Leeboards on coastal cruising sail cat?

Discussion in 'Multihulls' started by Markusik, Mar 12, 2020.

  1. Markusik
    Joined: Jun 2017
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    Location: Lake Michigan

    Markusik Junior Member

    One of my requirements for a coastal cruising sail cat 14m LOA 7m BOA is a shallow draft <0.6m with boards up. Construction will likely be cored composite, KSS-style. The boat is intended for liveaboard at anchor; performance and luxury are secondary to safety, accommodations and cost. With that said, it is intended to be fairly light, with composting heads, petrol outboard engines, and reduced water storage requirements thanks to watermaker.

    Due to air draft requirements, and the desire to step and unstep masts without a boatyard, the rig looks like it might be freestanding biplane of the junk-derived soft wingsail variety. This will make the CoE fore and relatively low. Two sails, perhaps 48m2 each, with 4-6 reefing points and no headsails.

    Mini-keels are out of the question. Asymmetric hulls for leeway mitigation might be an option, or could have unacceptable impact on accommodations or sailing performance on a boat this size (I’m not familiar enough to venture a guess). Daggerboards seem expensive, vulnerable and intrusive on accommodations, none of which are attractive considering I’d often avoid beating upwind.

    So I consider something like leeboards. In the area of CoE I’m thinking the lateral hulls will be parallel to each other and perpendicular to the waterline (slab-sided). It seems to me that a clamp on a pivot perhaps 0.3m above the waterline could hold a foil closely to the side of the boat. The clamp could be loosened to adjust the depth of deployment with the board raised, while the pivot would control angle of deployment; say from 5deg past perpendicular to lifting the board entirely free of the water. Offsetting the clamp would also be relatively easy until the wrinkles were ironed out of the rig. The board would be braced against the hull above and below the pivot.

    I understand the limitations of surface-piercing foils, and concerns like ventilation, cavitation and vibration. On the other hand I like the fact that the boards can be raised fully from the water, don’t interfere with bottom fairness, and can easily kick-up on hard contact. I’m good with leeboards on smaller boats, but seeking insights as to the feasibility of using leeboards (or asymmetric hulls) on a cruising cat this size. My thanks in advance.
     
  2. catsketcher
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    catsketcher Senior Member

    Don't do leeboards - If you want, think of a pivoting centreboard hung from the bridgdeck. Sedelmyer did this and some small cats did in the early days. Some Kelsall cats do this too. Shouldn't be too hard to get the engineering right. Make it big to handle the surface piercing effect and extend a case down from the bridgedeck.
     
  3. gonzo
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    gonzo Senior Member

    Freestanding rigs are usually buried in the hull. It seems really difficult to raise the masts off the partners and lay them on deck by hand.
     
  4. Richard Woods
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    Richard Woods Woods Designs

    A friend fitted leeboards to his cat. They banged and rattled a lot when sailing, even worse at anchor. The Stiletto 27 started life with a central daggerboard. But some one tried them in the hulls and they were so much better the 30 had that as standard. Back in 1950s Prout first Shearwater had central daggerboard but the quickly changed to in hull

    Don't use a junk rig. Don't use unstayed masts if you want to lower them without assistance.

    Try watercatchment instead of a watermaker

    Go smaller if you want a low budget boat

    Richard Woods of Woods Designs

    www.sailingcatamarans.com
     
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  5. rob denney
    Joined: Feb 2005
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    rob denney Senior Member

    Markusik,

    Great to see someone thinking outside the conventional box.
    Unstayed rigs make complete sense for cruising boats in terms of ease of use, low maintenance, cost and safety.
    Stepping/unstepping them is easier than a stayed mast. A hatch in the deck next to the mast is sized for a pole long enough to reach the mast centre of gravity (25-33% the mast length, less if the boom and mainsail are still attached), plus the bury (distance between bearings). The bottom of the pole sits in a cup next to the mast step.
    One end of a block and tackle is attached to the top of the pole, the other to a loop of line around the mast.
    The loop is pulled up the mast to the top of the pole and tied off to a halyard cleat or the gooseneck.
    The block and tackle is used to lift the mast vertically until it is clear of the deck bearing. It can then be rotated to horizontal and easily moved around the deck to where it sits.
    Far simpler, safer and quicker than undoing and redoing shrouds, back and forestays, rigging/derigging vertical booms and carrying fully rigged masts around the deck, especially if they are rigged with wire rather than rope.

    Junk wings are an interesting solution. I don't think they are quite there yet (too heavy, too many bits to break, the leading edge shape distorts in strong wind and tacking may be difficult), but it will be a lot of fun experimenting. I suggest you do any experiments at a smaller size to save money, time and reduce regrets when you have to cut something up or throw it out.

