Designing in Safety for Blue Water sailboats.

Discussion in 'Sailboats' started by misanthropicexplore, Apr 29, 2018.

  1. misanthropicexplore
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    misanthropicexplore Junior Member

    I'm reading about tiny to medium small blue water sailing cruisers, 1 ton to 10 ton displacement (About 20 to 36 feet long, if you do it that way).

    I wondered what people's thoughts are on features for designed in safety. (As opposed to safe actions by the crew, which are always your number one requirement). Some features I've heard mentioned are:

    An easy to handle rig to reduce crew fatigue.
    Speed, to get out of harms ways faster.
    Shallow draft, to allow a greater number of safe areas to weather a storm in.
    180 deg righting angle.
    Stern egress doors.
    Deep keel, to provide sea kindliness and stability.
    Simple systems to avoid breakdown and be easy to fix.
    Redundant systems, for back up.

    But design is compromise, and and a lot of those things are opposed. For instance, regarding simplicity, shoal draft, and deep keel, you only get 2 of those three. So from people who have designed small blue water cruisers, or cruised in them, how have you managed compromised for safe design?
     
  2. sharpii2
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    sharpii2 Senior Member

    I think the main point is figuring out what you want the vessel to do.

    Where is it typically going to be sailed?

    Is it going to have access to deep water berths? Is it going to always be around travel lifts? Is it going to sail primarily in deep water ports?

    If it is, then a fixed deep, short keel (which resembles an airplane wing) is the answer. It will give you the best windward performance and probably use the least amount of ballast for an adequate range of stability. Such a keel does not make the vessel more sea kindly, especially if it has a very high aspect ratio and a bulb on the bottom. What it does instead is to give the boat the maximum initial stability (great for sail carrying ability) at the expense of a snappy roll period. Other than a canting ballast keel, this is the highest performing mono keel boat hull form. A variant on this form is one with a drop keel, which can be winched up at least partially, to motor or sail in shallower waters.

    (see 3rd attachment)

    A compromise on this this hull form is having a somewhat longer keel, with a lower aspect ratio, so that it looks more like a fighter aircraft wing than glider one. This will probably need more ballast for an adequate range of stability, but will still perform quite well to windward, almost as well as the example cited above. It will most like be more sea kindly with a slower roll period. It will probably have slightly less draft too. A variant on this hull form might have a somewhat longer shallower keel, with a centerboard inside, to win back some windward ability, once it's in deeper water.

    (see 1st attachment)

    If the boat is going to sail mostly in shallow ports and is not always going to have timely access to travel lifts, a long shallow keel will then be the answer. Such a vessel will most likely be able to stand on its keel, at low tide, so the bottom can be cleaned and serviced. The price for this however is much less windward ability and usually more surface area under water. This makes for a boat that may not change tacks very quickly. It is also likely to require a higher percentage of its weight in ballast for an adequate range of stability, but not necessarily. In exchange for these short comings, this hull form is often the most sea kindly of the three, as the large area of the long keel tends to dampen sharp rolls. It also provides better natural course keeping capabilities. Such a hull form is usually showered with derision by the performance oriented sailing crowd, because of its poorer windward performance and its much larger whetted surface area. But it is loved by the off track cruising community, which tends to be less affluent than the more performance sailing one. A variant of this hull form has a centerboard or dagger board, which can be lowered, once the vessel is in deeper water, to get better windward performance. But this 'board had better be rather large, because it is going to need to produce most to the windward "lift", as the long keel above it is only effective at a much steeper angle of attack. This third hull form usually provides the greatest amount of sea worthiness for the lowest cost.

    (see 2nd attachment)

    Sailing vessels with an 180 degree range of stability are rare, almost to the point of non existence. This is because such a vessel requires a very high, narrow hull section and/or a very deep keel. The narrow hull section makes for very cramped cruising accommodations, and the extra-deep keel is a grounding menace. Sailing vessels come to grief far more frequently from running aground than from failing to recover from a capsize. Such a vessel is also likely to have relatively low initial stability, which will give it relatively poor sail carrying ability.

    Please note that all three hull forms mentioned above are all very seaworthy, if properly designed.
     

