Add Sail to Power Boat

Discussion in 'Boat Design' started by sheaftosser, Jul 11, 2008.

  1. sheaftosser
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    sheaftosser New Member

    I've been reading up on the research being done to add sail power to large oil tankers and thought hmmm....could I do something similar with my 26' welded aluminum cabin workboat? Can anyone point me to resources that would help me determine how crazy this idea really is?

    Not looking to substitute sail for power, just supplement. Small sail area. The boat is sort of a tri-hull so should be relatively stable under some small amount of sail, I would think. Looking to cut down on fuel bills generated by the 454 Chevy powerplant, maybe just potter along at a few knots per hour with sail up and engine shut off on calmer days on Puget Sound.

    Opinions welcome!
     
  2. Guest625101138

    Guest625101138 Previous Member

  3. eponodyne
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    eponodyne Senior Member

    Sheaftosser,

    I know the temptation to steal a caber and whack it into the middle of a boat is almost overwhelming, but....

    Go talk to your local kiteboard store. Kite as auxiliary/alternate power makes a lot of sense to me. Winds here in Minneapolis were about 20 MPH today, I had my 3-sq. metre stunt kite out and was getting dragged downwind (and I'm 6'3", 255 lb. and I work out all the time) right at the ragged edge of control. Imagine what a kite 4 times that size could do for your workboat. You could move at natural hull velocity, maybe a little more. You don't need to haul around a mast, boom, stays. You never have to worry about roach, luff tension, outhauls, downhauls, snotters, travellers, horses... any of that stuff.

    Go invest in a good soft stunt kite like my Prizm Stylus 2.8 or one of the Flexifoil traction kites. They run from just over a hundred to about $400 for a top-or-the-line Flexi or Peter Lynn kite. It's great therapy, anyhow; and you'll soon see why the kite option is looking more and more attractive.

    If you're interested, PM me with your snail-mail addy, and I'll send you some of my cocktail-napkin sketches (TM) with some ideas you may find useful.


    Good Luck!
     
  4. alan white
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    alan white Senior Member

    You've got a big engine in your boat for a reason. Your hull is designed to plane. Unfortunately, a hull designed to plane is not going to use a small power source well. Very low speeds are indeed possible with a kite, but for the same money and performance a square viking sail would work as well.
    You'd also have the benefit of sailing at up to right angles to the wind, making the sail twice as handy as any kite.
    Full-fledged sailboats do have lots to deal with, yes. But all of that is for going to windward. As described, a simple square rig has few parts and sail shape is unimportant (so almost anything can be used for sail cloth).
    Even with a square sail, however, your boat will absorb a huge amount of wind energy as you try to take advantage of stronger winds to go faster than a crawl. That underbody just isn't designed to move at displacement speeds of below six knots.
    A better bet would be a power boat hull designed to move well with 10 hp or less. Such a hull would do as well under sail as it would under engine power.

    Alan
     
  5. eponodyne
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    eponodyne Senior Member

    Alan,

    while you have vastly more experience in the design of boats than I do, I will take exception to your comparing a modern ram-inflated traction kite to a Viking squaresail. I have hundreds of hours--probably not 2,000 but close to it-- flying two-and four-line traction kites. I have used them on catamarans, canoes, kayaks, kite buggies and kiteboards and I am here to tell you that no squaresail can hold a candle to any comparably sized kite in reaching, running, or upwind performance.

    So much of the power surplus in a planing hull is necessary to lift the boat up over the hump and onto plane. With a kite, lift is built in. The thing can pull straight up just as hard as it pulls off to the side. So, no; a 26' aluminum workboat isn't designed to move well at 6 knots. But I would literally bet money with a 12 or 15 square meter kite, you could get it moving at 12-15 knots and be up on a (soggy) plane.

    For me, a big part of the appeal is in the extraordinary simplicity and lightness of the rig. My Cabrinha bow kite weighs about 9 pounds, lines and bar another 5. With the pump for inflating the leading edges and ribs, I'm still under 20 pounds all up and it stows in a package (they included a backpack just for it) about two cubic feet big. Two moving parts, the forward control lines and the bar. Hell, Sheaftosser could bolt a good stout padeye to the front of his wheelhouse, just below the windows, center the rudder and lash the wheel down, put a deck chair out there and get some good wind therapy in.

    No great pole sticking way up in the air, upsetting the roll period of the boat (although I understand that this may in fact be a good thing). No boom to crack your skull as you're takin' a whizz over the side. No halyard tapping the mast like a little anvil chorus of imps. No blocks to buy or maintain. No winches. An end to running rigging and its upkeep and expense.

    20 pounds and two cubic feet, stored. Six hundred bucks all in, for an overstock of last years' or the previous years' model. Seems like a great tradeoff to me.
     