    I have a leeboard on the proa I have just built in the Marshall Islands (Mini Cargo Ferry Prototype – HARRYPROA http://harryproa.com/?p=3155). It works well. No banging or rattling, kicks up in a collision and no ventilation or drag issues apart from those caused by material limitations. We are currently trying it with a case which removes the kick up aspect, but next time the boat is out of the water, we will revert to the kick up option. They make a lot of sense if aesthetics are not a big deal.
    I would also consider the single board under the bridge deck, although without a case, so it can kick up. There is no reasonable logic that suggests it will not work as well as an in-hull board, and the savings in weight, drag, interior space and fouling of 2 cases and boards are overwhelming. Even if they weren't, the result of a high speed collision or grounding with a case mounted daggerboard makes them an insane choice for a cruiser.

    The local canoe hulls here are slightly assymetric. Like assymetric Hobie hulls, they are pretty useless upwind. Assymetry works best if the rigs are a long way aft and the rudders are big and efficient. Or if you don't sail upwind.

    Smaller is cheaper, but longer is faster, more comfortable and safer. The trick is to go longer without also going higher and wider and filling the extra space with 'stuff'.

    If cost is an issue, you will get more boat for your dollar with a harryproa than you will with a cat. And it will take about 2/3rds the time, and less effort, to build.
     
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  6. Markusik
    Joined: Jun 2017
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    Location: Lake Michigan

    Markusik Junior Member

    Thanks all for the replies. I’d hoped to respond sooner, but we live in interesting times.

    Catsketcher, Rob, my review of a previous thread Bridgedeck centreboard why don't they work??? https://www.boatdesign.net/threads/bridgedeck-centreboard-why-dont-they-work.57051/lead me to believe a bridgedeck centerboard would need to be VERY robust to handle the stresses of being some .8m above the waterline. I’d considered a low profile nacelle, but hadn’t given much thought to a bridgedeck centerboard. I like the advantages of a single large board. Even considering this won’t be the most muscular of cats, it seems like the board and housing would need be very strong. That could be overcome with engineering, I am not the engineer for that job. Right now I’m picturing something like NACA 0008 with an axis of rotation inside the saloon, elliptical at the business end, on a 0.6m stock. The bridgedeck will be extensive, starting 2.5-3.5m aft of the bows (depending on mast placement) and ending 2m fore the sterns. With concerns about slamming already, a bridgedeck centerboard is a contender, but doesn’t eliminate leeboards as a possibility. For that matter, technically only a single symmetric board would be needed, like with daggerboards. Bracing the board against the hull above and below the pivot point (and doing away with my clamp idea at first) should let it work as a “windboard” or leeboard.

    Gonzo, I’m thinking the masts will be right around a fore full bulkhead, with full bury in the hull. I’d pictured a hinged tabernacle abovedeck, with a line run underneath the notched mast base acting as a 2:1 block to lift the mast, then using the windlass attached to a line on the mast base to control lowering the mast, but Rob’s idea seems simpler. I can think of several feasible ways to lift the mast from the post hole. More thought is required certainly, but I don’t think stepping and unstepping the mast is going to be the limiting factor. My next best alternative would be an A-frame, but the trade offs aren’t worth it for my purposes.

    Richard, I admire your designs and philosophy, but a smaller boat will not provide the 4 cabins and 2 heads the 4+ adults and 2+ children seem sure we need. Value, not low cost, is my driving consideration. I’m hoping to keep the budget for this under $400k USD and 4500 hours. The ability to step and unstep masts without a boatyard will save thousands most years. Regarding leeboards, I sympathize with your friend’s issues but hesitate to apply his experience to every leeboard. A variety of monos use them effectively, is there a reason why they’d be less effective on a comparatively flat riding multi than a heaving heeled mono?

    Thanks Rob. I’d happily go the Harryproa route, but I’m limited to a BOA of 7m. Correct me if I’m wrong thinking a harry with that beam isn’t going to provide the accommodations required.

