Design Issues for small, sail/human powered cruising boats

Discussion in 'Boat Design' started by scotdomergue, Jan 6, 2014.

  1. scotdomergue
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    scotdomergue Scot

    PS: the Marsh Duck weighs in at under 200 lbs including all sailing and rowing gear and a 20 watt panel, 14 amp-hour battery solar power system for running electronics.
     
  2. Skyak
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    Skyak Senior Member

    Hi Phil, welcome!
    I think the big difference in our opinions will be sorted out as we put numbers to these designs.

    For starters you are off the page for gear -at least off my page. I am thinking 70# per person and you are at 300+. It seems I am thinking backpacking gear and you are thinking tailgate party gear.

    At 17ft for a single you are optimized for 4kn or more and in a canoe loaded that heavily the thrust to maintain that speed is pro athlete level. The motor makes sense because it is a reasonable fraction of your all up weight and you can't reach design speed without it. Human powered cruising starts with the the thrust the human can maintain for long periods. Add the gear figure to the weight and there is an optimal hull specified. If the thrust available is low and the weight is large the hull is going to be shorter and wider and the cruising speed will be low. I am not telling you anything you don't know so I will get to the point -this low speed is unacceptable to you so you add a motor and continue with your design. The level of luxury you travel in and physical abilities are life choices. Human powered cruising does not work if you don't travel light and push hard...or go slow.

    About speed, for human powered craft we are looking at a cruising speed to length ratio of about 1. A typical setup would be a 17ft kayak, about 300 to 350lb all up paddled at an average 4 knots. That's about 6 lbs thrust. Now how much sail do we need to produce 6 lbs thrust in 10N wind? Not much. You can't expect to sail much faster than hull speed without shifting a large portion of your weight off the buoyancy center. What do you mean by "sailing properly"? Based on all the numbers in your post you are talking about displacement mode -keel boat performance ~1.33 or less. This is a reasonable match for our human/sail cruiser.

    You mention the Florida Challenge. What kind of gear weight are you planning for that?

    What do you consider reasonable for human power thrust?
     
  3. scotdomergue
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    scotdomergue Scot

    Very clear analysis, thanks Skyak. Personally I enjoy backpacking at a weight of under 20 lbs for food and gear for several day trips. While I carry a LOT more than that when cruising for weeks or months at a time on the Marsh Duck, her capacity is WAY more than I need, which is one of the reasons I'm looking at smaller.
     
  4. Skyak
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    Skyak Senior Member

    There is a tendency of empty space to attract more stuff. Humans feel emotionally diminished by having unused capacity so they lower their utility standards and fill the space. One of my favorite cartoons is of two scraggly survivors in a flimsy little inflatable on the ocean. One is looking in a rough wooden crate in the water and says to the other "I'm not sure what we will need a box of broken glass, rusty nails and tacks for, but we better bring it aboard".

    What I envisioned these sail/human powered craft being is a major upgrade to backpacking... better amenities,...better travel range to more places, at a lower environmental impact. My experience with backpacking was that the great destinations were literally crowded and a week long trip might get you one or two days past the mass of humanity IF you hike hard. Yosemite on the weekends has a greater population density than Detroit! I have a bad foot and can only walk or run 5 miles at a time, maybe twice a day so 'bike-packing' and 'yak-packing' are my solution.

    The amount of stuff a human can propel in a boat is limited, more than on foot but still limited. Within that limit I aim to enable as comfortable and entertaining an experience as any vacation. Light weight and mobility remove limits as well. A craft that is easily packed and carried would allow some grand touring -a few days in the wild with the occasional stop in a waterfront resort. If you look at a map there are lots of natural lands even in close proximity to civilization, and they are mostly shallow waterways.

    A cruising boat is more than a hull and propulsion. It's systems to handle all human needs on the trip and the bulk, weight and operation limits of these affect performance.

    I have been thinking about Phil's 'proper' sailboat and the one thing I see that can do that I will not have is the ability to sail open water through the night. Sailing performance might well be considered at active and passive levels. Sailing fast, hanging off the side of a narrow boat with one hand on the sheet and the other on the tiller is one thing. Having a boat that you can set the sails on and relax or make a hot meal is another and a desirable quality for a cruiser.

    Your marsh duck has some very interesting capabilities... amphibious trips. It doesn't just portage, it travels the road effectively. It will be a shame if your new project takes away time you could be exploring it's capabilities. Is there any possibility you would charter MD out on a BYOBike basis? Even if you determine it doesn't make sense, the consideration points out weaknesses -what is easily damaged, what is difficult to use or a potential safety hazard. You have a nice boat -the reason you are designing another rather than sailing it is that you have become a designer/builder.
     
