Thoughts on a rig please???

Discussion in 'Sailboats' started by john.G, Apr 24, 2009.

  1. john.G
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    john.G Junior Member

    Thanks Brent

    I've heard of him but haven't seen any of his yet, thanks for the steer.
     
  2. sharpii2
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    sharpii2 Senior Member

    Just a few points.

    1.) Multiple masts impair windward ability, because the aft masts are working in the slipstream of the foremast.

    2.) If you have three masts, you can afford to have 'all or nothing' reefing, where a sail is doused completely, so a junk sail is not as helpful as it would be on a single or even two masted boat.

    3.) You can probably get away with just two masts, if you can settle for lower aspect sails. an interesting rig to consider is the one john C. Hanna used on his 'Tahiti ketch' design. He had two short masts with a small jib and a low aspect gaff, on the main mast, and a Bermudan, on the mizzen. Both masts were nearly equal height, with the mizzen sometimes taller, so the boat, with sails furled, looked like a schooner. The beauty of this rig is that the big gaff sail comprises most of the sail area and is easily accessible. On the mizzen mast, you can hang a light air staysail in light air conditions. You can also vang the long gaff to the tall mizzen mast and improve that sail's set that way. All in all, it would never beat a fractional or even mast head sloop to windward, but it may prove much more weatherly than it looks. The jib and mizzen could be dropped and the powerful main, within easy reach and under excellent control, could lug you to windward in a blow. Even with a few reefs taken in. You would need a vang under the main boom, though, to keep it from twisting too much, but deck sweeping booms on a cruising boat are always a bad idea anyway.

    Sailing down wind could be done in down wind tacks, not dead before the wind. A twin jib could be raised up on the fore stay and flown wing on wing. The mizzen could be furled. The rolling motion would be far less than sailing dead before the wind as well.


    4.) What you need is adequate and reliable windward performance, particularly in scary conditions, not stunning windward performance. The Colin Archer's provided the former, not the latter. Against even a downwind sled, a race upwind would be a sad spectacle. For the Colin Archer, that is.
     
  3. john.G
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    john.G Junior Member

    thanks Sharpii2

    1. Yep... I agree. But a mid 50's hull with a beam of 12', a draft of 5'6" at a laden displacement of 20 t does not have the form stability to carry high masts... so to get any sort of sail area you have to have a few masts. Three allows each sail to be a high narrow airfoil.

    2. Very good point. Now that is something I hadn't thought about. Looks like junk rig can go to the junk pile.

    3. I know the tahiti ketches, a friend has one. I have been considering a low aspect gaff headed rig actually, before I considered the junk rig. Windward sailing is over rated anyway IMHO, subject to having a reliable auxillary. I have a 4LW gardener set aside in the shed as main power for this boat.

    Nelson's navy ruled the world with a tacking range of 90 degrees... and I've actually considered that as an option too. Probably as a course on the fore, a corse and raffee on the main , with a mainstaysail on a detachable stay, and fore and aft on the mizzen. The weight of yards up top ruled it out.

    4. The aforementioned gardner diesel coupled with 750 gallons of diesel will give the best windward performance there is. On a course of my choosing... ie light air, dead to windward for 2500 miles, I'll outrun a VO70. And the gardner will be still going in 20 years time... wich can't be said for the entire VO boat, let alone her rig and sails.

    *strikes junk rig from the options list*
     
  4. Brent Swain
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    Brent Swain Member

    As I point out in my book , in a peasure boat, "Efficiency " is the maximum output of pleasure for the minimum input of displeasure ( ie. work at a job you hate) regardless of speed. Peace of mind while cruising is a great source of pleasure ( efficiency).
    Brent
     
  5. john.G
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    john.G Junior Member

    Thanks Brent


    Now that one of the truest takes on efficiency I've ever heard. And I'd rather rebuild the engine every 12 k hours or so then sail to windward for the same 100,000 miles.

    I've heard the number thrown about that the average cruiser spends about 3 months sailing and 9 at anchor every year. For the past 15 years I've ran commercial boats, and to pay they have to spend 9 months at sea and 3 in port of a year. I have no problems about peace of mind under power.

    But... those commercial boats have all had either twin installations, an auxillary that could be slaved as a wing motor, or a get home sail rig. I want more then a get home rig, to my mind if I can generate hull speed with the wind abaft the beam under sail alone in moderate winds then that effectively doubles her range given that I'll be mostly in the trade wind belt. If the wind speed is lower then I can either take my time or run the main and motorsail. But in light air or for working hard to windward the engine is the primary form of propulsion.

    Thing is, I still want some degree of windward efficiency under sail. Just in case. Because I'm still alive in part due to being prepared for just in cases.

