Roof Box Boat - Roof top Nirvana - Missions Boat

Discussion in 'Boat Design' started by Skint For Life, Jun 21, 2014.

  1. Skint For Life
    Joined: Jul 2010
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    Skint For Life Junior Member

    Hi all,

    I'm wanting a large roof box boat for my 4x4 (89 Isuzu Trooper), I like the roof box boat concept: http://www.boatpack.com.au/photos-and-videos/

    The roof of my 4x4 is appx 2.2 x 1.3 metres. I'm liking the idea of a very lightweight little catamaran or trihull, something like: http://www.finnkayaks.com/index.php...=flypage_new.tpl&product_id=48&category_id=25

    I'd like a boat with the following qualities:

    #1 Boat appx the dimension of my roof
    #2 Designed for two people and gear, scuba or free diving
    #3 Small outboard power
    #4 Lightweight, one person needs to be able to drag it up beach, rocky shore, ramp etc. Then load onto roof.
    #5 Lightweight, two people need to be able to carry it up a rocky shore without issue.
    #6 Dive Capable, scuba/free divers need to be able to exit and enter the boat without tipping/flooding the boat.
    #7 Shallow draft to access places that would normally only be seen with a jetboat.
    #8 Overload capable, needs to be able to carry an extra 100kg over spec weight without danger to vessel or crew.

    Does anyone have any suggestions?

    Thank you in advance :)
     
    Last edited: Jun 22, 2014
  2. Richard Woods
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    Richard Woods Woods Designs

    Sorry to say I think you are asking for the impossible. A catamaran that small won't have the load carrying. The Finnkayak you linked to weighs 55kgs, rather too challenging to put on the roof singlehanded - and it only has 260kgs capacity.

    You want 100kgs safety factor, that allows 160kg for scuba gear, outboard, plus two people. I also suspect you won't be able to reboard as a skuba diver

    Richard Woods of Woods Designs

    www.sailingcatamarans.com
     
  3. philSweet
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    philSweet Senior Member

    Somethin like this? Deepwater recovery over bow. 3hp planes 1+junk. 4hp planes 2 + junk. 84 pounds. 2.9m. Fits between wheelwells in full sized P/U.

    Construction - 1 sh 6mm and 2 sheets 4mm ply. 6oz glass skin on outside. Some 1" foam sheets glassed to bottom on inside. I used fir marine ply. If you go with lesser stuff it will need to be heavier. I think I had about $700 in materials into it 8? years ago. Built it in three days on a table on my porch.
     

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  4. BobE
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    BobE Junior Member

  5. rwatson
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    rwatson Senior Member

    how about this

    Its amazing how big a boat you can carry - as they are quite light.
     

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  6. Skint For Life
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    Skint For Life Junior Member

    Richard, Thank you for valued input, I had an idea I may be asking a bit much, I just re-did the overload calculation and I think it'd be more like 50kg max rather than 100kg. Crew weight is appx 73kg x 2. Does this make it any more achievable?

    If we have to drop Scuba from the list then we could survive with just Free Dive, but the ability to Scuba would be great.

    The Finnkayak "spindrift" (2.4m) is heavier than I'd like, but being rotomould plastic isn't it heavier than something built of ply? Stitch and Glue?

    I'm planning on the roof rack having rollers on the rear to aid loading and unloading of the boat by one person. I suppose a winch could be used as well but I'd prefer to not go that heavy with the boat.

    Phil, that is a similar design to what I had in mind, although I see it's 2.9m I'm aiming for appx 2.2m x 1.3m. Thanks for sharing that, the pictures, the weight etc. It's all very thought provoking. Wouldn't Scuba bow entry bury the bow as this is the lowest volume of buoyancy?

    Bob, Thanks for that link it shows this idea is nothing new. I don't know how suited a monohull is to this application, it would have to be very wide with a hull shape similar to a RIB I believe to be able to be stable enough for Scuba. I don't think an inflatable is a sensible idea as the internal volume is very low for a boat this size.

    RWatson Thanks for the picture, I don't think a canoe is going to have the volume or stability required for Scuba.

    I see a New Zealand company (Rae Line) just up the road from me made a 2.5m FRP Catamaran called "Rae Line twin hull Super Dinghy" I've inquired about the weight etc.

    Thank you to everyone for their input :) I look forward to seeing where this goes.
     
    Last edited: Jun 21, 2014
  7. rwatson
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    rwatson Senior Member

    Yes, the canoe wont have the stability.

    One point to remember though, as I found out with my rig - the longer it is, the easier it is to load/unload.