  5. Petros
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    Petros Senior Member

    I have used a modifed junk sail that has always worked well. It is eliptical in form and boomless, so it is simple to handle and delivers remarkable sailing power, better than much larger "conventional" sloop sails.

    Whatever the benefits of a two masted ketch, for this type of travel I would not want the complications: twice the amount of rigging, twice the risk of equipment failure, twice as much stuff to mess with, set, adjust, etc. It is difficult to imagine anything more simple and effective as a single cantilevered mast with a fully battened boomless cat rig. A properly designed junk rig is very efficient on every point of sail, low risk of flogging, fast to drop, and fast to raise without fouling, very minimal hard ware. to me it is the ideal sail for minimalist sailing with less effort than any other configuration.
     
  6. Petros
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    Petros Senior Member

    here is a pic of our entry, it was quickly built but the configuration worked well: it sailed well and it paddled well. the location of the cross beam and the amas did not affect are paddling.

    [​IMG]

    another view of the configuration.

    [​IMG]
     
  7. SailorDon
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    SailorDon Senior Member

    I'm looking for more knots (mph) per stroke.

    After having rowed my Mandarin 17 (Selway-Fisher design Thames Rowing Skiff) for 640 miles over the past 10 months, I get the feeling I can get more performance out of a rowing skiff that is better fitted to my size and strength.

    In my quest for a cruising rowboat design that will provide me personally with better performance, I look for things like speed and stability. Fixed seat is also good since I've got bad knees. That's why I row instead of walk for exercise.

    "....maintain 4 knots rowing quite comfortably." really gets my attention.
    4 knots is 4.6 mph.
    I do all my GPS data in mph and statue miles from an old Garmin Zumo 550 GPS that I still use on my motorcycle. It is the data source for all my rowing for the past 10 months.

    For me, maintaining 4.6 mph is a stretch. In calm water with no wind, I'm good for about 2 miles and then I fade to 4.0 mph. As a member of the Medicare set (over 65), I don't aspire to achieve a championship rowing physique. The "human powered" part of my performance equation is 250 pounds and 6 ft. 4 in. with bad knees. It ain't going to get any better than that.

    As a check, this morning I made it my goal to average 4.6 mph for 2 miles. Here is the result.
    [​IMG]

    The wind was blowing about 10 mph out of SE. It is easy to see the effect of headwind vs. tailwind on my rowing performance. 4.6 mph "downhill" with the wind.
    I was lucky to average 4.0 mph into the headwind.
    The "selfie" (below) of my rowing this morning shows the relatively calm water part of my rowing, near to my dock.

    [​IMG]

    If I set myself in a Marsh Duck (and lock the seat to fixed position), will I be stroking along at 4.6 mph in comfort? Or will I be "busting a gut"?
    The best photo I could find of the Marsh Duck as an HPV is below.

    [​IMG]

    I would modify the design to "rowing only" and lower the foredeck and make the cabin into a relatively flat afterdeck to reduce windage (and lower center of gravity).

    If the Marsh Duck design could keep me cruising at 4.6 mph "quite comfortably", I would consult with the builder of my boat http://picnikyacht.com/ to see what it would take to build me a "customized" Marsh Duck.

    Is there any data (GPS track would be nice) to backup the 4 knots over a 4 mile run? (4 miles is a typical exercise or cruising run for me in good conditions.)
     
  8. Skyak
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    Skyak Senior Member

    Petro,
    that is the boat I recall. The hull looks wider than 18"... like 22" or more. No leeboads? just the triangular profile amas?

    Your modified junk sail has quite a few things going for it. Best plan form, flat low drag, doesn't flog, balanced for fast low force control and twist control is easy to add. The only things more I could want are camber control, eliminate mast drag/interference, and additional downwind sail area. High aspect ratio would increase performance but we are very limited in righting moment so it just isn't in the cards. Also due to low righting moment I favor tapered sail plans that reach all the way down to the deck. I am wondering what you would change on a sail rig you were building WITHOUT time and tool constraints?