    Your name came up in conversation the other day too. I was talking with someone who was impressed with the performance of one of your twin keels compared with his. What's the secret?:)
     
  6. Brent Swain
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    Brent Swain Member

    I cant my keels outward from the vertical 25 degrees. Thus, when the boat is heeled 25 degrees and the keel is upright , it is 100% more efficient at stopping leeway than a single keel of the same depth which is heeled 25 degrees. I use this to reduce the size of each twin keel to half the size of a single keel , keeping the wetted surface of them the same as the single keel. Angling them outward 25 degrees at the bottom also minimises the interaction of water forced between them. You won't get this advantage by putting two keels the size of a single keel , both dead upright.
    Brent
     
  7. Landlubber
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    Landlubber Senior Member

    Brent,

    Have you EVER seen twin keels that were't canted, never seen parallel twins in my life.
     
  8. Milan
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    Milan Senior Member

    I did, Hartley’s Golden Cowrie, ferro-cement flash-deck-sloop. (With a ply deck).

    Boat sailed reasonably well.
     
  9. Brent Swain
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    Brent Swain Member

    Many are canted far too little , forcing water to pile up between them, no easy way out. 25 degrees minimises the interaction between them.
    Brent
     
  10. john.G
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    john.G Junior Member

    Thanks.
     
  11. sharpii2
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    sharpii2 Senior Member

    1.) I think you would be better off with two masts and low aspect ratio sails than with three masts and high aspect ratio sails. After all, you have to drag them through the wind when the sails are reefed or struck. I would leave it to others on this thread to discuss whether it's better to have, say, four high aspect ratio sails or three low aspect ratio ones. I can anticipate good arguments on both sides. I am presently designing a boat of similar proportions to the one you're talking about. It is 20 ft long, 5ft wide, and has a draft of just 18 inches. I originally started with two masts, now I'm down to one. With all 195 sft of sail up, she will be a bit tender, but once reefed, she will stiffen up quickly. The benefit here is that all the sail is in easy reach from below decks, as it is centered over the middle of the boat.

    With two masts, I could arguably carry more sail longer, and would definitely be faster off the wind, but I would have trouble getting to and handling the fore most or aft most sail. The sail I will be using is a cross between a balanced lug and a Chinese lug. It will have the advantages and disadvantages of both. It will have the advantage of easy reefing, but have the disadvantage of only three reef slabs. it will look like a moderate aspect ratio lug, but will really be a stack of three low aspect ratio sails. Fully reefed, only about 30% of the sail will be up. At that point, the yard will join the boom at the tack, making a nice low aspect ratio boomed lateen sail, with the Center of Area (CA) pretty much where it was, laterally, when the whole sail was up. This (I hope) will be smug and handy in scary conditions. All in all, the rig has turned out disheartengly heavy and may need to be trimmed down a bit.

    Your proposed 55 footer will have proportionately far greater form stability than my 20 footer. And, with the engine, you can get away far less sail area.
    You may have far more options than you realize.

    3.) I didn't know Nelson's ships could go anywhere near that close to the wind (45 deg.)
     
  12. sharpii2
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    sharpii2 Senior Member

    I think D/L is one of the most misleading factors in boat design.

    The trouble with the Displacement Length ratio (D/L) in judging the performance and sea kindliness of boats is that it relies on two assumptions:

    1.) That the waterline at rest is, to a great extent, a given proportion of the actual length of the hull, even with the boat heeled over, and

    2.) That, when comparing boats with different D/L's, both boats have similar Length to Beam proportions.


    When both of these assumptions are correct, especially the second one, the ratio be very useful. A boat with a higher D/L will definitely be slower but more sea kindly. But when one or both are wrong, all bets are off.

    A narrow boat can have a very low D/L, quite south of 200 and yet be very sea kindly. Because of its slight Beam, it can have deeper sections and still have less displacement than its beamier sister. Because of these deeper sections it will most certainly have less sail carrying capacity per ballast ratio and ballast placement than a beamier sister with the same D/L number, but pound and slam much less

    A wide boat with shallow sections can have a high D/L number and routinely blast past its theoretical hull speed. This is because it can carry more sail per given displacement, ballast ratio, and ballast placement. Puddle Duck Racers are a good example of this. They routinely reach 4.5 and 5 knots on a 7.5 ft maximum waterline, even when quite heavily loaded. This is well past their 3.8 knot theoretical hull speed. Their typical D/L is around 400.

    Well into the 20th century, it was routine to make at rest waterlines very short, as a way of getting around rating rules. Had the D/L’s of these boats been assigned a number equal to, say 80% of their length or the actual number, whichever was greater, the history of yacht design may have taken a different, probably saner course. Short waterlines would be used only to improve light wind sailing and to denote a short boat, not to game the system.