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    Last edited: Apr 30, 2018
  3. rwatson
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    rwatson Senior Member

    Shallow draft, to allow a greater number of safe areas to weather a storm in.

    Deep keel, to provide sea kindliness and stability


    That usually means a tonne of lead weighted daggerboard, raised and lowered with winches, taking up huge space in the accomodation.
     
  4. rob denney
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    rob denney Senior Member

    Unstayed, with wishbone boom (self vanging and self stowing) is safer than any other as there are fewer pieces to break, the sail can be raised and lowered on any point of sail, the boat will perform upwind and there is no foredeck work.
    A long, light for it's length multihull will not only do this 2-3 times better than a mono, it will be more comfortable and safer if it does get caught out.
    Liftable keels and boards will allow this for any boat, but a multi will be lighter for it's length, so will draw less. And sit level.
    Multis fail this one, although there is no reason why they should ever get there. A simple sheet release will release the sheet at a predetermined angle of pitch or heel with no crew input at all. If the rig is unstayed, this will totally depower the rig in a second or two, well before it goes over. If this is not safe enough, it is possible to work a system of drains and buoyancy so the boat is self righting. see a video of a rough proof of concept model at http://harryproa.com/?p=424
    Not at all safe. Once you come out, especially in conditions harsh enough to require stern egress, there is nothing to hold onto. Death follows.
    Neither of these are provided anywhere near as well by a deep keel as they are by wide beam and length do on a multi.
    Absolutely. The unstayed rig is an excellent example. As is unsinkability and kick up rudders and leeway resisters in the event of a grounding or hitting floating logs or containers.
    For sure, but if the systems are truly simple, there is very little that needs backing up.


    The biggest cause of sail boat problems is human error. Offshore it is usually starts with tiredness and fear. A safe boat is one where the crew can stop sailing, drop the sails and sit out bad weather in comfort while catching up on their sleep and/or waiting for a break in the weather. This is harder in a deep keel boat rolling it's guts out than on a long, wide, shallow draft raft.

    Re weight. 4-10 tonnes might be "tiny to medium" in a deep keeler, but in a harryproa, it is between 40 and 60', with all the bells and whistles imaginable for extended offshore cruising. For simple boats, it covers from 50-80'.
     
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  5. gggGuest
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    gggGuest ...

    I think a large percentage of what you are going to get is folk displaying their biases and prejudices. To truly find out what the safest compromises are would be a very difficult task, because all you really get are anecdotes: "my xxx survived this storm, therefore it must be safe". And, of course, if craft A is better than craft B in one set of circumstances then craft B may well be better than craft A in another set.
     
  6. gonzo
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    gonzo Senior Member

    I think that, budget aside, you should get the largest boat you can handle safely and comfortably by yourself.
     
  7. misanthropicexplore
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    misanthropicexplore Junior Member

    Sharpii2: thanks for taking the time to sketch that for me and explain it. "Sailing vessels come to grief far more frequently from running aground than from failing to recover from a capsize." It seems to me then that shoal draft, and ability to recover from grounding would be more important...sort of like how most cars have seat belts, but most don't have roll cages. Are tandem keels just marketing hype or do they offer some real advantages? Do swing keels and dagger boards have any surprise dangers? Like a swing keel folding in when the boat is rolled and making impossible to right or something?

    rwatson: Yeah, to me, as an armchair sailor, accommodation isn't as important as safety, but I've talked to some people who've actually done some cruising that have a special vocabulary of curse words just for a keel case that they had to bang a shin on too many times, so maybe I'd feel different if I was actually doing it.

    Rob Denney: Thanks for the complete answer. I am familiar with the benefits of of unstayed masts, though I've heard more about them in the context of junk rigs. I've also heard about the benefits of wishbone booms, because I've read up quite a bit on Wyliecats, but I wasn't sure how much of it was marketing hype. I watch dollar signs appear in people's eyes whenever they say "carbon fiber" so I've gotten pretty suspicious it. Wyliecat makes a big deal about how their mast/sail combination works because carbon fiber can make such whippy mast end. How are they self stowing? Have you ever talked to someone using a wingsail? (Soft or otherwise). I've heard people say that because they can be adjusted for zero lift they never need to be stowed, but I feel like that could go very wrong in a cramped harbor or in a bad storm. I've read a couple technical articles that said proas are the only multi that can be made fully selfrighting, though I don't understand what what works on a proa wouldn't work on a catamaran. Wharram said that the way the pacific islanders survived bad storms in catamarans was because the boats weren't decked: they flooded up to the gunnels and become semi-submersibles. Since reading that I've wondered if a large water ballast capacity, only used in storms, would be a safety feature, or if the extra weight and complexity of doing that right would cost you so much speed and attention as to reduce safety in other areas.