  6. diwebb
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    diwebb Senior Member

    Hi,
    the kite option sounds quite reasonable as an alternative to a traditional rig, however several things need to be born in mind when considering use of sail power on this type of boat. Firstly a power boat uses prop thrust acting on the rudder to steer so steering will be a challenge under kite power. Also the point of connection for a kite rig needs careful consideration, to minimise steering effort it should be just forward of the center of lateral resistance of the hull, also to minimise heeling forces on the hull it may be better to consider an adjustable bridle connection to two padeyes one close to each side,( alternatively a full width traveller with the kite attached to the traveller), this would also allow for assistance with the steering. If you intend using the rig in anything but a downwind to quartering reach wind then some form of lateral resistance will be required, this could compromise performance under power. So lots of things to consider most of which can not be done in this sort of informal forum. If you are serious about this consider approaching a local naval architect for some more specific proposals based on an inspection of the boat.
    Sounds like an interesting concept but, as always, the devil is in the details.
     
  7. eponodyne
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    eponodyne Senior Member

    Leeboard. They sell the raw material at Home Depot in the form of 1/4", 5-ply birch underlayment. Waterproof glue and very low void. Easy to shape, easy to 'glass.

    I've put a lot of thought and hundreds of sketches into this idea; I think a traveller would work great. For a lower cost solution, a strong point (ideally a Samson post with its head just above gunwale level) about 30 to 40% of the way back from the bow (or right around the CLR as above), smack on top of the keel. The rudder will still work, just not very well; you may want to consider an auxiliary, larger rudder, with a pintle-and-gudgeon arrangement and a tiller (Or a quadrant and lines leading forward to separate wheel by the Samson post or lines or something.).


    Low cost, remember, guys? Doesn't have to outpoint a 12-meter or win tacking duels. Just a supplement for when the wind's fair.
     
  8. Munter
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    Munter Amateur

    One of the bigger challenges in using a kite as auxiliary power will be the launch and recovery. Keep in mind that typical kitesurfing lines are about 27m and there are four of them. When you launch they all need to be paid out without tangling. Recovery is the same. Remember - this isn't a toy kite anymore and if it is capable of generating a usefull amount of pull then that load needs to be considered when getting it back on board.

    These challenges aren't insurmountable by any means but they will add considerably to difficulty in making this work. Good luck!
     
  9. alan white
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    alan white Senior Member

    Eponodyne,

    You mentioned upwind performance. I have to ask you how that can be done. In a normal sailboat, there is a solid connection between water and sail frame, and this makes possible upwind sailing.
    With a kite rig, what mechanism allows for resisting leeway of the kite? i'm not arguing, just asking.
    Regarding the practicality of the kite, if the boat is 24 ft and 350 hp requirement, it will be nowhere near as usable as a displacement hull unless it has a very huge kite OR sail. What I mean to say is that average winds and a sensible kite or sail size and a good sized planing boat are not a practical mix.
    A displacement hull would be more practical for any kind of wind propulsion.
    While a sail or kite driven hull will move along, the planing hull on average will move at a substantially lower speed even if very strong winds will make it plane, in which case reasonably large waves are bound to develop as well.
    As far as comparing the overall differences between kite and simple sail, it's fascinating that you say the kites can go upwind.
    I don't know much about kites, but they seem interesting to me, especially if they can send (I won't say pull) a boat upwind.

    Alan
     
  10. eponodyne
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    eponodyne Senior Member

    Thanks for getting back on this, Alan.

    My so-far brief foray into kiteboarding and kiteboating has led me to a couple thoughts on working upwind with a kite. First of all, you don't point very high at all. Maybe 55-60 degrees off-axis with the wind (Sorry don't know how else to put this, I;m not a sailor). So, saying "send" upwind rather than "sail" upwind is probably a better explanation. What upwind progress one does make seems to be dependent on how far over one is willing to lean (on a board) and some combination of lateral resistance, hull form (The dismasted Hobie I tried it with worked upwind a lot better than the unknown drop-centerboard dinghy I tried it with), where the kite is in its effective wind window, and perhaps other factors I'm not aware of. It's hard to really pay close attention when your legs are deep in oxygen debt. I can work upwind a little higher than 45* if I hang the kite as far forward into the wind as it'll go, edge the board as hard as I can, then kind of , in combination, "slingshot" myself upwind while simultaneously moving the kite to the other side of the wind window. Hard to describe, very intuitive to do.

    When leaned over hard, I think the immersed area of the kiteboard forms a low-aspect, supercavitating foil. I can distinctly feel water spray and air being sucked past my lower legs and ankles.

