Hello everybody

Discussion in 'Fiberglass and Composite Boat Building' started by jeffb957, Dec 22, 2013.

  1. jeffb957
    Joined: Dec 2013
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    jeffb957 Junior Member

    Ok, I looked at Bateau.com's plans, and found most of them to be causticly ugly. :-( On the Glen-L site I like the waterlodge plans, but I'm having trouble seeing the differance between it and what I'm doing. Why is that better? What charactoristics make it perform better?
     
  2. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    The aesthetic considerations can be changed to suit and shouldn't be part of the selection process.

    The hydrodynamic idiosyncrasies between different hull shapes is quite complex. Barge shapes are best at supporting large volumes, which is directly opposed to efficient propulsion characteristics. This is why power and sailboats aren't shaped like barges.

    [​IMG]

    This is the smallest of my riverboat series at 26' on deck. It's flat bottom so easy to build, though a V bottom version is also available. This hull is efficient, requiring a modest, portable outboard to get to full speed. Full standing headroom throughout, while not looking like a Winnebago is parked on a floating box. In fact, this is a good description of a typical shanty boat (the Winnebago thing) as Winnebagos couldn't ever be confused with something efficient, nor easy to maneuver or requiring modest power, etc., etc., etc. There are some exceptions to the rule, but mostly placing 10 pounds of boob in a 5 pound bra is only initially interesting, while for practical purposes being hard to live with.

    Again, there are exceptions to this rule, but not in a short, fat and tall boat. It's just physics. The boat above has about a foot less beam then your proposed 16', so it's intrinsically easier to propel (which requires less energy). As a matter of fact, I'll bet with the same outboard as you'll use on that 16'er, Chiusa will use less fuel and go faster too. Chiusa's displacement is about 2,800 pounds at 7.5" of draft and though her Cp seems modest (for speed potential) at .56, this changes as soon as you crack open the throttle, climbing quickly into the low .60's, meaning she'll surpass her theoretical LWL restricted speed limits.

    As to "figuring out" these seemingly vague and subtle difference between hull shapes, well it's considerably more involved than you might think. It's a bit like asking an aircraft designer what makes some more efficient than others. They can answer, but you'll be quickly overwhelmed with a lot of verbiage and data, often accompanied with dry commentary on the principles, physics and dynamics of the various subjects. Yeah, even for a shanty boat. Welcome to yacht design and one of the reasons you'll receive lots of advice about purchasing a set of plans, rather then attempting to self design. You'll find the same treatment from elevator and aircraft designers too, simply because these professions place people in an unnatural state, one in which a design flaw, can cause you to drop 10 stories, or 10,000 feet with an abrupt halt at the end or in the case of boats, place you farther from shore than you can safely swim back to.
     
  3. jeffb957
    Joined: Dec 2013
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    jeffb957 Junior Member

    Hello again Par,
    I'm sure you are a very good yacht designer, and I must say your designs are much more appealing than many I've looked at. Your human relations skills are not quite on par with your design skills.
    You see, 9 years ago a friend of mine was wrestling with a problem. It seems the fuel manifolds on the two oldest space shuttles had developed a problem. There were internal screws inside the assembly that had pulled dimples into the internal surface of the manifold, causing a standing wave of turbulance in the fuel flow, reducing engine power and creating potentially damaging vibrations. Keith, my friend from NASA was leading the engineering team that was trying to solve this issue. He was looking into the idea of introducing a second set of perturbations in the fuel flow tuned so that the trough of the existing wave met the crest of the induced wave, thus cancelling out the problem. I pointed out that rather than doing all the serious calculus nessesary to create that effect, and compensate for the possibility that the dimpling of the surface might get worse on later missions requiring it all to be done over again, what was really called for was a sandable filler putty formulated to withstand the environment, and a sutible solvent to dissolve it when access to the screws was required. I'm happy to say that my idea flew on board the last couple years of shuttle missions.
    That same friend of mine was also chosen to lead the design team for the avionics for the Constellation Project, the next generation of heavy lift manned spacecraft. Keith ran into an issue of mounting hardware on the flight deck. Simulations showed the avionics rack they had designed was over weight limits, but when they attempted to lighten the structure, it began to vibrate beyond acceptable limits. I suggested the idea of deleating the entire rack, and simply adding a small L flange to the back of the chassis of each componant, and slotting them into a female recess in the wall shaped to fit them. The slot could be lined with vibration dampening material, and the componants bolted together with vibration dampening washers between the componants. I cannot fully take credit for the innovation, as the day Keith went to an engineering meeting to present the idea two other guys had similar solutions to present. Should the funding for Constellation ever be restored though, the flight deck will contain elements of my ideas in synthesis with those of others.
    I won't bore you with details, but I have also had input into the mobile launch platforms for the Theater High Altitude Air Defense System (THAAD).
    I am guessing you heard "Alabama" and assmed you were talking to a bucktoothed barefoot rural idiot. I guess there is no reason why you'd suspect that my town is the home of two major universities, NASA Marshall Space Flight Center, and major industrial and scientific centers like the Hudson Alpha Insitute, Boeing, Raytheon, Teledyne Brown, and General dynamics to name a few.
    The funny thing is this, I've never had any of my buddies from NASA, Raytheon, or Boeing suggest that I couldn't keep up with them intellectually. In short, if you can't explain to me why your designs are better than the designs offered by others, there's just no way we can do business.
     