    SailorDon,
    legs are a big add to rowing performance. You have a pretty nice setup and are doing well for a fixed seat. The only obvious drag I see is the lapstrakes. Narrower beam would cut drag but also cut stability which I don't think you want. Lowering you body in the boat increases stability but rowing efficiency dictates your position and I find older people tend to favor higher seating (as do people with leg problems). So my suggested upgrades would be some nice light deck covers fore and aft to cut wind drag and improve safety. A set of higher performance oars might be desirable -light weight, stiff, and low turbulence. Another possibility that takes more consideration would be forward facing rigs -they can change the leverage of your stroke, make it nonlinear, and possibly change your body position. I will leave it to Scott to figure what a Mod Duck can do for you.
     
  9. scotdomergue
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    scotdomergue Scot

    It's fun to see where people have been going with this thread!

    I've always been intrigued with junk sails, but have no experience at all. I suspect that a big headed, fully battened, modern racing-dinghy style sail would be faster, but I'm open to learning . . .

    Regarding rowing:

    I'm a bit of a neophyte with GPS, so can't provide graphs or other evidence. Sometimes when I was rowing I'd set the GPS where I could see it fairly easily and put on my glasses so I could read it. Toward the end of my cruise last summer, when I did that, I'd usually find it right around 4 knots, a bit more at one point in the stroke cycle, a bit less at another point. Of course, when I bothered to keep track, I tended also to focus more on my technique and consistency of stroke. I doubt that I ever maintained an average 4 knots for very long, though I often rowed for an hour at a time, and didn't feel I was expending more effort than during the periods when I kept track of speed. I'm not a very experienced or dedicated rower. I enjoy it. And by the end of 3 months cruising my technique had improved. Earlier I was usually in the 3.5 knot range. I seldom rowed for more than an hour or two in a day. I usually only row in calm conditions. If there's 10 knots of wind I'll definitely be sailing.

    I'm 66 and have some back problems. My back does not do well with more than rather short periods of fixed seat rowing. The way I do sliding-seat I seem to have no problem. I think that sliding-seat is a little more powerful, and even without the back issues doubt that I would be able to maintain 4 knots over time with fixed seat.

    I created the Marsh Duck to be a primarily sailing, secondarily rowing, cruising boat. Don, your boat is beautiful, and the Marsh Duck, as is, would probably not be any faster, if as fast. If you don't want sailing, you might look at Angus Rowboats. If you want to explore design possibilities and options, let me know. I enjoy designing, and might play with designs for your specific desires and priorities. The very light stitch & glue construction used in the Marsh Duck offers interesting possibilities.
     
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  10. scotdomergue
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    scotdomergue Scot

    PS: if I were designing for rowing performance, not sailing or sleep-aboard cruising, I'd do a completely different, though related design. Unlike the Marsh Duck, it would be pointed at both ends and without cabin. It would be lower and lighter, and for me it would be narrower. There is a trade-off between speed and stability . . . I suspect I could design a rowing boat that would be much faster than the Duck.

    With all the sailing and rowing gear and its solar power system for electronics the Duck weighs about 185 lbs. She'd be a little lighter if I had known then what I know now about building such a boat. I normally had 75 to 125 lbs. or more of personal gear and supplies aboard. Add my 175 that adds up to around 460 lbs. That's what I was moving at 4 knots. And I think the average when I was tracking it toward the end of the cruise was on the high side of 4 knots when I was in form - varying between 3.7 and 4.5 knots, mostly from 3.8 or 3.9 to 4.2 or 4.3.

    A boat I'd design just for rowing would probably weigh under 100 lbs with all gear (carbon fiber oars), so under 300 lbs including rower and a little water, food and extra clothes.

    I don't know about the power sustainable with fixed-seat rowing, but feel very confident that I could maintain well over 4 knots for 4 miles on such a boat with the rowing set-up I have on the Marsh Duck.
     
  11. SailorDon
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    SailorDon Senior Member

    Improving rowing performance to get extra 1/2 mph

    I made a relatively easy change to my rowing program about 3 months ago. I bought a pair of 8 foot long "wide spoon blade" Shaw & Tenney oars to replace the 8 foot long standard blade oars that the builder supplied with the boat. Please note that I wasn't going for absolute maximum performance. It is a choice between high tech, high strength materials (carbon fiber) and esthetics of a classic design Thames Rowing Skiff (wood required).

    [​IMG]

    I estimate 1/2 mph improvement in rowing speed with the "wide spoon blade" oars. However, if the wind gets over 15 mph and waves get to 2 feet high, I switch back to the straight blade oars for less splash on the glide stroke. (Oar blade hitting tops of waves when the boat rolls from side to side.)

