Long Distant Voyaging

Discussion in 'Stability' started by Sean K, Aug 22, 2015.

  1. gonzo
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    gonzo Senior Member

    A heavy boat will use a lot of its displacement to stay afloat, while a light boat of similar volume will have a higher load carrying capacity. The weight of a boat is not an indication of its load capacity.
     
  2. MikeJohns
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    MikeJohns Senior Member

    It's always important to put numbers to any observation to get perspective.

    In this case, lower Froude numbers where frictional resistance dominates smooth water performance and the boat is entirely in displacement mode:

    If for example I take the hull I have in Maxsurf at the moment; increasing Displacement and keeping the same prismatic coefficient for an increase of 40% to D it has 1/10 more WSA.
    Frictional resistance is directly proportional to WSA and to v squared. So it would need 10% more light air sail area or suffer a v/10 decrease in light air.
    Slower? A tad, a little fouling ( increase Cf) or a less than optimal sail shape and the difference could reverse between the two examples above.

    What if we made the difference in speed more significant at 1/5 rather than 1/10 ?

    If the craft goes 1/5 faster the frictional resistance goes up by nearly 50%. In other words the same boat would have to either halve it's WSA or add 50% to it's sail area to get just a 1/5 increase in v. That's why performance boats suffer lofty rigs and have high stressed gear (as low stress means weight).
    That's also why there's no where near the difference in light air performance for cruising boats than racing parlance and imagination might suggest.

    Interestingly (but also not so significant), a heavier boat actually has a lower overall resistance per unit of displacement than a light boat.
     
  3. MikeJohns
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    MikeJohns Senior Member

    Talking about most normal cruising boats for the same beam and LWL it's the same immersion for the same load regardless of D, What's important is the internal location of that added load.

    Light boats also have more adverse performance decrease with the same mass increase. A load that's significant for the light boat can be relatively insignificant for the heavy boat.

    The heavier boat absorbs the mass with a lower reduction of SA/D and significantly with far less or even no effect on GZ.

    For the light boat the load both increases the requirement to carry sail while at the same time reducing the power to carry sail. Arguably most importantly for the laden light boat intending offshore passages is a large reduction in LPS.

    The lightweight performance cruiser must keep the weight down in every regard.
     
  4. Steve W
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    Steve W Senior Member

    Absolutly, I don't know how many times I have seen boats advertised as having upsized rigging or overbuilt as if its a good thing when all they have done is squander much needed payload.
     
  5. michael pierzga
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    michael pierzga Senior Member

    Yup...thats the defect when going lightweight..you must sail the boat light.

    As a result when going light you must choose the longest possible boat that fits into your budget.

    Lightweight becomes expensive.

    Multihulls are the same. Once you overload them they become highly stressed dogs.

    A good looking lightweight oceanic cruiser for normal folks is the Pogo 12.5

    http://www.pogostructures.com/en/cruising-sailboats/pogo-1250/
     
  6. thatone123
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    thatone123 Junior Member

    Captain Bligh?

    Oh, come on, England never would have become a world power without daring small boat sailors. Chinchester continued the tradition, breaking records sailing small boats across the Atlantic and around the world in the 60's and later. Bligh did a feat of uncompressed daring with a small boat and the crew of the HMS Bounty. Many more have sailed much smaller boats long distance to set records and etc.
     
    Last edited: Dec 22, 2016
  7. Barry
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    Barry Senior Member

    There was a couple of guys who sailed the northwest passage on an 18 foot hobie cat, 450 pounds, I think the book was called Polar Passage, mid eighties prox.

    For a polar bear, this probably looked like two oysters in a half shell.

    Contending with ice and storms the guys probably were not firing on all 8
     
  8. thatone123
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    thatone123 Junior Member

    Oysters

    Had to think on the half shell joke than it hit me...funny. Speaking of half shells, if you look at the records of small boats setting records, many of them seem not much bigger than a oyster half shell. Really! Some of them are almost silly small like 6 to 8 feet and cross oceans. Not much different than space exploration. Look it up.
     
