best hull for short steep chop

Discussion in 'Sailboats' started by Brian Fredrik, Dec 20, 2010.

  1. MikeJohns
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    MikeJohns Senior Member

    A light boat can lose a lot of energy in pitching and is usually not the best configuration for sailing to windward.

    A heavier boat pitches less providing she's "powerful" enough to drive through the waves, the whole idea of very slim bows on light boats produces a similar effect, it reduces the rate of change in waterplane area relative to the longitudinal gyradius.

    The Naval Architecture process is to generate whats called an ROA which is to look at how the craft behaves at different speeds and headings for different wave energy spectra. A Narrow heavy boat can be very efficient to windward in a chop. But there's the whole design to consider here and no one parameter can be sensibly considered in isolation.

    Anybody with Seakeeper can get a good idea of a simple RAO
     
  2. philSweet
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    philSweet Senior Member

    Probably a dead thread, but a suitable DLR for a thiryfooter that wants to work through a chop is more like 450, not 300. Malabar Jr., Concordia 31, "Candle in the Wind", and my personal favorite Raeburn's Tarbert yawl (33' double ender,a lightweight at DLR=384).
     
  3. BATAAN
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    BATAAN Senior Member

    This is a very good and reasonable way to look at it, plus the comparisons actually do translate from kayaks to big boats.
    This vessel, based on 19th century workboat designs, at 40'x14.5'x5' and 46,000 pounds or so, does well until trying to go into short seas with light winds. Her huge round bow stops all that weight cold, and if designed for those conditions would be quite different. Her HF must be huge, too huge.
    But the bow always holds up the huge rig no matter what when running or reaching in very strong winds and cross seas and she steers like a lamb with a little short tiller, so it's all a trade off.
    If designing a boat for very choppy and short-sea conditions that required weatherliness, I would research traditional boats from places that are like that. These often benefit from hundreds of years of T&E and work well.
    Fairly heavy, not too blunt and without excessive buoyancy would seem to describe a desirable bow.
    But this must be balanced with a reasonable midship section and low ballast. Anything by Nigel Irens or Ed Burnett would qualify.
    See the drawing for a good example of a boat that would shrug off a very steep and nasty chop that stops others cold, and it is based on UK workboat types, but much improved and made with epoxy saturated wood construction for very high strength/weight ratio.
    A modern boat.
     

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  4. sharpii2
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    sharpii2 Senior Member

    A really neat boat. I bet it cost a fortune. Weren't those kind of boats ballasted with stone originally?

    All those nice curves. Almost a natural for GRP. But there probably wouldn't be a big enough market. And fitting an interior to all those curves would be quite time consuming.
     
  5. BATAAN
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    BATAAN Senior Member

    BERTIE cost $15,000 for hull and deck and requires little ballast. The originals were ballasted with stone or scrap iron. Her ballast is cement and boiler punchings and rock crusher balls between the frames, with some movable lead for trim. Maybe a ton total.
    She is a monument to old ways, and is therefore very cheap, with a plain finish and workboat rig. She's also immensely strong and has demolished a few things she came in contact with. Fiberglass
    The Ed Burnett design would set you back $150,000+, has a lead ballast casting and hollow mast, yacht lines underwater, and is a very good adaptation of old traditions to modern uses. She also would go upwind in a chop infinitely better that BERTIE. However, if I had to pick a boat under 40' to ride a gale out in, I'd pick BERTIE as I know just how rugged and capable she really is.
    Interiors are pretty easy in a traditional work boat and I have built quite a few. Little plywood is used, and that only for the cabin sole. It is much much easier than fitting an interior in a fiberglass hull.
    A Gloucester schooner's forecastle was usually built by one "interior joiner" in a week or so with hand tools. This included up to 18 bunks, galley cabinets, ladder and table. Those who are used to working with plywood and power tools in this situation are usually skeptical of these times, but they are a matter of record.
    I learned the art by closely studying old boats and their interiors and by working at Mystic Seaport. First the sole beams go down, then vertical bulkheads and dividers are erected on them, then the sole is fitted. Most interior components hang from the vertical stuff, with only the outboard edge of the bunks and dividers fitting to the curved ceiling. And this ceiling, or interior lining of planks, makes an easy surface to nail stuff to. In BERTIE the ceiling is fully caulked, which strengthens the boat and keeps dirt out of the bilge.
     

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  6. sharpii2
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    sharpii2 Senior Member

    Are you saying BERTIE, a 20 ton boat has only a ton of ballast?
     
