Boat Electronics


2012 design update:

The developement of the EC12 System Board radio and sheetline installation should be explored with the J Class boats for the same reasons used in the smaller model. This design has proven beyond hopes and provided reliability and ease of maintenance. It can be adapted for the model and building process shown here. EC12 System Board.

J Shamrock

The internal gear is simple and uncluttered. A radio rack will be mounted on the primary ballast at the strut tower for the winch, trim servo and power switch. This will be removable with one screw. The rudder servo will be on a board within its own compartment at station 70. The antenna will be internal in a tube.

Radio Rack
The rack was made from .064 aluminum sheet. The winch is a RMG 380 geared for 11 turns and using a 32mm SDS or the 26mm single wide drum.The trim servo is a Hitec 805BB 1/4 scale with 325 torque. The standard supplied arm is used with an extension for a total length of 2-3/4" and a Pekabe single block on the end. The power switch is low tech with a Radio Shack DPST switch. You can use what you like, of course, and configure as your design suggests. What is done here will not be the thing that you may loose by.

The aluminum was laid out, cut, drilled and formed. Yeah, I know, "Did it work the first time?" No, a second one was built.


The mounting tab is 3/4" and the rack is 4-3/8" tall from there and 4" wide. The mounting holes for the winch were 1-1/4 above the break and drilled according to the RMG manual. The winch and the servo were set aft of center for room in sliding onto the strut tower. Think about it.

Note the center hole of the winch. The 1/2" drill wants to chatter even after pilot drilling. Go slow, real slow.


The rack is to be fitted to the strut tower forward with two slide in slots to pan head screws. The rear mounting is slotted for alignment of the winch drum with the bow turning block. There is a cap screw and to tightened with a ball hex driver. The compression strut portion of the sub-structure section shows the fitting of the rack.


Jib Trim Arm
The arm supplied with the 805 servo was suitable. An extension was added to make the length 2-5/8 inches. This may be adjusted later during the rig pre-tune phase. The block was wrapped with a rubber band to slightly stiffen the free movement.
Rudder Servo and Mount
The rudder servo can be installed in the rudder compartment when the mount is designed and glued in. 3/16" ply was used here with 4-40 T-nuts glued in. A hole saw was used to make the ply do-nuts on both sides to stabilize the shaft. The varnish is for waterproofing. The last photo is of another design. It is beefy and we will see how the other works.

It might be noted that the linkage separation from the servo arm and the tiller was tight with the servo positioned here. A extra 1/4 to 3/8 inch further away from the rudder shaft will provide ample room for the linkage.

Receiver and Antenna
The RX is mounted on a post under the hatch liner on rib 45 with Velcro. The antenna tube traces forward through the stringers.
 Electronics Wiring
 Two batteries and one DPST switch are used. #2 battery serves the winch directly and powers the RX. #1 battery powers the trim and rudder servos.

Flat packs of AA batteries are used with 22 gauge wire. The extensions are also 22 gauge.
J-boat-wiring J-EBOARD021 J-EBOARD022 J-EBOARD023

It should be noted with this wiring that the positive (red) wire of the rudder and trim servo leads to the RX need to be removed from the plug (severed will work). This is because the winch is supplying power to the RX .