Rc modelboat scale speed

Post by **JIM BAUMANN** » Fri Sep 22, 2006 5:18 pm

hi guys

as a confirmed static modelship builder, a question has always vexed me...

Much as modelaeroplane builders have to make compromises with their flying models due to te 1:1 scale air,

Railway modellers have their pure steam railway laout driven by electricety-minus smoke et al,---operational modelshipbuilders have always to contend with the fact that the water is simply to 'Big'...!

surfing thru various parts of the net today I came across an example of excessive ' non-scale' speed...

http://www.youtube.com/watch?v=qeSbzx3G ... ed&search=

Presumably scale speed is usually much slower than one would think...?
certainly in Railway modelling most trains are operated at too high a speed for scale , but this Rc waterborne DD is surely outrageous...?

although quite conservative compared to ths 120 mph plus model boat...

http://www.youtube.com/watch?v=O8oRdXMl ... ed&search=

Curious and interested

JIM B

Post by **Timmy C** » Fri Sep 22, 2006 5:44 pm

Well, one thing good about those old Lindberg kits...you can make them go fast and if they tip over while sailing, you won't lose much

It was really low in the water though.

And did they attach an electric R/C plane motor onto that second boat? Dam...

ARH · Post by **ARH** » Fri Sep 22, 2006 5:49 pm

Well Jim, I hate to see this type of sailing, the guys should have just bought a speed boat, scale speed for a 1/24th scale model is about 4 mile per hour, about walking pace, I usually can tell by the wake pattern along the hull if it is going to fast.

How many DD do you see with a rooster tail at there stern,

Post by **Dave Wooley** » Sat Sep 23, 2006 12:51 pm

I was once involved with high speed models and attened a number of world championship events way back in the 1960s and 70s and even then I could get speeds of 50mph with few problems and keep the boat on the water and they were electric powered. For those with long memories and some vintage Model Boats magazines they will certainly know what I mean. But for scale model performace the DD in the video is way out. I agree with Ron walking pace is about right. In fact the slower the better. For scale models of say DD CGs BBs and CVs then if it is to look realistic and NOT toy like then put the brakes on the slower the better.
Dave Wooley

seaphoto · Post by **seaphoto** » Sun Sep 24, 2006 12:00 pm

When we run over here, we try and achieve a compromise between true scale speed and running too fast. When ;the wakes look right we are happy; for a DD that seems to be just a bit faster than walking pace, or at least mine LOL.

Kurt

ARH · Post by **ARH** » Sun Sep 24, 2006 4:43 pm

seaphoto wrote:When we run over here, we try and achieve a compromise between true scale speed and running too fast. When ;the wakes look right we are happy; for a DD that seems to be just a bit faster than walking pace, or at least mine LOL.

Kurt

But Kurt, We walk faster than you.

PATMAT · Post by **PATMAT** » Mon Sep 25, 2006 7:15 pm

I've seen plenty of discussion on this one! But-
a) It's not difficult at all to over-power a scale model ship, and the smaller and skinnier the model (like a Lindy Fletcher), the easier.
b) But due to the physics of water (thank you Messrs. Reynolds & Froude), things just don't scale down in line with the model scale. Result- You need to run a model at faster than "scale" speed to obtain realistic bow waves and/or planing.

Sometimes I see guys cruising around at something like true scale speed (I suppose)... just like watching a real freighter, you wonder if it's even moving!

Pat Matthews

Post by **Dave Wooley** » Tue Sep 26, 2006 4:00 am

[quote="PATMAT"]I've seen plenty of discussion on this one! But-
a) It's not difficult at all to over-power a scale model ship, and the smaller and skinnier the model (like a Lindy Fletcher), the easier.
b) But due to the physics of water (thank you Messrs. Reynolds & Froude), things just don't scale down in line with the model scale. Result- You need to run a model at faster than "scale" speed to obtain realistic bow waves and/or planing.

Sometimes I see guys cruising around at something like true scale speed (I suppose)... just like watching a real freighter, you wonder if it's even moving!