  9. sharpii2
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    sharpii2 Senior Member

    Lighter boats do not necessarily have lower rigging loads, especially in proportion to their displacement. In order to get the higher average speeds they are designed for, they must have greater sail carrying power. Many of these boats are capable of super-displacement speeds. Some can even plane on a reach.

    The old full keel lead mine could not do that. It could reach the top end of displacement speed, but usually loafed around at sub-displacement speed. For a twenty-footer, allowing for a WL less than its length, this would be around four knots. This speed requires far less energy per pound of boat than super-displacement or semi-planing speed.

    If the boats were of equal length, the lead mine might actually have lower rigging loads than its faster sister, even though this sister is significantly lighter. The lighter boat is likely to slam harder, too, into head seas, but is more of a dream sailing down wind.

    If I were asked to pick the worst point of sailing for the lead mine, it would be dead down wind. If I had such a vessel, I wouldn't even consider it. I would downwind tack, instead, the extra distance be damned. This way, the more tender-for-its weight lead mine will lay over easy, on its leeward side, with the wind pressure on its sails effectively limiting its rolling.

    The lighter boat, with its usually wider hind quarters will literally fly before the wind, making phenomenal progress, if it has a good auto pilot or a good hand on its helm. In fact, it appears that in somewhat wild conditions, doing such may be its best option. It has robust relative buoyancy, as the topsides volume is likely to be a far greater portion of its total hull volume. Not only that, but its usual short keel and relatively longer WL make it less likely to broach or pitch pole. If it heaves-to, like its heaver sister will be compelled to do, its occupants are likely to have a much harder time of it, even though the boat itself is likely to survive.

    If its heavier sister tries to fly before the wind, its longer keel, with its ballast spread out more length wise, its usually shorter WL, combined with its usually proportionately lower reserve buoyancy, creates an almost certain set up for a broach or a pitch-pole. In this case, given enough sea room, it's probably better to heave-to and call it quits for a while.

    Neither type, IMHO, is more seaworthy than the other. But one is far more preferable for a long voyage, with a small crew, on a small budget. I would only make the WL on the full-keel, lead mine longer, if I could.

    The devil in all this is that no boat one is likely to buy (on a budget) is likely to be either one of these extremes, but is likely to be somewhere in the middle. More likely than not, its going to be at least 30 years old, and its going to have some major problems. Since it will probably have to be modified somewhat for its new role, putting the needed repairs into it makes more sense than it would, if the boat was intended for more casual sailing.

    And no, you never will recover the money you put into it. This is true. But a voyaging boat, particularly one re-purposed as such, should be seen as more like an automobile than an investment property. The person buying it from you is likely to be just as broke as you were when you bought it.

    If I were to do such a thing, I would first get well acquainted with the boat. If I had to embark right after the boat was ready, I will first make short hops, nibbles before big bites, with each getting progressively longer, if possible. The more such trips I made, the wider range of conditions I'm likely to encounter. It is then I would learn my boat's strengths and weaknesses, and how best to exploit and/or deal with them.
     
  10. tane
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    tane Junior Member

    " My last ride across the puddle was on a Swan 40 (Frers)."

    how was that (by today's standards) rather strange companionway arrangement in action? there are some really tempting frers swan 40 on the secondhand market (yeah I know, old teak deck...!) but I imagine this forward companionway is extremely awkward for a cruising couple...even at anchor & much more so when the going gets tough
    please elaborate PAR!
    thx
     
    Last edited: Jan 27, 2017
  11. tane
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    tane Junior Member

    "...You usually want a different boat at some time in the cruise to the one you have whatever craft you are sailing...."
    wise words!!!
    (the objective is not to have this wish ALL the time...)
     
