Atkin "Ripalong"

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

  1. frank smith
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    frank smith Senior Member

    EStaggs , nice boat, and along the lines of what I am thinking , although the bulky topsides
    are more than what I would want . Looks like a little hook in the forward section , bit that
    might just be where the skeg fairs in to the bottom.
    Thanks
    F
     
  2. PAR
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    PAR Yacht Designer/Builder

    Frank, there's no hook on that hull. You're seeing the "fair body" of the skeg/hull interface. This is an example of a more modern warped bottom design. This would be typical of many "semi displacement" hulls, but in reality are actually under powered full plane hulls. A real semi displacement hull, can't even thing about the speeds that 25' Bieker can muster. There's also a huge difference in preformance and maneuvering abilities when you go from a fixed shaft to an outboard (or I/O or jet, etc.). You can trim what appears a fairly full bow (judging by the Bieker chine height) where you want it for conditions and/or speed, which is imposable with a fixed shaft, without tabs, which are limited themselves.

    I have a few designs of similar shape and dimension, also using outboards/I/O's and the occasional fixed shaft for the remaining throw backs amongst us. I've found you generally don't need the centerline skeg and if you do, the best approach is twin skegs well off the centerline, with much less "height". This cleans up the flow to the prop considerably and if shaped right, can permit the boat to take to ground bolt upright, rather then flopping over on it's midship bottom planks.
     
  3. bulk-head
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    bulk-head Junior Member

    Think twice before you buy anything for this PAR guy....
     
    1 person likes this.
  4. frank smith
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    frank smith Senior Member

    Par, you point out many of the benefits of the modern outboard . They are hard to beat on a cost and installation basis . I have never have liked ODs , but with the right motor it maybe would work, but the weight being concentrated in the stern means more width to carry it, I dont like the idea of an outboard in a well, you loose buoyancy and the sides of the well act as trim tabs , so that the benefit of being able too trim the motor are lost , and you are back to trim tabs , which i think a necessary anyway. Also I want to keep the stern uncluttered and gentlemanly. I think a shaft to an OD is the best compromise. I also want to keep the bottom so that it can be sheeted in ply, although the bow will most probably have to be cold molded ply.
     
  5. EStaggs
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    EStaggs Senior Member

    Speaking of outboards in wells, you hit on one of my personal boats, I built it in 2006:

    [​IMG]

    She's great for a reasonably wide range of speeds, will run at 30mph but pounds at that speed. Great in the 12-18mph range, however.

    E
     
  6. frank smith
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    frank smith Senior Member

    Very nice boat , I can across your web site describing the build some time ago. I like the Atkin boat that it was derived from, and may build one to replace the skiff I have now. In this case the outboard well works, and it it has the benefit of a short turning radius.
     
  7. daiquiri
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    daiquiri Engineering and Design

    That's a very good hint, thanks. :!:
     
  8. Easy Rider
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    Easy Rider Senior Member

    EStaggs,
    I like your skiff a-lot including the color. What is the finish? I don't like the well though. Frank and I seem to think much alike. "I think a shaft to an OD is the best compromise." I have seen this but on a fairly heavy 35' boat like a Rawson. Had a big 6 cyl diesel a-midship and a big Mercruiser OD. The drive shaft would need to be balanced very well and stay that way. Also much extra space was needed for the shaft in the boat. Pontiac had a car like that (Tempest) in the early 60s. I recall the high speed drive shaft was a problem.
    I'm not saying it would be a mechanical nightmare but maybe not too far off.
    Frank, relative to the OB well "the sides of the well act as trim tabs" How so?
    One of the greatest advantages of OB power is that one gains so much space in the boat and just turning around and wasting it is a tough call. I like PAR's idea w small bilge keels but I would thing in sharp turns you'd get the turbulence and that wouldn't be a good time for the prop to fail.

