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On DeckMovable Ballast

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CurlyBen View Drop Down
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Post Options Post Options   Quote CurlyBen Quote  Post ReplyReply Direct Link To This Post Posted: 27 Oct 05 at 7:06pm
I hadn't thought of it in terms of space, but the pod would have to displace the same amount of water as the lead weighed (or close to it) so I don't think it would take up any more room. Also you wouldn't need to make the daggerboard ballasted, if you designed it so that in the event of capsize you could pivot the arm down and pumped water into it then it would self right that way. Also the pump needn't pump from one pod to the other, you could have a one way dump valve to release the water from one pod whilst simulteanously pumping water into the other. Probably simpler that way.. you could also put a hydroelectric generator in if you were feeling fancy, propelled by the outgoing water. I still think weight is going to be a majot issue, in terms of batteries if nothing else..
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Post Options Post Options   Quote jpbuzz591 Quote  Post ReplyReply Direct Link To This Post Posted: 27 Oct 05 at 7:10pm

But if it is going to be "skiff style" surely having to dump and pump up water will increase the drag by the hull and will compramise speed, or am i just plain wrong here?

 

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Post Options Post Options   Quote Doug Lord Quote  Post ReplyReply Direct Link To This Post Posted: 27 Oct 05 at 7:23pm
At this point I think moving lead from side to side would require less power and most importantly less time. But I'm going to think about the water idea a lot more-it has some terrific advantages.
The water would probably work better on a laterally fixed wing but you couldn't count on it for a self righting system w/o a whole lot of complication as best as I can tell now.Also, since the design conception of the dynamic positioning of the pods(where they are when sailing) requires the wing to be curved you would definitely have to pump water from side to side or dump one side and pump from the center to the other pod.My gut feeling is that moving the lead will be simpler though I'm not positive about it.
Since this thing needs manual backup to any electric system the lead seems a lot easier to move by hand at good speed as compared to moving 200 pounds of water by hand.In fact a bicycle or hand crank lead moving system would be as fast as the electric version of the same system-water would be slow by hand-I think.
But, again, I'm going to look at it a lot closer and see what comes up....

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CurlyBen View Drop Down
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Post Options Post Options   Quote CurlyBen Quote  Post ReplyReply Direct Link To This Post Posted: 27 Oct 05 at 8:49pm
Here's an idea - as you're going to be filling the same volume everytime rather than trying to pump water exactly, why not use something along the lines of a piston - i.e. the piston retracts and so forces water in by vacuum, rather than having to pump it in. Could conceivably be done by hydraulics (avoiding electrics at all), probably easier, quicker, and more accurate to control, should require less effort. Work done is going to be the same to shift 200lbs of lead as it is to shift the same of water, provided the efficiency is the same, which is the harder bit. As for self righting, I may be wrong but I think the big racing tris (as in the 60 odd foot ones!) use a system to pump water to the top hull to right when they capsize.
JP - dumping water won't add drag as soon as the water has left contact with the boat, as it can't apply any force to the boat. The pickup system could, and as water is added the hull will ride lower in the water (maybe hydrofoils will be needed? this things sounding complex!) but as this is only going to happen when you're overpowered it's probably not going to be too big an issue.
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Post Options Post Options   Quote jpbuzz591 Quote  Post ReplyReply Direct Link To This Post Posted: 27 Oct 05 at 8:58pm

yeah suppose ben, personally i'm with most of the guys on the forum and think that maybe doug you are trying to bite off more than you can chew and like isis would like to see some action rather than just talk about it

 

