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  #1  
Old 03-05-2008, 03:35 PM
bobg3723 bobg3723 is offline
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A shipping container transportable multihull

Hello everybody,

I attached this jpeg for a multihull design concept to garner comment and constructive criticism. It is of a shipping container transportable double hull boat, the design of which has precedence in a polysesian double hull boat canoe call a "ndrua". The ndrua, as described in the literature, were double hulled displacement canoes (as opposed to the proa, which were a single hull canoe with a single stabilizing outrigger). Why my interest in this configuration? Well, I can tell you its not due to its unconventional use of the ndrua's larger displacement hull coupled to a smaller displacent hull. That would be a silly constraint on a road legal trailerable catamaran, where you can have two equal displacement hulls. But why would I even consider a ndrua configuration? Well, first and formost, my design is meant to be transportable in a 2.3 meter wide shipping container, and so a design decision was to increase accommodation in the main hull for the majority of the stores and people, with the smaller volume hull relegated to containing the fuel, waterballast, outboard motor, pivoting retractable keel and rudder. The sailplan is a conventional fractional rig between both hulls and the boat tacks like a conventional catamaran. The main hull has no keel, but does have a retractable rudder as a back-up. I'm exploring this configuration as an alternative to not have the need to place the hulls on a heavy transport cradle and to reduce the windage of two hulls having cabins. Chocks would be incorporated into the hull design to prevent slamming into the container's interior. The paired hulls can be rolled along the ground on logs or even a knock down light weight dolly could be carried onboard in the ama. There are three crossbeams connecting the two hulls and assembly would take place on the water. Once the crossbeams are placed loosely in the pillow blocks of the vaka and clamped firmly in the ama, the two hulls will then be unfastened from one another to allow the hulls to separate to their full overall beam using a block and tackle. A system of guy wire bracing add addtional stiffness between the hulls.

The beauty of not having a heavy transport cradle is that once the container is free of the boat, the container can be sent on it's way. No need for the cost of lot space at the marina to store a container. You're no longer tied to the container, and free to travel to the next port and obtain another container shipping once there, if you choose. Or leave the boat on the hard until the next sailing season.

I've included waterline calculations for displacements values of 1500 lbs for the ama and 2750 flbs for the vaca. I used Carlson's Hard Chine Designer to create the hulls and perform the calculations. The hulls will be of glassed plywood exterior and epoxied interior. So there you have it. Any thoughts or comments welcome?
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A shipping container transportable multihull-my-ndrua-concept.jpg  
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  #2  
Old 03-05-2008, 04:56 PM
masalai masalai is offline
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Ah Oooow, - - Here we go again
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  #3  
Old 03-05-2008, 06:18 PM
bobg3723 bobg3723 is offline
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Here we go again?

Did you climax?
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Old 03-05-2008, 07:12 PM
masalai masalai is offline
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Somehow I was reminded of this... Build yourself a boat and do a lap, crazy or not? I don't know why...
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  #5  
Old 03-05-2008, 07:24 PM
bobg3723 bobg3723 is offline
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Originally Posted by masalai View Post
Somehow I was reminded of this... Build yourself a boat and do a lap, crazy or not? I don't know why...
Hey looks who's back, Masalad! So, it doesn't take much to titilate yourself, does it?
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  #6  
Old 03-05-2008, 07:34 PM
masalai masalai is offline
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Easily entertained, Sorry bob but those flat sides & flat bottom was just too much for me... No offence intended, but it probably happened... multiple chines - at least below the waterline to make the shape a little more inherently robust and "fair"... I cannot see how you would stretch the beam... A very rough approximation would suggest around half the LOA or more & to pack/make 2 similar hulls would make more sense... look at forums relating to proa style boats - all have a similar problem -to find out tack and capsize...
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Old 03-05-2008, 07:44 PM
bobg3723 bobg3723 is offline
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Masailai, Masalai. Goodness. And to think of all those fast cruiser trimarans out there capsizing on a tack. Oh, and by the way, you really should learn the difference between a conventional displacement hull and a stabilizing outrigger of a proa. Stablizing amas on proas does not equate to bouyant amas. Don't confuse the two.
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Old 03-05-2008, 07:50 PM
masalai masalai is offline
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Even Melanesians who use "outriggers" on their canoes, know what I have suggested.... Good luck, learn to swim & to turn it back up after it falls over....
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Old 03-05-2008, 08:23 PM
bobg3723 bobg3723 is offline
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Those melanensians have NOTHING on us Filipinos ;-)

If you thumb your nose at this, then you'll just hate Sharpies. ;-)
If the nose slaps a little in the chop, nothing says you cant put a radius there. You have to remember that the decisions about which this boat is "faired" is biased towards maximimzing cabin room within the conifines of a shipping container. At the very least, you should be able to go below decks into a pipe bed, cook a meal, sit on a chair like a human being to read the funnies and not have to tumble ass of teakettle over a sleeping partner just to get to the head. The flat sides and bottoms are what they are. A quick build. I would'nt live in the damned thing and I wouldn't want to expose much structure to the forces topside either, hence at 5 foot six inches, you'll be ducking your head down below just to squeeze off a loaf. You get to where you're going, beach it and and carouse with the natives, or snooze in the secluded shallows of a lagoon. There is no stopping point between Fiji and Raritonga in this puppy. No sir. This things not meant to motor more than two or three days at the most, hence the shipping container.

