Atkins - compared to modern design/materials

Discussion in 'Powerboats' started by Standpipe, Feb 26, 2015.

  1. Mr Efficiency
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    Mr Efficiency Senior Member

    If it got half that mileage, (35nmpg), it would be a wonder of the waters, but the quoted figure, that would be the wonder of all wonders.
     
  2. PAR
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    PAR Yacht Designer/Builder

    Yeah, we seem on the same page Tom. I too have liked the Sea Brights, but for what they were, not what they might be. The built down hull aft is draggy, but in a surf is a real benefit backing out and turning around, not to mention landing with a breaker under your butt.

    Robb's Rescue was a unique thing, with "free form" round bilges and everything, so I'm not sure what how to evaluate it, but videos of it underway clearly show what it can do. Granted it was under powered and this power was fairly heavy for it's output, further holding her back. He could have saved half the engine wight and doubled (maybe tripled) the output, using a garden tractor engine, which would have offered a considerable boost in it's abilities. Other then a full up Hickman sled, I don't think any of these hulls can match a skinny flat bottom, though they'd be more comfortable in a chop, comparatively.
     
  3. Easy Rider
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    Easy Rider Senior Member

    I don't think Atkin's invented the Seabrights and they don't represent the bulk of their designs.

    In the Atkins lineup there are boats of all kinds. And their sailboats don't look like motorboats and their motorboats don't look like sailboats, except the motorsailers. Flat bottom, V bottom and round bottom. Commercial and pleasure. Why are most of their boats so beautiful and seemingly perfect? From time to time I go to the Atkin plans and always come away inspired.

    The mindset of the day must have been extremely practical (compared to today) as many of their designs were referred to by the word "utility". Nobody would ever do that today.
     
  4. PAR
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    PAR Yacht Designer/Builder

    The Sea Brights are a well known type and around long before Billy was born. Both (billy and John) had a good aesthetic eye, which is important if a design is to stand the test of time. There's lots of clever designs that look "dated" in just a few years, but it takes a master's skill, to develop a set of lines that look good a half a century down the road. These are the ones we continue to focus on and studying how they did it and why they still appeal, is part of the process of learning about design. It's the same effort to understand why a particular hull form does better or worse than another, just a different area of study.
     
  5. Mr Efficiency
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    Mr Efficiency Senior Member

    I'd suggest the design of many of the powerboats, particularly those with a little turn of speed, reflect the availability of engines at the time, and their power to weight ratios.
     
  6. Rurudyne
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    Rurudyne Senior Member

    Sandpipe, if you are worried that the scantlings for an old design may be heavier than necessary you could get Gerr's Elements of Boat Strength and run the numbers , comparing to the indicated dimensions in the plans. I'm guessing they'll be close but at least you'll have a breakdown about why they are what they are and if there's a difference in favor of Gerr you can at least have a sense of how much can be shaved off.
     
  7. PAR
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    PAR Yacht Designer/Builder

    The only problem with running a new set of scantlings using any formulas (like Geer's) is you're still stuck with the weight. If you have a 2 ton powerboat and by recalculating the required scantlings you can make it a one ton boat with the same strength and stiffness, it's still a two ton boat, if you expect it to perform on the designed lines, it was drawn at (pretty much a necessity). Where scantling rules really help, is if you'd like to change a carvel to a strip plank (as an example), so you end up with an appropriate set of scantlings for the new build method.
     
  8. Rurudyne
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    Rurudyne Senior Member

    Well, yes. Especially with a newer, lighter engine than may have been available at the time if talking really vintage plans (just yesterday I read a description of the powering travails of a particular pretty little design whose first engine, IIRC, had been an 8 HP that weighed 500#).

    But at least you get to choose how low in the boat you want your newfound needed ballast to be. :)

    Also, I believe you might be able to finagle some extra headroom in the cabins of some old designs without marring their appearance by having to raise the roofline (one particular design I'm thinking of is Alligator from The Rudder, 1911, which had an attractive profile and some tall keel and keelsons).
     
  9. tom28571
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    tom28571 Senior Member

    Good analysis and mostly true. In many planing powerboats it would need some modification though. Most of the old guys knew that weight was the enemy of speed and their boats would have been faster if lighter weight was possible through material not readily available to them.

    Unlike a displacement or semi displacement boat, a full planing boat needs to be under control with all combinations of waterline or hull immersion. A displacement boat usually works best only when the weight is near the design weight. In a planing boat, weight reduction while maintaining balance is almost always a good thing if speed is the goal. If top speed is not the goal, then making the boat lighter can be a disadvantage to comfort and safety.
     
  10. Easy Rider
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    Easy Rider Senior Member

  11. Mr Efficiency
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    Mr Efficiency Senior Member

    She'd have a distinct bow-high attitude doing the 16mph, you'd have to think.
     
  12. Easy Rider
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    Easy Rider Senior Member

  13. Mr Efficiency
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    Mr Efficiency Senior Member

    I love this, referring to the "Tang".......

    A water tank is not shown; it may be better to carry water on week-ends in a stone crock or jars. :eek:
    Sounds like things hadn't progressed much in water containers since antiquity ! :D
     
  14. Easy Rider
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    Easy Rider Senior Member

    Mr E,
    What do you think?
    Would Tang trim nicely w a 65hp OB?
    Moving some heavy things fwd of course.

    Saw pics of one of these (several have been built) and she ran quite bow high as an OB.
    http://www.atkinboatplans.com/Cruisers/Hope.html
     

  15. Mr Efficiency
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    Mr Efficiency Senior Member

    Well, on a quick perusal, I'd venture to say if the "Hope" trims nose-high, the Tang will probably be more so. I doubt moving weights forward has enough of the desired effect. When they speak of 15mph etc, that would, I assume be flat-out, which is not what is practicable to maintain anyhow.
     
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