C of G issues again

[Paulrjordan]

Hi Gang..Eddy wrote me an email to which I sent the following reply
today. The problems he's encountering are well known to us so the
following might serve as not only a record to help him get his lovely
looking "Forceful" running well, but also for those who eventually
want to build sidewheelers that are as pleasing to operate IN THE
WATER as they are to see OUT of the water.

Eddy Matthews wrote:

>Hi Paul,

>Have you had any time to think about my problems with my model of
>Forceful?

Hi Eddy!

I most certainly have been thinking about your "Forceful" and been
itching to get a reply off to you. (Damn work keeps getting in the
way!)

>Apart from minor technical problems with my gear drive, the main area
>for concern is that the model is VERY sensitive to trim (side to
>side) and the slightest change in ballast will result in the model
>leaning to one side or the other... It is also VERY unstable in a
>turn and leans at an alarming degree.

I recognize this is EXACTLY what happened to my 1/64 "Director" when I
first acquired her...she was very unstable and nearly capsized at
every turn! (I suspect that's why the previous owner sold her to me
for $25.00!!) Wanna know something ?...ALMOST EVERY MODEL SIDEWHEELER
I'VE EVER SEEN SUFFERS (or used to) FROM THE SAME PROBLEM..and it's a
fundamental mistake that can be AVOIDED during construction...and most
times after!

If it makes you feel any better I spent two afternoons a couple of
weeks ago solving the same problem with a beautiful scratch built
model Bristol Sidewheel Tug here in Victoria. The problem, Eddy, is
that your Centre of Gravity (C Of G) is too high in the boat. A COG
which is too high creates too much "top hamper" or the tendency for
the vessel to roll outward in a turn. Simply..she's unstable! You'd
think that, because of the "extra beam" created by the wheels of a
sidewheeler, they should be more stable...right? WRONG! This is ONLY
an illusion as the wheels have no flotation whatsoever and only serve
to extend the outboard weight and the rolling moment of the
hull like a lateral teeter-totter (a see-saw in England!).

The rule for C of G is the higher it is the less stable the boat..the
lower it is the more stable the boat becomes. Mind you, in many
conventional model boats a C of G which is too LOW creates an
unrealistic "stiffness" which prevents it responding to the effect of
waves as a real ship would. In a model sidewheeler you cannot have TOO
much stiffness... the exaggerated outboard weight of the wheels make
it absolutely essential to bring the COG to the lowest possible point
in the model.

Remember that YOUR beautiful self feathering paddle wheels are quite
heavy and will only serve to accentuate any instability issues by
extending weight OUTboard (the see-saw!). You HAVE to compensate for
this. I eventually reconstructed my paddlewheels from styrene to
reduce outboard weight...but I am not suggesting for a moment you do
the same. (I'd kill for a nice set of self feathering brass wheels
!!!)

MOTORS, DRIVE TRAIN and BATTERY(IES) - relocate them so they are as
far DOWN in the hull as possible. Because my "Director" had been
scratch built, I literally cut the cross ribs in the battery and
engine area down to their bare minimum to allow everything to be
mounted as close to the "floor" of the hull as possible. Your twin
540 motors are NOT LIGHT and if you have them even slightly too high
they will substantially heighten the COG. Your styrene hull should
be pretty clear of cross ribs and you should be able to make an engine
mount VERY LOW down.

In my opinion the 540's are a little big (and too heavy) and you
should consider smaller and lighter low revving motors with STYRENE
(as opposed to brass) gearing to the paddle shafts. DO NOT LISTEN TO
WHAT ANY OF THE MANUFACTURERS RECOMMEND FOR MOTORS AND GEARBOXES IN
SIDEWHEELERS..THEY ARE GENERALLY DEAD WRONG and recommend motors that
are generally FAR TOO HEAVY and more powerful than they need to be. It
actually takes a quite small motor to adequately turn sidewheels at
the desired 180 top speed RPM. At this point you might consider a
pulley drive, but (except on the motor shaft) again avoid the use of
metal pulleys/cogs and drive chains in your power transmission to the
paddle shafts.

The drive on my "Director" was originally through a couple of heavy
brass gears mounted at the paddle axis..and THIS contributed
significantly to the instability by once again lifting the COG. I
couldn't believe originally this would make such a difference until I
replaced the drive train with a rubber belt drive and STYRENE pulleys
(the beautiful metal ones which I had made for the paddle axles were
STILL too heavy and made the boat roll!!!!). I'll try to get some
pictures of my own belt drive system to give you an idea of how I
tackled this problem.

SUPERSTRUCTURE...KEEP THINKING COG in everything you do with the boat.
The biggest problem for my buddy with the Bristol Sidepaddler was he
built this Prizewinning model TOO well and made the superstructure and
additional superdetailing far too heavy (2 turned brass smoke stacks
6" long!!!!). You must be conscious of this "above deck" weight issue
and lighten ANYTHING ABOVE THE PADDLE SHAFT AXIS. IF, after you have
mounted all your electro/mechanical equipment and superstructure, the
boat still needs ballast to get her to float at her correct waterline
(remember the outboard edge of "Director" sponsons are are barely over
18" above the water)place your ballast as LOW and as close to the
for/aft keel line as possible. We are ALSO trying to keep WEIGHT
INBOARD to compensate for the outboard weight of the wheels.

If you find that before ballasting, the boat (with its superstructure
on) sits too low in the water (i.e sponsons to close to water level)
then obviously your overall weight is too much and you need to reduce
the size and weight of electro/mechanical equipment and anything else
which can be lightened/removed.

