Carbon Fiber Catamaran with an adjustable CG & adjustable turn fin

Discussion in 'Gas Boats Forum' started by Jim Allen, May 27, 2019.

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  1. May 27, 2019 #1

    Jim Allen

    Jim Allen

    Jim Allen

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    Both of these systems were shared with me by a very capable Australian model boater. The 1/16" thick turn fins are machined from spring steel stock. They are machined to a full wedge, leading edge to rear edge with carbide tooling & a simple fixture. The turn fins can be adjusted in position & depth when mounted to the side of the cat.

    The adjustable CG system allows the CG to be changed without moving anything in the hull. Machined brass weights of 2, 4, 6 & 8 ounce amounts are clamped to two 8" long, .625" OD carbon fiber rods that are mounted between two .078" thick carbon fiber plate bulkheads. The rods are mounted in the lowest position possible in both sponsons.

    Both systems are very simple to make & both provide running site adjustments to be made.

    Jim Allen
     

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  2. May 27, 2019 #2

    Terry Keeley

    Terry Keeley

    Terry Keeley

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  3. May 27, 2019 #3

    Jim Allen

    Jim Allen

    Jim Allen

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    The .020" thick paper templates were made before cutting the .078" thick carbon bulkheads. This became necessary because the inside of the carbon fiber hull is slightly different in the mounting areas. I also did not show how the weights are to be clamped to the two .625" OD carbon fiber tubes. When everything is finished & glued in place I will take better photos.

    JA
     
  4. May 28, 2019 #4

    Jim Allen

    Jim Allen

    Jim Allen

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    These photos show what the adjustable weight system looks like after the front & rear bulkheads have been glued in place with JB Weld Quick. This system will also lower the CG of the hull because the weights are sitting in the lowest part of the hull. With a hull weight of 4.5 lbs., I can't wait to test this thing out!

    JA
     

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    Last edited: May 28, 2019
  5. Jun 6, 2019 #5

    Jim Allen

    Jim Allen

    Jim Allen

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    I decided that clamping the weights was much better than using a set screw to hold them in position. However, this process was much more time consuming. Notice the wider slot cut opposite the clamping screw side which has a thinner slot. Doing this makes the brass piece flexible & therefore it is easily clamped to its carbon fiber tube.

    JA
     

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  6. Jun 13, 2019 #6

    Jim Allen

    Jim Allen

    Jim Allen

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    The adjustable weight system is now complete with the addition of a 5/8-11 nylon bolt, a 5/8-11 nylon nut & a hard 1/8" thick rubber retaining washer. Finger tightening of the 5/8-11 nylon nut against the hard rubber washer, locks the carbon fiber rod mounted between the two bulkheads, securely in place.

    Jim Allen
     

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  7. Jun 14, 2019 #7

    Julio Almazan

    Julio Almazan

    Julio Almazan

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    Nice job, Jim Allen... very good job.
     
  8. Jun 21, 2019 at 1:45 AM #8

    Jim Allen

    Jim Allen

    Jim Allen

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    I'm posting photos of the machined steel strut which is used on the cat. The strut's design will allow the propeller to be moved 1.250" forward of most standard units. The machined strut bushing is made from B-10 Bearium material. It is removable from the strut housing & it remains with the cable, prop shaft assembly when removed. Precision machined slots locate the upper 1/8" thick upper section & the 5/64" thick skeg. Both pieces are machined to a full wedge before silver soldering. The strut can be easily set at various angles with 1*, 2* or 3* wedges placed behind the one piece strut mount.

    Jim Allen
     

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  9. Jun 22, 2019 at 1:37 PM #9

    Jim Allen

    Jim Allen

    Jim Allen

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    This is what the completed strut assembly looks like after silver soldering the three main pieces together & the anti rust steel black has been applied. A one piece mounting bracket & the Ernst engine mount thrust plates make it very easy to change the struts angle at the lake.

    JA
     

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    Last edited: Jun 22, 2019 at 4:08 PM
  10. Jun 23, 2019 at 9:04 PM #10

    Christian Lucas

    Christian Lucas

    Christian Lucas

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    Hi Jim,

    i know you are crazy but this boat is a hammer thingy. I like the full carbon hull and the presicion maschined parts, looka great. And i like the outrigged turnfin. For the adjustable c.g. i have a different seeing where the waights have to placed. When i run Naviga F1 triangle race with an outborder tunnel i first placed the batterie at the lowest part of the hull in the sponsons on both side. Moving for and back has plenty of room to find the best position belong to water condition. But when i run this triangel course turns, they are very tite , sometimes the boat makes a outside roll over.
    After some such roll acrobatic i changed the position of the batterie and placed it in the middle of the hull under the midsection just behind where the pilot sit. All as well for- and back to adjust c.g. and the best thing was that the boat dosnˋt roll over the side , no matter left or right turn. The reason was that now the waight was in the middle concentrated and the sponson can now follow faster a moving moment when a small waive hit the hull from the side or other belongings want to lift the sponson out of the water. They can do as the moment of inertia for the longitudinal axis is much lower . If the waight is placed moore outside inertia moment is higher and the spnoson will grab depper in the water and maybe will stumble.
    Have it in minde , it must not happen to your hull , maybe only my tunnelboat was infected by this illness , but better to tell. Have fun with this tunnelhull.

    Happy Amps Christian
     
  11. Jun 24, 2019 at 2:18 AM #11

    Jim Allen

    Jim Allen

    Jim Allen

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    Hi Christian,

    Thanks for the information. I know next to nothing about a catamaran & even less about a tunnel hull. However, my HTB 360 tunnel hull runs on a rail down the straight away without any rocking & turns right or left without any problems at wide open throttle. I have an adjustable weight system on this hull also with 16 ounces placed where the photo shows.

    Thanks again.

    Jim Allen
     

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