Slingshot inspired twin rigger

[rhomodel]

Whilst I'm in the completion stages of building the slingshot with a rear exhaust engine, I gave it a good thought on what to do with some QDP engines that I do not need anymore since changing to BZM for the offshore classes.
Several years ago I build world's first twin inline rigger, this time don't want to be as innovative and radical as then..
Always loved the sound of 2 seperate engines buzzing and hope that will be the case when this build is finished..
Twin rigger seems to sound nice, but needs some work to get the QDP's to work: main challenge is to move the red ignition coils from side mount to top mount ( I call it Zenoah position) so 4 inch mounts can be used to limit the width of the assembly: I like twins, but don't like the barndoor size of them. I also needed ( or at least felt the need) to make the boat a little longer: so stretchted it by 5 inch. as can be seen in first image.
Second image is a loose fitting of the parts and hold all together with clamps.

 

[Mike Hughes]

Sweet deal. My twin tub is 8 3/8 wide. Built custom mounts to make them fit. Also went with no pull starters. It helps with the length issues. My boat is 54" tip to struts. Link to a thread Something New that i am working on.
Mike

 

[rhomodel]

Thank you Mike, I had read your build-up as well. Good stuff of both of you! Luckily I have a friend who made me custom motor mounts in 3 mm stainless so it would fit rails 4 inch apart: 10 mm rubbers and 82 mm wide mount. \He also adjusted the Zenoah style 3 bolt support to the QD 4 bolt through the starter spacings. This would make the whole tub 212 mm wide or 8 1/3 inch. Used aircraft ply, that although is only 3 mm thick is 7 layers so plenty strong.

 

[rhomodel]

For this build I chose to first do the reinforcement deck of teh RCbox and rearcompartment: That would allow for easier access to impregnate with epoxy and reinforce all joints from the inside with a bead of thickened epoxy. Also tried to add some mechanical fitting of plates, so that the structure not only has to rely on teh bonding power of superglue and epoxy, but also has structural strenght.

After that cured turned the box around and glued the bottom sheet in place: nothing too difficult, but clumsy due to the size of the panel. Added some "design" weave cloth in the engine bay to ensure that compartment is 100% fuel proof e=and no discoloration on the woodgrain to take place.

 

[rhomodel]

Here's the interior close-up. Also some nice exotic wood that I will shape to act as fender... Sponson tips I will use teak I think..

 

[rhomodel]

Today I had intended to make a few sponsons, but I didn't fancy all the jigsawing. Instead I worked on the engines and milled new ignation plates of the QuickDraws so the redcoil could be mounted in teh normal, zenoah position. As written earlier this allows for much more narrow placement of the engines. You can also use this concept to convert a standard QDP to fit a 4 inch rail tub (with the side mounted plate the narrowest you can go is 5 inch unless you go a-symmetric.
To explain on the pictures; I made the plate out of 8 mm thick 7075 T6 alu, (QD uses 1/8 inch, or 4,3 mm). This leaves litte thread for the mounts. However the 8 mm is too thick to have the flywheel mounted, so needs thinning where the wheel sits.. Simply make an adaptor to hold the raw plate and turn it off in a rotary devise in the mill, or lather. I choose lathe.
|Other pictures side by side comparison of normal vs converted engines.

 

[Wasted wages]

Did you cut to fit the glass cloth inside of each compartment, or did you sandwich it between the floor and sides of the tub ?

Do you glass up the inside walls of the compartments too ?

 

[rhomodel]

It's a retrofit, so cut it to size to fit each compartment. For now only the bottom, but when everything has cured and the tub still flexes a lot I will also do the outer side walls for stability. Probably unidirectional carbonfiber. Currently the outside walls are only 3 mm wood ( about 1/8 inch), the inside spar 6 mm (1/4 inch).
Or alternatively do as the slingshot add cross fittings where the booms/ gas tank sit and in the engine compartment. Or may be combination of both.. have to see..

 

[rhomodel]

Past several days have been working on sponsons. I should have ordered with the Slingshot kit a few pairs of extra sponsons, but couldn't know I got carried away. Anyhow the jigsaw has done it's work and I used many a blade.. Now I feel I'm employed in a sponson production line..