Conclusion
I am confident if you look around your "Forceful" you will find all
kinds of COG issues taking place and if you embrace this philosophy
mercilessly, you will eventually end up with a lovely "stiff"
sidepaddler which is stable and an absolute delight to handle. Mine
took hours and hours of experimentation learning the "hard way" and
this is why I started PADDLEDUCKS.. to in some way communicate and
help other modelers prevent these problems DURING the construction
stage rather than after the boat has been launched!

If you have ANY more concerns, please don't hesitate to contact me
immediately..as I'VE BIN THERE, buddy! It's going to take a few trips
down to the pond..not to mention filling the bath up a few times
during the night..but it will be worth it in the end.

>I'm pretty sure these two are linked and if I cure one, the other
>will also be cured.

Not necessarily so....treat every problem as a separate issue.

>Since you have your own "Director" class model and seem to have been
>there and bought the tee-shirt, I'm eagerly awaiting your
>suggestions. BTW, please don't think I'm hassling you.... If you're
>too busy right now to get involved in a long email conversation,
>please just say so - I won't take offence!.

>Regards
>Eddy (Webmaster of Darlington & District Model Boat Club)
>http://homepage.ntlworld.com/edward.matthews/ddmbc.htm

Eddy...no prob at all..and sorry it took a few days to reply..I am
already anticipating the excitement when you finally post a message in
"Paddleducks" that your "Forceful" is running as good as she
looks..and she WILL!

PJ

[Edward Matthews]

Many thanks for the detailed replies PJ.... You've basically
confirmed exactly what I was thinking.

This is going to take a while to sort out.... Now why didn't I ask
BEFORE I started building? :-( Aren't things always easy with the
benefit of hindsight?

After taking a really good look at everything, my plan of action is
as follows.

1. Replace the 540 motors and gear drive system with some lovely
little Buhler motors I've managed to find from a company in the UK
called "Motors Direct". These motors (although 12volt) have built in
gearboxes which give a 110rpm output and weigh only a fraction of my
current setup. "Motors Direct" also do a lovely little 1:1 belt drive
system to transfer the power to the paddle shafts. Beleive it or not,
these motors only consume 160 Mah under load!! And they have so much
torque that it's impossible to stall them no matter how hard I tried!

2. Replace the current gel cells with nicads.

3. Rebuild the main superstructure using lighter materials. This is
an area which is WAY TOO HEAVY! And is probably THE major cause of
the models instability.

4. the internal mods (motors, drive system, and nicads) will allow me
MUCH more room inside the hull so I can get everything positioned as
low as possible - The current setup is VERY tight and some components
are not ideally positioned.

That's the basic plan anway.... Although not necessarily in the order
I've listed them above - rebuilding the superstructure will probably
be tackled first as it is undoubtably the area causing the most
problems.

Comments are welcomed...

Regards
Eddy

[Paulrjordan]

Hi again, Eddy:

These Buhler motors sound exciting...110 rpm is about as slow as I'd
go..but they are certainly little motors which sound like they mean
business and draw very little current. I wonder if they have a 6v
version? I couldn't find a suitable one on their website at:

http://www.buehlermotor.de/cgi-bin/sr.exe?standardmotorstartus

<SNIP>

> That's the basic plan anway.... Although not necessarily in the
> order I've listed them above - rebuilding the superstructure will
> probably be tackled first as it is undoubtably the area causing the
> most problems.
>
Actually you might consider leaving this to the end..get the motors
and drive train all sorted out and with the new weight distribution
and layout you MIGHT be able to run some additional ballast (or
preferably more battery power) down low in the boat and inboard. See
how much you can "stiffen up" the hamper before modifying the
superstructure.

Consider adding or enlarging a couple of (metal) bilge keels...I took
mine off and forgot to put them back...the boat still hasn't got em
back on but she's already pretty stiff without em...although they
won't do any harm once they go back on. (The original "Directors" had
bilge keels!!! hahahaha.. I bloody wonder WHYYYY!)

Also try lightening the paddleboxes first..I mean substituting the ply
for styrene sheet. It's the outboard weight that's the real killer
here. My heart bleeds when I think of the gorgeous work you've done
on the superstructure and I'd be loath to take the knife to it before
I'd exhausted EVERY other possibility.

Search the decks, Eddy and see if there's anything made of brass/metal
which could be made of wood...anything invisible you can discard or
drill holes through. The funnels..are they solid or hollow..THAT can
make quite a diff! ..but please don't start chopping anything up YET.

Keep us posted as and when you get more thoughts on this. We'll be
listening.

PJ

[Edward Matthews]

Sorry no pics of the inside at the moment... I'm the worlds worst
photographer and I rely on other people to do that side of things for
me :-) I could probably do a quick sketch of the layout if necessary,
but it would only give a vague idea of how I've done things. The
540's only pull 1 Amp each at full load (measured with the paddles in
the water) on 12 volts, so 2 Amps total current.

There isn't any ballast, the model sits at the correct waterline with
the batteries only.... Thats two 6 volt 4.5Ah batteries wired in
series to give 12 volts..... One reason why I thought of switching
from my geared drive to a belt setup... The belt drive would produce
more RPM and should allow me to use only a 6 volt supply - Which
*should* give me about the same RPM as the current 12 volt setup -
Then I'd have some ballast to play around with.

Constructive comments are welcome....