Catamaran tender to replace rib?

Discussion in 'Multihulls' started by DennisRB, Jul 4, 2014.

  1. Manfred.pech
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    Manfred.pech Senior Member

    At the first look they are similar: A clever combination of a dink and a small catamaran or simple - a box with pontons.

    [​IMG]

    But I think there are differences compared with the designs of sailhand. The hulls seem wider (beam/length ratio) and shorter, the bottom flat, less rocker, less room in the box and shorter extensions at the stern which means that there can be more squatting with the bigger engine.
    The distance between the pontons seems less which results in more interference and hence more drag.
    In a short chop there can be pounding/hobbyhorsing, but the wider hulls might have more displacement at the same length.
    As already said the red/orange boat will need a stronger motor for the same speed as the four tenders we can see here from the pics of sailhand.

    To understand it better it would be helpful to have fotos from the bottom.

    [​IMG]
     
    Last edited: Jan 24, 2017
  2. sailhand
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    sailhand Junior Member

    you got it manfred the hulls on the little orange dinghy are your standard powercat hulls nothing at all like mine. you can put the little orange dinghy inside mine and walk around it. mine are not revolutionary at all, I cant understand why no-one has done it before. I have seen plenty of off the beach cats with decks and small outboards of some sort and they are not very successful. they go fast but cant carry any payload and are limited in there functionality. all i have done is modified sailing type hulls to suit a heavier payload and faster optimal speed and built a more suitable "tub" to sit on it. I have not seen another boat like this anywhere on the net or in real life I think mine is the only one ever done like this. I have not reinvented the wheel or anything like that just put two different pre-existing things together to create something slightly different and for my purposes it works really well. I think it is really simple yet it works well so why not!!! couple of pics attached the one on the roof of the hilux is deceptive it shows the size of the dinghy but not really the hull shape and rocker very well.
     

    Attached Files:

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  3. DennisRB
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    DennisRB Senior Member

    I see you are next to Brians tender. Is yours a lot lighter than his? He has a 20 hp on there I think! But mainly so he has a 3rd 20hp as spares for his main engines.
     
  4. DennisRB
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    DennisRB Senior Member

    Have you got a pic of the hull so we can see the shape?
     
  5. sailhand
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    sailhand Junior Member

    Hi Dennis, bryans tender is over a 100kg I think from memory. He did have a 15 suzuki 2 stroke that we trialled on my dinghy but after they lost the boat when they were travelling in thailand with us Brian swapped to the 20's on schools out and then decided to put the 20 on his tender as you say to have spares for the main motors, a good idea I think or maybe Bryan just wanted to get to the fish before me, I think it's probably the latter. My dinghy and motor combo is around 70 kg all up, so much lighter. Sorry I don't have any pics that show the hulls very well. The keels are flat as that shape has the shallowest draft and also generates more hydrodynamic lift like a pair of water skis. We will be heading back to brisbane soon so I'll let you know when we get there and you can come and check it out if you like.
     
  6. Manfred.pech
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    Manfred.pech Senior Member

    Strakes

    Hi Sailhand, thank you for the very interesting pictures. I do not know if you wrote already of the strakes to be seen at the sides of your tender. These prevent the water crawling upwards and so reduce the wetted surface and hence skin friction when speed is raising.

    [​IMG]
     
  7. sailhand
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    sailhand Junior Member

  8. Manfred.pech
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    Manfred.pech Senior Member

    Amazing! Very fast for the small Yamaha. Very low wake. It is a good result of the long work and research you have done with the different hulls and the distance between, the strakes, the bridgedecks, the fight with the weight and interferences, the foamcores, the resins and the best methods to join them. I have not seen it better.
    Thanks a lot for sharing!

    [​IMG]
     
  9. Shredderf16
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    Shredderf16 New Member

    Sailhand,
    Amazing design, my Admiral really liked the step on step off feature. We're building a house on a small island in the USVI although mostly live in Texas. We need a 12 foot dinghy to go from the main Island of St Thomas to our island. Mainly just the two of us but occasionally building materials and for diving off of it. Really don't want another Rib and they are expensive there anyway. I have a full shop on my farm in Texas and am planning on sending a container of building materials anyway, so building it is no problem. I would like to buy plans from you. My wife is a electrical power engineer who is very good at autocad and microstation, I'm sure she would exchange dry feet for digitizing your plans if that would speed things up. I've looked at these cat dinghies over the years and yours seems to be the most versatile I've seen. Please PM me at the email on my profile if you're interested.
     
  10. brian eiland
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    brian eiland Senior Member

    But I do not think that small vessel is going to meet you needs to move building supplies from St Thomas to another island??,...particularly across open water down there with the trade winds blowing up a bit of a chop..

    Might be OK for a few people, but not big loads.

    With plywood and a few good glued on 'D-shaped' foam collars you could build a nice catamaran freight dinghy that would handle slightly larger HP that you might need for that job.you were talking about.

    http://www.boatdesign.net/forums/boat-design/homemade-rib-howto-49063-2.html
    http://www.boatdesign.net/forums/boat-design/homemade-rib-howto-49063-2.html#post693142


    Brian



     
  11. sailhand
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    sailhand Junior Member

    brian is right if you want to carry heavy loads a long way this is not the boat you want. a larger version of this has been drawn for a friend with a 60ft cat and he is building it at the moment I believe. do you have any legislative restrictions about motor size or any other restrictions ie transport storage etc to restrict the size of the vessel you can use. the 3.5 metre version that features in the video is more suited to use as a tender. I have had 7 people in the tender but only from the shore to an anchored vessel about a 100 yards away in calm water. I would think the max practical load for this size dinghy, the bridgedeck is only 9 feet long, is lower than what you need at around 340lb. the hullform is easily pushed and works well because they are skinny hulls, but skinny hulls have low load carrying capacity. a larger version of this would be suitable for heavier loads and longer open water travel with a heavier load. how far are you intending to travel in open water with it.
     
  12. sailhand
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    sailhand Junior Member

    also thanks for the autocad offer. I have autocad and have been using it for about twenty years. if you want this plan or a slightly larger one I can supply the drawings in a dxf file to simplify things. you could also then use them to cnc cut your foam panels
     
  13. sailhand
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    sailhand Junior Member


  14. Jolly Mon
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    Jolly Mon Junior Member

    Sailhand, great job on your cat! I’ve been working on a cat design too. My first one is 12 feet long(3.7 meters) and does 10 knots with a 4 hp yahama. I’m also using it as a tender and would like to get the weight down some on the next one. This one was about 75kg hull only.

    Will you share your layup. What fiberglass you used and type and thickness of core material?

    Rob
    FB08EAF6-711F-43BB-9EF9-0EBD4D323CF4.png
     
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