  4. PAR
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    PAR Yacht Designer/Builder

    Jeff, my apologies, as I did assume your requests and questions where much like the typical (and often) ones expressed here. You'd have to admit, your skill set(s) wouldn't be considered average, though my assumptions haven't helped.

    The subtleties of a chine sweep or it's relation to the centerline, can be a bit of black magic, though with some study, you could select one that serves well.

    With your power and speed requirements, you'll need a hull capable of full plane mode, which as you'd imagine is a significantly different set of shapes than displacement mode. With the windage of a box like super structure, this hull would need to be efficient at climbing over the "hump", should do so quickly (relatively low speeds) and if possible also offer low speed efficiency (not a hallmark of a full plane hull). Lastly will be weight and this will drive you nuts (at least it does me). Short, fat hulls require lots of power to get to speed, while long, lean hulls much less so. Complicating this is power to weight. Making a 16' jon boat get up and scoot on 20 HP isn't particularly difficult, as generally these are little more then a hole in the water, with an outboard strapped to it. Typical displacement for a craft like this, including crew, controls, outboard, fuel and steering is in the 1,000 pounds range. Assuming (there I go again) a 20 HP outboard, you'll get 20 MPH on a little puppy like this. Now add a cabin, some furniture, maybe water tanks, a couple coolers full of beer and Fidel the wonder dog and you've doubled (easily) your displacement and you speed is now in the 14 MPH range. This is within your target speed rage, but is also at a point where boats transition from displacement to full plane mode and what we call the "hump".

    Without a full up dissertation on hydrodynamics in this area, simply put, as a 16' hull, particularly a fat one, with a lot of weight and windage (relative to it's size) runs smack into a huge drag wall, just as you punch up near 10 MPH. Power requirements to climb up over this wall (bow wave and frictional resistance) rises exponentially, momentarily. Once you've pushed through, resistance drops, as you leave the self generated wave train behind, but you have to have this available power or you have to reduce the wave train and/or resistance. A narrower boat does this handily, without the need for more power, as it's wave train is smaller, even if it's resistance is similar. For example, Chiusa (above) makes very little appreciable wake (wave train) at the top end of her displacement speed range. Her entry is quite fine and her forefoot shape is intended to move water with limited pressure bleed off, to control eddy making. These considerations permit her to climb the hump with less power.

    A similar approach can be used in you boat, though you'll have to live with having the accommodations stretched out longitudinally, rather the laterally. Conversely, if you insist on a 2:1 beam/length ratio, the wave train will be quite large, necessitating a lot more power to overcome. A hull like this might require 50 HP to get the same performance envelop.

    Building ease will be much better with a flat bottom and initial stability will also be greatest too. Instead of attempting to improve straight line tracking with hull shape, you'll be better off (drag wise) using well shaped appendages instead. Outboard powered craft generally steer very well at speed, but tend to wander around at low or displacement speeds, so a skeg is typically employed to address this concern. A V bottom requires more volume (read weight), which is one of the things you'll want to keep an eye on. Since your not looking to blast along at 30 knots, I'd kiss off the V bottom shapes in favor of the more stable and easier to build flat bottom.

    Have you made any sketches of your hull yet, or just looking at published designs for ideas? Have you thoughts on a build method you'd prefer and possible accommodations you just can't live without (offering an idea of weights)?
     
