FootyCAT Build Log

Ok here we go again
There were loads of mistakes I made in the last one mainly due to me trying to scale a Hobie Tiger.

So I have gone for balance with the existing hulls and refined a few improvements along the way.

Cut some new ones and took them for vacforming, result was that I had two different sections
Plug No1. for a central rudder
Plug No2. for multiple rudders (back up if No1. does not work)

Vac’d shapes were cut out and sanded to give flat areas for decking

Next, I Ca’d a Post Office rubber Band to the edge of the box to form a seal for the hatch.
I will still put the RX in a baloon (Belt and Braces)

I will use electrical tape on the front edge so as to form a hinge for the hatch

Slidey-inny-outy thing

So the next thing to do was to CA the sildey-inny-outy thing to the hatch.

Next I placed a bit of my best scrap wood against the sander until the shape was right for a very tight fit into the inner square tube.

Cut and sanded this allowed me to fit the gudgeon to the tube with glue and a screw.

The whole assembly is then inserted into the aft end of the larger tube and secured with a screw eye through to hold the whole thing in place and doubles as a fair lead for the main sheet.

Rudder and keel

Tradboat had very kindly sent me a photo of a Dart 16.
Now this was interesting as I spotted that that it had no keel.

So I thought that had to be worthy of experimentation.
I also wanted to see if I could further reduce the weight and try to get down to an all up weight of 200g

So looking round the work shop I spotted a pair of asymmetrical wood helicopter blades that I had been using on Prop-a-Footy (gone back to R&D)
I cut the blade in half and reshaped the topand stripping the outer plastic coating off.

Using some 2mm titanium wire I formed a U shaped pintle and drilled out the leading edge for the wire to be a very snug fit.
It was soon evident that there was a certain element of binding and so I opened the hole up to 3mm and inserted a teflon tube and CA’d it in situe trimming off the excess once dry. No more binding

Now I turned my attention to the rudder horn.
Made from an offcut of aluminium section, I drilled and fashioned it to accept an adjustable nipple that has an allen key grub screw arrangement.
To allow it to swivel left and right, I did not do it up tight and then secured the washer and nut with CA to stop it getting loose.

Hatch electronics and painting

Now it was the turn of the servols (Brissle speak)

In the previous FootyCAT the slidey-inny-outy thing had been underslung to the compartment and it would catch the water. I had one servo mounted in the hatch and another through the lid.

I had decided that it would be far safer to have everything mounted in / on the lid after all even with a vastly reduced compartment there was plenty of room.

Holes were cut and servos stuck to the underside with Zap-a-dappa

Next I turned my attention back to the rudder giving it a couple of primer coats and a coat of Royal Blue Gloss sanding between coats.

I then left this to dry in my spare vice while I got on with the hulls.


The hulls come out from vac forming one per sheet.

If I decide to go to a kit then I might consider having both hulls and the central section as one section - we will see.

Using a scrawker (hooked knife) I held the blade flat to the hull and pulled it backwards toward me a number of times to scribe the plastic and eventually release the hull. I repeated the process on the 2nd hull and then sanded both to ensure they were perfectly flat.

The shape of the bow when vac formed produces a webbing effect and needs to be trimmed off. However before I do this and to add additional strength, I apply some of my Goop to the inside and also at the corners of the transom.

Now the all important bit whats the weight? A whopping 18g


As this is still an experimental craft, I will use a flat deck.
I know that this is not ideal as it does not shed the water well and has resistance to surfacing but in the grand scheme of things that may come later.

Cutting thin strips from the scrap round the edge of the hull vac forming, I stuck them with my goop as inwales inside the hull.

This slightly increases the internal width of the hull without adding vast weight but does have the benefit of doubling the adhesion area.

Goop to the rescue again and the deck was stuck onwith a slight flange over lay.

Having left these to dry, I then did an pressure air test. I clearly did not want any water getting in and needed to find out if there were any leaks.

To do this you use your thumb and fore finger to gently squeeze the hull sides.

Detecting where any leaks are is a matter for the individual
Water and see the bubbles but then the hull is wet and you have to wait to get it dry before applying more glue.

Ear those fortunate to have good hearing should be able by holding the hull to the ear, hear where the air is escaping

Eye The eye is the most sensitive method but carries a health warning!
Some glues like CA will stick to the eye - so please do not attempt this without ensuring that the glue has completly dried - even the fumes can cause problems.
You have been warned and I take no responsibility for your actions.

These can be cured by brushing some Contacta to the edge and allowing capillary action to take place.

Once dry re-test and once satisfied the flange can be cut of in the same method used for releasing the hull described previously.


Clearly this was something that I got wrong last time, so I was determined not to muck it up again.

I filled a basin with water and using masking tape I secured the central section to the two hulls and floated her to see where the water line was

Masking tape on the deck allowed me to mark my progress and on the side to check how the CLR was moving in conparison to the changes.

