Coastal Cruiser - Walter's Solar/Electric Catamaran
My wife and I love kayaking, but as we get older it becomes less enticing to go out on a weekly basis. Sailing seems ideal at a distance, but in reality it is a lot of work and maintenance. Hobie catamarans looked like a lot of fun, but my wife was pretty clear on her aversion to capsizing. Instead of a Hobie catamaran, I decided to build my own boat using already existing parts.
With this article, I hope my solar powered boat, Coastal Cruiser, will inspire others to seek more eco-friendly marine recreation.
The first boat in 2016 was made from the hulls of a Hobie catamaran. I removed their hardware and made a stainless steel frame to connect them and provide a floor. The first motor was a trolling motor powered by two lead acid marine batteries.
Walter's first boat in 2016
We quickly found that trolling motors are, oddly, only for trolling so I upgraded to an electric outboard of my own design. It was essentially an 11 hp golf cart motor that drove the propeller via a cogged belt.
Belt Driven Motor
The boat was now powered by four LiFePo4 Lithium 100 ampere/hour batteries. This was great for a calm river. We could cruise all day at 4 to 5 knots with a maximum of about 8 knots. Its footprint was 20 feet OAL (overall length) by an 8 foot beam (width).
The one problem with this motor was that the belt was enclosed in a tight space and the normal dust from a rubber belt built up and caused a failure.
My 2018 model is an improved version of the original motor using a Johnson lower end.
Current Outboard and Backup
Increasing the Boat Size
We tried the second version on Long Island Sound, and it was obvious after the first waves, that, as they say in Jaws, “We’re going to need a bigger boat.” The problem with a bigger boat is the maximum you are permitted to trailer without an escort is 102 inches. Plus, winter storage is very expensive.
Solution: A Boat That Folds
I determined to figure out how to fold up the boat so it could be transported on a trailer.
My boat design uses three outrigger arms on each side operated by hydraulic cylinders that contract the boat when traveling on a trailer and navigating narrow waterways. The front hulls fold up manually and the rear hulls are raised by hydraulics.
Since the boat went from a 7 foot beam to a 12 foot beam, I needed a proportional length for the width. I added hull sections so the OAL went. from 20 feet in length to 33 feet. Although the trailer size is 7 foot by 20 foot, on the water the boat opens to 14 foot by 37 foot.
2018 Boat Loaded on Trailer
The boat is very stable. The Hobie had dagger boards through the hull to assist in making the boat more maneuverable and track in a straight line. The problem with a rigid board is that it’s unforgiving when (not if) you hit something. I mounted the dagger boards on a shaft so that they are spring loaded down and will be pushed back by rocks. A hydraulic cylinder lifts them up.
Design for Comfort
The design of this boat is a bit more elegant than the first model. It has a floor space that is 8 x 10 foot. There are four plush upholstered chairs, a table in the middle and two marine coolers for storage or additional seats. There is a nicely shaped, stylish console with three cabinets and four drawers. It has a full array of instruments, controls, computer and monitor built in to the console, visible in full sunlight (2000 nits).
The console hinges forward to reveal the eight lithium batteries (two banks) and the hydraulic pump and controls, seal this compartment when it is set upright. The steering and outboard lift is hydraulic.
Incidentally, lithium batteries are recyclable so the solar boat is not the dirty energy some suggest.
By making a “Boat Float” out of eight 55 gallon drums we’re able to keep growth off the hulls. We use a pool motor to pump water in and out of the barrels. Evacuation time is about eight minutes.
Solar Panel Placement
I had originally tried placing the solar panels in front about a foot off the water, but unfortunately we had a very dramatic example of how heavy a two foot wave can be. It bent the panel supports and pushed it under water so that we could only travel backwards. For the current model I made my own bimini top and structured it to hold twelve 100 watt solar panels on its surface with fabric that snaps on underneath.
Front View 2018
Cruising and Parking
We retract the main hulls and raise the rear ones when coming into our slip. This makes navigation easier, (the waterway isn’t as wide as it looks when you have a current and a wide boat). It also allows us to rent a more economical slip. Cruising is quiet, stable and peaceful (if the swells are less than one foot). Our favorite area is the Thimble Islands. We go out on one bank of batteries with the solar panels assisting and return on the other. There is plenty of power to be out all day. The excess comes in handy if the weather changes and you want to get back in a hurry. When at our destination we can cruise at two to four knots with just solar power depending on the time of day and year. Overall we go faster than the average sailboat without the work.
Walter Meltzer is a member of CT Chapter Sierra Club and cofounder of two laboratory automation companies. See more at Walter’s blog:
Additional Technical Details and Photos
For those readers interested in the technical details of the performance and the construction plus additional photos, click here.
Technical information 2018 model:
OAL – 37 ft extended – 21 ft fully contracted
Beam – 14 ft extended – 7 ft fully contracted
Weight – 2250 lbs
Draft – 12 inches
Motor – Motenergy ME1004 – 10.75 hp at 48 volt.
I run at 25 volt which produces about 6 hp
Batteries – 8 Lithium 12.6 volt LiFePo4 100 ampere hour
These are run in serial/parallel for 25.2 volts
200 ampere hours per bank
PVC (solar panels) - twelve 100 watt panels (at equator)
In Connecticut they will output 80 watts at noon in July
Max total – 960 watts – approx 4 knots
Modes: Charge Bank 1
Charge Bank 2
Speed Data – (approximate readings):
2 knots - 15 amps - 500 watts - 1/2 hp
3 knots - 20 amps - 500 watts - 2/3 hp
4 knots - 40 amps - 1000 watts - 1 1/3 hp
5 knots - 60 amps - 1500 watts - 2 hp
6 knots - 100 amps - 2500 watts – 3 1/3 hp
7 knots - 160 amps - 4000 watts - 5 1/3 hp
8 knots - 250 amps - 6250 watts - 8 1/3 hp
Approximate Cruising Time without solar panels:
16 hours at 3 knots
8 hours at 4 knots
5 hours at 5 knots