    Sorry I got testy, but I think one of the things that's keeping more people from exploring the kite rig is the thought that they only work downwind. I have found they also do very well on a beam reach, best of all on a broad reach (all things you suspected), very well when running (moving the kite in a "s" pattern or a figure-of-eight moves more air over the kite, creating apparent wind. It's entirely possible to move faster than wind velocity directly downwind. Dave Culp had a very technical explanation up on his website at one point, it may still be there. Try your Google-fu and see what you come up with.

    I don't know whether displacement or planing hull forms are the best for a kite rig. At present, I'm leaning toward the idea of an i550 with tandem daggerboards. So much of present sailing hull design is hung on the ideas that the hulls need to provide lateral resistance (true with a kite) and also deal with the enormous, and enormously complex and variable, loads that are encountered with the ubiquitous marconi rig. Engineered to deal with angle of heel. Weight aloft. Windage of rig and stays. Forces of traveller and horse and mainsheet. Forces that need not be present with the kiterig.

    The kite rig is still in its infancy. Different shapes and sections are just now, within the past 10 years, being modeled and tested. But I've used it and I am here to say it has made a believer out of me.
     
  11. Petros
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    Petros Senior Member

    A power boat hull is totally not suited for sail. I have seen it done and it is hardly worth the effort, it was clumsy and not very effective, it also hampered its use as a power boat.

    If you want a sail boat, get one. Do not waste time and effort compromising your power boat.

    The best thing along these lines you can do on your power boat is to stand on the deck with a large beach umbrella. Simple, inexpensive and will meet your goals of moving you along at a few knots, and it has other uses as an umbrella as well.
     
  12. alan white
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    alan white Senior Member

    Here is what I am thinking right now: It must be impossible to go upwind with a kite because the kite must perforce be pulling downwind in the opposite direction.
    Would beam reaching be possible? I think, to some degree, but somewhere between running and beating to windward, the foil shape of a normal sail develops and there is a transition in the way the sail propels the hull.
    The kite, on the other hand, couldn't propel the hull at all as soon as it is pulling aft of the beam, at least not in the direction desired.
    The last commenter was correct, I think, in saying that the particular boat described would be a very poor candidate for sailing by any means, kite or sail.
    Yes, anything can be tried if money and time are no object, but given what is already common knowledge of hull design as applicable to different types of propulsion, it wouldn't make sense to modify the boat described.
    On the other hand, kite sailing is interesting as a means to pull a boat in a general downwind direction and there are thousands of miles of sea lanes where such propulsion makes sense, especially as a way to increase speed by using a higher strata of wind.

    Alan
     
  13. Guest625101138

    Guest625101138 Previous Member

    Alan
    Modern kites are efficient foils. They will sail to windward. Maybe not as good as a high aspect sail but they are still being developed.
    http://www.youtube.com/watch?v=eK7jR0TU4v0
    Look at the angle of the kite relative to the wind.

    Also note that the kite works in undisturbed air so windspeed is higher and direction steadier than the wind on the water. You get lift as well so the hull drag is reduced. The point of connection can be low so the heeling force is also low.

    The kits are getting to be very efficient foil shapes. Learning from paragliders:
    http://www.youtube.com/watch?v=HFFpjSWMqPs

    Rick W.
     
  14. eponodyne
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    eponodyne Senior Member

    Seriously, Mr White, as a sailboat designer, you could put yourself right on the cutting edge of yacht development if you went out and bought yourself a power kite and spent a few weekends on the beach, seeing how it works. How it could work. How you could make it work better.


    So upwind performance sucks. So what? So did conventional sail rigs for centuries. This phase won't last forever. The more people interested now, the faster the knowledge base is developed. Give it a try. What have you got to lose? A few hours on the beach and a couple hundred bucks?
     

  15. Munter
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    Munter Amateur

    Alan - plenty of kiters around the world would disagree with you on that one.
    Your comment is a bit like saying sails can only push you downwind because sails can only push in the direction of the wind. Apart from the vertical element the force vectors in a kite can be thought of as similar to a boat.

    I have no problem kitesurfing the 1.5kms upwind of my preferred launch spot to get to the flattest water. Actually upwind can be a lot of fun because you can really crank the board over and throw huge spray downwind.

    I don't point as high as an etchells but from tracing the disturbed water behind me I'd say I'm pointing perhaps 55-60 degrees off true wind direction. I don't have a compass with me so this is just an estimate of course. Maybe a GPS plot would a good tool here.

    As to what is stopping me getting upwind faster - I think it is the variability in power. With a low total mass (me + 3kg board) and a very short waterline length (sometimes zero) the fluctuations in power result in rapid acceleration and deceleration. It can be hard to get consistency in tracking. Maybe addressing this would be one way to get upwind faster with a kite.
     
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