  5. jeffb957
    Joined: Dec 2013
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    jeffb957 Junior Member

    Hello Par,
    Apology accepted. I did very much present myself as "just an average guy." It's never good to come off as too much of a "know it all" unless you have professional credentials to back it up. I do not have an engineering degree, but what I offer to my friends in that world is actually just "country sense." The avionics mounting idea actually was inspired by the design of frameless semi trailers of the type work with. The fuel manifold idea came from my dabbling auto body work. My biggest handicap in understanding boats is lack of vocabulary. Terms like "Skeg" and 'Chine" are not always self explanitory. when you add in appreviations and technical shorthand it becomes even worse. for example, it took quite a while to determine that when you referenced Cp, what you meant was Prismatic coefficient. I'm still working on digesting the meaning of that, as it is a big chewy bite, itself surrounded by other unfamiliar terms, but I'll plow through it eventually. The Froude Number concepts are something I'm going to have to look at when I'm a little less worn out. That's getting into territory where I need to be firing on all cylinders to get it.
    As far as boat design goes, I probably unintentionally caused you to make an incorrect assumption. the speed I quoted, 15 knots if I remember correctly, was pretty much chosen at random. My wife and I are middle aged, and have no raging desire to go fast on the water. For us, the ideal boat trip is to cruise along at the speed of a brisk jog while we spot/photograph wildlife. We'd like to have the ability to head in towards shore and put out a gangplank to go collect samples. We also like full stand up room, and the ability to have a good queen sized bed to spend a night or two before motoring back home. For our purposes 10 MPH is plenty fast. The primary factors for us are space, comfort, and shallow water ability.
    In terms of accommodations, the biggest thing for us is that good queen sized bed. I need that queen sized bed to be a Morgan bed of the type that folds up on a wall to allow a table to be set up, both for meals, and for general use. Next is a rudimentery galley, although a table to set up our trusty coleman camp stove, and a couple of dishpans to wash dishes in would suffice. A water tank with an electric pump would be nice, but is not strictly required. Finally a head of some sort, although a portapotty would suffice. We don't need a lot. We have been primative campers for decades until we built the camper, and in a lot of ways, it is just a hard sided tent with a good bed and A/C.
    As an aside, when you used the term "windage," were you referring to the concept of the wind pushing a boat off course, or were you referring to wind resistance slowing down the boat's forward motion?
    Most of my planning thus far has been looking and plans available online. I like the Lisa B plans I referenced, but she is a bit small I must admit. I had intended to look into adding 4 feet to her amidships to end up with a total length of 20'. I have also been looking at this plan in the 24'X8' size. http://www.glen-l.com/designs/house/dsn-sfn.html I have read in other places that the two seperate bow waves meeting under the boat create turbulance that limits performance of the boat, but would that really be an issue while cruising at the speed of a brisk jog? I like the Super Huck's looks, and the nearly 3400 pound load capacity gives a lot of flexability, but the 12" draft is deeper than I really wanted, On the other hand, I'm sure the Huck would handle better as well.
    Thanks,
    Jeff
     
  6. PAR
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    PAR Yacht Designer/Builder

    The 10 to 15 MPH range is the butt kicker of hydrodynamics. In most small to medium size craft this is the zone where you are transitioning from displacement mode to full plane. It's easy to live on one side or the other of this range, but hard to target some place within it and have a comfortable boat.

    If you can live with the lower speed range, then the longer and leaner a hull you can live with, will produce the best speed/least resistance/least power requirements. With a Cp that will permit the speeds you desire, these leaner shapes are much desired. For example, lets say you have a 16 LWL and a relatively low Cp. You "qualifier" (Speed/Length ratio) would be how much over the sq. root of the LWL can you push her, with the power available (assuming not enough to fully plane off), before resistance over powers the hull form. A fat 16'er would be lucky to push a barge like hull to 1.2 times the sq. root of the LWL, meaning she'll max out at about 5 1/2 MPH. Reduce the beam to a 3:1 beam/length ratio and the same power might permit you to get closer to a S/L ratio of 2, meaning your speed will be in the 9 MPH range and a significant difference, for the same available power.

    Of course the Super Huck needs a lot more power than your proposed 15 HP. A 15 HP on a Super Huck will just barely push it around.

    The low buck way might be to park your current, freshly built trailer on a set of pontoons. A deck fore and aft and you're good to go.
     