Hi Patmat Yes you are correct in what you say but is it the bow wave effect or the over all appearance, ie- very slow speed that determines how realistic a warship/ship should appear in model form that's the question. I've seen many skippers criusing there models ships with the intention going for a water speed record.
Dave Wooley

Andy G · Post by **Andy G** » Tue Oct 03, 2006 10:35 am

PATMAT wrote: b) But due to the physics of water (thank you Messrs. Reynolds & Froude), things just don't scale down in line with the model scale.

No...I disagree. There is the old Froude formula to produce realistic wakes: divide the real speed by the square root of the scale. Works a treat.

Try this handy gadget, if you've got the flash/shockwave player installed on your browser.

Andy

Post by **Dave Wooley** » Wed Oct 04, 2006 5:45 am

Andy G wrote:
PATMAT wrote: b) But due to the physics of water (thank you Messrs. Reynolds & Froude), things just don't scale down in line with the model scale.
No...I disagree. There is the old Froude formula to produce realistic wakes: divide the real speed by the square root of the scale. Works a treat.

Andy how can this work in practice? . In order to produce the equivalent wake pattern you have to be travelling greater than the scale speed. Dave Wooley

Andy G · Post by **Andy G** » Wed Oct 04, 2006 6:14 am

Dave Wooley wrote: Andy how can this work in practice? . In order to produce the equivalent wake pattern you have to be travelling greater than the scale speed. Dave Wooley

That's correct - but I think we have a difference in terminology. I would refer to the Froude speed as the scale speed for a particular model. Scaling the speed - simply dividing the original speed by the scale factor - is never going to produce a realistic wake.

If anyone's unsure, here's an example:

The full-size Dreadnought could do 21kts, which means that travelling a ship's length took some 14.8 seconds. On my model at 1/72nd scale if I were to simply scale the speed, and take this amount of time to move the model seven-and-a-bit feet, I'd be driving the model at about half a foot per second. Hardly any wake.

Since water doesn't scale with our models (viscosity, gravity, etc. remain full size) Froude realised that wake patterns could be recreated by moving any model at the scale speed - equal to the real speed divided by the square root of the scaling factor.

The scale speed calculator works on this principle. If I put in 21kts and 1/72nd scale, for the Dreadnought, I get Ron's "walking speed" of just under 3mph - about four feet per second - which produces a realistic wake. Or at least it will do, once I get to that stage!

Andy

ARH · Post by **ARH** » Wed Oct 04, 2006 8:57 am

Yes it does work, my new DD works out at 4 mph, the one thing with models you can get the wave patern , but never the bow patern, you know that throthy water in front of the ship, Iron Duke just cuts though it like a knife,

Post by **Dave Wooley** » Wed Oct 04, 2006 9:27 am

The simple question is why do modellers insist on increasing speed to produce a wave patern /wake to mirror that of the full size ship. The model then becomes unrealistic and toy like.
Dave Wooley

Andy G · Post by **Andy G** » Wed Oct 04, 2006 9:53 am

Dave Wooley wrote:The simple question is why do modellers insist on increasing speed to produce a wave patern /wake to mirror that of the full size ship. The model then becomes unrealistic and toy like.
Dave Wooley

I suppose that's partly what drives us to build big. The difference between the scale speed and the scaled speed is (once again) the square root of the scale factor. The bigger the model (smaller the scale factor) the less toy-like things become.

The only other option is to slow reality down. Adjust viscosity and surface tension. Change gravity...

Hmmm...no wonder CGI took over the role that model-making used to play in the cinema.

Andy

Post by **Dave Wooley** » Wed Oct 04, 2006 11:27 am

Andy G I think you made an interesting comparison. When referring to the cinema and the skill of the cinematograph technicians re-working the film . Speedup film/ then slow it down, touch up film, net effect the model takes on a more life like appearance, re- the film Sink the Bismarck is a good example. Although scale i.e. larger the better is a major contributing factor, in reproducing some of the effects found full size. Although as Ron said the true effect is almost impossible to reproduce on our type of models only the pattern and waveform.
Dave Wooley