An Electrified Horizon Cat

[cdflan]

           An Electrified Horizon Cat
I fell in love with the Com-Pac Horizon Cat (1) on first sight when it was introduced at the 2002 St. Petersburg Sailboat Show.  Probably nostalgia as it seemed a duplicate of the 20' Crosby catboat that a boyhood buddy's father trusted us enough to let us cruise all around Narragansett Bay.  No auxiliary power in those days and although the Horizon Cat is offered with diesel or outboard options, neither seemed appealing in a boat this size.  Hence the quest for alternatives and the eventual focus on the practicality of electric propulsion.

There are a large variety of electric drives available today ranging from large inboard mounted electric traction motors to something resembling a trolling motor.  As important or probably more so is the choice of a battery system.  The first major branch for that decision is lithium ion versus lead acid.  The power density of lithium ion for a given weight, space, voltage, current draw and charge characteristic is clearly superior to lead acid.  On the negative side is the much higher cost, need for protective circuitry and risk of runaway fires.  On a displacement boat with a keel, weight is not a problem.  Space is a problem on this boat for an inboard installation to find room for both a motor and a battery bank (particularly lead acid) as well as managing the center of gravity. Depth of discharge, efficiency at high discharge rates and rapid charging which weigh heavily in favor of lithium, were not important in this application for auxiliary power and overnight charging.  In the end, lower cost and lower risk led to an AGM lead acid choice.  

The battery decision, desired cruising range and the associated space limitation pretty much dictated that the power unit needed to be an external integral motor/propeller package.  Other considerations about motor mounting, propeller shafts, shaft seals, struts, further tipped the decision that way.
Of the products available today, the units produced by Mastervolt and Torqeedo were the best potential match to my requirements.  The PodMaster (2) clearly provided the easiest installation to the hull but required sizeable space for the associated control unit and would require widening the keel to accommodate the width of the mounting pad.  On the other hand, the Torqeedo (3) units are all outboards and would require substantial modification to install in the Horizon Cat.  In the end, the compact design of the Torqeedo power unit, the width of the fairing which perfectly matched the flat on the keel and the miniaturized control module won out.

Next was the question as to how much power was required to get reasonable cruising speed with reserve capacity for adverse wind and current.  There is considerable literature on how to calculate required power (4) but specific data for this boat wasn't available.  It was possible, however, to get the approximate RPM for the Horizon Cat required to reach hull speed and using the power curves for the optional Yanmar diesel engine, it would require just under 6HP or 4 KW.  This was consistent with estimates from the literature and also matched available products from both Torqeedo and Mastervolt.

With the power requirement defined, the questions turned to battery capacity, cruising range and available space for installation. The calculated hull speed for a 17.75' waterline is 5.65 knots which would theoretically require 4KW.  At a more efficient cruise of 80% hull speed, power requirement would be about 30% of maximum or 1.2KW.  I chose an arbitrary limit of 8 hours which at 4.5 knots would give a range of 36NM and require a battery capacity of just under 10 KWHr.  

So as not to keep you in suspense, the final results from speed trials were a max speed of 6 knots at 4KW, cruise at 4.5 knots for 40 NM at 800 watts or 5 knots for 30 NM at 1250 watts.

Both of the power units selected operate at 48 volts so a battery bank with 208 AH capacity would be needed.  Survey of user comments on batteries for this type application focused on products from Trojan, Lifeline, Odyssey and US Battery.  Trailer Boats magazine had an excellent article in the May 2011 issue that covered battery technology and available products. (Trailer Boats ceased publication that June but reprints can be found on the Trojan website (5).)  Of all the 12 volt AGM batteries, Odyssey offered a unique form factor in their PC1800-FT with a width of less than 5" and the right AH capacity.  My thinking was that the 5" width would allow 4 batteries to slide into the space where the diesel inboard was normally mounted.
With motor and battery selection made, system design and installation details were the next task.  The first problem was that the combined width of the four batteries and the sliding tray was just a hair wider than the space available.  Com-Pac suggested that one of the batteries could be located in the keel forward of the centerboard trunk in lieu of ballast which turned out to be an elegant solution and helped with keeping the CG within bounds.  

The remaining three batteries were mounted on a tray and strapped down beneath the companionway step where the diesel engine would normally be mounted.

