Request your input on my design

Discussion in 'Boat Design' started by richardf, Jul 15, 2013.

  1. Mr Efficiency
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    Mr Efficiency Senior Member

    Without a clear indication of the conditions likely to be encountered on the particular area of the ICW he intends to traverse, it is difficult to evaluate what boat might be suitable. It is presumably pleasure boating, and the fun soon goes out of it if in an unsuitable design.
     
  2. richardf
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    richardf Junior Member

    ICW in Florida is mainly calm, river like, conditions, but bays and rivers have to be crossed, winds can whip up some nasty chop, and the tidal currents can get pretty strong. The St John's river has to be crossed to get up near Georgia, and it is near a mile wide at the crossing. There are very big ships iin the river which can probably stir up a pretty big bow wave. The river crossing is about a mile, I think. Open ocean is only about 2 miles away, if that.
     
  3. HakimKlunker
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    HakimKlunker Andreas der Juengere

    I have difficulties to imagine this style of boat being in a speed contest with a -say- jet ski...

    Weight: If this boat would be extremely light in weight, I expect it to be uncomfortable at rest (berthing; anchorage); if fuel economy and operational costs are major factors, it would be an idea to -early- have a closer look into the most suitable drive system set-up and choose the right corresponding hull shape for it.
     
  4. DCockey
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    DCockey Senior Member

    Sounds somewhat similar to the conditions that Tom Lathrop designed his Bluejacket 24 for. Perhaps he'll comment.
     
  5. PAR
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    PAR Yacht Designer/Builder

    The ICW has patches, as Tom pointed out, that are much less desirable for some boat types. There are untold numbers of "problem" spots and chart inaccuracies. Mantanzas Inlet is often mentioned as is Bakers Haulover Inlet and other constantly moving shoals, exposed areas, etc. The west coats of Floria has some protected lengths, but is mostly exposed to the gulf. On the Atlantic side, you can stay "inside" most of the way, though you have bridges, traffic and shoal issues, plus some odd current and tide conditions to contend with.

    Well planned, the ICW is a nice ride, safe and very serviceable. An experienced skipper will have few problems, especially in a sound boat. A houseboat of typical configuration will have difficulty in some areas. My riverboat series less so than other, but still could be mismanaged into a problem on the ICW.

    Florida isn't nearly as bad as the Carolinas and portions of Georgia, so Tom may be biased, because of the patch he lives in.

    Richard, 24' - 26' powerboats generally are large projects and not as simple as you'd hope, if only from the scale of things. Add some complexity from it's ability to tolerate rougher sea states and accommodations and the issues can exponentially increase.

    Cooper Jr. is fully capable of handling whatever you encounter on any portion of the great loop or ICW. She has berths for 4 adults, a standup head as well as full headroom in the pilothouse. Of course she's a full plane boat and requires the power to achieve this. Her skeg keeps slow speed handling predictable and she's fully trailerable. An outboard bracket would free up some cockpit space, eliminate the need for a splash well and a swim/boarding platform could easily be worked in. And thanks Richard, though it's really foolish to design ugly things, if you expect folks to buy plans or have you build one (I've built 2 Cooper Jr's for clients).
     
  6. tom28571
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    tom28571 Senior Member

    Sure David, I can comment on a boat designed for two people to cruise the ICW and other similar waters. There is a lot of variation in conditions to be found there from smooth and fairly tight channels to wide open and often very rough passages. No one design is going to always be best in every condition and you must seek a compromise that best suits the individual goals. My main goal is efficient operation in what is usually known as the transition speed range for power boats. This is from about 10mph up to 17mph or so which is usually avoided by powerboaters.

    Most designers start with a displacement hull and make it faster so that it is a semi-displacement craft. Because this usually results in a heavy boat that requires more power and fuel use than I wanted, I took an opposite approach. That was to take a fast planing boat and make it run efficiently at low speed. There are too many facets of the design spiral to easily get into here, anyone interested in my approach can look into my website www.bluejacketboats.com in a article I wrote for the old "Boatbuilder" magazine called http://bluejacketboats.com/info/designing-liz/ .

    The result is a boat that is an ICW cruiser for two people that can run at any speed comfortably from idle up to a max of 23 or 24mph. Of course there is a relatively small transition range from about 8 to 10mph where efficiency is at a minimum but it is hardly noticeable from the helm station as the bow rises very little with the trim actually being highest at top speed. Looking at a series of photos at the bottom of the home page shows how this looks. Notice that the stern does not sink or squat at all, evidenced by the white boot top at the stern remaining at the same level throughout the full speed range.

    There is no magic in doing this, just having a goal and doing what is necessary to stick to it. It is clear why commercial boats are not capable of this performance and that reason is cost of manufacture. Solid fiberglass construction results in a boat too heavy and lightweight composites are expensive and require more labor cost to produce. Fortunately, the home builder has no such restriction and also has access to the best appropriate materials which are plywood and modern liquid joinery techniques. With a proper design, the home builder can build a boat superior to those available from manufacturers that is more efficient and still able to handle the expected water conditions of the ICW.

    I stayed out of this thread because I don't like to start with goals that contain specifics of how a thing is to be done. I start with a list of performance, accommodation, cost, appearance and a few other goals and let the method of getting there be dictated by those. This is a result of my engineering training that I believe to be the best way to start any project.
     