  7. rwatson
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    rwatson Senior Member

    Yes, but if you read the fine print, you will see that the topsides can be varied to suit.

    The main appeal of the houseboats, as Par commented, is that they will plane, for those times you would like to travel a bit faster.

    I had the topsides re-designed to ease the ugliness.
     

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  8. jeffb957
    Joined: Dec 2013
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    jeffb957 Junior Member

    The pic you attached is certianly a lot more appealing than what that had to show. Nice redesign :)
     
  9. jeffb957
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    jeffb957 Junior Member

    Hey Par,
    A stroll through craigslist shows me that used motors in the 50 HP range are common and cheap, while the smaller motors are not as common and seem to cost as much or more. This leads me to the conclusion that I'm most likely going to end up with a 50 rather than a 15. It seems a bit foolish to buy a 15, when a 50 can be had for roughly the same money. There is much to figure out here :)
     
  10. michael pierzga
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    michael pierzga Senior Member

    Part of the outboard motors mission is to charge batteries, choose a motor with the most DC output.

    As a boat gets bigger and heavier the outboard sits lower on the transom and begins to submerge its transom clamping mechanism. This mechanism is expensive and rapidly deteriorates when submerged.

    The Honda 50 with the xl long shaft , 25 inch...is a good choice. It will keep the clamping mechanism dry.

    Keep an eye out, these motors are popular on the pontoon boats

    http://marine.honda.com/outboards/motor-detail/BF50


    Its possible that there are other motors with a 25 inch shaft.
     
  11. michael pierzga
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    michael pierzga Senior Member

    The boat that Par proposed has a good shape for inland cruising with pilot forward. It will be very quite and easy to operate

    I dont think that you could cruise it on its drawn waterlines. Too light.

    Cruisers carry a ton of junk in the trunk like water, sewage, fuel, batteries, anchors, fenders, lines, bikes, beer, supplies......
     
  12. PAR
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    PAR Yacht Designer/Builder

    Good observation Michael, though she's drawn fairly light, her PPI is substantial and she loads down neatly and evenly. She's spec'd with a 20" shaft, while a 25" is better for the reasons you mention, they're not as commonly available, unless ordered new.
     
  13. jeffb957
    Joined: Dec 2013
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    jeffb957 Junior Member

    Well, having spent a while doing research on different plans available I've come to the reluctant conclusion that the "houseboat 20" plan from bateau.com, built with the flying bridge option is as close as I'm going to get to what I really want.http://www.bateau.com/studyplans/HB20_study.htm?prod=HB20 I just need to do some planning on how to "scrub some of the ugly off it."
    I'll definitely need to raise the main cabin roof by 6 inches, and likewise raise the foredeck height by that same 6 inches to give the forward berthing compartment a little more headroom. I'm a tall guy, and banging my head is not acceptable. I also want to extend the cabin roof/flying bridge floor back to the transom to create more upper deck room, and more sheltered space on the aft deck.
    I'm also going to have to find some good looking railings to go around the fordeck to try to lessen the boxy feel of the bow of the boat.
    Anybody have any thoughts on the feasability of the changes?
     

  14. PAR
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    PAR Yacht Designer/Builder

    Give Jacques Mertens a call and see how much headroom is available over the berths forward. Generally you don't need much over a berth.

    The cabin could live with some additional height, but the boxiness will become more so. You could cheat this by increasing the cabin side just a few inches while using more roof crown to gain the headroom. To further hide the boxiness, the sheer should be raised a few inches too.

    The barge bow will be difficult to hide, though it could have the bow rounded considerably, which would help a little. When working with such shapes, it's difficult to make a silk purse from it.

    Extending the cabin roof aft to the transom over the cockpit, will make getting into the boat very difficult. If you want shade in the cockpit, consider a fold up bimini or umbrella, instead of a hard top, other wise climbing down to the boat, from a higher dock, will be quite awkward to say the least, if there's a hard roof over the cockpit.

    These "box" boats are the pinnacle of ugly to me. There's just not much you can with them, because it's not shaped like a boat. It's more akin to a large concrete mixing tub or a dumpster, than anything most think of as a boat. Some suggest form follows function, but I insist it doesn't have to be ugly, even if it's minimalist and functions well, unless the designer hasn't any real skills. Maybe with some ginger bread and mascara . . .
     
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