The standard battery platform is located aft of the starboard berth under the cockpit seat and was the perfect location and size to mount a ProTournament300 Quad battery charger and a 48v to 12v Kelly Controls converter.  The charger provides current and balancing to all four batteries simultaneously and maintains a float voltage after full charge.  The converter supplies the house panel with the standard 12 volts and avoids unbalancing the bank by drawing from a single battery.  The back of the bulkhead at the aft end of the bunk provided mounting for the switchgear.  A 30 amp shore power receptacle was connected to a double pole marine breaker that fed a 110v ac duplex outlet and the battery charger.  The dc side was controlled by a 130 amp switch/breaker for the motor power and a toggle switch for activating the 12v converter that feeds the standard house electrical panel.  Wiring for the motor circuits was #2 tinned marine cable (heavier than required for the 83 amp max current but chosen to minimize voltage drop).

The motor installation was a bit more complicated.  The Torqeedo Cruise 4.0 is designed as an outboard motor with optional remote control or tiller control.  The motor/propeller unit is supported with a heavy, round stainless steel tube surrounded by an extruded aluminum fairing.  The tube is clamped to the transom mount mechanism and topped with the housing for the control module.  Modifications started with removing the control unit (two power leads, a sensor cable and the mounting clamp); removing and discarding the transom mount and slipping the fairing off.  The plan was to install a fiberglass tube through the keel extending into the cockpit to a height that would allow remounting the control module beneath the seat grating under the tiller.  Com-Pac felt this was feasible as they use a similar arrangement for the rudder stock tube in some of their boats.  Fore and aft placement was touchy as the flat section of the keel narrows towards the stern limiting the aft location to accommodate the fairing width.  The forward location was limited by not wanting the control module to protrude into the cockpit area.  Initial decision was to cut off the projections on the aluminum control module base casting (which was done) but eventually we had to mount the control head sideways to meet all the constraints.  The motor support tube was cut down to a length that gave the proper tip clearance for the propeller and adequate extension above the fiberglass tube for a split collar and mounting of the control module.  The fairing was cut to match the angle of the keel.  Assembly included rubber sleeves around the tube and rubber pads at the keel and tube top for vibration isolation.  The unit was locked into place with set screws in the split collar bearing on a plate over the top of the fiberglass tube.  The remote throttle was mounted on top of the teak grate just below the tiller.

The finished boat was launched in early October.  She sails well, handles well and the electric motor is a joy.  Quiet – a bit of whirring when under power;  responsive – just drop your hand from the tiller and push the throttle as you come into the wind when rounding a corner in the channel; economical – about $1.10 for a full day under power; and virtually no maintenance!

Speed-power data was gathered in a sheltered area with light wind using the GPS and power readout which is provided by the control module and is shown below.    .
Speed   2.9   3.9   4.3   4.7   4.9   5.2   5.4   5.5   5.7   6.0
Power   250   500   750   1000   1250   1500   2000   2500   3500   4000
Range   98   64   54   34   31   25   21   17   13   12

Speed is in Knots; power is in Watts; range is in Nautical Miles based on 80% depth of discharge and the rated battery capacity up to 1250 watts.  Range is probably optimistic above that due to decreasing amp hour capacity above a 25 amp draw.

Based on this data, an efficient cruise speed under power would be between 4 ½ and 5 knots.

I am very grateful to all of the people that helped me with information, answers and suggestions but especially grateful to the staff at Com-Pac Yachts for advice and letting me do this project as well as to my Torqeedo dealer that provided the info for dissection of the power unit.

The boat was christened  NOSTALGIA !

References:
1.   http://www.com-pacyachts.com/trailerable-catboats/horizon-cat.html    
2.  http://www.mastervolt.com/marine/products/podmaster/podmaster-421/   
3.  http://www.torqeedo.com/us/   
4. a)  Dave Gerr's design books
   b)  http://www.mindspring.com/~jimkerr1/sebebts.htm
   c)  http://www.electricoutboardhandbook.com/
   d)  http://electricseas.org   
   e)  http://groups.yahoo.com/group/ElectricBoating/            
5)  http://www.trojanbattery.com/pdf/trailerboats_batteryguide_201105.pdf

[capt_nemo]

Congratulations on a design and installation job VERY WELL DONE!