    I make compromises to rowing performance to keep the boat in shape to "compete" at wooden boat shows. (All show and no row.) So far, 2 "first in class" trophies and 1 "second in class" trophy, but sad to say, the judging was all on land. For instance, my most recent entry (and 1st in class) at the Madisonville Wooden Boat Festival 2013.
    [​IMG]

    I have compromised the classic Thule posts for bronze oarlocks for better oar handling.

    I conclude that my Mandarin 17 has been an excellent learning tool from which to proceed to a rowboat design that is better suited to my rowing activities.

    I'm not restricting myself to wood rowboats.
    What got my attention on the Marsh Duck design was the stated 4 knot cruising speed when used as an HPV.
    I might be better off going to a Heritage 18 from Little River Marine.

    [​IMG]

    Before my Mandarin 17, my only rowboat was an Achilles 9 foot inflatable dinghy.

    [​IMG]

    Excellent stability, but my max speed was 3 mph and I could only maintain that for 30 seconds before I dropped back to the cruising speed of 2.5 mph.
     
  12. Tiny Turnip
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    Tiny Turnip Senior Member

    Scot
    These may be of interest:

    [​IMG]

    Angus Rowboats: http://www.angusrowboats.com/Cruisingrowboat.html

    Aw, nuts - the Angus Rowboats site seems to be down - try googling them - you should pick up a cached copy with luck.

    [​IMG]

    Solway Dory: http://www.solwaydory.co.uk/products/sailing-canoes/osprey-outrigger-sailing-canoe/

    My own Solway Dory ketch is here:

    http://www.boatdesign.net/forums/sailboats/solway-dory-trimaran-48550.html

    I would add that the SD tris paddle easily when there is insufficient wind to sail.

    [​IMG]

    The Osprey is their glass production tri; pictures (their new boat and my ketch) are ply with glass outriggers
     
    Last edited: Jan 11, 2014
  13. scotdomergue
    Joined: Jan 2009
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    scotdomergue Scot

    Thanks for beautiful pictures and various thoughts. I'm familiar with the Angus Cruiser, and their other boats. I'm primarily interested in sail cruising, only secondarily in human power. I'm having fun playing around with tri designs, and may build one if I expect to have a second person cruising with me. But tri's are heavier and more complex than mono's. I suspect the next boat I build for myself will be a mini-Duck, 16 feet long with 24 to 28 inch beam, using kayak paddle for human power, similar but smaller cabin and sail (compared to the Marsh Duck). This will be for light weight (less than 1/2 the Marsh Duck I expect) and simplicity, and easily getting into places for which even the Marsh Duck is a little large.
     
  14. scotdomergue
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    scotdomergue Scot

    Don, your boat is beautiful! Congratulations on the show results. What is her beam and what does she weigh? I wouldn't attempt to compete on the beauty and all show no row events. I suspect I could design and build a boat that would give you adequate stability and the extra 1/2 mph rowing, but it wouldn't set up nearly so nicely for an elegant picnic!
     

  15. Skyak
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    Skyak Senior Member

    How? High performance picnic basket? Carbon fiber champagne flutes? An exercise tuxedo? :D

    Based on the GPS data posted he might go faster at the start with a longer hull but his overall time and distance would improve more with pacing in the current 17ft. But then again, exercise is the goal, not speed.

    Exercise is a very different purpose from cruising or race -exertion is the goal as opposed to the other cases where it is the scarce commodity you optimize against other goals. You have a very good solution with some extra benefits -good looks, versatility and nostalgia. For the purpose of exercise I would add a heart rate monitor with bluetooth and a smartphone app that can combine GPS with heart rate and long term tracking.

    Look deeper into exercise theory and you will find 'better' is more difficult and less efficient. Rowing's most desirable exercise trait is hydrodynamics - the harder you push the harder it gets, making it unlikely you will injure yourself -but this is true of all human powered water craft. The negative is that it works a limited number of mussels and it is asymmetric (more back and biceps than abs and triceps). The oarlocks make it focus on specific large mussels without requiring the development of the small control mussels. Even the stability of your nice wide boat is considered a negative in exercise, depriving you of balance development. Go to a personal trainer and see, machines are for beginners, as soon as possible they will have you lifting awkward loads on unstable footing. With this in mind I can tell you that a kayak would be a better upper body exercise than any new rowboat for all the considerations above.

    I have a CLC Pax 20 that is my exercise machine. My test of whether I am slipping is to cross the lake my parents live on as fast as I can -3.5 miles in less than 30 minutes. If I could maintain that speed for more than half an hour it would be my race boat, but as it is the boat is optimal for someone stronger than I.
     
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