Feedback request on sailing-rowing-cruising design and materials

Discussion in 'Boat Design' started by scotdomergue, Mar 9, 2010.

  1. scotdomergue
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    scotdomergue Scot

    I think I’m happy with the design (see attached drawings), but this is the first time I’ve tried to design and build a boat. I’ll be very interested in any comments, ideas, suggestions. I’m willing to consider major or minor modifications, or even starting over. She’s 20 ft LOA, 64 inch Beam, waterline beam is 48 inches (when loaded to 5 inch draft).

    I want the boat to be fun to sail and to row (sliding seat rowing for power/speed, aerobic exercise, and fun), and to perform well both ways. I want her to be very seaworthy, and have taken ideas from the design of ocean rowing boats. I believe she would be capable of crossing oceans, even surviving a hurricane. All compartments are watertight (cabin with under-floor storage/ballast, forward storage compartment, 4 storage/ballast compartments under the cockpit floor, and 6 more storage compartments under the side decks). The cockpit is small and shallow, about 7 cubic feet, self-draining through the centerboard hole.

    I intend light-weight composite construction. I hope to bring her in under 150 lbs including all sailing and rowing rigging. Current plan is:
    - Core of 9.5mm (3/8”) CoreCell for hull and 6mm (¼”) for everything else, with
    - 5.2oz Carbon/Kevlar hybrid fabric and Epoxy on the outside - carbon for compressive strength and Kevlar for toughness, resistance to abrasion, etc.; possibly with a light (~2oz) glass over it to more easily get a smooth finish.
    - Kevlar (4 or 5 oz?) with epoxy for Interior surfaces and partitions.
    - spars: un-stayed carbon fiber with foam core for flotation.
    Any thoughts about the suitability of these materials? Issues or problems? Alternatives?

    Sail rig can be cat, sloop or ketch (to be determined; will probably start with cat and experiment).

    She’s intended primarily for minimalist cruising. I enjoy traveling by bicycle (self-contained, months at a time) and backpacking, so I don’t need to carry much. I think reasonable load capacity of the current design is around 600 lbs - that’s me plus about 430 lbs of food, water and gear - plenty for my needs, and then some! Even with a second person along there’s far more carrying capacity than backpacking or even bicycling. I imagine most of my use will be alone and lightly loaded for draft of less than 4 inches (not counting board and rudder). At maximum load draft would be about 6 inches.

    I’m very interested in whatever you might have to say.
    Thanks,
    Scot
     

    Attached Files:

  2. Guest625101138

    Guest625101138 Previous Member

    Scot
    This might give you some more ideas:
    http://adventuresofgreg.com/blog/2010/02/23/inside-passage-trip-report/
    There are many archived pages on the boat development and construction.

    The boat is yet to cross an ocean but so far it is performing to expectations. It would move along reasonably well with a small fixed sail or parasail. It is a much more easily driven hull than you have drawn. Displacement is roughly the same. The construction is quite a lot stronger than you are planning.

    The low wind drag combined with the large diameter prop gives it the ability to make headway in very heavy winds. It will be capable of about 1kt into 60 knot winds

    It could be built in glass to save money but would be a bit heavier than the CF version.

    Rick W
     
  3. scotdomergue
    Joined: Jan 2009
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    scotdomergue Scot

    Rick, thanks! Very interesting boat and project.

    At 30 ft long by 4 ft beam WITHIN is significantly longer/bigger than my boat. If I understand what I’ve read on his website she’s also significantly greater displacement (he mentions getting the 1000 lbs of boat launched, which I assume includes lots of gear, and maybe supplies as well, but doesn’t include crew). I expect total displacement of my boat, with me on board and fully loaded with gear and supplies to be about 750lbs. For much of my use I expect it to be under 400 lbs (rigged boat 150, me 170, supplies 80).

    While his hull SHAPE is easily driven, wetted surface will be significantly greater than mine - and if I understand correctly, that is the primary factor determining resistance for a human powered boat. So, given that we’re talking well under hull speed I suspect that my boat will actually be faster, due both to less wetted surface and the greater power and efficiency of sliding seat rowing.

    Of course, my boat is primarily a sailing vessel, only secondarily human powered. That should make covering distance easier and generally faster.

