Crackerbox.

	Manufacturer: Homemade Type: Crackerbox Length x Width: Weight: Owner: Peter van Leeuwen.
Motor: Hardware: Prop: Top speed: Materials: Wood.

 

The complete crackerboxbuilding story.

Here are the pics from my latest project the building of a 1/4 scale Crackerbox.
This is how i have done it.
First i got a lot of info from the net you will be amazed what shows up when you try to search for pics of crackers on google.
Than some guys had the plans on file and mailed them to me (thanks again Jerome and Paul).
In the meantime i have forwarded them to some more and now a lot of the guys are building Crackers also.
I specially like to thank Julius for making the decals !!
Click the images as there are bigger ones behind them !!!

List of materials.

3 mm marine or birch plywood./bulkheads.
2 mm marine or birch plywood./side sheeting.
1,5 mm marine or birch plywood./bottom and deck sheeting.
6 mm marine or birch plywood./engine mount.
5x10 spruce for bottom stringers.
6x6 spruce for side stringers.
3 mm epoxy or aluminum sheet for skeg.
30 minute epoxy (zap)for bulkheads and stringers.
24 Hours or laminating epoxy 500 gr for laminating and waterproofing.
2 Sq mtrs of 49 gr glass cloth for the bottom.
Rubber isolators for engine mount.
engine mounting hardware.
Flex shaft adapte.r
Stuffing tube box and flex shaft.
Strut and propellor.
Rudder.
Trimplates (home made).
Engine (zenoah or weed eater type).
Radio equipment 2 channel radio,standard servo,1/4 scale servo (min 8 kg torque) 2700 mah reciever battery, switch harness and preferred a FAILSAFE !!
All the stuff to connect servos to throttle and rudder.
Filling base coat (simprop or automotive) 4 cans.
Spray paint (simprop or automotive) 4 cans.
PVC tube to make a stand.
Tools:scroll saw, delta sand machine (b&d mouse) dremel tool,sandpaper 100 to 1200 grit,X acto knife.

Let me remind you that working with paints and paint thinners can be harmfull and hazardous i dont take any responsability or liability if any thing goes wrong.
Using machinery to build this boat should always be done with the proper eye,hand and hearing protection.
A dremel tool cuts flesh easier than metal.!!!!

MADE THE PLANS AVAILABLE ON THE NET!!
(See below this page for the plans, and folow the instructions there.........)

The First steps The Bulkheads:

The first step is to print out the files, i used Ulead i photo plus and printed them as a poster.
This way they came out the right size exactly the 1.27 mtrs i wanted to make this boat.
Using 3 mm birch plywood i taped the drawings of the bulkheads to the wood and cutted them out using a scroll saw machine, this way its so much faster than doing this by hand but you can do that also.
As there were a lot of flaws in the plans i corrected the misstakes before putting the bulkheads and keel together.
Used epoxy glue troughout the complete building proces as this is the only way the joints stay together under heavy stress.
For the stringers you can use anything you like but the precutted ones from the hobbyshop are very handy.
Fixed some of the joints with CA gleu and later glued everything with epoxy.

Putting on the bottom sheeting:

After sanding the bulkheads and the bottom stringers completely flat to minimize the risk of hook you are ready to to put on the bottom sheeting.
Dont use the ones on the plans as they are way off but use new sheets and draw the lines of the keel on it and make sure you have a overlap of about 2 cm at the chine.
Before you start gleuing make sure everything fits seamless at the keel this will take the hassle of puttying the lot.
First do one sheet make sure you have a lot of heavy things around to weigh the bottom down and use washpins to hold the sheeting on the side stringers to forn the chine.
This is the most important thing to do as this is the bottom of your boat and this will define the running of the boat.
Use lots of epoxy to make sure its glued everywhere.