  7. BATAAN
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    BATAAN Senior Member

    23 tons. Yes, she has a ton or less. BERTIE is barge-like in her form stability and 14.5 foot beam, also the beam and turn of the bilge extends very far fore and aft. The stability of the hull form has to be experienced to be understood. We have been knocked down hard several times, putting the mainsail in the water and she comes back up so fast you have to hold on.
    Also have broached badly in gales, sliding sideways down wave faces with the breaking sea, and I have never had worries as to her stability.
     
  8. BATAAN
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    BATAAN Senior Member

    Add a 400 kg SABB 30 hp engine which acts as ballast, and 50 gallons of fuel.
    Despite anti-ballast of 100 gal of water and 50 gal of fuel that live on deck, the dinghy (sometimes 2) and all, it doesn't seem to make much difference.
    About 400 feet of 1/2" chain on deck in mangers most of the time too, but it goes down the hatch and on the forecastle floor when we go to sea off soundings.
    Few European small coasters had chain lockers and most followed this practice. It's lovely not getting the mud and stink below when we are often anchoring.
    In the old days a "good" coaster was one that would sail empty in most conditions when not carrying paying cargo, as the labor and cost of ballast (gravel, shingle etc) were not necessary. See "Westcountry Coasting Ketches" by W.J. Slade and Basil Greenhill. This sometimes got skippers in trouble if caught out in bad weather and couldn't stand up to her sail. Sailing work was all about profit. Most east coast US centerboard schooners that used to carry the bulk of trade along the coasts were the same, very little ballast as a proportion of displacement.
     

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  9. sharpii2
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    sharpii2 Senior Member

    Still, less than 5% ballast seems incredible. But, then again I have seen things like this before.

    The original SEA BIRD displaced around 5,000 lbs, but had an iron ballast slug that weighed only 700 lbs. That comes to a little over 14% ballast. I then calculated her keel area and thickness, allowing for taper at both ends and came up with 10.3 cf. I then multiplied that by 35 lbs/cf and came up with close to 360 lbs. That added to the 700 lb keel, pushed the ballast/ displacement ratio up to to 21%. And that's assuming fir was used for the deadwood and it's weight counted the day she was launched. As she sat in the water, the deadwood and bottom planks would become saturated, raising the fir deadwood's weight another 300 lbs. This would increase her ballast displacement ratio to 28%, which seems much more reasonable.

    Looking at SPRAY's lines drawing I can see a full length keel which was probably made of oak, if you could get it. Even if not, since the boat stays in the water, it and the deadwood are probably saturated. If it ever came out of the water in a severe knock down it should add considerably to the righting moment. On top of that, you have thick bottom planks that will soak up maybe anther ton of water. Then, I imagine all your water and fuel tankage is kept low, as well as most of your other stores, which, if they are below the center of hull volume add to righting moment as well. BERTIE probably would not recover from being turtled, but would be one tough boat to turtle.

    My LOLA boat is designed to recover from being turtled (see attachments). She has relatively high sides and a relatively deep "V" bottom. Fresh water, ground tackle, and other heavy stores are kept in lock down compartments in the bilge. They should add to the righting moment, even in a turtleing, if they can be kept in place. Due to her volume and weight distribution, only wave action would be able to turtle her and only in extreme cases, as I am learning from you. The long shallow bilge keels would lose much of their sideways resistance by the time the deck edge met the water, so the wave may push her sideways rather than flip her.

    There is a price to be paid for all this. That is sail carrying ability. LOLA's masts must be kept short for economy (who wants to put an expensive carbon fiber mast on an ugly box), as well as for self righting reasons, so BERTIE can carry, proportionately, much more sail area than LOLA. BERTIE would probably shlep right by, in a light breeze, powered by her massive sail plan as LOLA sat there.

    It is interesting to note that BERTIE and LOLA were designed to meet the same goal, a relatively inexpensive boat that can put to sea. BERTIE accomplishes that goal by using traditional design, skilled construction, and low cost materials. LOLA meets that goal through more modern design, less skilled construction, and more moderate cost materials (good plywood is probably still more expensive per weight than decent timber). LOLA would be built pretty much like an airplane. The bulkheads would serve also as molds, and be installed before the hull is sheeted. I imagine BERTIE's were installed after the hull was planked (to avoid 'hard spots', which may cause unfair compound curves).