    Easy Rider
     
  9. PAR
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    PAR Yacht Designer/Builder

    Sharp turns on a warped bottom hull, particularly hard chine, will produce all kinds of turbulence, regardless of where the skegs are located. If the bilge skegs are small and well positioned, there is no appreciable turbulence to worry about (in regard to starving the prop). You have to look at what's going on in a hard, high speed turn and see how the skegs may affect things, but in actuality, the boat is scrubbing speed off exponentially in these types of maneuvers, unless they are very brief. So, unless you are intentionally attempting to run a tight corner slalom course, in which case you'd probably not want any skegs, it's unlikely you'll have to worry about skeg turbulence in corners.

    I think you all are over playing the weight of and outboard or I/O issue, as it's not that big a deal in modern powerboats of this general class. In smaller craft, yes there can be some argument about weight issues, but not at this scale. An outboard or I/O offer quite a bit in terms of cabin space and cockpit space and the huge difference in maneuverability just can't be discounted easily. I have a 28' fixed shaft Chris Craft, with a small block Chevy amidship and a 50 gallon steel tank mounted under the aft deck about 2 feet over the LWL, directly on the transom. So, the weight issue isn't indigenous to outboards and/or I/O's.

    Outboards in a well do permit trim adjustments, if the well is designed properly. I think the other assumptions about well mounted outboards are also unfounded too, such as buoyancy lose. Think of a well mount as a boat with two transoms, one load bearing and the other stylish. Locating CB's and CG's in optimized positions isn't any more difficult in a well mount then a conventional transom mount. Of course there are some "quirks" to each arrangement, but name anything that doesn't experience this in the design process.

    Anyone know what the story with this Bulk-head member is? It would seem in his short number of contributions, he's managed to piss off more then a few. So what's your story Butt-head, you have any experience or just a cryptic screen name with the inability to get along. Only have access to the net when you're at the shelter? What's your story/excuse?
     
  10. frank smith
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    frank smith Senior Member

    I did not see it and dont know what it is about .
     
  11. EStaggs
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    EStaggs Senior Member

    Easy, I went traditional over contemporary. Glass, S3 water-reducible high build primer, and a coat of Kirby Grey Green oil based. It is cake to touch up, brushes nicely, cleans up easily, and I love the stuff. Cheap too, compared to Awlgrip.

    Yes, there is a fair amount of turbulence that comes off that boat's skeg in a hard-over turn. It feeds a bubble trail to the engine, cavitates, and requires getting off the throttle or widening the turn radius.

    What you give up in a tight turn you gain back in spades with handling in wind, and biggest of all, tight quarters maneuvering. This boat is incredible in that I can move her directly sideways if needed. She's as maneuverable in marinas as any twin screw I've ever operated. Do love the hull, but she's a bit small for our forays out 40NM for albacore.

    E
     
  12. Wayne Grabow
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    Wayne Grabow Senior Member

    PAR: Your comments are always well-reasoned and informative and speak favorably for who you are.

    Likewise for Bulk-head, his comments speak for who he is. Unfortunately not a very positive image; probably best ignored.
     
  13. Easy Rider
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    Easy Rider Senior Member

    PAR,
    I know your'e well liked and respected on this forum but can't imagine why you feel the need to call someone a "butt head" much less have the gall to actually say it. Does being that abrasive give you power? I'm not trying to get even by being abrasive w you but I do wonder why you do it. I'ts a bit like seeing a nice girl looking like a sweet librarian that has an unbelievably foul mouth.
    Frank,
    Interesting about the maneuverability in close. Never thought of that. Thanks for the paint info ..I really do like that color. I have an aluminum skiff about the same size and want one about 24'. Kinda like Atkin's Russell R or another similar boat called Little Effort. I love skiffs and we have plenty of them here but they are almost all Lund and Crestliner types. I have one of the latter.

    Easy
     
  14. PAR
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    PAR Yacht Designer/Builder

    Eric, you must have interpreted post #78 differently then I. If I'm in error, I'll happily change my tune, though the Butt-head comment was a dig at the user name, more then anything else.
     

  15. Easy Rider
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    Easy Rider Senior Member

    I'm OK w that.
    I like to sling a bit too.

    Easy
     
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