    I’m very interested to see that his boat is built from CoreCell and Carbon - very similar to mine. I’m not completely clear as to why he used a combination of uni and bi-directional carbon layers (instead of just bi-directional). His hull may be significantly stronger related to impacts, though I’ve read that carbon is brittle, and I don’t know just what difference that would make. I want Kevlar on the outside because it is tough - very resistant to abrasion or cutting. For a boat that will be mostly cruised in coastal waters and drug up on a beach now and then, this seems important. Since Kevlar is weak in compression, using the carbon/Kevlar hybrid fabric seems to make sense, though I can also imagine one layer of carbon and another of Kevlar. I’m a little reluctant to use carbon on the inside because I’ve read that it’s fibers can easily be rather prickly while Kevlar just gets fuzzy. I believe I’ve read that the inside layer need not have nearly as much strength as the outside layer, that compression is less important, and that Kevlar is good on tension.

    Any further thoughts about any of this is very welcome! I’m quite aware that my knowledge and understanding are limited at best, and some may simply be wrong.

    Any opinions out there about the best amounts and layering of materials? Do I need to have this engineered? If so, any recommendations about who might do that?

    Scot
     
  4. Squidly-Diddly
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    Squidly-Diddly Senior Member

    I like it, but I'd want one without the little cabin unless

    really planning for ocean crossing and hurricanes.

    I think that would make it a much better and fun sailor, as well as possibility of two sliding seat rowing stations.

    Could you get by with a stout tent on the stern for "living space"?
     
  5. scotdomergue
    Joined: Jan 2009
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    scotdomergue Scot

    Once I get the bugs all worked out, you can build yourself one without the cabin! It's a key piece of what I want. Perhaps that's partly a matter of living in the northwest where it often rains, and wanting to be comfortably "at home" just by throwing the hook over the side. I also want the sea-worthiness and potential for self-righting provided by the watertight cabin. I won't be surprised to find myself doing some voyaging in her - perhaps the Caribbean, perhaps across oceans. Losing the cabin would definitely decrease windage. In what other ways do you envision her being better and more fun to sail without it?
     
  6. Guest625101138

    Guest625101138 Previous Member

    I have inserted some comments. You have a few misunderstandings about hull shapes. The really fast sailing boats are trimarans. When sailing at speed there sail on a single long, slender ama. The fastest sailing monos are long and slender with canting keels to counter the heeling moment from the sail.

    Within is designed to punch through waves while the pilot is in relative comfort and safety, protected from the elements. This aspect of the design has been reasonably well tested. There is no reason why crossing an ocean in a small boat should be a physical hardship.

    Rick W
     
  7. scotdomergue
    Joined: Jan 2009
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    scotdomergue Scot

    Rick,

    Thanks for your additional thoughts.

    I particularly appreciate your thoughts about combining fabrics. I’ve recently become aware of how that could create problems - and am unsure how to address it. Your suggestion to create test panels is good. I found Greg’s experience with that very interesting. As in so many things about boat design, there are multiple goals that often require compromises. In my case I want toughness and durability on the outside to withstand dragging the boat up on beaches and contact with barnacles or oyster shells that can cut, as well as general wear and tear. Unfortunately Kevlar, which is very tough, lacks the compressive strength of Carbon or even glass. It‘s also a pain to work with and particularly to fair.

    Any suggestions on the best materials and layering for my purposes? Any suggestions about who to talk with about appropriate and cost-effective engineering?

    I completely appreciate the Within design. It’s very appropriate for Greg’s purpose. My intentions are rather different. I will use my boat primarily for solo cruising in coastal waters, probably starting with the (mostly) protected waterways between Olympia, WA and Alaska. I want to be able to explore shallow bays and estuaries (for example in Florida where I kayaked and canoed in inches of water) and to drag her up on a beach. Deep, heavy keel bulbs and canting keels are not options for a variety of reasons. I’ll often anchor in a sheltered cove for the night, enjoying the evening out in the cockpit if the weather is good, hanging out in the cabin if it’s miserable. Good performance in all conditions and on all points of sail (as well as rowing when it‘s calm) is desirable; maximizing speed is not important. I greatly enjoy sailing in a good wind with feet hooked under a strap and body out over the water, as well as all the other options in an open cockpit boat, including rowing.