The engine Mount:

After you have done the bottom and the side sheeting just the same way you did the bottom sheeting you can make the enginemount.
As i used an aircooled zenoah GD2 i have used a 3 point mount .
Those who use a Pum zenoah can make a 4 point mount and those who use a homie have to decide for themselves how to mount the engine.
Make sure you make the mount wide enough to put the engine in between the rails, also for those with a weedeater engine these are heavier than zenoahs so put the engine further back.
Make sure that you define the centre of gravity before you put in the enginemount as this is quite important and you dont want to add lead weight later.
Than fit the stuffing box tube according to the plans for subsurface or like we did for semi subsurface.

Glass cloth to cover the bottom:

To protect the bottom from hitting any debree in the water i have used a 49 gr/Sqm glass cloth.
After you have filled all the gaps ,hooks and dents in the bottom sheets you can put the glass over it.
Dont try to do the sides also in one time !!!
If you want to do so do one side at a time.
Make sure you have the right temperature in the room 20 degrees celcius and wear rubber gloves as this 24 hour epoxy sticks to almost everything.
I have used a foam roller to roll on the epoxy and than put the cloth over it.
When you put the cloth on make sure it is straight and tap out airbubbles with a dry paintbrush.
Let it dry and clean with acetone before painting
some epoxies have wax in it to better relaese it from a mould so your paint will not stick to this.

Setting everything up:

Now that youve done the bottom its time to set up the hardware and mount the enginemount and engine.
Preinstall the transom hardware and fit the radiobox.
As there are many different setups and hardware you can use i can only be your guide on this.
I have used the hardware from MTC germany i sell at my shop so i work with that.
The radiobox i made from wood and epoxied it inside and out so tis completely waterproof.
Install the complete built radiobox after you have installed the transom hardware and engine so you can determine the CG.
The CG should be in between 30% and 35% from the transom.
A more forward CG creates a easier running boat but it will be slower.
Dont forget the cockpit and drivers as they weigh in also !!!

Engine installation:

As the engine installation is done in the step before you have to determine if you run a stock muffler or a tuned pipe.
If you decide to use a tuned pipe try to keep it below deck and make sure its free from the radiobox.
If you use a pipe use a wet pipe as this is a lot smaller than a not wet type.

The deck sheeting:

After you completed the setup and determined the CG take everything out again and epoxy coat the complete inside of your boat.
In the 3 front compartment you can put some kind of floatation in case anything goes wrong.
I have used styrofoam in sealed plastic bags but you are free to decide yourself ( soda bottles will do fine also)
Than put on the deck the same way as you made the bottom sheeting , use some overlap at the side again and sand that down later.
Than paint the complete boat with a thin layer of epoxy paint, dont forget to clean again with acetone.

Trimplates:

It is very usefull to have adjustable trimplates.
I have made them myself as there are no scale trimplates this big.
This is how i have done it:
Use a 1.5 mm aluminum sheet, determine the size you want to have them, bend 90 degrees at 1,5 cm from the side.
I have used graupner turnbuckles but dubro also have nice 1/4 scale turnbuckles.
The lower ends i have drilled and tapped 2mm thread in the plates make sure you use thread lock and nylock bolts on everything gas engines resonate !!!

Base Coat and Skeg:

After the epoxy dried and you have claned it its better to apply one or two layers of base coat before sanding.
i have used Simprop "grundierfuller" but an automotive filling primer willdo also.
After painting sand it to get a smooth surface, paint and sand it as many times untill you get the result you like (i did mine 4 times).
Make sure this is done right as every flaw will show in the end result.
made the Skeg from 3 mm epoxyplate and gleud it in the slot i made for it.
Make sure the skeg is big enough (20% bigger than the plan) and its placed at the CG.
The place at the plans is too much forward and will cause your boat to make too wide turns.
Make the skeg from a tough material as it sticks out and if it hits anything it will break easily.
If you feel the boat turns too wide make the skeg smaller but only small parts at a time and then try it.

Next step: Painting.

For downloading the building plans:

Plans 1 & 2.