    IMHO, a ratio I discovered years ago may be a better indicator of sail boat performance. This is what a call the ‘Heft factor’ ( Hf). It is based on the Beam of a boat compared to its Displacement and Length. It is calculated as follows:

    Displacement in Cubic units * 20/ (((Beam)^2) * Length) in linear units

    These numbers would taken from the actual dimensions of the boat, excluding, perhaps such things as guards and rubbing strips. Hiking trapezes, seating wings, and other out board crew seating arrangements would be included. As would canting ballast keels (some how). It is quite clear that in order to have high speed, a sail boat (and even a powerboat) has to have a moderate to low Hf. A low Hf would be 0.5 to 0.75. A moderate one would be 0.75 to 1.20. 1.20 to 1.80 would be high. And 1.81 up would be very high.
    The proposed 45,000 lb 55 footer, with a 12 ft Beam would have a Hf of around 1.80, and with reasonably deep forward sections should be quite sea kindly

    A typical ‘Open 60’ has a Hf south of 0.50, even without a canting ballast keel. I once suggested that future ‘Open 60’s’ should be subject to the following rules. 1.) they be able to recover from a 120 deg. Capsize, and 2.) Their Beam plus their Draft not add up to more than half their Length.

    A Puddle Duck Racer with a D/L of 400 has a Hf of around 0.83, which is on the low side of moderate.
     
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  13. Timothy
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    Timothy Senior Member

    sharpii2 I would be very interested to know more about your rig. I have being playing around with a similar concept. When fully reefed in the lateen configuration would the lug (yard?) be strong enough for the increased load.
     
  14. sharpii2
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    sharpii2 Senior Member

    Damned good question.

    The truth is it wouldn't.

    This is because of the high loading on the sail in its reefed condition. My estimates are well in the neighborhood of 6 to 7 lbs per SF.

    So now the design calls for a gallows line from the top of the mast to the end of the yard, to keep it from bending down excessively.

    The only other alternative is to make it very strong. And strong is another way to say heavy. And at four times the beam above the waterline, you can't stand heavy.

    Seeing this problem, I have already shortened the rig by one foot and am considering shortening it some more.

    The rig (which I am working on now) has been shortened from 195 SF to 183 SF, and now may have to be shortened to 171 SF, Just to get the yard lower.

    The yard, as presently designed, will weigh 16 lbs. It will take at least twenty times that weight in ballast foot/pounds to counter that. I know I will not come close to that. I console myself by recognizing that the yard will only be that high in light wind conditions. In heavier air, the yard comes down with the sail.

    But, still, this has been quite a learning experience for me as to why sailboats look the way they do.

    Modern rigs can have more power simply because they have less weight up in the air and they usually have massive amounts of ballast and/or deep ballast keels. The only alternatives seem to be very wide Beam or multiple masts with long bowsprits and boomkins.

    I have sketched two alternative rigs for my boat design. One is a mast head cutter, and the other is the rig I suggested earlier in this thread, a large gaff mainsail ketch.

    With the cutter, I found the mast only 3 ft taller and probably lighter in construction. This is because it takes no bending loads and is well braced with spreaders, stays, and shrouds. The loads it takes are almost pure compression. It could be, essencialy a hollow box. Even counting the approximately 135 ft of cable (about 20 lbs) it will need to hold it up, it will most likely be lighter per given sail area and almost certainly have less top hamper.

    The ketch, I haven't done much work on. I do know, even with its almost comically huge mainsail, that its gaff will be shorter than the yard on my original rig and it will be much less high up.

    The penalty, though, is more masts. I dealt with that by putting them at either end of the living quarters portion of the hull.

    I will probably go with the original rig. The other two might be options for others who might want to build my design.

    At least now I know what I am getting into with this rig. And what I may be giving up.
     

  15. MikeJohns
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    MikeJohns Senior Member

    re: Colin Archer double enders

    This is worth a mention. They are well superseded by safer and more efficient hull-forms. It was the strongest hullform for trad wooden construction since it eliminated the transom, but the lack of reserve buoyancy aft makes them prone to being pooped and they have a very unpleasant pitching action. They lack the flatter stern sections to damp that motion. This tends to dictate the course sailed and makes some windward courses almost impossible.

    Modern 'double enders' benefit from a much more buoyant stern and are in reality just a rounded transom.

    These old Colin Archers boats are not particularly weatherly nor are they particulalry good performers, they are heavy slow and comfortable which made them easier to handle.
    The old engineless pilot boats that evolved around the world are generally a superior hullform in all regards and they had to combine speed comfort and safety.


    Back on the subject
    If you are going for a long narrow hull, if its shallow draft it will chronically lack power to carry sail ( look to the dellenbaugh angle ), will roll abysmaly both in a seaway and at anchor and you would be better off in all regards with a multi-hull particulalry if you are chiefly coastal sailing and you really want speed, shallow draft and grounding ability.
     
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