    I want my boat to be very sea-worthy and can easily imagine exploring the Caribbean in her and possibly crossing oceans. If she can be made strong enough to survive hurricanes (as do ocean rowing boats), so much the better. I’ve included the same sort of watertight compartments you mention in Within, as well as floatation from the same materials and additional built-in foam floatation. I recognize that her shape is inherently less strong and that she will not be nearly as strongly self-righting as Within.

    Regarding hull shape:

    As you note, combining sailing and human powered performance involves compromises.

    Displacement performance is limited by waterline length. Within at 30 feet won’t run into this limitation until more than 7 knots, my boat at 20 feet will reach it a little under 6. Greg will not run into this limit in Within on human power alone. Clearly the size of Within is needed for that 420kg, not maximum speed. I don’t expect to be able to row up to hull speed for more than short periods of time, and as noted maximum speed is not of great concern. So additional length is not needed for maximizing speed, in either case.

    For a given length, the greater the waterline beam, the greater the wetted surface and the greater the resistance. Obviously, a narrow hull will have less resistance. Olympic sculls are extremely long, narrow and light for this reason. This also contributes to the speed of the trimarans and the fastest monos that you note. Each has its method of countering the heeling moment of the sails - methods that are not appropriate for my purposes. It is my body weight, out as far as possible combined with hull shape (wider and fairly flat) that provides this in the boat I intend to build. Yes, of course, this is a compromise. I could easily drive a 20 foot scull with 20 inch beam to hull speed, but it wouldn’t be much good for all the other things I want my boat to do! I expect to be able to row my boat for extended periods at 4 to 5 knots in flat water, at least when lightly loaded, which will be most of the time. People with far more knowledge and experience than I have indicated this is realistic. We’ll see how it works out!

    Given a particular waterline beam, length also adds to wetted surface and resistance. There is a reason that Olympic 1x racing shells range from 25 to 30 feet length, depending on weight and strength of the rower, not longer. I’m sure that Greg could maintain higher speed in calm water in a shorter boat for this reason, but it wouldn’t have the load carrying capacity nor, perhaps, the performance in rough conditions.

    If I’ve misunderstood something here, please explain. I’m always happy to learn, particularly when I‘ve got something wrong.

    Regarding pedal power vs. rowing: Rowing is obviously more difficult in rough conditions. I can easily see Within’s pedal power, as well as shape, being more effective than ocean rowing boats in these ways. In calm conditions driving the same hull shape I’d be surprised. Sliding seat rowing uses the entire body and is one of the most aerobic forms of exercise. Pedaling uses mainly the legs and is somewhat less aerobic. I expect that there is more power being generated with sliding seat rowing. The transmission of power into forward motion is less clear to me, but I would imagine that from body to modern hatchet blade to water would be at least as efficient as body through pedals, whatever method is used to make the 90 degree transfer from sideways to lengthwise spin, shaft, and propeller. In any case, this is all speculation on my part. If you can explain your reasoning or give me references indicating that pedal is more efficient, I’ll be very interested.

    Scot
     
  8. scotdomergue
    Joined: Jan 2009
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    scotdomergue Scot

    Materials????

    I’ve been spending a lot of time finding and reviewing old threads on the Boat Design Forums that deal with Kevlar, Carbon and Glass options. I’ve also been researching via other websites. What to use is NOT clear. Summarizing what I think I‘ve been learning:

    KEVLAR: strong in tension, weak in compression, wicks water so very problematic if it can get wet, very tough and resilient, a pain to work with and particularly problematic if toward the outside and therefore needing repair for small scars. I like the toughness, but it seems that there are too many drawbacks to use it on the outside as I’d been thinking. Perhaps it would make sense as an inner layer on the outside and/or as the only fabric on the inside (light weight compared to glass, strong in tension, not likely to shed bits and irritate skin, doesn’t need fairing on the inside and probably not even filling - though it might be a problem if water got on it occasionally?). All this isn’t completely clear to me.

    CARBON: light and strong, easier to work with than Kevlar, but not as easy as glass; also stiff and brittle, might shatter with severe impact and might be more likely to damage the core if that happened? It is much less tough that Kevlar and may fail all at once after enough abuse. Given that light weight is a high priority, it’s probably a good fabric to use. Perhaps best to have a layer of glass on the outside to protect it?

