National Ship Design Competition. Need Help

[Submarine Tom]

Then you probably wont be able to help me, but thanks for replying.

-Tom

[PAR]

Tom if you offer him lines, he loses the whole point of the exercise, not to mention the race with the design you've posted.

Some light reading and simple math will get him in the ball park, but nurse maiding him through the problem solving aspect, seems self defeating to say the least.

Tad has answered the basic questions of hull form and stability. Assuming the OP has sufficient math skills to figure out about how much boat it will take to support his 6.6 pounds of cargo, building materials and propulsion, they can extrapolate a reasonable set of lines from what's commonly known. A displacement form is the obvious choice, likely considering the supplied propulsion unit will pretty much suck. So, the usual applies, do a weight study and work with what you have (power) for a hull shape.

[rwatson]

Originally Posted by HaveANiceDay

To rwatson:
Thank you for your reply. I will think about what you said. That part with increasing the electrical output, could you explain it little bit more detailed?

Hull design aside - one of the big issues is power versus weight.

With electrical motors, more power = more battery weight.

Since the course is so short, as a long time fan of electric slot cars, battery longevity and speed will be a huge part of the success formulae.

The first question is - does the mandatory ballast have to be steel ?

If not steel, then far better to make it all as batteries ( probably rechargeable) ,so you have an enormous power source. I would then run say 4 electric motors, at a rate that will last the 100 metres, flat out.

If it has to be steel, and you have to have batteries as extra - you could build the steel sheet with a matching copper or zinc sheet, held in a plastic or epoxy container, separated by electrolytic paste - in effect creating a reserve of power to achieve the same thing. It would not be as efficient as lead batteries, but maybe it would give you an 'edge'.

Check out some options on the internet about how to incorporate steel in a battery. It doesnt have to be long lived.

[daiquiri]

Originally Posted by Submarine Tom

Hi,
I'm trying to help this kid out.
Is this a reasonable hull design for 1-2 m/s?

Regarding the speed, this is imho a case which can be simulated with a reasonably good accuracy with Michlet. Contact Leo Lazauskas for help, or post a more detailed drawing (beam and draft numbers at various significant longitudinal stations) so someone can perform a run for you.

Regarding the maneuverability, I believe it will be extremely sluggish. The underwater body will oppose a big resistance to turning moments and the rudder appears to be way to small to have any authority worth talking about. You need to define maneuverability goals first, imho, and then design the rudder accordingly.

Seeing all that draft, I'd suggest you to not leave the helm in Capt. Schettino's hands.

Cheers

[tom28571]

Originally Posted by Submarine Tom

How would this 90 cm, scale container ship perform in a speed, stability and maneuverability contest?

20 cm draft

12 cm beam (7 cm at water line)

2 - 3 knot max

7 kg displacement

CofG & CofB as below.

NACA modified wing as below (next post)

-Tom

I don't know but I do have a 122cm LOA X 11cm draft model that is very similar ready for towing tests as soon as a tow boat is ready. One major problem with this concept as a container or bulk carrier is that it will not be stable unless well loaded and this will pose a problem at the dock. Loading and offloading will have to be coordinated to take this into account.

[jehardiman]

Originally Posted by Submarine Tom

How would this 90 cm, scale container ship perform in a speed, stability and maneuverability contest?

I think poorly. Too much wetted surface for good speed. The stability might work. but remember that a vessel rolls about the CG, so you will be dipping the sponsons all the time which will degrade both speed and maneuverability. I think maneuerability would be horrible, not only is the rudder too small compared to the projected area as daiquiri pointed out, but it is also too low compared to the CG. Rudder force will cause a large heeling moment, which will again cause dipping of the sponsons. IMHO, if you want to go with this design, you should raise the prop shaft and rudder area.

[hoytedow]

Originally Posted by Mr Efficiency

I'm not sure I know what I'm looking at.

With the light directly overhead the photos have too much glare, making it hard to see the lines. Try oblique lighting new photos.

[Submarine Tom]

Thank you all. I agree entirely with all your comments.

Sorry about the picture quality, I've tried many angles, this is the best I could do.

He went with a conventional, FreeShip design. I was hoping to evolve some ideas into a winning hull but we are out of time. He cut the sections today.

The rudder, prop, motor, battery, R/C gear is all standard for the whole nation as is the 3 kg above-water-line payload and 3 kg ballast plate.

He's got loads of thrust from the video I've seen so hull speed will be hull speed, He'll get points in maneuverability, stability, creativity, and detailing/finish.

Cheers, thanks again for your input.

-Tom

[Leo Lazauskas]

Originally Posted by rwatson

Hull design aside - one of the big issues is power versus weight.

With electrical motors, more power = more battery weight.

Since the course is so short, as a long time fan of electric slot cars, battery longevity and speed will be a huge part of the success formulae.

The first question is - does the mandatory ballast have to be steel ?

If not steel, then far better to make it all as batteries ( probably rechargeable) ,so you have an enormous power source. I would then run say 4 electric motors, at a rate that will last the 100 metres, flat out.

That's a very sensible strategy that worked before in a race for (larger)
electric/solar boats in Canberra a few years ago.
One winning entrant (an Australian ex-naval commnader) modified
an existing long narrow dinghy by changing from a cut-off transom stern
to a canoe stern, and using the maximum allowable weight in lead-acid batteries
placed low down.

[Submarine Tom]

So, the kid did okay.

I'll let him tell you all about it but here are some pictures from the event last week.

http://www.youtube.com/watch?v=E_vfz...78q6QdQsIeb0=*
and
http://www.youtube.com/watch?v=WfNEG...ture=youtu.be*

-Tom

P.S. The faster boat works out to about 2.4 knots over the 50 m course shown.

And, they ended up over 8 kg displacement.