Carbon Fiber Catamaran with an adjustable CG & adjustable turn fin

[Jim Allen]

Both of these systems were shared with me by a very capable Australian model boater. The 1/16" thick turn fins are machined from spring steel stock. They are machined to a full wedge, leading edge to rear edge with carbide tooling & a simple fixture. The turn fins can be adjusted in position & depth when mounted to the side of the cat.

The adjustable CG system allows the CG to be changed without moving anything in the hull. Machined brass weights of 2, 4, 6 & 8 ounce amounts are clamped to two 8" long, .625" OD carbon fiber rods that are mounted between two .078" thick carbon fiber plate bulkheads. The rods are mounted in the lowest position possible in both sponsons.

Both systems are very simple to make & both provide running site adjustments to be made.

Jim Allen

 

[Terry Keeley]

Neat!

 

[Jim Allen]

The .020" thick paper templates were made before cutting the .078" thick carbon bulkheads. This became necessary because the inside of the carbon fiber hull is slightly different in the mounting areas. I also did not show how the weights are to be clamped to the two .625" OD carbon fiber tubes. When everything is finished & glued in place I will take better photos.

JA

 

[Jim Allen]

These photos show what the adjustable weight system looks like after the front & rear bulkheads have been glued in place with JB Weld Quick. This system will also lower the CG of the hull because the weights are sitting in the lowest part of the hull. With a hull weight of 4.5 lbs., I can't wait to test this thing out!

JA

 

[Jim Allen]

I decided that clamping the weights was much better than using a set screw to hold them in position. However, this process was much more time consuming. Notice the wider slot cut opposite the clamping screw side which has a thinner slot. Doing this makes the brass piece flexible & therefore it is easily clamped to its carbon fiber tube.

JA

 

[Jim Allen]

The adjustable weight system is now complete with the addition of a 5/8-11 nylon bolt, a 5/8-11 nylon nut & a hard 1/8" thick rubber retaining washer. Finger tightening of the 5/8-11 nylon nut against the hard rubber washer, locks the carbon fiber rod mounted between the two bulkheads, securely in place.

Jim Allen

 

[Julio Almazan]

Nice job, Jim Allen... very good job.

 

[Jim Allen]

I'm posting photos of the machined steel strut which is used on the cat. The strut's design will allow the propeller to be moved 1.250" forward of most standard units. The machined strut bushing is made from B-10 Bearium material. It is removable from the strut housing & it remains with the cable, prop shaft assembly when removed. Precision machined slots locate the upper 1/8" thick upper section & the 5/64" thick skeg. Both pieces are machined to a full wedge before silver soldering. The strut can be easily set at various angles with 1*, 2* or 3* wedges placed behind the one piece strut mount.

Jim Allen

 

[Jim Allen]

This is what the completed strut assembly looks like after silver soldering the three main pieces together & the anti rust steel black has been applied. A one piece mounting bracket & the Ernst engine mount thrust plates make it very easy to change the struts angle at the lake.

JA

 

[Christian Lucas]

Hi Jim,

i know you are crazy but this boat is a hammer thingy. I like the full carbon hull and the presicion maschined parts, looka great. And i like the outrigged turnfin. For the adjustable c.g. i have a different seeing where the waights have to placed. When i run Naviga F1 triangle race with an outborder tunnel i first placed the batterie at the lowest part of the hull in the sponsons on both side. Moving for and back has plenty of room to find the best position belong to water condition. But when i run this triangel course turns, they are very tite , sometimes the boat makes a outside roll over.
After some such roll acrobatic i changed the position of the batterie and placed it in the middle of the hull under the midsection just behind where the pilot sit. All as well for- and back to adjust c.g. and the best thing was that the boat dosnˋt roll over the side , no matter left or right turn. The reason was that now the waight was in the middle concentrated and the sponson can now follow faster a moving moment when a small waive hit the hull from the side or other belongings want to lift the sponson out of the water. They can do as the moment of inertia for the longitudinal axis is much lower . If the waight is placed moore outside inertia moment is higher and the spnoson will grab depper in the water and maybe will stumble.
Have it in minde , it must not happen to your hull , maybe only my tunnelboat was infected by this illness , but better to tell. Have fun with this tunnelhull.

Happy Amps Christian

 

[Jim Allen]

Hi Christian,

Thanks for the information. I know next to nothing about a catamaran & even less about a tunnel hull. However, my HTB 360 tunnel hull runs on a rail down the straight away without any rocking & turns right or left without any problems at wide open throttle. I have an adjustable weight system on this hull also with 16 ounces placed where the photo shows.

Thanks again.

Jim Allen

 

[Jim Allen]

I constructed the built in radio box shown with waterproof & fuel proof materials. The carbon fiber engine rails are used to provide two sides of the box, which saves weight & increases the box's area. The front & rear sides of the box are 2 mm (.078") thick carbon fiber plate, the bottom & top 3/32" thick G-10 fiberglass & the servo mount bases 1/8" thick linen based phenolic. The servo mounts are custom machined 1/8" aluminum.

 

[Jim Allen]

The fact that the rudder servo shaft does not line up with the rudder arm shaft does not prevent a very solid connection between the two shafts. The custom machined 90* angle block shown not only allows a solid connection between the two shafts, but it also allows both shafts to be adjusted in length individually. Notice the four flat machined areas on both 5/32" piano wire shafts which engage the four 8-32 locking set screws. A final system to possibly be added to the cat will be radio operated trim tabs.

Jim Allen

 

[RaceMechaniX]

Jim, Is the block supported by a sliding rail or some other means? Or just the two pushrods?

 

[Jim Allen]

Hi Tyler,
No sliding rail or support of any kind is necessary. The entire machined aluminum connecting block is free to twist according to the movement of the ball clevises used at the servo end & the rudder arm end. The entire unit rotates slightly around the ball ends as though it was one straight, very rigid piece!
JA

 

[Julio Almazan]

Hi Jim:

Hi Tyler,
No sliding rail or support of any kind is necessary. The entire machined aluminum connecting block is free to twist according to the movement of the ball clevises used at the servo end & the rudder arm end. The entire unit rotates slightly around the ball ends as though it was one straight, very rigid piece!
JA

Very, very good work... I like it so much that I download it to my database... if you agree, off course.

 

[Jim Allen]

Hi Julio,

Of course I agree! I'm working on the radio controlled trim tabs. Instead of using one servo with complicated linkages, I'll use two waterproof servos (IP rated) with a direct 5/32" piano wire rod to each trim tab. The rear end of this cat's sponsons are angled which will require some tooling to get things lined up properly.

JA

 

[Jim Allen]

I machined the 1/8" thick G-10 fiberglass & the 1/32" thick carbon fiber pieces that make up the radio box top. Next, I'll machine the 1/8" plexiglass radio box cover & attach both antennas.

Jim Allen

 

[Jim Allen]

After CA glueing the 1/32" thick carbon fiber plate to the bottom of the 1/8" thick G-10 fiberglass top plate, I machined a 5/32" wide lip for the 1/8" thick acrylic radio box cover to sit on. Addition of the two antennas, one "Y" outlet for the two trim tab waterproof servos & foam insulation for the receiver & battery complete this part. Next come the trim tabs which will be operated as a slave with the rudder servo or independently.

Jim Allen

 

[Mike Byer]

What ignition coil are you using?