  7. DCockey
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    DCockey Senior Member

    Why is an engine which provides planing speed required? What happens if a smaller engine, say a "high thrust" 20 HP? Her top speed will be significantly limited. Anything else that makes using a "small" engine fundamentally a bad idea?
     
  8. PAR
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    PAR Yacht Designer/Builder

    Not at all David, Cooper Jr. could live with a 10HP engine, but she'd drag her butt and ask quite bit from that 10 HP outboard. Even with a 20 HP outboard, she'd ask a lot, just to drive her with a level of authority, in opposing wind and current situations. She could live with a 50 HP, but my minimum recommendation is a 75 HP, which gets her well enough into full plane, that contrary currents and windage aren't much of a concern. Simply put, she was designed as a full up plane craft. Now I could have decreased her beam, lightened up her structure, tucked up her buttock aft a bit and put a 20 HP on her with semi plane results, but that's not what the original SOR required. As spec'd a full load and a 75 HP outboard gets 18 MPH and a light load is in the 23 MPH range. Her hull form maxes out around 37 MPH (longitudinal stability/drag) and you'll need over 200 HP to get there. She's stoutly built, not light and not slim, just a hearty, cold weather cruiser.

    I like the BlueJacket approach. I played with a similar set of concepts a some years ago, though I ended up splitting the area on the chine flats among multiple strakes, instead of a single wide one.
     
  9. tom28571
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    tom28571 Senior Member

    Another reason that boats like Bluejacket are not found at boat dealers is preconceptions of the boat buying public, particularly those with lesser experience. These start with what the public believes boats should look like. The most successful and largest selling boat in this class is the C Dory. Now a dory is a great boat for the use it was originally intended. As a small cruiser, it has some basic problems and the most important of these is inadequate waterplane or bottom area for a planing boat. This makes the bottom loading too high for quick planing or efficient running at low speed. Add to that the heavy fiberglass construction and the hull weight of the C Dory 22 is as heavy as the BJ24 and a much smaller boat than the 2' would indicate as well as needing almost twice the power. There are other issues related to the wide flare of the topsides that are what many people are attracted to in the first place. When true dories become either powerboats or sailboats, they usually are not great at either. Some few have been able to make them work well, like Kilburn Adams with his Skiff America 22. Kilburn makes the bottom wider than a true dory and builds very light to keep the bottom loading within reasonable limits as well as limit the power needed to make the boat meet his performance objectives.

    Another commercially available cruiser in this class is the Rosborough 246, a very nice ICW boat. It is from two to three times heavier than the Bluejackets, needs more than double the power for equal speed and costs way over $100K. You will need a more powerful towing rig and a heavyweight trailer, whereas the other boats mentioned can be towed by family vehicles. These are only negatives depending on your objectives and all are capable of offering pleasure to many people so I'm not saying that my way is the only way, just the preferred way for me and those who have built them.
     
  10. richardf
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    richardf Junior Member

    Tom,
    If you want to see a bunch of cookie cutter, monstrously heavy, plastic boats, with huge oiutboards (sometimes 4) on the transom, got to the Beach Marina public launch on the ICW in Jacksonville. The in thing now is 20-35 foot center consoles with gigantic HP outboards. There will be dozens per hour launched on the weekend there, all towed by monster, gas guzzling pickup trucks. Nary a wooden boat, nary an economical cruiser for just the enjoyment of boating, nary a practical vessel. It is a sight to behold, and confusing in this supposed bad economy. Reminds me of the bass boat craze in the 80's when everyone was mounting 150-200 HP on the back of a 16 foot boat. Because the pro bass tournament fisherman had them to get to the best fishing hole first, every one else had to have one also. At the marina I was talking about in Jacksonville, there is a nice restaurant that overlooks the boat launch. You can sit there, have a beer, and just shake your head in disbelief. I guess I don't know what I am missing.
    Your Bluejacket 24, as well as Paul's Cooper Jr. are really nice, practical boats, that I know I would enjoy owning.
    Richard
     
  11. tom28571
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    tom28571 Senior Member

    Three weekends ago I was on the mark boat for our Leukemia Cup Regatta. It was a Boston Whaler 32 with a pair of 250hp Yamahas. A bit overkill by my standards but OK when we had nearly 40kts in the afternoon. Last weekend, I was on a Nordhaven 35 as an RC boat for Sunfish races. Now that is a real cruiser for those that can afford it. Tomorow I am RC on an old Navy whaleboat with a Perkins Diesel that makes 5 to 6kts tops and will roll your guts out until the flopper stoppers are down when anchored. It will save your life on the ocean but will not be comfortable while doing it. Last Sunday two dull colored Homeland Security boats came into the harbor for fuel. Up forward on both was a very intimidating 50 Cal machine gun. In between all these, there are always some that look like running shoes and some that are like the ones Richard mentions. Hang around any coastal harbor for a while and you will see just about everything that will float and some that don't even do that very well.

    I generally avoid any mention of "perfect boat" threads since no such animal exists.
     
  12. PAR
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    PAR Yacht Designer/Builder

    The perfect boat is the one you can live with.
     
  13. tomas
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    tomas Senior Member

    You mean like these?

    [​IMG]

    [​IMG]
     
  14. PAR
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    PAR Yacht Designer/Builder

    Purdy little beasties, all in a row . . .
     

  15. LP
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    LP Flying Boatman

    Just like a bunch of little dolphins doing a tail stand...............All in a row. :p

    20130215_7Marine.jpg

    (Maybe baby killer whales.)
     
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