P offshore scratch cat build thread

[Jesse J]

Few plans are out there allowing us to have a jump start on a scratch build. I came across Lonewolf (Shockerman) 8 years ago and he generously gave me his plans. I have built half a dozen different permutations of these plans and have recently scaled them to 34" and tweaked the tunnel height/width, tunnel attack, downward force from deck and angled out the sides somewhat aggressively.

I have watched my slomo vids and seen that many cat rolls are initiated with a forward pitch and slight roll - then the water slips up over the deck and initiates the death grip. SO, I thought a slightly outward slant (not unlike a mono bow) would add lift in such a pitch/roll event and so far in the 24" and 12" it has worked great. For the 34" hull, I decreased the angle so as to not add lift to the bow, which if racing near 60, this could increase blow over potential.

This set of plans is pretty simple and requires a good bit of patience; trial and error fitting and some design-as-you-build technique.
Before I started adding CF rod, plate and cloth, it was pretty economical... but now its strong. I have not gotten these plans laser cut, rather I plot them, cut around the parts and paper glue them to the balsa. I use a combination of utility knife and straight edge and bandsaw.

supplies:
3/32" balsa sheets (6" wide by 36" long)
1/32" ply sheets (same dimensions)
1/4" square stock (bass)
3/4" 45 triangle balsa stock 2x36"
1" and 3/4" trailing edge balsa stock 2 each x 36"
5/8" leading edge for wing (front of the tunnel)
CF rod, 1x3mm by 36; Cf plate (1mm) and CF cloth
CA and kicker
West Systems epoxy (I used 205 hardener)
US composites 2 part expanding foam (2lb/cubic ft)
industrial rubber cement (for adding the ply skin to the balsa sheets)
Sandpaper, block
building board 7.5" wide, 2" deep and 36" long wrapped in wax paper

I will be less verbose in the posts but will answer any questions that may arise.

pic 1: dog with a boat for scale. the frame goes together pretty quickly and I recommend using a building board wrapped in wax paper. The flatness is crucial and the closer to the exact tunnel width the better. I forgot the wax paper and thus in pics 3-5 you see I used some CF strands to beef up the corner. then I covered my booboo on the tunnel side with 45 angle balsa. I got the idea from my M1 Super Cat hull.
Pic 5 shows my motor mount CF plate - this will be designed for either twin or single. In fact, I'll be putting in the tubes and motor mounts for twins just in case I want to see how fast I can get her going.

[Jesse J]

framing done

I used a fair bit of the CF rectangular rod (1x3mm) to strengthen the framing. Balsa is light but weak until you get her skinned. So, keeping with light, I reinforced each or the rear bulkheads and the rear stringers - where the open cavity will need it.
Some cross bracing up front will keep the deck firm supported until the glue dries. I ran some of the CF rod along the rub rail to help with the shape and also provide superior strength when a fellow club member comes over for a hip check. in the last shot, you see a pretty flat, zero attack tunnel. This was a suggestion from Jay Turner, who helped design the Motley Crue. Not only does it decrease the amount of air packed in the tunnel, it brings the deck down more for increased down force.

[Jesse J]

the way I skin a cat

I like to build up the strength along the sides first. Along the back you can see my CF ride pad supports, motor mounts and/or battery trays. These were cut to fit flat on the bottom and provide chine support to the rear sides. Once I got the sides in place (balsa grain running long-ways), I sanded and controlled that the ride pad area was perfectly flat, square and equal on both sponsons. I added a little triangle to the very first bulkhead to help with the tip shape. Once I was happy in the trueness of the sponson shape, I skinned the bottom with balsa. Then sand until flat and w/o bumps.

I always use a sanding block, not only to keep the lines straight but to keep the surfaces flat. Balsa is soft and dents easily. I also like to sand in all directions but not in circles. I was using 100 grit for shaping, 220 for smoothing and then 320 for final finishing. You don't want the balsa too rough for the contact cement used to hold on the ply skin.

the rear is always a challenge - unless you like a flat one. I like a good bit of shape back there and some overhang is always more attractive. With stingers, you can hang them under the extension and I have created a little space for them, actually still designing them now.

[Jesse J]

finishing the skin

last few shots of the skinning process and the finished product. You can see its still a little rough - don't want to sand too much! I made a simple faux transom overhang for the time being, but have since modified it to kinda hide the rudder bracket and strut mount (for single drive) as well as make the nacelles for the stinger mounts.
At this point I started sealing the interior of the tunnel and next postings will be the cf cloth to reinforce the sponson fronts.

[Jesse J]

cf ing the sponsons

here is the inside of the sponsons with a healthy dose of CF cloth. Also you can see the evolution of the ride pads. Original Shocker plans have the sponsons stepped, but I decided to only step the ride pads (1" trailing edge balsa stock). Here I also used a 3/4" trailing edge for a continuous spray rail (no step). The angle of the sponson bottom and steps was influenced by my M1 super cat.

You can see I did the ply second skin cross ways - adding significant stiffness to the finish. This way the epoxy will not soak in as much and the skin has a tougher shell.

[Jesse J]

stinger nacelles

This is pretty much how she sits today. got the stuffing tubes installed, SV27r stingers and wire drives installed. I had to disassemble the faux transom but deciding and designing as I build is my style. I wanted to allow for either/both twin and single motor applications. The rudder can be inline or offset (just add the offset bracket). I wanted to get these twin drives finalized before skinning the deck.

[Peter A]

[domwilson]

Jesse, You got talent and skills, my friend.

[Jesse J]

Jesse, You got talent and skills, my friend.

Thanks man! Hey buddy, sorry I ain't got no kickin groves with this thread... Maybe I will when I maiden voyage this sexy cat. Hope you doin well!

[srislash]

Very nice bottom on that cat Jesse. She should be a good runner. One day when I have the time I'll scratch build one.

[domwilson]

Thanks man! Hey buddy, sorry I ain't got no kickin groves with this thread... Maybe I will when I maiden voyage this sexy cat. Hope you doin well!

Doing good. Setting up for another speaker design. Need your tunes! I've been buying the CDs.

[Brushless55]

Looking good as always Jesse !

[Jesse J]

Ok, Jim the legend convinced me to finish this bad kitty as single motor and get her on the water... stay tuned.

[flattrack]

Hey Jesse, did you do any figuring for the ride pad width and where you put the steps or just figure it out as she goes? I agree with Mr. Jim, let it stay single motor so one day we can wish to keep up with it.

[Jesse J]

Hey Cory, figuring, yes. I looked at my M1 Supercat a lot. P offshore - open class. hopefully in a month or less.