    I imagine traditional bulkheads were built of planks that were ship lapped together, which would mean each plank was mainly cut for length. I can imagine this would be infinitely easier to do than to cut and fit a plywood bulkhead, which would have to be cut to the hull's sectional shape. So I can see how a more traditionally constructed cabin interior might go together faster than a more modernly constructed one, especially if it is retro-fitted.
     

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  10. BATAAN
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    BATAAN Senior Member

    Half our fuel and all the water lives on deck, like most traditional coasters. The low deck height above WL and wide beam make this not as disadvantageous as one would suppose, and greatly help an easy motion.
    Plywood is a pain in butt to fit, finish, and preserve unless totally glued and encapsulated. I always make a complete template for any complex plywood part when working on others' boats.
    My dinghy is plywood and epoxy and Awlgrip though, and tolerates benign neglect and very hard use.
    This is not a SPRAY copy, though she does use the hull lines, a good bit modified as Pete Culler and I discussed through many letters.
    I call her a "Spray-oid". She's faster than SPRAY by a good bit (I've raced copies against her quite a few times), goes to windward better, is easier to handle and still self-steers for weeks at a time without a vane gear.
    BERTIE's hull is Red Fir backbone, Port Orford cedar frames (6x4 at heads 6x8 at floors) on 12" centers, 1.75" POC planking, 2" fir deck on 4x6 beams, steel hanging knees on the mast beam, two bulkheads with pass-thru of double diagonal 1" POC with felt between and fastened with clench nails.
    The sole is ply, some of it dumpster scavenged over 30 years ago. The fore cabin top is ply covered with canvas, that's it.
    BERTIE's carrying capacity of about 10 tons and her huge midships hold make her a voyaging machine that's hard to beat.
    I see you have bilge keels on your design. Be sure to take into account bouncing down hard (crossing a bar at too low a tide) on something that isn't flat, also going aground while being swept sideways by a strong current.
    Life isn't all going to windward in a short, stiff chop.
    The rig we carry is what Slocum intended for SPRAY when he set out on his big voyage, as the accompanying article will testify.
    See SHIPBUILDING, in the construction section of this thread.
    Fair winds.
     

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  11. jak3b
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    jak3b Junior Member

    Bataan I want one
     
  12. BATAAN
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    BATAAN Senior Member

    jak, they're not that hard to build, you just need commitment.
     
  13. sharpii2
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    sharpii2 Senior Member

    I thought you said that BERTIE was built to SPRAY's lines, but BERTIE was planked outside those lines rather than inside of them, which accounts for her greater displacement and greater Beam.

    The only other difference I'm aware of is BERTIE sports a much larger rig, made possible by using a very easy to reef Chinese lug. From what I can surmise, the original SPRAY ended up with a rig of about 1,000 sf. IIRC, BERTIE carries about 1,600 sf. Accounting for BERTIE's greater displacement, that would be the equivalent of about 1252 sf on the original SPRAY. I understand BERTIE has a transom hung rudder where SPRAY had an inboard rudder and a sharply raked transom. My guess is that BERTIE has a longer waterline than SPRAY did as her transom seems to show much less rake. My guess is that BERTIE has SPRAY's hull lines extended further aft and, due to the up sweep of those lines, her hull sits deeper in the water which could also help account for her 27% greater displacement. Have I left anything out?

    My guess is all that weight on deck combine with her huge Heft factor, would make it harder for a wave to capsize her. Think of all that inertia.

    Also, if you had to build a new BERTIE today, how much do you think it would cost you?

    Perhaps you should sell the plans.
     
  14. PAR
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    PAR Yacht Designer/Builder

    I think most of you are going about the OP's original requests the wrong way. Going to windward is fairly easy, but as Mike has pointed out, this single parameter on this hypothetical SOR is but a drop in the bucket. Brian hasn't returned to see the debate, but I'll add there are many production yachts that will easily fill this scant requirement. Personally, I expect considerably more from a yacht then comfort in a short chop. In fact, I'd probably accept a rough ride in a short chop, if she could claw to windward like a crack ho after a dropped rock and pull a 2.3 S/L off wind.
     

  15. sharpii2
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    sharpii2 Senior Member

    I hear ya.

    But speed was only half of what was asked for. Comfort was asked for too.

    I think You'll agree, really fast boats aren't all that comfortable.

    I remember reading about one "open 60" skipper who had to sail quite a distance up wind (back tracking) in dirty weather to save a fellow competitor.

    He never said his boat had any trouble doing it. But he did say it was like riding in a truck with square wheels.
     
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