Tension circle house
June 8, 2008 at 12:23 pm #586
I have put a proposal onto the wiki called “Tension circle house”. In some ways it is the opposite of the spar buoy idea. Instead of going skinny and deep this goes wide and shallow.June 8, 2008 at 2:19 pm #3125
Wayne from model scaling thread:
>In large waves, the people in the house are really going to get shaken around a lot. We want to minimize interaction with big waves.
We want to minimize discomfort while still getting affordability and safety. Minimizing interaction with waves is one approach, taken by the spar buoy design.
When I look at the big wave videos I think the big problem is when the motion of the boat is out of phase with the motion of the waves. My design intent is to never be out of phase with the big waves. My motion should be like a raft that is following the waves and not like a boat which can have big motions out of phase with the waves. In theory if you put a glass of water on a raft, the water inside will stay almost still relative to the glass even though really the raft, glass, and water are tipping. The sideways accelerations from the wave is just right to balance the angle of tilt. The surface of the wave is sort of “level” as measured by the water in the glass. I don’t think my design will feel like it is shaking too bad. Staying in phase with the waves, and the large width, should make it more comfortable than any of the boats in the big wave videos.
Now spending the same money on a spar buoy might give you more comfort during the storm. If the spar is affordable there may not be much need for this design. But if a spar turns out to be too exensive and this is affordable, then people might be willing to have a little more discomfort during infrequent storms to save money.June 8, 2008 at 11:19 pm #3127
I am toying with the idea of making a 50 foot diameter version using PVC pipe to make the outer flotation and then using a kite to pull me from Anguilla to Bermuda (downwind). Would sort of demonstrate controlled floating in the Sargasso Sea. Not very serious yet. Would want to test it for at least a month anchored in the ocean here. Want two people, a sea kayak tied to me at all times, lifejacket, communications, etc. Probably just dreaming for now, but I think it could work for not too much money. Could trash it after we got there and fly back. Another advantage of this design is it should be easier to move through the water than a spar buoy.
I love my peddle powered kayak by the way:
With peddle power I can make good speed even in big waves and wind. Would want a big two user version (they did not have these when I bought mine).
I suppose a regular life raft would be better for sleeping, but with two people it might work. Shipping an inflatable back is probably easier too. Could be reporting my position with http://www.orbcomm.com/ and if I ever stopped reporting, or sent a message saying, “help”, then a boat at the ready in either Anguilla and/or Bermuda would come and rescue me (standby fee and rescue fee negotiated ahead of time).
About 12 years ago I used a kite to pull me about 10 miles from another island directly to the harbor I was using in Anguilla on a tiny boat I made:
Maybe in a few years one of my boys will think going to Bermuda on our own creation sounds like fun.June 9, 2008 at 2:30 am #3133
Looking at http://en.wikipedia.org/wiki/Seakeeping . I think my design gets very high marks. Since my design is floating like a ship these should apply:
- Size : A larger ship will generally have lower motions than a smaller one. This is due to the fact that the relative size of the waves is lower.
- Displacement : A heavier ship will generally have lower motions than a lighter one. Given that the wave energy is the same for each vessel and provides the exciting force, the one with the greater mass will have the lower accelerations.
- Stability: A stable ship will tend to follow the wave profile closer than a less stable one. This means that a more stable ship will generally have higher accelerations but lower amplitudes of motion.
- Freeboard : The greater a vessel’s freeboard the less likely it is to immerse the deck. Deck immersion is often a seakeeping criteria as it affects mission capability in a number of ships.
The Tension Circle House displacement will be ok for small ocean going vessels and size (width), stability, and freeboard should all be really good. So by metrics used to evaluate ships I think this design can do very well.June 9, 2008 at 4:19 am #3134
My intuition is the opposite of yours. The large moment arms on your design should cause it to be very sensitive to big waves, with large and annoying accelerations. But I can’t prove it. Until such a design is thrown in a wave tank and measured, my opinion has to be treated as a relatively uninformed opinion.June 9, 2008 at 9:03 am #3136
I hate to keep referencing something I read so long ago (perhaps 25 years ago), but I remember that the experience of Thor Heyerdahl’s team with the Kon-Tiki balsa raft was somewhat counter-intuitive to them as well. I have ordered a copy to re-read, but it will be a while before it gets to me. As I recall, they had some fairly experienced sailors, and were expecting the raft, a pure surface vessel with essentially zero draft, to ride very roughly, but the fact that it slid over the surface of the wave and almost never had to crash through one made it remarkably free from some of the problems they expected. Essentially, as mentioned elsewhere, it was always in phase with the wave. I believe that was somewhere in the realm of 50-60 feet in length (not sure on this point).
They were also able to tack surprisingly far into the wind, for a vessel with no keel. They had only vague drawings and descriptions of the keel boards, so they more or less randomly stuck some in between logs and lashed them in place. Only later did they realize that these keelboards were an active component to steering the vessel, and should be made to raise and lower.