    With that 16ft canoe, at about 45 kg, it was a doddle to roll off the roof rack single handed. If it is long enough, you can rest one need on the ground, as you lift the other half down of even that high roof. If you used rollers on the end of a long boat, it gets even easier.

    With a shorter hull, you end up with having to bear the whole weight at some stage between the rack and the ground.
     
  8. gonzo
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    gonzo Senior Member

    An inflatable will fit in the bed of your truck and have a large load capacity.
     
  9. BobE
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    BobE Junior Member

    I stumbled across these pictures on a random woman's blog some time ago while doing a jeep Cherokee roof rack photo search. She saw it in a race track parking lot and took the pictures in order to make a red neck joke, but dang, I'd like to see that in person and in action. Somebody has one heck of a flat towing rig for their rv.
     

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  10. Skint For Life
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    Skint For Life Junior Member

    RWatson, Thanks for that info on it being easier to load when longer, it makes perfect sense.

    Gonzo, The 4x4 is an 89 Isuzu Trooper so it's an SUV not a Ute. The inside will contain a camping bed so on the roof is where I want the boat.

    BobE, That looks like a crazy setup :) I want to keep the boat weight down so all that complicated launch/lift gear can be avoided. The boat itself though looks interesting, obviously in my application it would be flipped over. I like the fact that it's very wide with vertical sides, I expect this would make it more stable for Scuba entry/exit. Perhaps a lightweight version could be made of ply, I wonder what the weight and load capacity of a boat like that would be.

    Thanks guys :)
     
  11. rwatson
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    rwatson Senior Member

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  12. BobE
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    BobE Junior Member

    That’s an aluminum jon boat. I believe the brand is Sylvan and they are either out of business or only making pontoons now. Those Jeeps are about 12’ x 5’ so I’m guessing that boat is about a 1648 (16 - length in feet, 48 - width of bottom in inches).I am just guessing, but… Probably weighs close to 300lbs. Load capacity probably around 900lbs.
    I've got an old Montgomery Wards 1231 that I car top like a canoe. Max beam is about 40" allowing it to just barely fit on the roof of most compact cars without a roof rack. Probably weighs 100lbs or so. Not sure what the load capacity is for it, it was made before they had to label it. It will carry two guys and fishing gear, but it can get a little low in the water depending on the size of the guys and amount of gear. With a 31" wide bottom it's really not a whole lot more stable than a canoe. They tell me jon boats don't get really stable until the bottom is around 40” wide or more. I use mine on ponds, small lakes, channels, streams, small rivers, calm waters. Jon boats are not exactly what I would consider sea worthy…
    With all the flat panels I don’t know if you could save much weight with a wooden jon boat unless you make it smaller. Otherwise it may end up too flimsy.
    Check out the Meyers Sportspal canoe. It is lined with closed cell foam that they claim makes it unsinkable, and it has foam sponsons which they claim allows your dog to climb in and out without flipping the canoe over.
     
  13. Ike
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    Ike Senior Member

    While traveling in my motorhome I have seen similar set ups. It's a way to stay legal because most states (USA) don't allow RVs to tow two vehicles. Usually though it's a pickup with the boat and trailer on top. This has got to exceed the tow weight limit though. Mine is 6000 lb and with the weight of the towbar, my Chevy trailblazer and whatever junk is in the trail blazer it is close to the limit. Add a boat and trailer and it would be way over the limit.

    The advantage to the Meyers canoes is that those things on the side are polyethylene foam. So as the canoe tips they become immersed adding buoyancy and stability. When the canoe is upright the foam is not in the water and does not disturb the canoe body shape. Are they stable enough to allow a diver to board? I honestly don't think so, but without the tanks and weights, etc they might.
     
  14. philSweet
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    philSweet Senior Member

    To answer your question, with a 3hp ob on the back, about 225 pounds can load over the bow. If there is a second person, they need to be all the way aft.
     

  15. portacruise
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    portacruise Senior Member

    Lightweight mentioned 2X and shallow draft probably means an inflatable or folding boat, with all your other considerations. Both types have also been used for diving. Here's one of the simpler folding types which can be configured for diving and can hold up to coral, scratches, dragging, etc., also has a diving accessories model: http://www.porta-bote.com/
    There were free plans online for a simpler, similar version sometime back, the main issues being finding long sheets of the hull material. I have owned one in the past and used to run river rapids without visible damage because the structure conforms and surface is somewhat self lubricating allowing it to slide easily.

    PC

     
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