    I’m not married to the junk idea, but it does have some good points for my purposes. Modern junks (either soft wingsails like discussed in The design of soft wing sails for cruising https://www.boatdesign.net/threads/the-design-of-soft-wing-sails-for-cruising.49425/, or with camber sewn into the panels between battens, or a “split rig” have come a long way from the low aspect ratio flat sails of yesteryear. I’m planning to experiment with a combination of double-luff ”envelope battens” to improve the leading edge, like David Tyler did, but sewing camber into the panels instead of hinged battens for camber. The things I feel junk-style offers me are;
    A) can be reefed or depowered immediately and singlehanded at any point of sail, by releasing the halyard or sheets respectively.
    B) tends to spill wind in a gust, protecting against the cat’s high initial stability.
    C) “fanned” designs (see picture with mono using sewn camber, yes the sail is made from polytarp) can lift the yard well above the masthead. This will let me get below common bridge heights without unstepping the mast just by reefing. To me, the sail in question looks close to a decently high-aspect ratio ellipse. The owner/innovator Arne Kverneland reports being well pleased, without difficulties tacking (perhaps the monohull momentum helps).
    D) junk cat rigs, like in the picture, tend to have their masts well fore. This works for me, as the foremost and aftmost hulls would be devoted to full bulkheads and reserve buoyancy, not accommodations. The boat I consider is intended to have a large bridgedeck saloon, starting with the bridgedeck perhaps 2.5m aft of the bows. If the CoE physics allow, I’d put the masts in the hulls immediately before the saloon corners, with full bury in the hulls. Abovedeck, I’d envisioned tabernacles designed to help with lifting the mast from the post hole and controlling the lowering. With the masts immediately fore the (upright, Lagoon-style) saloon windows I’d use the saloon roof as an end cap for the sails. This would give the saloon visibility unhindered by sails, good for an internal primary helm. The sails starting just above the roof would help keep the CoE and mast height low. Visibility of sails would be using a camera or optical solution, not that junk rigs require much tending.
    E) biplane, whether junk or not, plays well with my plan I think. Stresses on the crossbeams would be lower. The rig would not impact accommodations much. If I were to have 5.8m between mast centers, with battens set to the outermost sides, I’m reasonably sure I could have two ~3:1 aspect ratio sails of at least 50m2 each. Presuming the saloon roof is 2.75m above the waterline (bridgedeck clearance of 0.8m, plus thickness of floor and roof, plus 1.88m saloon headroom), and the sails start immediately above the roof, the mastheads could extend 12.75m above the roof and still keep the air draft <=15.5m. If I were to use a junk rig, there should be enough distance between mast centers to prevent fouling sheets on the opposing battens. The balanced design of the junk limits the force of jibes, and likelihood of accidental jibes, although I might need to sheet in a bit before jibing to prevent collisions between battens.
    F) whether using a rectangular or fanned junk, the non-triangular sail shape should leave a good deal of rooftop potentially unshaded for semi-flexible solar.
    G) the sails can be made by laymen using inexpensive materials. The battens, rather than sailcloth are stressed; torn sails can be readily repaired, and tears cannot progress beyond the one panel.
    H) like Rob Denney, I’m a believer in the virtues of a freestanding rig for cruising. I think they lend themselves to easy downwind sailing. By designing with freestanding in mind, avoiding the tensions and compression, the build could be easier. If I were to use the junk rig, the masts could be simple tubes, without tracks, no longer (and preferably well shorter) than 16m. Non-rotating, stabilized to limit movement and wear in the post holes and tabernacles. This would significantly limit the potential points of failure, all of which would be easier to monitor.
    I) no flogging sails, minimal foredeck work, no storage of multiple headsails.
    J) freestanding should allow greater freedom making alterations to the rig in the event I found junk unsuitable.

    Thankfully I haven’t started throwing money at this project yet, and I appreciate all the input so far. Any ideas to accomplish my requirements (BOA <=7m, air draft <15.6m modifiable to <4.7m by 2 crew on calm waters, water draft <.6m with boards up, 4 double cabins, 2 heads, large saloon, ample solar) are welcome. Cheers!
     

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  7. rob denney
    Joined: Feb 2005
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    rob denney Senior Member

    Sure do. I have just returned from the Marshall Islands. Boarded 5 planes, flew on 3 of them. Took 3 times as long as scheduled and included overnights in Accident and Emergency in 2 hospitals.

    008 is pretty skinny. I use 0012, sometimes 0015. Supporting a board under the bridge deck requires a bit of left field thinking and geometry, but results in almost the same loads on the board as if it was in the hull and significantly less structure. Lee boards also work.

    By far the simplest, quickest and easiest way to raise/lower an unstayed mast is a trench in front of it and a pivot at the deck bearing. If you have enough space for the trench and are raising/lowering regularly, this is the way to go. With a bit of organisation, the rig can stay attached.

    No reason why not. The C50 has 2 doubles in the windward hull, 2 singles in the lee hull and is 7.9m wide. It would not take much rejigging to provide the extra beam in the lee hull and reduce the beam overall. Easier again if you don't include the tender, although the reason for the 7m beam would have to be pretty good to sacrifice the advantages of the big tender. 8 people on a 50'ter (or even on an 80'ter) is a crowd. Sleeping them is one thing. Feeding, watering and entertaining them another thing entirely.

    My next project is a variation of a junk rig for all the benefits you list and fewer of the drawbacks.
     
  8. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    Bolger had a solution for a selfstanding mast and a tabernacle. He designed a slot on the deck for the buried section of the mast to come up and above the deck. Block and tackle at the foot of the mast is used to bring it up and control it going down. It precludes the mast being all the way forward, and needs a bulkhead aft of it.
     

  9. rob denney
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    rob denney Senior Member

    Markusic,
    A video of a harryproa with leeboard. This is held in place by glass tow wrapped around the board and onto the deck for the top and onto the cockpit floor for the lower one. The lower one does very little once the sideways load is on as it is all taken by the chine. It is made of timber with a layer of light glass. The section is near enough an ogive, reversed at the top, created by feel with a planer followed by a grinder. It can be lifted and held in position by wedges but doesn't kick up. After it gets damaged because someone forgets to lift it approaching the beach, it will be replaced with a kick up version. More on the build and boat at Mini Cargo Ferry Prototype – HARRYPROA http://harryproa.com/?p=3155 and Mini Cargo Ferry – HARRYPROA http://harryproa.com/?p=2944
     
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