Simon's Balsa Cat

[Simon.O.]

Here is my new Cat. I spent hours reading here and over at rrr to get all the design tips that I would need to build this one.
As with my other builds, I plot the key dimensions onto a large piece of card on my bench and then "fill in the gaps" with curves and lines to suit.
This is the result.

Length 25.5" 650mm
to rear of sponson bottom 23" 585mm
Width 8 3/8" 210mm
Tunnel 4""x 3/4" 100 x 20mm

600 brushed can
Tamiya car esc
8 x Cameliom Nimh
062 wire drive
Kyosho 42x1.4 prop....for testing
All my hardware

This may get a moderate turn 540 in for trials as soon as it arrives.

There is a rigger on the way

[Simon.O.]

A few more

[Eyekandyboats]

looks great. is there any engineering into the hull or did you just use your eye " it looks right" and build it ?
BTW. why do you have a kyosho prop on there?

[Simon.O.]

Its first run was a sucess, it did not sink or flip :thumbs:
Acceleration is instant and it it up flat on the plane in less than 6 feet.
It turns like its on rails with a slight lean in, wot and full rudder will spin it round so quick and sharp it will out perform my ob tunnel round a mark.
I will now play with strut adjustments with the shaft above and below the sponson line and with positve / negative thrust lines.
At the moment the Kyosho 42 x 1.4 prop seems to be the go but I have a few plastic octuras that I can try.
For a brushed Ni.. powered boat I am very happy.
I have a 23t 540 on the way that will be trialed in a couple of my hulls to see what happens.

[Simon.O.]

looks great. is there any engineering into the hull or did you just use your eye " it looks right" and build it ?
BTW. why do you have a kyosho prop on there?

It is pretty much there is the bow, there is the motor, there is the prop, that will do for a deadrise, sketch a basic outline.
Make more coffee, do a slightly better drawing.
Start building and see what happens.
the kyosho prop is one that i have had a lot of fun with on some of my other boats so it is here for trials.
I have a octura 534 purple plastic to have a spin with too.
I will have a 531 soon to try with the 23t 540 that is on its way.
Metal props are quite expensive here so I will stick to the plastics for now.

[G Doggett]

Well done Simon, it looks great.
Nothing beats the satisfaction of designing and building your own boat from scratch, particularly if it performs well.
Graham.

[crazzy maxx]

nice work
is that a wood out drive???

[Stealth Assassin]

Interesting freeboard. I like It... Wood rudder bracket, Midevil but, It works!

[Simon.O.]

That is a wooden spar for the strut and rudder / water pickup.
It was made that way to keep the whole varnished wood thing going.
I wanted to route the water pickup hidden but this way was easier.
The exit for the water is straight down into the tunnel. The main reason for this was that is the shortest route, it would look ugly coming out the side too.
Another reason is that a certain German once said that visable water outlets are for pesimists. Think about it !

Thanks for the comments guys !!

The rigger is coming soon.

[Simon.O.]

Last night I rebuilt two old Tamiya motors, anyone remember the Technigold and Technipower. These were the 21t speed demons from the '80's.
Well the TG lastet about 2 mins on the tunnel with 8 cells before fatal failiure.
The Technipower was sent into this hull with full water cooling.
In go 8 warm Nimh 4000's and tape the hatch down.
Roll a fag, poke the boat in the lake and do a control check.
Take a deep breath and go wot !!
That near cost me a new set of skiddies.
No graceful take off here.
It went near vertical then straight onto the plane, and I mean straight onto, no transition at all.
This thing screams while spinning a octura 534 with the shaft above the sponson bottom line.
Wot + full rudder turns are now out of the question.
It runns about 15% wet when it is actually on the water. in a straight line it sits nose slightly high and with a fast skip almost like a chatter.

I am glad that my tunnel design packs just the right amount of air in there.
It will be interesting with a bow on breeze because I believe that this will blow over.
I have seen dozens of vids of your guys BL lipoed boats and alway felt second best, well now I have something that really opens MY eyes and it is brushed on Ni cells to boot.
I have another can on the way and some smaller props.
Back in a few days with more results.

[Simon.O.]

o.k back to the Cat.
I have been developing and tuning this hull along with the Hydro.
I have found some interesting handling characteristics that have arisen since I have given it more power.
I am swapping between a 23t 540 and a Graupner 600 bb sp with a variety of props.
At the moment my favoured configuration is the 600 with a 438 prop.
It is a little skippy at speed so I am about to play with strut depth to see if I can calm it down a little with minimal loss of speed.
Cornering is still spectacular as it changes direction like a pinball.
I am keen to have a go with a flat planning surface that is about 1” or 25mm wide on the bottom of the sponsons.
This will give a zero degree deadrise for the first 1”out from the tunnel in the rear half of the sponson.
I have chosen to run it from half of the LOA as it currently runs with a nice nose up attitude and appears to run on the last 30% of the hull, not bad for a bottom that has no rocker.

So in summary here are the next trials.
Lower the strut and play with thrust angles from positive to negative.
Add planning (high speed riding ) surfaces to the sponson bottoms.

Btw. This is running 6 x 4000 mAh NiMh cells.

I am not happy to provide plans for this hull untill I know that it is a performer.
Those of you with BL + Lipo setups would find all sorts of design anomalies.

[Stealth Assassin]

You need to get these runs video recorded so, we can see them In action. Do you draw up plans on paper or cad? Or did you just make the parts from scratch as a one time build?

[Simon.O.]

See post #5.
Yeah , it is very much a one time build !
I have a design concept and some good notes scrawled down on paper, a lot of coffee, sheets of balsa, tube of CA and a couple of good knives.
I love creating.

Now that it is built and the hydro too, I like to go to the pond and try different power combinations untill I find a good one, then it is into setting up the hull just right using the strut and Cog changes.

They are both in the same "can" at the moment as they need hull alterations to iron out some design features.
This is going to mean additions to the bottom of the hulls for the Cat and to the bottom of the sponsons for the hydro.

This is fun.

[Stealth Assassin]

I like your Ideas on shapes of sponsons(I have alot of drawings that have not yet come to life). hull design Interest me the most, I like designing a hull better than running It and I am not crazy about mounting rudders, flex shafts, servos and motor mounts either... Yeah I can do It but, I would rather watch over someone else doing that part of It for me!
Where are you from?

[Simon.O.]

Where are you from?

Born in England
Raised in: England, New Zealand, Solomon Islands, Fiji , NewZealand.
I like to research, design , build , try , rebuild , try ........... It is a hoot !!
There is so much satisfaction in the completion of a project.

Back to this hull.

Today I trialed it with the strut set so that the shaft was just below the hull line.
The acceleration was way better and cornereing was sharper too.
Top speed "looked" the same.

I have now fitted a new surface to the hull bottoms.
It goes 3/4 "from the tunnel outwards and is flat. No deadrise here . This is from 50% LOA to the rear of the hull.
I will trial this in the morning.