Having found the desired point, I semi-secured the sections together with Zapp-a-dappa. This is strong enough to hold the structure securley but still allow me to take it apart to move it if needed.

I did consider a slot and screw arrangement inside the electronics compartment down into the deck but decided against it for fear of leaks.

So now I hear you shout whats the new weight?
The last hull was 299g.
This one is 202g !!
Very nearly saving a third of the weight.
I could have saved more by going to smaller and lighter batteries, who knows maybe thats for the next one?

Now comes the fun part to see how she sails and play with the slidey-inny-outy thing


Well I could not have picked a worse afternoon to try FootyCAT out.
17 gusting 24 mph winds and me dodging the showers.

Not knowing what to expect, I had put the very smallest of sails I had and this was from my now retired 507, that I used to steam about with on days that everyone else had given up on as it was too windy

Still I was determined to give her a go and go she did with grace and agility and a rate of acceleration that I found surprisingly quick on her 1st run across the pond till she was hit by a gust that somersaulted her over in the blink of an eye. (you were right WaltH)

thankfully I had put the 2.4Ghz receiver in a balloon but I had not put a tyerap round the neck so some water had got in and stopped things from working ~ thankfully it was fresh water so a bit of drying out and I’m sure she will be fine.

So what next?
First thing I think will be a smaller sail and to try to make the hatch more water tight then another trial to see where we are.

One thing is for certain she turns well so no need for a change to the rudder set up.

Once I have tested a smaller sail set up, if she still somersaults then I will have to consider re-installing the keels with some sort of weight. However I am loathed to have to accept this at this stage.

Short as it was the experience has made me want to perfect it.
More another time


This is very impressive,and a very worthwhile experiment. Some of your results were very surprising. I had expected it to submarine very quickly, which it apparently did not. I had expected it to turn poorly, because the rudder was too close to the longitudinal center, but apparently it turned quite well.

The upside-down stability problem is counter-acted on some catamarans by a small float at the top of the mast. This aids in re-righting by the crew, but in the absence of a live crew, may not be useful.

It should also be noted that a catamaran with a weighted keel will still be stable in the upside-down position, but the damping of a keel may prevent a rapid flip-over in a gust. You may be able to use a relatively small weight.

Hi Walt,
Thank you for that ~ it just so happens that I have a yellow ping pong ball that will be very suitable for the job

I think that it is very interesting that the yellow hulled FootyCAT did not have these characteristics ~ it may have been due in the first instance to her having keels and small weights. ~ Damn shame I built her too well and she would not come apart.

I have been thinking that as the Kudder (thanks AndrewH) is working well I might just add some weight to that and see if it helps?
There is also the option of making the Kudder pin longer this will enable the turning moment to be further aft and also move the CLR further aft and weight if I have a hollow Kudder.

This will have to be done with some care as it will disturb the point at which the water line breaks at the bow and stern.
Alternatively I could go to a canoe stern but taller all things to be tried in this very interesting experiment.

If that is the case I will make a plug by slicing the existing Kudder lengthwise and vac forming that. This will then give me a hollow Kudder in which to put ballast.

However would this be allowed under the current rules as ballast is not meant to move?
If I went to a canoe style I might just have to do the hull in two halves due to the webbing effect

More thoughts otherwise known as “Zen and the art of FootyCAT building”

A chat with Robbie Nevitt (Yeovil MBC) reminded me that I had used a foil on the rudder of my first Bottle Boat to help counter its desire to try an emulate a submarine - (and with its bulbous bow it did not slow down) the foil certainly helped and the view from astern gave the impression of porposing.

So I am now going to make a new “kudder” (comined keel and rudder) in two halves from MDF that will include a foil and the kudder horn.

Once vac formed this will allow a number of things to happen

  1. Balast can be added as lead before sealing
  2. the foil and horn can be internally strengthened

I am also considering a Skudder but that might just need a direct drive

Well better get on with it I suppose

Well some thought and alot of very careful sanding and shaping from an original wooden symetric heli blade has resulted in this new plug for a “Kudder”.

The eagle eyed amoung you will note the absence of the horn. Never fear it will be put on however I thought I would show you how far I got this evening.

The foils were pinned to the plug with titanium wire and glued.

Once the horn is fitted and I am happy with the finish I will get it vac formed

Skudder ~ No its not a Footy launched surface to surface missile to deal with marauding Minstralette, venomous Vortrekka or bothersome BUG’s (and I would need a SubRoc to deal with ZBF)

This is a Self Kanting Rudder (I cnow it should be spalt with a “C”)
Most of you may also know this as a pendulum rudder

The main benefit to this type of rudder is that it is always perpendicular no matter how the boat heels and therefore does not induce rise or worse dive.

However my thoughts are to take it a stage further and to allow it to act as a righting force for FootyCAT. This would of course rely on a stayed or trapped mast as there would have to be a floatation device at the top.

