Crafting Mast Step for Outrigger

Discussion in 'Boat Design' started by BobBill, Sep 14, 2013.

  1. BobBill
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    BobBill Senior Member

    I am crafting a glass version of the venerable Malibu Outrigger using a cast off ’84 Hobie 18 port hull and cast off Hobie 16 s'bord hull…recycling them, if you will.

    The 18 footer is the same length as the Malibu O but much lighter. I fixed a stem crack forward of the dagger slot and added glass to the stem line bow to stern.

    The mast step is forward in the hull, ala MO.

    I cut out the deck to take a 5 inch curved Viking inspection port to install the step in the hull (unstayed stubby mast to carry long yard).

    The plan is to place the mast step low, over a weep pipe, just above the keel or stem line. I added epoxy/Kevlar/carbon reinforcements to hull sides ostensibly to reinforce sides for added supports. I also placed a 6 inch long x 1.5 inch PVC weep tube pipe to the layup’s surface long stem or keel line.

    I planned the mast to be T6061 T6 Tube (3-3.25 OD) stepped to plate just above the weep tube…using a clay or play doh dam and fill with epoxy matrix to support a carbon step tabbed to hull part and s’bord.

    The distance from the step to the deck port is planned to be PVC or some sort of tube I can make in which will encase the mast when stepped…

    I was going to use an aluminum ring or two at deck to support the mast there, but it occurred to me that will be a tricky task because of the small deck hole etc. Arm in hole makes it a feel deal…

    So I was wondering if I might be better off adding carbon strips across deck (beam is about 12 inches there) and around the port hole, that would stiffen and strengthen deck area to take mast pressures?

    A carbon deck/brace/support partner might be a little spendy but would preclude some tricky work inside hull and so on. I could also add carbon tubes to support the mast tube from the step to the deck and across the beam...

    Does that seem feasible? I have made a rough illustration to help visualize the mast area…

    Diagram and pic of model are included to clarify.

    Thanks.
     

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  2. peterAustralia
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    peterAustralia Senior Member

    hey bob bill

    assume you have seen this
    www.tacking-outrigger.com
    I added a new 17ft outrigger today

    looks like an unstayed rig you have there
    I would fix the pvc tube to the hull with 9mm plywood, to keep it all in place. Make a kind of cross reinforcement,,, top, right, back, forward, Also these plywood supports could go up a few inches, lower the pressure on the mast, giving more bury. Just my opinion. I have seen an example of that type of reinforcement somewhere. Might be able to find the pic again.

    Your center of effort of sail looks pretty aft. Overall it looks a lot like Chris White's dragonfly tacking proa,,, and also the new tacking proa from John Harris of CLC

    mastpartner+and+rudders.jpg

    n peter evans
     
  3. BobBill
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    BobBill Senior Member

    Peter, Thanks. I have the link and you are correct that the rig does resemble White's Dragonfly design. I basically used the Malibu plans I acquired and went from there. Odd story. I was going to "recycle" a set of Tornado hulls, Marc here offered for free. They would have been perfect. He reduced the beam for legal highway travel. But I could not locate a decent trailer, after looking for some weeks. Then a gent a scant 4 hours from home came up with a trailer - if I took two hulls he had been storing in his mom's yard...seemed fair and those hulls happened to fit the design and not too beat.

    BTW, I used White's jpeg as a basis for the design using P-Shop, to keep my perspective...as I recall that rig has a shorter loa.

    Anyway, I am going over your pics and will peruse those on the proa site, again, to see if I can come up with some added ideas.

    The stubby's base will be down inside the hull a good 25% of a meter, so if I can strengthen the deck with carbon/metal where the stubby passes through, it will save much work, if it works.

    Here is a pic of my Kite Dinghy mast iron as an example that got me thinking I could do this in some way.

    It is just a metal ring at top and the hull form at the step...old but effective.

    It occurred to me that I might be able to use the carbon/Kevlar/metal-strengthened deck to emulate the metal ring the Kite employs, considering it is a stubby and the base is about as deep in the hull...also the long yard flexes to de-power the ring in gusts etc.

    If I have to brace the deck from the inside as well, I might be able to manage that using carbon rods or tubes and carbon tape.

    I like your set up and would like to copy but keep it below the deck somehow, but the wee port opening makes that near impossible, and the reason I thought of building up the deck thickness to do the same thing...

    What I did not mention is that if this works, next year I will add a small cockpit aft of the dagger case, for sitting comfort.

    If I am right and the new addition to the site is Tim E's at end (it is a beauty) can you post the beam specs, weight etc also?

    I am keeping the overall beam of this "outrigger proa" to 8 feet for trailering and planning to use Hobie 18 dagger and rudder. Might add electric bailer when cockpit constructed, if ever.
     

