Planing Hull Sailboat

Discussion in 'Boat Design' started by alrfetting77, Apr 6, 2011.

  1. alrfetting77
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    alrfetting77 New Member

    Does anyone know of a design in wood for a planing hull sailboat that is 16-20' and will take an outboard of about 40hp? In the 70's, Lofland made the 17' "Picnic" and now MacGregor makes a 26' version and Rhodes a 22'. Thanks.
     
  2. philSweet
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    philSweet Senior Member

    Welcome alrfetting. A bit more info on who it is for, where it might be sailed, and what you intend to do with it would be helpful. If you intend to build it yourself, tell us a bit about your skills and background. Are you looking for plywood or plank-on-frame?
     
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  3. alrfetting77
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    alrfetting77 New Member

    alright! finally, some help. :) thank you. I will be sailing on inland lakes and rivers. I want to maintain a shallow draft of 12" or less with the keel raised and still be able to plane off under power of a 40-60hp outboard. Top speed is not important and I wouldbe happy with a top speed of 20-25 mph. I'm not looking for a speed boat or anything like that. I do intend to build it myself but have not built as much as a canoe at this time. I will be completing my workshop this summer and plan on getting started on my first canoe this fall. Within the next two years I would like to be building this sailboat. My skills are above average in the workshop, I hope. I am a construction worker and have worked as a carpenter for a couple of years and have been a plumber for the past 10 years. I know a plywood boat would be easier to build and possibly stronger and lighter but I really like the looks of a plank built boat. So, I am open to both possibilites. Again, thank you for any help you provide.
     
  4. ancient kayaker
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    ancient kayaker aka Terry Haines

    It's definitely a good idea to start with small boat like a canoe for your first venture into boatbuilding. I am a firm proponent of the "start small" approach . . .

    I'm not clear why you want to put a large motor on a sailboat though; the weight will mess up its sailing qualities.
     
  5. PAR
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    PAR Yacht Designer/Builder

    It's very rare for any multi purpose craft to be particularly successful. Flying cars have and do fly, but they pretty much suck as either a plane or a car. Amphibious cars also have been tried and do work, but they really are lousy boats and crappy cars.

    The same will be true of a full plane, powerboat/sailboat. The Mac 26 is a sailing joke, though it does blast along with it's outboard nicely, not nearly as well as a real powerboat of similar accommodation.

    The reasons are fairly simple, the physical qualities that make a sailboat a good one, are in direct conflict with those of a powerboat. Just walk down to your local marina and study the shapes, it will become quite obvious. The powerboats are very angular, with aggressive, sharp, well defined shapes and edges. The sailboats are exactly the opposite, soft, round, blended forms, without the crisp, hard edges and broad flat panels of the powerboat shapes. Now, you be the designer and try to merge the physical requirements, attributes and qualities of these distinctly different shapes and you quickly see why there aren't many craft like this (much the same as flying cars or submersible aircraft carriers).

    Can it be done? Sure, but will it preform well as either a powerboat or sailboat? Probably not. Generally, you have to pick one. Now you could have a boat that does one thing well, while muttering along as the other. Sailboats with a substantial engine do this regularly and some special sailboats, called motor sailors preform quite well as both, but being up on full plane isn't one of those things they do. My point is, establish a list of requirements this craft must, absolutely must meet. Then see where everything shakes out. It's easy to want everything in one package, but when the package becomes too heavy, you then must prioritize your needs and whittle down the package to a manageable size. Oh, of course this will have to be a custom design as there just aren't any plans for a craft like this currently.
     
  6. messabout
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    messabout Senior Member

    Par is telling like it is, as he always does. You can not have it both ways.

    I have built a bunch of boats, both sail and power. I also have a bad habit of picking old boats out of the boneyard and then messing with them.