 

[JoePeters]

Past several days have been working on sponsons. I should have ordered with the Slingshot kit a few pairs of extra sponsons, but couldn't know I got carried away. Anyhow the jigsaw has done it's work and I used many a blade.. Now I feel I'm employed in a sponson production line..

Are you using the stock sponsons or are you making them longer/bigger for the twin?

 

[rhomodel]

I use about similar size sponsons: they are not a copy of the real slingshot sponsons, but like the whole boat inspired by, eg the sloped sides and curved back. Reason I use about same size is that I think the tub has enough buyoancy due the exra lenght and double radio box of which one will only be used for flotation.

 

[rhomodel]

I have been quiet for a while on this, but have been steadily working on it. Most (invisible) work was on the engines as I had to rework a lot: turn down the cases to accomodate full circle cranks, mill the ignition plates, take apart and clean 5 engines (yeah if you don't sell stuff it just piles up) and turn various parts on the lathe. Engines nearly ready.
On the tub I did notice however that the 3 mm side walls and 9 mm centerspar, in combination with 1.5 mm bottom and cloth laminating are not enough the prevent flex in the engine bay-booms area. So decided to laminate with, I think is 280 gram carbon fiber on the insides..

Next will be the booms, for which I have been waiting on for over 4 weeks now. Do have a question: given the width of the tube: would it make sense to make each boom out of 2 parts of carbon tube, and attach each with a coupler and 2 setscrews to the tub (4 in total), or just make one long boom out of a single piece carbon tube? This so if ever you encounter something to make a boom break you only have to replace half a section, rather than a 60 cm piece of expensive carbon tube?

 

[Bubba Hass]

Hi buddy , great build and great looking rigger set out and some great ideas .

my Sexy ***** RR with 350 Zens inch s 9.5 inches inside our rails are .250 or 5 mm rails that where used for the torque and weights of the 350 zen motors together we used the drop style slim line Speedmaster mounts as they are so easy to install and Rick solid with the 1/2 rubber cushions .
I strengthened the 2 boats we ordered off Ralph as 80 % kits , with 300gram twill which made it rock solid .

 

[rhomodel]

Great build bubba.. Yes I felt the same that the tub really could benefit from some strengthening. Out of curiousity what props are you running? My single engine is doing 2914-2 or octura 2170 easy, so I fear I must go much larger on a twin..

 

[Bubba Hass]

Thanks
Yes props I have a fair few pairs for the big girl
Starting point was 3017
Been running 3019 and now into 3021,3023 in the 38 range
Running 2714 / 45 series
Also running the COCR CC3 + 10

 

[Timbo Whalen]

my Sexy ***** RR......

Badass lookin' boat, Bubba!

 

[Shane Bastick]

Hi buddy , great build and great looking rigger set out and some great ideas .

my Sexy ***** RR with 350 Zens inch s 9.5 inches inside our rails are .250 or 5 mm rails that where used for the torque and weights of the 350 zen motors together we used the drop style slim line Speedmaster mounts as they are so easy to install and Rick solid with the 1/2 rubber cushions .
I strengthened the 2 boats we ordered off Ralph as 80 % kits , with 300gram twill which made it rock solid .

Fantastic twin Bubba, great job

 

[Bubba Hass]

Badass lookin' boat, Bubba!

Thanks Tim yes I like racing it that for sure

 

[Bubba Hass]

Fantastic twin Bubba, great job

Thanks Shane

 

[rhomodel]

As I'm waiting for building supplies to be delivered can focus on some "nice to have" items: a Carbon fiber turnfin and also a carbon fiber set of tanks.
Initially I intende to use just IV bags as fuel tank, but as the fiber reinforcement added considerable weight, I want to add some extra buoancy. Solid tanks will provide an additional 1,2 liter..
Turnfins made of CF I had done in the past when the whiplash was just released. However it was either excessive thick or too flimsy due to the lay-up method.
Now that I can vacuum lay-up these I expect the strenght to increase, with less resin trapped and without adding too much thickness over the 3 mm SS turnfin I now use on my other hydro's.