Intrigued by electrical propulsion of boats and cars, I particularly enjoyed reading your most informative post.

Keep us informed as you continue to gain experience and performance data on your system.

capt_nemo
Sun Cat "Frisky"

[Aldebaran_III]

What an interesting post. Lot's of great information there. Well done on electrifying the HC.
I looked into it when I was buying my new HC. I had kind of settled on Super B lithium batteries (out of Holland). The TCO over the life of the batteries actually worked out lower than Lifeline AGMs. Unfortunately the up front cost was too much.

I would have used a Torquedo, but I was going to take the easy route and install it outboard. Your permanent mounting solution sounds great and keeps the sweet lines around the stern of the HC.

I sure there are a lot of people here who would love to see some installation photos. Especially the inside and outside details of the motor mounting and thru-hull.

Great job,
Cheers,
Derek

[Bob23]

Very interesting indeed! I'd be curious to see the ranges and performance while motoring into a headwind and/or current. This would be a wonderful repower project for a 23. A job very well done and artfully reported upon. We are all waiting for photos.
Bob23

[Aldebaran_III]

The pics are showing now. It's a really great job, it all looks so professional.
That prop must be very efficient with all that clear water around it. Also I would imagine it puts plenty of water past the rudder for low speed steering.

Cheers,
Derek

[cdflan]

Did a yacht club cruise this past weekend, 32 NM each way.  Closed hauled with light winds out bound so motor sailed at 3-400 watts at 4.5 KT cruise.  Broad reach on way back with 3.5 KN under sail so kicked in 2-300 watts to cruise 4.5 to 5 knots.  Trip time about 7 1/2 hours each way. Didn't drop below 60% of battery capacity.

[Eric in Seattle]

Thanks for sharing this information.  I am very intrigued by this concept and will seriously consider this type of setup for my Sun Cat Daysailer when it becomes time to replace my outboard.  I am used to inboard engines and dislike the hassles of an outboard (i.e. raising and lowing the engine, priming the fuel, multiple pulls to start (sometimes) and finally turning both outboard and rudder).  It seems as your solution is much more practical that an inboard and eliminates all of the hassles of an outboard while cleaning up the stern.

Could you provide a little more detail as to how you actually cut holes in your boat and installed the fiberglass tube?  Did you do the work or have a shop do it? A couple close-up pictures of the tube installation would be appreciated.  From the one picture that shows the motor protruding from the hull, it appears that the hole in the hull has been cut to match the shape of the shaft as opposed to a round hole from a tube.  It appears to be a much cleaner installation than a motor dropped through a tube but I can't see how one would install or remove the motor without taking it apart. 

[cdflan]

Eric
We did the hole in the keel as the boat was being built which made it a bit easier but you could do a retrofit almost as easily by going through the cockpit sole and then the keel.  The hole is round (the foil shape you see is an aluminum extrusion, cosmetic fairing) and the "spine" of the motor is a 40 mm. heavy wall stainless tube.  More on that later.  Don't know the Suncat that well but the tricky part would be glassing the tube to the hull on the inside of the keel while working under the cockpit. (It would also be feasible to epoxy the outside with a small filet and then relive the aluminum fairing to fit over it.)  For the tube, I ordered a 2"OD, 1/8" wall fiberglass tube from McMaster Carr.  Since the deck/cockpit molding was put on after the tube, Hutchins drilled a large hole in the cockpit sole and then bolted a tight fitting aluminum plate around the SS shaft to the sole which you wouldn't need to do.
For the installation, I removed the transom mount/clamp assembly and the control head.  Both are just clamped around the "spine".  The parts list shows an exploded view of the construction on this web site  -  http://www.torqeedo.com/images/pdf/pdf_ersatzteile_usa/Spare_parts_list_Cruise_2.0_R_4.0_RT.pdf.  I cut down the foil shaped fairing to match the angle of the keel and a length to give 1 1/2" prop tip clearance.  Also had to cut down the length of the SS tube using a standard pipe cutter.  The motor/tube unit was slipped up through the tube with a rubber gasket between tapered fairing and keel.  It is held in place using a 1 5/8" SS split collar which was remachined for the 40 mm tube diameter; two holes were drilled axially and threaded for set screws.  The tube was cut about 5" above the sole, topped by a rubber washer, 1 3/4 SS washer and then the split collar was clamped on.  The set screws draw the unit up against the keel and provide compression for the gaskets.  The two power leads were then cut to the new length and compression terminal lugs applied.  The control head was then reclamped to the tube and the cover installed.  I cut the handle/ends off the cover to make it more compact and mounted it sideways so that it was out of the way under the grate between the seats.
Send me your email address and I'll send you some of the construction pictures that show the hole/tube, etc.