    I redid an old Thistle (17 foot very creditable sail boat) into a beach cruiser. I used a much reduced rig and she sailed well enough. It would not plane with the small rig but a class legal Thistle will plane in a breeze, especially with the spinnaker in place.. I clamped a Johnson 9.9 on the reinforced transom. The 9.9 was way overkill. The engine was strong enough to make the boat plane but the boat did more skipping than clean planing. Not something a sane person would want to endure. Just above idle the boat would make about 6 knots with practically no wake. In a no wake zone I could easily outrun a Cigarrete or Donzi. That was a pleasant boat to use and it would have been just as happy with a 4HP motor. At another time I resurected an old FD (Flying Dutchman 19 ft.) The FD is a fierce planing sailing machine. It would achieve a mushy plane with a 4HP engine and one occupant. Maybe 12 mph. The last one was a M20 scow (20 foot tunnel hulled scow) also a very quick sailboat. Yeah I had a motor on that one too. A 2.2 Hp Tohatsu and it would go like hell.....well almost 10 MPH. kinda sorta on a plane. In all of these misbegotten adventures with sail/power, there was never any illusions about achieving great speed. It was all good fun and frolic, but at a lower speed than you seem to want.

    You will not need a 40 or 50 motor on any 18 to 20 foot boat that will actually sail decently. Sorry about the bad news but you must decide whether you want a fast sailboat or a fast power boat. You can't have both in the same package. And one more thing. If you go fast with a motor, the mast is going to be a serious drag factor and a general PITA. Your sail boat will then need to be complicated with tabernacles and such.
     
  7. PAR
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    PAR Yacht Designer/Builder

    I put a hot 5 HP on a Force 5 for a while. I didn't use the rig, as it was a small cove fishing machine for a while when I lived in St. Pete. The thing would go like hell, but was pretty unstable at WOT. I latched onto a lemon shark in that boat once. The damn thing dragged me all over the cove until it finally broke the line. It was almost as fast as the outboard.
     
  8. philSweet
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    philSweet Senior Member

    A Yamaha 20 hp twostroke will take a lightish built 17-18 foot planing skiff to 20 knots with 250# payload and 16 knots with 700# payload (two adults, 5 crabtrabs, fishing gear, and a cooler.) And it sails pretty decently too. I used a flat-topped Hobie 16 main with 20' hoist and a Hobie 18 jib set to self tack. But with that weight aft, you need a wide transom and hard chines aft. Plywood is a better bet. Hull 7mm okume with 3 layers 10 oz weave on outside, one on inside. Topsides one in and one out. Requires transverse framing every 10" aft to take the pounding. Resaw oak 4x4 to 3/8" for floorboards. Figure on a boom that can be removed easily, A forward folding bimini, and a foredeck in front of that. I fitted a longshaft motor and tiller steered while sitting on the aft deck. A remote helm would have been nice, and would have looked better. One thing that's unavoidable- Sailboats get pushed nose down when powered up and motorboats get pushed nose up. You will be motoring quite nose high if you have the forward buoyancy to sail hard.
     
  9. Dave Gudeman
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    Dave Gudeman Senior Member

    Of course you realize that this isn't really an engineering analysis because it is too value-laden. That is, it is too bound up by value words like "good" which are entirely dependent on requirements.

    There are plenty of successful amphibious craft. Quite a few military trucks are capable of crossing water. They are adequate trucks and if they are not great motorboats, they serve their purpose which is to get people and cargo across streams and small rivers in places where there are no bridges. There are sea planes which aren't great boats either, but they serve the function for which they are designed.

    Sure, there aren't any vehicles that function both as the family mini van and as the weekend ski boat. Your analysis would apply to this situation because it isn't practical to build a vehicle that is both competitive with the specialized purpose of a family minivan and the specialized purpose of a ski boat. But that is because these are specialized purposes rather than general needs. Amphibious trucks don't have a purpose as any sort of specialized boat, they just need to be able to get across the water.

    And this is the same reason that the Mac 26 is successful. You say that the sailing is "a joke", but that is because you are thinking in terms of racing or long-distance cruising or some similar specialized application where the Mac can't reasonably compare. But most Mac owners don't care about that. They want to get out on the water on the weekend and just enjoy themselves. Maybe they want to teach their friends some of the basics of sailing. When they are sailing they don't care how fast they are going and when they care how fast they are going they don't sail. The Mac serves the dual purpose of being a boat that you can sail and being a boat that you can move quickly from place to place (either on the water or on a trailer). It is a brilliant compromise that does what it does very well. If only it had better accommodations, I'd buy one.
     
