Atkin "Ripalong"

Discussion in 'Powerboats' started by frank smith, Dec 1, 2010.

  1. tom28571
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    tom28571 Senior Member

    Frank, the warp starts at the bow and continues all the way to the transom on a true warped plane bottom. On a monohedron, the warp also starts at the bow but becomes a constant deadrise from about station 6 all the way to the stern. Each station represents 10% of the waterline length. Suggest some basic reading to start with Dave Gerr's "Nature of Boats" followed by Ted Brewer's design book and others until you are familiar with what a hull bottom shape looks like for different applications. Until you have some basic understanding of the fundamentals, it is hard to ask a good question or understand the answer.

    The photo you sent offers no clue to its true underwater shape other than near the bow so no comment on that. Also, please reduce the size of the posted photos as only a part of it would fit the screen at one tome.
     
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  2. frank smith
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    frank smith Senior Member

    Unfortunately I lent Gerr's book to friend and did not get it back. I have Brewers book .
    I have been finding info all over the net as well as here , but at this point I am just gathering info .

    Thanks for your help
    F
     
  3. tom28571
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    tom28571 Senior Member

    The net is great, especially forums like this one. The problem is that you need some background before getting on the net so you can make informed decisions about the conflicting advice found here. Advice found here can be valuable or worthless or even less than that. All advice should be taken with caution, including mine.

    Another note about the hook as seen on the Atkin boat is that the same effect of aiding early planing and holding the bow down can be had from the aft warped bottom, depending on how it is drawn.
     
  4. Mr Efficiency
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    Mr Efficiency Senior Member

    Wow, is this how you log up "reputation" points on this forum ? Most rottweilers are friendlier. No doubt deep down PAR is a nice guy, right ? :p
     
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  5. frank smith
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    frank smith Senior Member

    Tom , that info is real meat , and just what I need to know . I will look for info on that and other stuff mentioned . that will keep me busy for a while.
    All my books are on sailing design , so I have to hunt down some books on power hulls.

    I have found a few designs along the way that are good and would do the job. That is probably the way to go.
     
  6. Mr Efficiency
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    Mr Efficiency Senior Member

    Without that deep keel, the old "Ripalong" would be a broach-prone horror, there is plenty of drag in that appendage restricting the speed, too.
     
  7. frank smith
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    frank smith Senior Member

    I assume that its normal operating speed range was the mid teens . It probably turned a large wheel and worked well for the technology of the day.
    I'll bet it would do ok today . After all they still make Harley's .
     
  8. Mr Efficiency
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    Mr Efficiency Senior Member

    Horses for courses, if you are happy to potter round at those speeds, is the right thing for it. I agree mid to high teens would be its go, the 25 mph stuff is not its range of realistic operation. It might even be viable with a non-turbo diesel, that would put it in an interesting niche.
     
  9. tom28571
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    tom28571 Senior Member

    Pottering around? Most coastal cruisers would be very excited to be able to "potter" along at speeds in the teens. Taking long cruises at these speeds is an unattainable goal for most of the trawlers and similar cruising craft on the ICW. Either the boat just won't make those speeds or the fuel use rules it out. The cruising boat that can run in the mid to high teens with good fuel economy should be welcomed. We are not discussing the boats that adorn most all of the boating magazines that zip out for an hour or two with a bikini laying on every horizontal surfaces.

    The ability to also run in the 20's when that is needed or advisable is a plus. Atkin's Ripalong was a good shot at that goal but there have been some advances in both power and hull design as well as more serious weight control that are available today.

    The boat that meets these goals is not the ideal for high speed or taking those bikini's out for the afternoon but can be fine cruising at all speeds up to its designed max. It can also be capable of good performance in the wind and water conditions to be found along inland and coastal waters.
     
  10. Mr Efficiency
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    Mr Efficiency Senior Member

    Tom, the nagging problem I see is the down-sea running, the achilles heel of semi-displacement boats. It will kill efficient operation. Other angles to the waves, no dramas. It is just that combo of wavelength/speed that can make them work hard, that makes me hesitant.
     
  11. tom28571
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    tom28571 Senior Member

    Not so sure about down sea running as being an Achilles heel of semi-displacement boats. Some semi-displacement boats are better hull forms than others and, in any case, some discretion on the part of the pilot is in order for a coastal cruiser. As a case in point, I'm thinking about some of Devlin's boats here.

    Another factor is that a properly designed full planing hull can be had that offers good cruising accommodations and runs economically in what is usually called the semi-displacement speed range.
     
  12. PAR
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    PAR Yacht Designer/Builder

    At 25 MPH Ripalong is traveling at well over 5 S/L ratio, which places it considerably into full plane mode. Even at the modest speed of 16 MPH, she's pulling a 3 S/L, which is full plane, so I'm not sure what this talk about semi displacement mode is, but this boat is a full plane model.

    Precisely, though this one wouldn't be one of those designs. Semi displacement, much like it's full displacement counterpart, is a LWL derived limitation (assuming the usual shapes are employed). For a boat of this size, semi displacement would range from about 7.5 MPH to about 15 MPH.
     
  13. tom28571
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    tom28571 Senior Member

    Probably we have a communication problem here but I consider relying on S/L to determine whether a boat is planing is questionable. I consider planing or not planing to be a function of the boat itself rather than its length. Some boats of the same length and beam are fully planing at S/L of 3 and some are still plowing along in semi mode at the same S/L ratio.
     
  14. daiquiri
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    daiquiri Engineering and Design

    Sure, you have to consider the weight too.
     

  15. PAR
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    PAR Yacht Designer/Builder

    Most boats that can reach a S/L of 3 are fully up on plane, though yes, some shapes are still "climbing", but I wouldn't consider these the "usual suspects" as far as shapes are concerned, particularly if efficiency is being considered. At about 3 S/L the wave train displays all the characteristics of the plane mode, though we could debate if it's 2.8 through 3.2 on each specific wave train generated from the different shapes. I've seen some really efficient designs "get up" at a fairly and very low S/L's, your powerboat design is included here, but as an average figure, 3 is reasonable. Personally, I think 2.5 is the beginning of full plane from a wave form view point, but others debate this, so I can live with 3.
     
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