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    Last edited: Sep 14, 2013
  4. BobBill
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    BobBill Senior Member

    I will post diagram of CE with semi crab claw and pic of alternate rig. The illustration not to scale. The hull is near identical to MO and the daggerboard is further after than in pic, say about 2.6 meters from bow, with the MO dagger case being about .5 meter closer to bow putting CE about .3 meter ahead of box...rudder is to be longish at a meter. The MO CE on right is a hair off, but CE location is fairly accurate...

    Looks to be carbon at deck for reinforcement to stubby, with (maybe) carbon rods and metal ring or multiple layers of metal.
     

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    Last edited: Sep 16, 2013
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  5. BobBill
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    BobBill Senior Member

    Just updating pics and will post finished when boat is sailing. Using Hobie hulls and sails for Hobie on carbon surfer/AL spars ala MO original semi claw yard boom rig. Most of boat is castoff items, hulls, sails, etc, but much crafting required, mast step, gooseneck, aka (beam) anchor points, etc. Weather here is finally conducive to finishing.

    In deference to clarity, boat is an outrigger, not a tacking proa as some might prefer.
     

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  6. BobBill
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    BobBill Senior Member


    Peter, I wrestled with your comment for a bit and have decided to use your advice, but below the deck, if I can.

    Plan to use turnbuckles (cheap ones from box store) as braces as you noted fore, aft, port. s'board...if I can. High stress point needs heavy boxing.

    Yes, the boat is much like White's but also Malibu Outrigger base. I had not seen the CLC rig but seems a bit small and the Lateen rig not a fave.m Recycled some old Hobie hulls destined for land fill.

    Thanks. Hope to go wet in month.
     
  7. philSweet
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    philSweet Senior Member

    I don't think the Hobie 18 hull is going to support the mast. The hull is a thin glass outer shell over a fairly low density foam about 1/2" thick, with a thin mesh veil on the inside of the foam. The mesh is just squeeged on with low strength, mostly bubbles resin. Your mast arrangement sounds like it will just grind the foam to dust in half an hour.

    What I would do is make a port and starboard pair of splashes 4' long where the mast is going. 3 layers of 1708 or so. Then saw the boat in half, remove 2' of foam from each side,and install the splashes inside the skins while they are still a bit green. Bog them in on aft piece and secure with 10 screws outside to inside. Install a bulkhead, secure with screws, and tab. Bog the rest, slam the bow together and then run about 100 #8 screws into the hulls over long battens. You will want a bulkhead in the bow also. The deck can presumably be scabbed with 1708 and wooden stringers on the topside. The hull skins can be ground back and married properly as a last step, after you've pulled all the screws out. Put masking tape on the faying surface on the battens so they don't stick.

    Then you can build a mast step between the two bulkheads on the inside. All that can be prefitted before you get the goop out.
     
  8. BobBill
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    BobBill Senior Member

    Phil, correct...Hull needs stuff. Did as you suggested, but added liner of Kevlar, carbon and glass on sides and stem, and deck-4 layers carbon, planned to add carbon step column and anchor with cheapo turnbuckles, 4-ways minimum, maybe add wood/carbon frame around deck port where mast arrives above deck...still working on details. Studying your knowledgeable advice and may incorporate, without sawing, bulkheads perhaps...instead of anchored turnbuckles...much appreciated.
     
  9. BobBill
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    BobBill Senior Member

    Phil, might be your approach is solid, but a bit overbuilt. I think something like this might do...with 4 struts... or upper and lower reinforcements...and the current Kevlar/carbon layers.
     

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  10. BobBill
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    BobBill Senior Member

    Her is latest version, not yet in place, of planned mast step. Not much space to work with and working blind. Should handle the stresses. The various blocks and disks are held together by 4-inch ss wood screws.

    The second pic is to give idea of stubby etc. Version of the Malibu Outrigger using cast off Hobie 16 hull as outrigger or ama and H-18 main hull.
     

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  11. philSweet
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    philSweet Senior Member

    The problem is the Hobie 18 hull isn't as you've drawn it. You show a solid hull and it is a cored hull. You need to get the mast load distributed to the skin, and that requires about a four foot patch where all the foam core has been removed and a lot of shell thickness added. You're just going to shear the foam and grind it to dust. Cut the boat in half and do it right, then put it back together. It's about a four hour job to get it back together, then you have to fill the holes and fair the exterior on another day. As drawn, you will have side loads of up to a ton on the top and bottom of the hull. Doable, but that is pushing things a bit. If you can torque the mast directly with the forward crossmember without involving the hull, that would cut the loads by about 3/4.

    Have you calculated a total righting moment when flying a hull? Probably about 4000 foot-pounds?. The hull is about 2' deep at the mast step, correct? The hull has to transmit 4000 foot-pounds from the mast to the crossmembers. It wasn't originally designed to do that.
     