    GLASS: not as strong as the others, tougher than carbon but less than Kevlar, less expensive, easier to work with. With less strength, one must use more which also means more epoxy; the result is significantly heavier. S-glass is 40% stronger, 20% stiffer and also tougher/more abrasion resistant than E-glass.

    I’ve seen the idea that the layers on the inside and outside of the core should be identical. I’ve also seen the idea that the outside layer needs to be significantly stronger than the inside. ????

    Lower cost is nice, but minimum weight is a much higher priority!

    I wasn’t planning to vacuum bag, and I’ve seen that defined as important to realizing the full weight advantage of carbon. Just how important? (how much extra weight if not using? compared to other fabrics?)

    I’ve seen the idea that combining a stiff fabric (carbon) with more elastic fabric (Kevlar or glass) causes the carbon to take all the pressure, the others only involved when the carbon fails. I’ve also seen the idea that all the fabrics in a matrix work together with the bonding material (epoxy) creating a result that has it’s own, different characteristics which will be different from those of the individual materials.

    Would anyone like to step in and help me understand all this? Any recommendations about the materials and layering that would be most appropriate for what I want to accomplish?
     
  9. Guest625101138

    Guest625101138 Previous Member

    Scott
    Greg's boat is the lowest drag hull shape for his 150W, able to carry 420kg and sufficient stability to allow him to walk on the cabin top. It was optimised within these constraints. Ask yourself why are rowing shells the shape they are?

    Rowing does involve a lot of muscles and is able to produce high power in relatively short bursts. It is the way to get highest power in a short burst if well trained at it.

    For endurance effort cycling is considerably more biomechanically efficient. You will find papers on the topic. I have attached abstract of one. Other figures I have seen state rowinf at 22% and cycling at 27%. It is possibly to improve the efficiency by adapting the device to the person and the person being well trained. Generally cycling is quicker to train.

    With rowing the overall propulsive/mechanical efficiency is around 70% or a bit higher for an easily driven boat in calm water - it can be in the high 70% for a rowing scull at sprint speed. As the boat gets heavier it deteriorates. As the sea state worsens it deteriorates.

    The propulsive efficiency of Greg's prop is 85% and the mechanical losses about 3% so overall efficiency is over 80%. The efficiency is not highly sensitive to sea conditions.

    Rick W
     

    Attached Files:

  10. messabout
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    messabout Senior Member

    A boat of that size and configuration is not even close to having the ability to survive a hurricane. A cat 4 or 5 hurricane has such power that it is unimaginable. Having endured a few of them, and viewing the aftermath, gives me great skepticism about the ability of any small boat. Thirty foot waves coming from more than one direction is not the stuff of small boats. Never mind crossing oceans. On a bad day you would probably not survive a crossing of the Gulf Stream from Miami to Bimini, About 40 miles or so. I do not wish to be a naysayer, I do wish to admonish nice people to beware of unrealistic expectations.

    Sea lore is full of stories about miraculous feats of survival, some in small boats. What those stories do not reveal is that there were a lot more seamen who did not make it than those who did. On top of that there is the distinct possibilty that some of those heroic survivals were/are based on fiction.

    With that tirade off my chest, I would say that you have a boat design that would probably make a very capable, versatile, and fun camp cruiser.
     
  11. scotdomergue
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    scotdomergue Scot

    Rick,

    Thanks for the info on biomechanical and propulsive/mechanical efficiency. Very interesting!

    Regarding hull shape, in my last message I noted that Within seems well designed for Greg's purpose and explained my understanding of why rowing shells have that shape. I don't think we disagree about this.

    You haven't mentioned anything about the suitability or not of my hull design for MY purpose. I'd be interested in your thoughts.

    Scot
     
  12. Guest625101138

    Guest625101138 Previous Member

    I reviewed the design of the CTD canoe that crossed the Tasman a couple of years ago. They had a big problem with the hull shape that was rectified but the cabin windage was a heavy drag. So I would suggest you look at making the aft cabin more streamline.

    The structure in the mid sections need to be looked at closely because it is quite shallow.

    If you intend to make the boat yourself then you need to develop your process. I suggest you make test samples. You should test what you can achieve with vacuum bagging versus not bagging as well.

    There are a variety of tests standards for testing composite panel layups. Some include wear resistance. ASTM have some and Boeing have some interesting ones. You can do drop tests, wear tests, adhesion tests, bending test, twist test. You will probably be surprised how much variation you can get with the process used as opposed to the materials used.