    gggGuest: yeah, you're not wrong. Compromise is always the result of values, and values are always individualistic, but I'd still like to hear the thoughts of people with experience.

    Gonzo: you wouldn't think that's controversial, but seems to be to some. I've always heard a boat should be as long as the the seas are tall, so don't take a 20' boat into 30' seas, but Yrvind thinks the smaller it is, the safer to single hand. Perhaps that only applies to expert sailors (like Yrvind) in custom boats? I've noticed a lot of very small, all-weather cruisers tend to be more like oil tankers, or almost submarines, with most of the mass below the water line and decks nearly awash.
     
  8. gonzo
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    gonzo Senior Member

    I've done a lot of ocean cruising in smaller boats (21-25 feet).
     
  9. misanthropicexplore
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    misanthropicexplore Junior Member

    I have no ocean experience at at all (yet). I have several thousand miles of river and lake canoeing trips, usually 2 - 3 weeks at a time, but that's not really the same at all, unless you're Don Starkell. Do you think Yrvind is right? That a sailor should have the smallest boat that will keep his stores? Or do you think that a single hander should have the biggest boat he can afford and manage?
     
  10. PAR
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    PAR Yacht Designer/Builder

    Most boats can be made to self tend, easy to reef, rigged for solo operation, self steer, etc., so the primary thing is skipper and crew awareness. Surviving a knock down is all well and good, unless no one knows what to do when it happens or how to avoid it in the first place. Crew preparation is the most critical element of any offshore yacht. As you gain experence, you'll quickly develop preferences about how you want the boat setup and the way things are done aboard. These work out intuitively mostly, though just paying attention to other cruisers, can offers ideas. These adjustments to your ideals about things are an evolving, ever on going process, that doesn't change until you die.

    In a nut shell, you can't design or prepare any yacht for every eventuality, so you make do with what you have and insure the crew is ready. Your crew is what will save the boat, not some random piece of equipment or clever design feature, so focus on them and your own skill sets, so if the shiit does hit the fan, it's something you've prepared for, possibly rehearsed and though a pain in the butt at the time, you'll laugh about it in the next port, rather then be the headline.
     
  11. misanthropicexplore
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    misanthropicexplore Junior Member

    "Your crew is what will save the boat, not some random piece of equipment or clever design feature." As in, people and processes make a bigger difference than products. That sounds pretty spot on. It's pretty much how military training works: drill and checklists, that way then when crap happens, the response happens by the book. So I 95% agree, but that last 5% keeps me asking questions. I don't know much about sailboats yet, but I do know a fair amount about motorsports , and random pieces of equipment and clever design features can be the difference between a car that's safe for an amateur to drive on the road and one that gets professional drivers on a closed course killed. A gimmick is no substitute for skill, but gimmicks can protect you when skill fails.
     
  12. gonzo
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    gonzo Senior Member

    We all have preferences that are neither right nor wrong.
     

  13. rob denney
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    rob denney Senior Member

    The Wylie cats perform well and as far as I know, do everything the brochure says they will.
    Carbon is 3-4 times the price of glass and you only need half as much (roughly). You also need half as much resin so the cost difference is not huge. The resulting lighter boat needs smaller rig and motor, so it is worth considering in many cases. It is no harder to use than fibreglass so building your own mast, rudder shafts, etc is easy. It is expensive if it is used near the limits as to get the absolute maximum values from it (or from fibreglass), requires ovens, controlled environmenys, autoclaves, etc.

    The sail drops into loops of line beneath the boom.
    Lots, and designed and built a few myself.
    My experience as well.
    The cat is at 120 degrees when the mast hits the water and the weight of the boat turns it upside down. The proa stops at 180, is much easier to right.

    the latter.
     
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