  12. Windship277

    Windship277 Previous Member

    Thats a broad statement. The worlds smallest boat to cross the Atlantic...5'10" April Fool was her name. Back during the late 1800 and early 1900 the Atlantic was regularly crosses by men in 12-21 foot boats. Small boats have advantages that big boats dont. Yes...some died. That dont stop us. Youd be nuts to try it without the knowledge and experience needed. Tanya Aebi, in the 70's went around the world in a Contessa 26 without much experience, hardly sailed before, but she had what it took. You have to have THAT too. If you dont "get" sailing, every trip, no matter the boat, might be nuts. You put a good sailor in a good 21 foot boat and he'll go anywhere, so, excuse me Par, your words are...hmmm...whats the word...
     
  13. Windship277

    Windship277 Previous Member

    Yeah...I dunno. The light boat has far less weight to move. Wouldnt it boil down to sail size?

    So, your advise is even though you have the will, the dream, you advise is: unless you can afford a big expensive boat, dont even think about it and old boats are junk". Dude...old boats are the best. I could post a list of old boats that you can get on and go....cmon.... Heres 1, ok? Alden 30. Can buy for 10 grand and less still. I could go on and on. Its a problem if you think you need a ton of stuff that you do not really need.
     
    Last edited by a moderator: Jul 15, 2017
  14. dsigned
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    dsigned O.R.C. Hunter

    This is a frustration I have with a lot of conversations in the boating community. A boat that's "only" $200k used is within reach of maybe 10% of the US or Western world, which puts it at a fraction of 1% of the world population. Regardless of whether or not I personally can afford it (I can't), making sailing more expensive is (in my opinion) responsible for its decline in the US. Even racing relatively small boats, you can expect to be easily outspent. But unlike many other activities, this is simply unnecessary. To be sure, I would like to be able to get the biggest and bestest boat that I can afford. But let's make comparisons that are fair here: even relatively small fiberglass boats are safer than the boats Columbus sailed (much less the Vikings before him). The Nina was 50 ft, 50 tons and capable of maybe 5-7 knots, if Wikipedia is to be believed. And it carried 24 dudes.

    I suppose my point in this is that cost is a real issue, and rather talking about the "minimums" for a given task, it might be better to start thinking about "what's the best boat that could be built for $50k"? I say this, because someone is going to have $50k, and is going to attempt whatever crossing or passage in whatever they can get their hands on. And rather than taking potshots at their ferrocrete boat from the half million dollar multihull, help to make designs that are more accessible. Or don't but at the very least don't criticize those who are making do without.
     

  15. PAR
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    PAR Yacht Designer/Builder

    This is more misunderstanding, Dsigned. The sailing market in the USA has been in decline since the end of the 1970's. In the early 70's there were more than a dozen, small trailer borne cruisers (Catalina, Hunter, MacGregor, etc.), now take a guess. Sailing has been outgrown by simpler, easier forms of pleasure boating, where the only skill you need, is the ability to get a second mortgage so you can make a purchase.

    Sailing always has been costly, in fact only in the last 50 - 60 years has it become common man stuff, while prior to this it is was little more than the blue bloods desires to outdo each other. Attempts to make a poor man's sailor have been repeatedly tried with little success, though plenty of one designs and open classes still show considerable activity. When I was a kid, I was active in the local racing community, but an outcast. I showed up with a homebuilt, crappy lines, hardware store blocks, contrivance and reveled at coming in third in a fleet of blue bloods, with their state of the art machines. It used to really piss them off, which is what I enjoyed most, because my dad wasn't the mayor, local congressman or corporate lawyer, but simply a diesel mechanic. He was ex Navy, but didn't know a thing about sailing, though happy to learn I liked it.

    Sailing, unlike powerboating requires some serious interest. Firing up a small block powered, fat butted puddle scooter requires you just avoid two things; bumping into hard sharp stuff and enough fuel to get home. Sailing though fairly intuitive to most, requires some understanding, possibly some training, certainly lots of practice, etc. In our every instant gratification world, it's not much of a wonder why sailing is in serious decline. The pleasure boat market has sailboats now rivaling canoes, kayaks and paddleboards is total sales. This is reality and it's not going to change any time soon, unless foiling sailboats start powering past bowriders. Of course foiling a sailboat requires some costly gear. Welcome to the 21st century . . .
     
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