Modern designs of keelboards could be made to help steer this circular design (or an oblong one, or a catamaran style) as well. Instead of just a balanced, symmetrical keelboard to make it “go straight”, you could have a series of keelboards on each side. Port side is a “wing” shape that creates the water version of an aircraft’s lift, thereby pulling you left. Starboard is oppoosite. Right down the middle you have a standard keelboard that is symmetrical.
Each keelboard can be raised or lowered via either electric motor (could then be computer controlled) or hand crank to desired depth down to the design limit of the length of the board. In various combinations, they provide varying degrees of vector change. The boards with active lift (port and starboard) also come with a slightly higher drag penalty, but for steering something so broad and potentially un-managable, that seems like a small penalty, this is not a racing sloop.
It would be much better than a rudder, either forward or aft, as the force is applied along the length of the vessel, and in terms or drag, it’s probably greater absolute drag but more efficient in terms of vector change/drag, since a rudder is just brute force deflection. I would think this arrangement of keelboards makes sense whether you are trying to sail or if you were power-driven on such an unwieldy type of vessel.June 9, 2008 at 1:48 pm #3144
If you are testing a model in a wave tank, and then with the same model change to waves 1/2 as high as before, does it mean:
a) Testing as if waves on the prototype (full scale version) were 1/2 the size
b) Testing as if the prototype was 2 times as big as before
c) Both (a) and (b)June 9, 2008 at 2:05 pm #3145
If you are using a kite to pull you, you can actually turn by changing where on your boat you put the pull. I have done this on http://cate.com/vince/boat I could hold the kite rope off to one side or the other and get more pull on that side, so it moved faster downwind, and I turned to the other side. This was easy for a small kite.
I have also done it with a larger “two string kite” were really it was one long rope that went through a pully on my boat. The kite then tries to pull that part of the boat forward. If you are heading mostly downwind and can get the kite like 75 degrees to the right or left of downwind, this can be enough steering to get where you want to go (no keel or rudder needed).
I have also done it with a daggerboard and rudder, so I could tack back and forth with the “2 string kite” and even go upwind. Back 12 years ago this shocked some people, but with kite skiing today this is less shocking.
If you wanted to do the first trick with a big kite you would have to have some mechanism, like the track for the rope holding down a mainsail even while you tack back and forth, that would let you move the point on your boat that the kit was pulling at.June 9, 2008 at 2:11 pm #3147
I find it hard to imagine taking to the open ocean without some form of reliable powered movement. I realize it was done for thousands of years, but it’s not a risk that really appeals to me.
I would want to have free moevement, not dependent upon winds being in the right quarter, and it seems like a multiple keelboard scenario as I described above might help with steering- what do you think? I’m looking for an evaluation of this idea, not alternatives…June 9, 2008 at 2:14 pm #3146
thebastidge, probably the steering effect came from drag. A primitive shape might create as much drag as lift. The modern catamaran sailing vessel is a highly evolved craft. Many still show a daggerboard or centerboard in both hulls. It’s more to please the public eye than for effectiveness. For a ship shaped craft, a rudder is probably the most highly developed steering mechanism. I captained a small swath a few years back without rudders. It needed them. It was extremely difficult to steer a straight course.
In general, power vessels don’t need boards, just rudders. For non shipshaped vessels, rudders probably don’t help. Vectorable thrust would be the solution.June 9, 2008 at 2:29 pm #3149
That’s really not a option at all. The existence of the field of Marine Archeology should be thought about by anyone heading to sea.
“keelboards” would only be effective on a sailpowered vessel. We’ve (meaning the sum total of human knowledge) pretty much figured out that you can’t sail a spar.
DP or thrusters with someone at the helm 24/7 will be required if it’s not moored. The nanny-states have gotten together (the IMO) and decided you can’t intentionally design and build a hazard to navigation.
A spar is probably the poorest choice for a DP vessel, because of it’s profile. The energy requirements would be immense.
Evaluating the idea- I don’t see it as applicable to the seastead. Boards are only effective on a sailing vessel and you can’t sail a spar.June 9, 2008 at 2:37 pm #3148
So my “Tension Circle House” or a “Spar Buoy” are designed for stability and not speed through the water. If they get 1 MPH they are probably doing well. If you really mostly just want to live on the ocean that is fine. Even for me going over 500 miles from Anguilla to Bermuda it would be less than a month.
However, the push on a daggerboard or rudder at 1 MPH is just not much unless they are very sizable. The amount of mass going past the rudder goes up linearly with the speed and the speed that you push the water to the side with goes up linearly as well, so your total sideways force from the rudder goes up with the square of the speed. So 2 MPH has 4 times the rudder authority, and 1/2 MPH has 1/4th of when at 1 MPH. A seastead moving at 1 MPH has 1/100th the rudder authority of a boat moving 10 MPH with the same sized rudder. That is part of why I kind of like the kite idea.
The trade winds go clockwise around the Atlantic with high dependability, at least near where I live. I imagine living in the Sargasso Sea and sort of slowly circling around this area. Don’t really expect to go into any land ports. Just need enough control that two different seasteads don’t bump into each other but can stay nearby if they want. With sea anchors and kites I think we can do that.
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