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Post Options Post Options   Quote 49erGBR735HSC Quote  Post ReplyReply Direct Link To This Post Posted: 27 Oct 05 at 9:17pm
I hope this project works for you Doug but there are a lot of contradicting criterias in your design. For a boat to be fast, it has to be light and dynamic as stated by a few people before. Looking at your RC designs, the equipment you are using on the deck is going to create a lot of drag. Most High performance skiffs are kept as simple as possible to allow for crews to concentrate on sailing the boat as quickly as possible. Reaction times have to be quick too and I don't think its the best idea relying on mechanical equipment to enable a boat to sail effectively and the more complicated that it is, the more prone it will be to failure. If the boat has weight balancing it in a width respective, what sort of method will be implied to balance the boat in a longitudal direction? All high performance boats need continuous adjustments in fore and aft trim to be sailed effectively, if we didn't concentrate on trim on our boat, we'd be stuffed. Using a skiff design with low buoyancy at the front might not be the best option......
Dennis Watson 49er GBR735
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Post Options Post Options   Quote CurlyBen Quote  Post ReplyReply Direct Link To This Post Posted: 27 Oct 05 at 10:15pm
I think there's still plenty of problems - the ability to react quickly's still going to be hard, and I had a few other points I can't remember now - but I think that water ballast is more feasible than fixed weight ballast. I think it could be quite interesting, but I'm not sure it's really going to work on a small boat. 20 or 30ft and with 3 or 4 crew and it might be very interesting...
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Post Options Post Options   Quote Doug Lord Quote  Post ReplyReply Direct Link To This Post Posted: 27 Oct 05 at 11:08pm
There are many modern high performance boats that require mechanical systems to allow them to work properly. I can't see any reason why sliding ballast horizontally wouldn't work assuming it was designed to be a reliable system. And the mechanics-either electrically or human powered are extremely simple-don't see any problem there at all. It's been done on models; Bethwaite's planning on doing it on a large ocean racer. Even if you did it electrically it would require much less power to move a given amount of weight horizontlly as opposed to moving a short lever attached to a long canting keel. Not only that but moving the weight quickly side to side could be done manually with no electric power at all.
I sure don't see the drag you were referring to especially on a 17-18 footer where the weight is enclosed in an aerodynamically shaped wing-it would be far less than a crew on trapeze!
As to moving the weight fore and aft: I think I mentioned earlier that the wing and crew seat would be able to move fore an aft to some degree and the boat would most definitely use a rudder t-foil.In fact experimenting with a retractable forward lifting hydrofoil for partial lift w/o an altitude control system is part of the agenda down the line with this boat.Pitch control should be precise and more than adequate just with the t-foil rudder and fore and aft weight movement.
   I mentioned earlier about the speed the weight could move-either manually or electrically and it would be faster than a crew.
I just got thru doing some research on the water idea brought up earlier and water would simply not be able to be moved fast enough.It would require a 480 gallon per minute pump(!) to have enough speed to move the water as quickly as lead can be moved and you would be just plain out of luck if you lost electrical power because there is no hand pump that could do the job remotely quick enough.
-------------------
The question I'm most interested in exploring/solving is whether or not the fixed wing system(side to side-same as Bethwaite/Langman) would be
superior to the original idea where the wing itself along with the ballast moved as well.Like an IC sliding seat. The original rc test moved both the rack and the weight so that there was nothing to leeward at maximum RM. The Bethwaite/ Langman systems are fixed racks with buoyancy pods. The fixed version would seem to be safer from a capsize perspective (for a disabled sailor) but presents a problem in a pitchpole in that it would not recover w/o the active effort of the crew . So either version requires a ballasted daggerboard for the ultimate in safety which would be required if sailed by a disabled crew. And there is no other boat currently being built anywhere that I know of that would offer the combination of self righting safety and high power to carry sail as is represented by this boat(at least in this size range that the crew sits down inside).Not even the new Bethwaite LAS(Lead Assisted Skiff) offers the power to weght ratio this boat potentialy does combined with a selfrighting capability.
   I apprecate everybody's comments and thoughts on the concept; it is a work in progress and I sure don't have all the answers yet but I'm working on it. Please take the time to look seriously at the ideas here and let me know what you think-especially as regards the two different wing systems...
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Post Options Post Options   Quote 49erGBR735HSC Quote  Post ReplyReply Direct Link To This Post Posted: 28 Oct 05 at 6:24pm

I think keeping the boat as simple as possible is the best idea. Have a look at modern day skiffs and see how simple the deck layouts are, for example the 49er, the new rules 18s (Murray design), 29er, Musto Performance Skiff, etc. I don't think any heavy boat can be described as a true skiff. My personal opinion is that the balasted boats are going to be an equivalent to small sport-boats, which is not a bad thing. The foils idea seems good, but a lot of development on the foils alone will need to be carried out. Is there no way of designing a skiff which relies on an active crew but can have a fixed position for the helm, maybe a happy compramise. There are a few disabled sailors who are sailing cats successfully just now, maybe this idea should be promoted more as well as developing balast reliant boats. 

Dennis Watson 49er GBR735
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Post Options Post Options   Quote Granite Quote  Post ReplyReply Direct Link To This Post Posted: 28 Oct 05 at 6:58pm
Why not just go for a multi hull Tonns of stability and speed with out the complexity and vast expence that that brings?


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