  12. BobBill
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    BobBill Senior Member

    Phil, I know you are correct, it is just a rough sketch to give idea.

    I am not that good to cut in half. I guessed close to your figures, and have about a quarter inch of carbon. Kevlar in interior and about half that on the deck area, and, when the step is set, going to load the sides and base with carbon/glass from top to bottom.

    I figured the step to be a problem that cannot be fooled with so saved it until last...might have to mess more...cannot fail...

    Right now am messing with the akas and trying to get them approx with shims to rough level when on water and adjust later.

    You are right no doubt and I thank you for the heads up, again. I knew the hull was cored and weak, and why the odd step design, to shift the pressure or spread to keel area and sides more.

    Punting, I am, with strong lean on carbon/Kevlar strength.

    I suppose I could wait until next year to slash the hull, but I don't know if I have the gonads to do that and get it back right. I have only my garage to work in.

    Will seriously think on the advice and see if I can come up with alternative to give more strength to the area.

    My fifth boat rebuild and this one is a dilly. Just about everything I have had to craft from scratch...from stem to stern etc, even the gooseneck and aka pillows (as I call them) I had to custom craft. Slow it is.

    As I said, will get brain kicking. Been screwing with it for 4 hours now and have to recoat the carbon spars, mahogany rudder I crafted and a rail with poly, again.

    I will be back and if you have more ideas, shoot.

    I remember I once thought of just pouring a poop load of epoxy into the area after I dammed it, but the exotherm reaction would burn the thing up, so I opted for doing in layers.

    Crazy, I know, but Reagan closed the sanitarium I was living in...so here I are.
     
  13. sharpii2
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    sharpii2 Senior Member

    If it were my boat, I'd forget about an unstayed mast. The main reason for this is that the hulls weren't originally designed for such.

    As pointed out by some excellent posts here, the main hull needs to be structurally re-designed and rebuilt to make this work. Seems like a lot of high risk trouble here.

    Add the fact the mast itself may not be up to the job. It could bend right over, above the mast step, like a cheap curtain rod.

    A simpler solution may be to perch the mast on a crossbeam and hold it up with stays.

    The mast does not necessarily have to sit at the mid length of the crossbeam to work. It can be significantly closer to the main hull.

    The thing to remember, in this case, is the mast is going to be under greater compression when the float hull is to lee than when it's to windward, and the loads have to be calculated, assuming that.

    Below is a drawing of an asymmetrical staying arrangement for strap on sailing rig, for a kayak, as an example.

    There is a pair of shrouds on the port side, but only a single shroud on the starboard side.

    The single starboard shroud has a lanyard to facilitate setting the rig up.
     

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  14. P Flados
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    P Flados Senior Member

    BB

    Here is a way to structurally connect the outer skin to your cloth buildup on the inside:

    • Locate a couple of places on each side to connect the outer skin to the inner buildup
    • Use a hole saw to cut through the outer skin,
    • remove the foam,
    • Cut some strong plywood disks approx same thickness as foam
    • Glue wood disks to the inner buildup
    • bevel the outer skin around the hole
    • Build up the whole area with glass
     

  15. BobBill
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    BobBill Senior Member

    P Flados, Thanks.

    And Sharpii2 also.

    I did forget to mention that I have (slowly) come to terms with the idea that stays may be required, though it was not part of the original plan (using original Malibu Outrigger plans which was all wood construction using ply etc. Its mast step design was basis of the base and the concept).

    My simple recycling conversion plan may have to adjust to the reality of physics.

    But, better safe than sorry, so...not the first time on this build that I have to alter the scheme. I wanted it free standing like orig as simpler set up etc, but seems the best alternative, at this point.

    Still, after some thought, I do have one question.

    Yes, the Hobie hull is cored, but, why worry about the core material, if one can strengthen the inner surface?

    Would not the stress be borne by the inner surface and not directly affect the outer hull surface?

    I reviewed the original Malibu Outrigger plans for its mast step and, and, outside of its being wood (mostly Douglas Fir) and so on, its strength seems to be how is is boxed to the ply and frame, similar to Peter Australia's excellent example and reference above, but his external support would require deck restructure, which might drastically alter the deck arrangement, but could be accommodated, so, it seems to me, the inner hull surface is the key etc.

    Carbon is some hellishly strong stuff. I am not a short-cut person. It is a boat.

    Make sense that the inner surface is the more important?

    For reference: The stubby mast is 12' 6061 T6 x 3.5 OD, .125 wall thickness. The yard is 25' with low half T6 and upper half carbon, boom is 16' loa, mostly carbon, 2' T6. Both deployed as noted in the above pics. Using stays, if that is the case, should pose little problem, save the added work and cost.
     
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