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
    Joined: Mar 2006
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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
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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
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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
     

  10. Markusik
    Joined: Jun 2017
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    Location: Lake Michigan

    Markusik Junior Member

    This is intended as a floating home for an extended family. Regular crew will include four adults ranging from mid 30s to late 50s and two young children. Four double cabins and two heads are a bare necessity, with additional berthing options in the saloon. Most of my income is passive now, but as the crew changes over time (folks lose desire or ability to live aboard, kids move on, etc) we might rent out spare cabins for supplemental income.

    We intend to do several “Great Loops”; winter in Caribbean, sail up east coast of North America in spring, summer on the Great Lakes, take the Mississippi or Tenn-Tom down south in autumn, repeat. If the Loop gets dull, we will likely stick to the east coast of the Americas. When the children are old enough to appreciate it, we intend an Atlantic crossing in late spring, then cruise the Rhine-Main-Danube at least once. Being able to raise and lower masts without a boatyard will save us lots of money and hassle.

    Grand Traverse Bay Grand Traverse Bay - Wikipedia https://en.m.wikipedia.org/wiki/Grand_Traverse_Bay on Lake Michigan is real treat to sail (three months of the year) and where we would spend much of our summers; protected waters, pristine beaches, many good anchorages, easy access to amenities, good fishing, minimal (5cm) tides, and where we have the most roots. A 7m beam gets me from the barn where this would be built to Lake Michigan (and ocean access) directly and fully assembled. After that, the reasons for a 7m beam are more a matter of intended use on canals and rivers; generally, narrower is better. 7m will allow me free storage on the hard in Florida or Michigan if need be. 7m is the limit for the Canadian Heritage Canals. 7m BOA is not an absolute requirement, but a practical limit. For that matter I could build longer, I’m considering my self-understanding and the knowledge that size is inversely proportionate to the likelihood of completion. The slab-sided cat with significant medial flare in the hulls, minimal rocker, and boxy bridgedeck saloon strikes me as a relatively easy build, in my inexpert opinion.

    The large tender as auxiliary propulsion is brilliant Rob. I’m more familiar with the maneuverability of a twin engine cat. I was picturing Yamaha T25 high-thrusts (finally available in the States) for the cat idea. How big would a harry tender need be, to be suitable for a Neander Dtorque 50hp diesel outboard (175kg)? I’d consider that route despite the cost. I expect a harry can be quite maneuverable with the twin inline rudders, how is it with the motor in reverse? I thought I knew the harryproa website well, but I’d never seen that video. Nice crab claw. I’m eager to see what you come up with for the junk rig. While the envelope battens are nice to improve the leading edge, and eliminate some of those parrels that offend the western eye, I’m not the best qualified to combine them with sewn camber; sewn camber really seems like the cheapest and simplest way to increase performance. Using the saloon roof as an end cap does seem to offer an opportunity to modify the tack parrel, mast lift and the topping lifts/lazy jacks.

    My wife is not sold on the harry idea; accommodations are a much higher consideration than performance for her, and the videos available on YouTube did not inspire her. I’m proceeding with the cat plan for now. With modifications, according to her something like a Lagoon 440 would suffice for the crew. I’m hoping my design will slightly exceed the accommodations and performance of the 440 at a lower cost (IMO, very possible). Entertainment is not a serious concern; homeschooling our children will occupy a good amount of time for my wife and I. One crew is happy with a tablet reader and spending time with grandchildren, another is happiest fishing. Much of the entertainment will consist of excursions shoreside, and WiFi. Watering is one reason the design will include a watermaker. Since we will be chasing warm weather for the most part, solar gain shower bags should help in that regard; still, good water and ample photovoltaic are considerations. Feeding is the real issue. We generally avoid restaurants and focus on healthy foods. On land we eat lots of home-sprouted salads, fish, fresh fruits and veggies. Aboard, the fresh fruits and veggies aspect may suffer, whereas the sprouting and fish shouldn’t be an issue. In any event we will need a blast freezer for fish (48kg), 200kg weight allowance for dry provisions, ample refrigerator/freezer/cooler space. Food storage can be down in hulls, but a full galley-up is an important social aspect and requirement. Available electric appliances (light, inexpensive induction cooktops, microwave ovens, oversized toaster ovens etc) should help keep costs and weight down. I’m thinking that the comparatively light, durable and inexpensive photovoltaics will exceed the LFP battery capacity (probably no more than 400Ah@24V). Air conditioning is not on the requirements list at least.

    I’m familiar with the Bolger tabernacle and the trench, but have trouble trusting it to a 50m2 sail on a stable cat. My tabernacle idea incorporated elements of this, but is still in the works. Topic for another thread.

    Regarding leeway, the bridgedeck centerboard idea is becoming more appealing, for all that it is a more difficult piece of design and engineering. With a shallow draft, rounded bilge hulls, minimal rocker and significant windage I’m concerned with tracking and turning; the bridgedeck centerboard seems like it would make a good pivot point for turning, and help with tracking, allowing more freedom for adjusting CoR than a leeboard. The first bridgedeck crossbeam still seems like the logical place for the centerboard axis. How much wetted board surface do you think would be required? The standard thought of 4% of sail area (100m2, so 4m2 of board) seems impractical. Reefing the sails is an option, perhaps not ideal. I’ll see what I can find in the archives about bridgedeck centerboard design.

    Thanks again for the input. Plenty of food for thought.

    Cheers

    https://junkrigassociation.org/Resources/Documents/Arne Kverneland's files/Junk Rig for Beginners.pdf
     

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