  10. PAR
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    PAR Yacht Designer/Builder

    I'm not sure what point you're attempting to make, Dave, but my observation that multi role craft have historically sucked, is quite accurate. Sure you can take a ridiculous military spec and cost over run it into fruition, just because you have a congressman on an appropriations committee, that'll shepherd it through, but in reality a craft solely designed for it's task, will far exceed what you'll arrive at when another craft is encumbered, with the burden of a split personality. Please don't mention specifics, like the Duck or a Mac 26 as they both are inescapably impaled by their "other" role. What a duck can do, a Chinook can do a whole lot better as an example and frankly most power and sailboats in the Mac 26 class are better then the Mac 26 in every way you measure them. Sure you can find a market, just like a congressman to ploy your "unique" venture on, but no one takes any of these craft seriously. At least you don't get repeat customers buying their second or third Mac 26 or yet another Aerocar. Once burned shame on you, twice . . . There's absolutely nothing "brilliant" about a Mac 26 other then the marketing techniques it's taken advantage of.
     

  11. Dave Gudeman
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    Dave Gudeman Senior Member

    Hmm. Let me try to make the point again: all vehicles (actually, anything ever built by human hands) are compromises. You never get a vehicle that is at once the fastest, lightest, most fuel-efficient, most comfortable ride and cheapest to build vehicle in the class. If you want it faster you sacrifice fuel efficiency. Or maybe you just spend ten times as much money for lighter materials so it can be faster and more efficient. There are always compromises.

    Now, I'm not saying anything you don't already know, but the point I'm trying to make is that the cross-purpose vehicles that you are panning are just another point on the compromise scale. The compromises that are made with such vehicles are no different in principle than the compromises that are made when deciding what kind of engine to put in a power boat.

    The Mac 26 had to compromise just like any other vessel. It can't sail as well as a sailboat that doesn't worry about going faster than hull speed and it doesn't have the accommodations of a same-sized power boat that doesn't have to worry about water ballast or windage, but it can do something that most other sailboats can't --motor to the dock at 15 Knots, and it can do something that most other power boats can't --sail.

    I'm just using the Mac 26 as an example. I don't have any emotional attachment to it. The same can be said of sea planes, car planes, amphibious trucks, and other sorts of multi-character vehicles. Of course they are compromises. Of course they have to make more compromises in each area than specialized vehicles would have to make in those areas. That doesn't make them "bad". "Bad" is not an engineering term. It makes them less suitable for certain purposes, and at the same time more suitable for other purposes.

    What you are thinking of as "good" is just those sets of compromises made by the classes of vehicles that sell the best. But these aren't "better" than other vehicles, they are just more suitable to the needs of the majority of people in the majority of situations. That doesn't mean that they are more suited to everyone in all situations.

    Common airplanes are not considered multi-purpose even though they can move both in the air and on the ground, but that's just because most people have to land eventually. If airplane pilots never needed to land, they would buy lighter, faster, more fuel-efficient planes without landing gear and would scoff at those lousy over-weight planes that are designed to land on the ground.

    It's all a matter of perspective --of experience, what you are used to, what you need, what others around you need. There is no engineering fact of the matter that specialized vehicles are good and multi-purpose vehicles are bad. It's all about what you want the vehicle to do and what compromises you are willing to accept.

    As to your comment that no one buys a second or third Mac 26: (1) if they don't satisfy the needs of the majority of people, that doesn't mean they don't satisfy the needs of anyone. (2) Since boats can last half a century, I'm not sure why anyone would buy a second one. (3) If someone uses a Mac 26 for a few years and then sells it to buy a sail boat or a power boat, that doesn't make the Mac 26 look bad. It let someone play around with both sailing and motoring enough to decide that they prefer one or the other. What would have been a better alternative? That they just randomly pick one type of boat to begin with to see if they like it? There is a 50/50 chance that things would have worked out worse for them.
     
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