As I see it depending how long the rudder was, it would then be able to generate sufficient leverage to right FootyCAT, either on its nose or on its side with the Skudder resting on its stops to allow it to right it self.

Your eager comments are as always very welcome as I enjoy sharing my ideas with you.

It is fair to say that this is on the back burner for the minute till I see how FootyCAT fairs with her foiled Kudder ~ but as you will see from the model it will need a direct drive.

With regards to Footy legality the rudder is allowed to move but it does not say in which direction and if you do not have ballast then it cannot move if its not there!

(thanks go to Mike Mayhew for the loan of the model)

Andy - I would recommend cable steering for your canting rudder. I use cable steering on all the larger classes of model yachts I’ve built. It provides a one-to-one servo to rudder linkage (even throw, no gain or loss of leverage in converting rotary motion to linear motion and back to rotary motion) and doesn’t need to be in line with the servo. Originally on Brujo the rudder servo was mounted horizontally, the fishing line “cable” was twisted 90 degrees in its travel from the pulley shaped “drum” mounted on the servo to the one mounted on the rudder.

Here is a shot of my old Bantam with cable steering.

And, yes, this boat used full size servos circa 2003 and is a pre-box rule 7-3/8ths inches wide at the deck line. You’ll notice the stock Futaba winch servo arm (unmodified), which took a wide sweep almost touching the starboard wall when the sheets were trimmed in.

Bantams sailed really well upwind and on reaches but I wasn’t too impressed with their downwind running. I usually tacked from broad reach to broad reach on the downwind legs. I’ve had a lot of fun sailing the three boats I produced to this design, particularly when the going gets rough.

Neil thank you for that, I will certainly bear it in mind as I did not exactly relish sticking the servo on top of the rudder.
Are you saying that you had a canting rudder on the bantam as well?

I am looking for some other photos of canting keels on model boats do you have any by any chance?


We read your Cat-a-log with eager anticipation, scanning for new ideas, fascinating pictures and new words in equal quantities:D

Nigel has a tilting keel on Papabois, indeed its a:
he enunciated carefully. A gyro would seem to be a good way of controlling the keel .
Neil’s cable idea is good, and will accomodate the cant. Dental floss is a good cable for these forces

So when you announce these days “I’m going to do the vacuuming, dearest” you may gain marital brownie points, but you also get a handfull of FootycaT hulls:D (Or 'ulls as we say in 'ull)

So with the kudder now vac formed, I realised that the vertical sides of the foil webbed and these had to be cut away, I also had to consider how to fill the structure

The original kudder was 8g inc servo horn and being wood added some buoyancy.

Having cut the two halves out, I shaped a section of lead sheet to the inside with tin shears. this then made the whole thing way too heavy at 72g!

Clearly I did not want to induce too many changes at once and wanted to see if by just adding the foils to the kudder it worked however I did not wish it to be adding buoyancy.

The solution I decided was to cut strips of the scrap plastic and stick them to the inside of the kudder - this gave it far more strength and rigidity but only put the weight up to 16g

In the end I did not add a horn to the Kudder plug, as I decided it could double up as a plug for a rudder and I might need the horn on either side

So I stuck two bits of scrap plastic together and sanded it to shape and stuck it in place - first drilling a hole for the connecting rod.

It was at the vital point that my QA inspector poked his nose in - thankfully he gave his approval :paw:


Well the winds were much lighter today, and just as well, with a 3rd of the weight of FootyCAT gone while she accelerated well she also dug her nose in and pitched poled 3 TIMES ~ thankfully my good friend Lawrence had just completed one of his projects the Clevedon Club Rescue Boat, so this was an ideal chance for him to test it out.

It seemed that i had gone too far trying to lighten the weight and the foiled Kudder was not over coming the the problem on its own.

So i decided to make a number of modifications.

  1. Whilst the Kudder gives very good steering control, I have decided to reintroduce the keels ~ however rather than bring them through the hulls i have attached them to the flati nboard side of the central compartment.

This has a major benefit ~ using Zapp-a-dappa glue the grip is strong enough to hold but to let go with gentle effort - so this allows me to move the hulls.


keeping well in with the missus and the vaccing ~ i turned my attention to another idea, that of a set of hydrodynamic spoilers ~ being an ex-submariner, i do not like to call them hydroplanes as this would imply that they were controllable ~ they are not and are fixed to the inside of each hull.

The theory being that when closed hauled and one keel lifted they do not interfere ~ however when the bow is depressed they come into action.

So following some advice from another friend i cut some plasticard 65mm long going from 10mm to 0mm and stuck it to the inboard side of each hull at an upward angle with the trailing edge just above the water line.

As the bow is depressed in a closed hauled attitude the hydrospoiler does not come into play however if both hulls are depressed both fixed hydrospoilers provide lift.