Electronics & Navigation

General Overview

Goal
To provide a state-of-the-art tested system that will making passagemaking enjoyable and safe. Our philosophy was to keep the systems simple, capable of operating independently, and have redundancy where appropriate. One of the key elements was to provide continuous situational awareness – knowing the position of the boat at all times.

Considerations
We researched various configurations of electronics. We needed systems that would withstand the stresses and abuse of ocean sailing and require a minimum of maintenance and service. We selected – as our primary manufacturers - Furuno and Simrad. Their products received the highest marks from past customers and met our functional needs.

Implementation
The Autopilot is one of the most important items on the boat because it relieves the crew from hand steering. On long passages manually steering the boat can require a lot of human energy that can be better directed to other tasks of cruising. We selected the Simrad AP-20 as our main autopilot with a hydraulic linear drive unit. The autopilot has large LCD display for readout and is interconnected to the instrument system. A dedicated “intelligent” computing unit AP-2012 serves as the brains and junction box for communication. It utilizes ROBNET- Simrad, and NEMA protocol, to establish reliable digital communications to all systems in the boat

Limerence required a special fiberglassed shelf to mount the linear hydraulic drive unit and a customed tiller arm attached to the rudder through the steering quadrant. This was a major construction modification in the rear lazarette, because the shelf and quadrant must withstand considerable stress loads generated by the autopilot.

The autopilot has the capability to use steering information from three sources, the compass, GPS, and a wind vane mounted on the mast. It has a powerful internal computer that has seastate algorithyms ensuring the system corrects itself smoothly in various sea conditions. This is particularly important when going downwind. The Simrad autopilot has exceeded our expectations.

Because of the important role an autopilot plays we have a decided to keep our existing Autohelm 4000 mounted on the wheel as a backup. It has low power requirements, maintains good compass heading, and has been service-free for ten years.

Radar is the next most important tool for providing safety and security especially in fog, rainstorms, or operating at night. We selected the Furuno Model 851 LCD open-array 4KW unit with a 2.4 degree horizontal beam width. The unit is housed in a waterproof Edson enclosure located under the companionway dodger. It is mounted on a custom built stainless adjustable bracket which permits a wide viewing range. The unit has good fidelity and target definition with all sizes of craft. On a trip back from Catalina we spotted a low flying helicopter! The other feature we really like is the ability to have other integrated information on the radar screen - i.e. depth, boat speed, compass direction, and lat/long position, and even course deviation. This information is fed to the radar through the autopilot and instrument system. There is a guard zone that can be set around the boat, if another vessel comes into this zone, an alarm is activated. When sitting in the companionway on watch at night , all the information you need is to be safe and aware of your surroundings is displayed on the radar screen. Below, at the navigation station, is a Furuno model FMD-811 remote. It has the same read-out and functions great when working at the chart table.

C.A.R.D. 060 -Collision Avoidance Radar Detector unit provides another level of protection from collisions. It is located at the navigation station and provides an audio and visual alert when detecting another vessels radar. This is utilized when our radar is turned off, and the real benefit is significantly lower power consumption.

A Simrad IS15 provides the general boat information system for depth, wind and boat speed, and navigation information, and an alarm function. There are three individual readout displays – one in the cockpit, another at the navigation station, and a third in the v-berth . Each unit functions independently. The display in the forward berth gives reassurance when at anchor at night. You can check boat heading, depth, and wind direction. There are also several alarms for low and high water when at anchor. A data computer distributes the information on a two wire proprietary Simrad protocol. It also transfers it’s information to the autopilot. We have retained our existing Signet depth finder as a backup to this high tech approach.

Our position is maintained by two Furuno GP-31 GPS (Global Positioning System) units mounted in the Nav. Station. A master GPS controls the input to the autopilot, vhf radio, and personal computers navigation software. A second identical unit is strictly backup but could be easily put into service if the main unit fails. We also have a Lowrance Airmap handheld GPS as an additional backup.

We have a personal computer on board that is interfaced to our GPS unit, S.S.B Marina and Ham Radio. The Jeppeson navigational software provide a platform to view electronic CD-ROM charts manufactured by Maptech and SoftChart. The screen overlays Limerence’s position on the chart and provides excellent situational awareness. This is no substitute for printed charts, but an additional aide for safety and fun. We also operate our e-mail program “Sail Mail” with the personal computer when we are away from the dock and phone lines. We intend to use this extensively when updating this web page.

Results
We use pleased with the results of our projects. All systems exceed our expectations and we are looking forward to testing the systems in the long haul. We have learned that this is not a plug and play world and buyers should beware. There are lots of neat products out in the market place but there is still significant difficulty for them to be compatible.