern, by shifting mast from middle of forecabin roof, to aft of wheelhouse roof.

    Closing in the keel was done bit by bit combined with propulsion tests of the electric drive. We started with electric drive in old prop aperture, then replaced old rudder with azimuthing electric drive, and hung a enlarged rudder behind. I'm going to move drive and rudder one more time, further aft next time I'm working on boat.

    We went motorsailing after every minor modification before proceeding.

    We were impatient to use the boat, and I got tired of working on her in the heat, so good excuse for sea trials. er, ICW trials.

    Por favor, Confidence, Senor.
     

    Attached Files:

  10. Yobarnacle
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    Yobarnacle Senior Member

    If you want to see my calculations, we'll need to get together. I can do higher math, no problem. I carry the formulas used to generate HO 229 Sight Reduction Tables in my head. With a $15 student calculater with trig functions, and those formulas, I avoid carrying 6 volumns of Ho 229, each covering 15 degrees of latitude.
    For centers of areas, its easiest to cut them out of thin plywood, and balance on a metal edged ruler. Balance this way and balance the other way and X marks the spot.
     
  11. viking north
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    viking north VINLAND

    After reading over your mods. the biggest challenge i see is the CE/CLR lead. Typically a sloop rig is in the 15% range. Have you done a scaled underwater profile cutout. The balancing on the head of a pin is as good as it gets to determine CLR. My other concern is the location of the radar transmitting antenna. Check the manuals radiation pattern level off the deck at your helm location. It must be well above your head. The brain, and eyes are very susceptible to the power and short wavelengths involved. Mine will be mounted halfway up the mast. Many are pole mounted well above head height at the stern,which i'm not a fan off, often wonder what the radiation reflection off the mast and rigging coming back at the helmsman and cockpit occupiers would measure. Bet it's far stronger than that of a typical cell phone.(There are now dire concerns with brain tumors associated with their use) Nice looking boat--strange i haven't bumped into this design before. Looking forward to seeing it in the real.-- Geo.
     
  12. Yobarnacle
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    Yobarnacle Senior Member

    Thanks Geo
    I'm considering one of the new 3G radars. Low power, low emmissions, excellent resolution short range. Maybe i'll get one, maybe not. I will have a chart plotter conected to a 22 inch flat screen monitor and AIS. The AIS shows commercial traffic position, speed, course, name, ect. And more important, they'll see me. AIS is a low power, low weight, 0 maintenance device.

    As to radar radiations. I don't want to start a fight by challenging peoples beliefs. But the reason I turn off the radars when a hand goes top of wheelhouse to change a bulb or something, is so he doesn't get knocked in the head by the scanner. The deckhands all believe it's so I don't cook their nuts. The 500 watt microwave in the galley radiates them far more than 20 watts produced by radar. IMHO
     
  13. Yobarnacle
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    Yobarnacle Senior Member

    Yep, I get centers of irregular curvilinear areas, like hull sections, profiles, immersed areas by balancing. Never tried it on a pin, but it's fast and easy on a steel edged ruler. Balance once, mark the line, turn section, balance again, mark line. X marks the spot. Center of bouyancy, or metacenter, or resistance, or even gravity if its a homogenous substance like a fuel tank.
    Unfortunately, accomodations and machinery spaces need calculation of weights of individual components and how they relate to and affect the center of the mass. Tedious. My new stern I treated like a tank. One full of foam.
     
  14. Yobarnacle
    Joined: Nov 2011
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    Location: Mexico, Florida

    Yobarnacle Senior Member

    Electric Propulsion

    Here are the components of my electric drive. Only used the prop from the Seagull and adapted it to the trolling motor. I have 4 of these 11 inch props. None are for sale. Kort nozzle is 13 inch. Trolling motor developes 160 lbs thrust with its plastic props. How much thrust do I get with the Hydrofans and Kort nozzles? Don't know, but it feels like a lot more and theres a lot more prop wash. Maybe the Minnkota Riptide trolling motors won't endure long. I'll find out. Hope it's later than sooner. Each component is excellent in of it's self. Together they create synergy. The total is greater than sum of the parts. I'm pleased with both the speed and economy of battery power I get. I use it motorsailing, more Synergy, between motor and sails.. I included an updated drawing showing correct scale of props and kort nozzles.
    Any suggestions to improve function further?
     

    Attached Files:


  15. viking north
    Joined: Dec 2010
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    viking north VINLAND

    Interesting stuff, you've been planning this for some time and now finally having the fun in building it. Acculumative engineering --I need a machine to do this, what off the shelf items can I mate up/modify to have a go at it, hell of a disease isn't it, once engaged the brain doesn't want to shut down. I always carry and keep a notebook next to my bed. I can see my visit might involve some hands on, is there a place i can plug in the 26ft. RV just in case? :)
     
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