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Author Topic: Submersible Yacht  (Read 3625 times)

andrewh

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Submersible Yacht
« on: November 06, 2008, 10:17:26 AM »

It's obvious, really :}
Displacement boats are limited in speed by the water-line length
12 inch long yachts (footys) are limited more that bigger ones
So a fast racing Footy must not be a displacement boat :}

the options seem to be:
Planing - noone has yet seen a footy plane while sober
Hydrofoil - there is a secret project known as Pants/BLX which cannot be revealed (yet)
Submerged hull - see my new creation ZBF which took to the water early this morning

The pure concept:

The real boat:

And out of the water


As I said it's obvious really :}
The Hull is the black torpedo shape - it contains:
 the batteries, (4 x AA, laid down by the rules)
two servos
receiver
not much air
lead ballast

Access is by untaping the nose cap (at the moment)
The odd-shaped cream coloured bit I call the Buoyancy Compensator. or BC. 
It touches the surface at rest in calm conditions (like this morning's photo), but as the boat heels or dives it presents a greater volume to resist the leaning.
The sail is  a MacRig (but you knew that) and is footy legal  - less than 12 inches above the box.

Sailing trials next
Oh, yes, the servos drive rudder and sail sheet arms via carbon fibre concentric torque tubes - you can see the operating arms at the top.
Now for something a little less conventional
andrew
More details available if anyone is interested;it is perfectly reasonable to shake your head, pityingly :}

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kno3

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Re: Submersible Yacht
« Reply #1 on: November 06, 2008, 10:48:14 AM »

Is it faster than a normal footy?
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andrewh

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Re: Submersible Yacht
« Reply #2 on: November 06, 2008, 11:08:10 AM »

kno3
The honest answer is don't know, but it could be!

The hull is capable of being much faster than a conventional footy hull (not only does it not have the surface drag but it doesn't have a lead bulb on the end of the fin either)

The only minor design issues are driving a submarine with a sail, keeping the water out and the driver (me) trying to figure out where the hull is and which way it is  going,
but they laughed, at Christopher Columbus, too, when he invented steam :D
andrew
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kno3

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Re: Submersible Yacht
« Reply #3 on: November 06, 2008, 11:16:40 AM »

I don't know anything about hydrodynamics, but wouldn't the submerged hull also be subjected to drag like a floating hull? It has to move through water too, after all.
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andrewh

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Re: Submersible Yacht
« Reply #4 on: November 06, 2008, 11:47:47 AM »

I know a little about hydrodynamics, and the key point here is that the maximum speed of a displacement craft is proportional the the square root of the waterline length - and that's an absolute, and irrespective of how much power you stick into the hull or anything else!
(see tugs in general and Springer tugs in particular)

The limit comes about because of wave formation, and a recognised way to completely avoid the problem is to run submerged (see nuclear subs and olympic swimmers who would swim the whole length under water if permitted)

So yes, it still has drag, but MUCH less than a conventional hull (because it is really small)

The pic shows a Razor hull with ZBF hull plugs next to it
I am certain that if I were to motorise just the ZBF hull as a submarine it would have a good turn of speed
Do you sail? 
andrew
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dreadnought72

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Re: Submersible Yacht
« Reply #5 on: November 06, 2008, 12:21:43 PM »

Hmmmmm.

Is there a righting-moment? Yes there is.

Is there resistance to sideways movement? Yes there is.

So why does this seem insane? I'm not sure - but I can't help thinking that your buoyancy compensator will turn into a short-length hull when heeled - and thereby cause short-hull-length problems.

Andy
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Enjoying every minute sailing W9465 Mertensia

kno3

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Re: Submersible Yacht
« Reply #6 on: November 06, 2008, 10:52:02 PM »

...
Do you sail? 
andrew

No i don't sail, but would like to.

And thanks for explaining. I didn't realise that a hull behaves different if it is completely submerged. will have to think about this.
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Tester

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Re: Submersible Yacht
« Reply #7 on: November 07, 2008, 07:56:52 AM »

Does the Buoyancy Compensator float on the surface, if so doesn't that have a surface area to cause drag. Also as it heels to compensate it will increase volume as you say, won't that also increase drag.

Interesting concept can't wait to see the sailing video


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andrewh

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Re: Submersible Yacht
« Reply #8 on: November 13, 2008, 04:52:48 PM »



Buoyancy Compensator just kissing the surface - camera too

and afloat and sailing in gale force winds last weekend

So that's a successful build - Darcy is in the pics, but remember she is covered in chromatophores
andrew
now for a challenge - perhaps something radical.  How about you?
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andyn

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Re: Submersible Yacht
« Reply #9 on: November 13, 2008, 06:34:33 PM »

Blimey he's been fiddling again, this can't be good.... {-)

Not very scale is it? The eyebrow is up ;D

I would actually like to know more about these footys, one has taken my fancy in my quest to have far too many boats than I know what to do with....
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andrewh

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Re: Submersible Yacht
« Reply #10 on: November 14, 2008, 12:24:12 PM »

Its a poor thing, but mine own :}

Andy - the eyebrow can relax - no-one in their right mind would build a full size thing like this - that's as crazy as a steam-driven submarine or an aircraft carrier made of ice {-) {-)

WARNING
Footys are dangerously addictive and have a very high fun-to-length coefficient

(I have no idea what was amusing them; I'm sure my seams were straight)

The best resources spin off from:
  http://www.rcsailing.net/forum1/forumdisplay.php?f=61
Ignore liteFlight - he's a nutter
and
http://footy.rcsailing.net/
There are plans available for free download

happy to help but don't want to bury you
andrew


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AndyT

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Re: Submersible Yacht
« Reply #11 on: January 08, 2009, 02:57:21 PM »

I'm sure I was winning at the time when Trevor decided to perform the disappearing trick.

I never did find my 2.4Hz rubber duck antenna after that
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