As you can see, I left a lot of the hardware details off the pic, the crossbeam configuration, then cabin accomodations, all that. That'll come later.

Cheer,
Bob
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Old 03-05-2008, 08:54 PM
bobg3723 bobg3723 is offline
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Goodbye!

Me swim? Yeah that's me waving my hand as I go down with the ship. See that hand, how many fingers do you see?
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Old 03-05-2008, 10:22 PM
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the1much the1much is offline
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are those sides as high and flat as they look??
and why the biggie on fitting in a shipping container
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Old 03-05-2008, 10:57 PM
bobg3723 bobg3723 is offline
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Quote:
Originally Posted by the1much View Post
are those sides as high and flat as they look??
and why the biggie on fitting in a shipping container
Four foot ten at the belly. Yes, Sharpies can be that flat on the sides.

Container shipable liveaboards are just another gimmick to sell you a $200,000+ boat that you can ship anywhere they'll offload a 40 foot length connex. The latest I've seen for said connex shipments from SE asia to the U.S. West coast was quoted at $2000.00.

I want the pilot of the vessel I'm traveling in to be AirFrance or Continental, and have them drop me off in Fiji where my container awaits.

Cheers,
Bob
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Old 03-05-2008, 11:21 PM
charmc charmc is offline
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Bob,

Congratulations on putting an idea up for input. Looks like the early feedback focuses on the very flat sides and bottom. I have to say that's my first impression also. Might be just esthetics; on the other hand I don't see that being anything other than a teeth rattler at any speed in a chop.

I do understand your concept, I think: a day sailer big enough for some short overnight trips, a few hundred miles max, and that can be disassembled and stored in a shipping container whenever you want to relocate to another base.

There is a good article on the relative merits of ndrua vs proa sailing characteristics here: http://www.multihull.de/down/ndrua-gb.pdf

I notice that the drawing of the ndrua in the article shows a much more tapered bottom on both the vaca and ama, with rocker and sharp ends. This is one reason for its claimed speed and manuverability. Real ndruas used a clamshell sail on a short inclined mast and shunted (swapped ends with the rudder and sail) rather than tacked.

It appears that you are diverging significantly from ndrua design. I don't have any idea how your changes will affect performance. Don't get upset, but I don't think you do, either. Maybe build a model and do extensive testing before commiting to the full scale one.
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  #14  
Old 03-05-2008, 11:25 PM
bobg3723 bobg3723 is offline
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Quote:
Originally Posted by the1much View Post
are those sides as high and flat as they look??
and why the biggie on fitting in a shipping container
I meant to say within "constraints" of a shipping container. Homeland Security wouldn't buy my excuse that I had seperation anxiety over my boat if I actually stowed aboard as it shipped. ;-)

Cheers,
Bob
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  #15  
Old 03-06-2008, 12:19 AM
bobg3723 bobg3723 is offline
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Quote:
Originally Posted by charmc View Post
Bob,

Congratulations on putting an idea up for input. Looks like the early feedback focuses on the very flat sides and bottom. I have to say that's my first impression also. Might be just esthetics; on the other hand I don't see that being anything other than a teeth rattler at any speed in a chop.

I do understand your concept, I think: a day sailer big enough for some short overnight trips, a few hundred miles max, and that can be disassembled and stored in a shipping container whenever you want to relocate to another base.

There is a good article on the relative merits of ndrua vs proa sailing characteristics here: http://www.multihull.de/down/ndrua-gb.pdf

I notice that the drawing of the ndrua in the article shows a much more tapered bottom on both the vaca and ama, with rocker and sharp ends. This is one reason for its claimed speed and manuverability. Real ndruas used a clamshell sail on a short inclined mast and shunted (swapped ends with the rudder and sail) rather than tacked.

It appears that you are diverging significantly from ndrua design. I don't have any idea how your changes will affect performance. Don't get upset, but I don't think you do, either. Maybe build a model and do extensive testing before commiting to the full scale one.
Hello Charmc,

I concure with you that a scale model test will need a proper assessment with established norms. And please feel free to put forth questions, comments and constructive criticisms.

I also read that PDF. It was an interesting read. Truth be told, my concept for a container shipable multihull has less to do about historical multihulls and more to do about cabin ergonomics, motoring efficiency, quick build properties, container constraints, and accessibility of container ports. The simple fact is that favorable winds are not always there when we want. And a minimalist camp bout geared for the tropics is where I take my que. I did not include the pics yet, but for longer term anchorage, a tent and awning would be set up between hulls, which I know would be more favourable than down below. It still all exists as a DXF file for now. I'll post more as they develop and look forward to your questions.

Cheers,
Bob
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