    For the type of boat you have it is likely to be most economic just to use glass. However there is a wide variety of glass layups and you need to have some understanding of where to use what. With the bulkheads you already have there is unlikely any need for additional frame stiffening. You will need to reinforce around openings.

    The most likely wear points are on the bow and stern so these can get some extra attention.

    Aluminium and fibreglass work reasonably well together for making attachment points. There are simple ways to prep the aluminium to get good adhesion with epoxy.

    It pays to also build a small model of the boat in balsa or thin ply to find the high stress points. This can save on more expensive engineering evaluation.

    Rick W
     
  13. scotdomergue
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    scotdomergue Scot

    messabout,

    Thanks for your thoughts and mild tirade - those are always fun - and for your positive view of my boat as a camp cruiser. I'm not used to that term. It makes me think of beach cruiser and cruising dinghy, both of which are similar to what I'm trying to create in some ways. The main things I want that are not usually associated with those types are the cabin, very light weight, sliding-seat rowing, and much greater seaworthiness. If I could find a boat with the particular combination of characteristics I want, I'd buy it rather than design and build!

    Regarding surviving hurricanes: I remember reading that a corked bottle is about as seaworthy as anything afloat. As long as it isn't broken, it bobs along through anything. Size isn't the main issue. A number of ocean rowing boats around 25 feet in length have survived hurricanes. If you are interest, you might read "Rowboat in a Hurricane" by Julie Angus or Rowing the Atlantic by Roz Savage. It wouldn't be a pleasant experience, but appears to be much less dangerous than many other activities (deep wreck diving for example - that comes to mind because I recently read the book "Shadow Divers").

    One tiny boat, only 14 feet, Little Murka, attempting to cross the Atlantic during a year that turned out to be particularly bad for hurricanes, survived 4 before it's crew of one called for and was rescued 31 hours into the 5th. The boat, with no-one aboard, later washed up on the rocks of Ireland. It has been repaired.

    I've incorporated ocean rowing boat ideas in my design. That said, I fully intend to get a lot of experience gunkholing and otherwise cruising in relatively protected waters before I ever venture out on the open ocean. I may never decide I want to do that. All to be seen sometime in the future.

    In what circumstances have you experienced hurricanes?

    Scot
     
  14. scotdomergue
    Joined: Jan 2009
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    scotdomergue Scot

    Rick, Thanks! Very helpful comments! It will take me a bit to digest and consider. Do you have a quick guess as to the weight penalty for using glass rather than more expensive materials - just for the finished hull, NOT including centerboard, rudder, rigging, hardware, etc. 20%? 50%? You mentioned that Greg's finished hull was 54kg. In glass instead of carbon do you think that might have been 65kg? 80? Or?
     

  15. Guest625101138

    Guest625101138 Previous Member

    The weight penalty is not much. The main advantage with CF is stiffness - CF typically at least 4 times as stiff as glass. If you are concerned about abrasion resistance and shock absorbing then glass stacks up well. CF has about twice the UTS of glass but a CF panel inevitably fails on the compression side with the tension side at half UTS so the higher strength does not add much regarding panel ultimate strength. Glass panels feel almost rubber when compared with CF.

    For your boat I doubt that there would be much benefit in using CF and it will cost a lot more. The multiple chine lines you have on relatively narrow strips will provide some inherent stiffness in the shape.

    You could probably work on average of 2kg per sq.m. with either glass or CF. You may want to go a bit heavier in heavy trafficked areas and the wear zones. You could alternatively use a partial bulkhead under the rowing deck for example.

    Do you know the total surface area?

    It is unlikely that overall structural stresses will be a control on the design of such a small boat. You tend to find that local point stresses set requirement. You need to be able to jump about on it without fear of hull damage. So you are a point load of maybe 80kg acting on a very small area. You do not want the panels to permanently deform under these conditions.

    The exception to point loading being the constraint, may be where it necks down to the centre portion. If you are not competent at structural design then a model will help you here.

    I also suggest that if you are serious about intentions to get a long way offshore then you have the design reviewed by someone qualified. It is normal engineering practice for any critical structure to undergo an independent design review. Your life could depend on the structural integrity if you are a long way from shore.

    Rick W
     
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