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  1. #21
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    Quote Originally Posted by 706jim View Post
    I once had a student trying to machine a car wheel rim out of billet carbon fiber.

    No, you didn't read that wrong, he laminated a zillion layers of carbon into a huge block and then tried to cut it to shape on our GR15 router.

    And no, it never came close to completion.
    The "old" British Top Gear show had a great saying for such things:

    "Ambitious, but rubbish".

    [And the never being completed aspect is a good thing]

    Here's a report of a better approach:

    Bucci Composites completes testing of new carbon fiber wheel | CompositesWorld

    For those actually interested in such things, there's some videos on YT of the Koenigsegg carbon wheels being built up, interesting stuff.

    Making 280mph Capable Carbon Fiber Wheels - /INSIDE KOENIGSEGG - YouTube

  2. #22
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    Quote Originally Posted by Milland View Post
    I'm not sure what you designed, but my thought is two or so ramped longitudinal fins (much like miniature keels) in front of the props from ~1/4" 316 stainless. The ramp to push debris down below the prop, the fin to minimize drag.

    Actual sizing and mounting is up to you, but you have to think about the ship's design and how the strain of impact would be passed into the structure. If you allow an impact to "rip" the fin off, perhaps a few stainless cables attached to prevent loss? But then you have to make sure the cables can't foul the props.

    Screw it, or more correctly, de-screw it and go to magnetohydrodynamic drive...
    And...The ramp angle lead to lift the boat rather than slamming into a dead stop.

    We have a rock pile leading to Harsons Island South Channel..many a boat has made the trip up and on the rocks.. Good we dont have sharks in Michigan.

  3. #23
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    Quote Originally Posted by Milland View Post
    Wait - now we're starting with a giant block of 316 stainless? Or do you propose billet fiberglass?
    There have been a lot of really good boats made from billet wood, I don;t recal hearing of anyone ripping a prop off one either.

  4. #24
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    They already make really good prop protectors, and they're cheap. Called "depth sounders" and they have alarms and work super.

  5. Likes Vancbiker liked this post
  6. #25
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    Quote Originally Posted by Ziggy2 View Post
    I think you need to research your idea and concept much more than you have.

    Your number #1 concept will most likely greatly reduce the performance of the props. There has been a lot of research done in this area an your design as it currently stands will reduce the prop performance. There is a lot that goes into the ring design and shape plus how the prop blades need to be changes to accommodate the ring.

    The second design will also increase the drag but not affect the prop efficiency as much however this version will most certainly cause large localized hull loads if run aground. In other words, unless your significantly increase the hull strength in the struct area, you will likely rip the bottom of your boat out and be setting on the bottom before you even know it.

    You have not mentioned exactly what you mean by a "performance trawler" which makes me think more of a 42ft. semi planing hull with not a lot of keel depth. There are very good reasons why your concept is not used and I think it would be very prudent for you to understand why. If you proceed without doing the research, I suspect that you will have a very high probability of your boat becoming another statistic setting on the bottom.
    Yes, I am hesitant to do this at all because of the issues. You are correct in the type of boat. If you search for a 42 PT (Preformance Trawler) for sale in Port Clinton, Ohio, that's it. The only reason I am thinking along these lines is when my brother-in-law brought it from Tampa to Ohio they bent a shaft in Lake Ocechobee and hit a log somewhere damaging a prop and shaft. I may be flaying at windmills but my experience is with sailboats. When you hit a log it just goes bump. Aground you either wait or heel it and kedge off. I could just leave it alone and trust American Express.

  7. #26
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    I would use west system G/Flex structural epoxy. It has a tensile strength of ~3500 PSI, but a low modulus of elasticity... in other words it has enough flex to deal with the constant flex between the hull and skeg. If you are determined to use fasteners, I would model them after shear bolts used in snow blowers and other augers. At the junction between the skeg and hull, turn a grove ~50% of the way through the bolt. When you hit something the bolts will shear before the hull.


    Sent from my iPhone using Tapatalk

  8. #27
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    Quote Originally Posted by Milland View Post
    Wait - now we're starting with a giant block of 316 stainless? Or do you propose billet fiberglass?
    Aroooneeum... Please try to "keep up".....
    Milling a 100m fishing boat ?


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