[capt_nemo]

In 2009 I printed out a photo on ebay of a 2001 Sun Cat with a Minn Kota RT55EM electric trolling motor mounted on top of a stainless bracket attached to the underside of the aft end of the keel. The bottom of the prop was at or slightly above the keel bottom which protected it. Ran the short single control wire up through a waterproof hole in the hull. Charged his 2 Optima D31M Deep Cycle batteries with a 55 Watt Kyocera Solar Panel mounted on the boom gallows.

Installation looked well thought out, quite clean, and most importantly SIMPLE!

Just more food for thought.

capt_nemo

[Eric in Seattle]

Thanks for the info cdflan and capt nemo.  My email address is kuehlfamily@msn.com if you want to send me some pictures.  Your original posting inspired me to look into various electric motor options.  I really like the concept of Mastervolt's Podmaster or Krautler's submersible flange motor (Google them).  Either one could be mounted on the hull directly aft of the keel.  Unfortunately both are very expensive and a full installation of either would probably cost more than the boat is worth.  It would be nice if there were options similar to these in the same price range as a Torqeedo.  The trolling motor option that capt nemo mentioned is certainly a less expensive option but I've read that trolling motors aren't adequate as a primary motor for a larger boat because they don't have the required torque (power) to be able to effectively maneuver the boat.

[skip1930]

My old boss had one of those electric dock tenders boat in his 'toy box' used to ferry people out to there boats hanging on cans.
It was a very pretty looking boat. As far as I know it has been sitting in storage for many years.

Milwaukee South Shore harbor used one of these for a few summers. They sold it off.

Let me say this about that.
A very interesting and noble experiment.
I think back at the 200+ manufactures of electric vehicles that have come and gone through the ages.

I guess if the sailor has deep pockets electric is the way to go.

We have a guy who owns Austin Straubel Machine shop in Green Bay who drives his two Tesla's, one two seater [$?] and one four seater [$90 k] and fly's a twin engine jet [$1.7 million] here in Sturgeon Bay. His son works at the Tesla factory in California.

I'll be a believer in battery powered things when a fully loaded, battery powered, Boeing 777 fly's non-stop New York to Japan on one charge.

skip.

[CaptRon28]

I occasionally sail my diesel powered Horizon in a fairly large local reservoir. No gas or diesel allowed, so I picked up a mid-size electric trolling motor which I mount to the aft swim ladder on a home-built bracket. There are photos and a better description in the Horizon section. Boat already had 2 deep cycle batteries so power was not an issue.

It works, but I'd rather not be out on the lake heading into 10+ knots of wind with the trolling motor. Also has problems trying to hold the boat into the wind to lower the sail. Max speed is maybe 2 knots and change.

[capt_nemo]

I usually raise and lower sail with no power on at all. The OB is lifted, tilted, and secured before I concentrate on raising sail. Lowering sail is usually accomplished first before lowering and starting the OB. Just allow plenty of sea room for drifting around. Doing one thing at a time greatly simplifies life aboard and helps to avoid potential injury.

With a little practice and taking your time it's easily done.

capt_nemo

[cdflan]

The PodMaster was my second choice and the Krautler products look excellent but limited presence and pricing info in this country.  There are a large number of potential products and this site lists most of them  - http://www.nauticexpo.com/boat-manufacturer/electric-motor-1626.html.  Yes, electrics have come and gone over the years but Elco is still around after over a hundred years.  Battery technology (and controls to some extent) have improved to the point where it's feasible for many people.    As pointed out in my original post and the post about my 32 nm cruise, I can cruise all day (7 to 8 hours) at 80% of hull speed. As for wind and current, deduct the speed of the adverse current from the table above and you have the answer.  No question that going through an inlet against a couple of knots either requires patience or a splurge of battery capacity.  Haven't tested impact of head wind but impression is maybe 1/2 knot.
Pod Master has been installed on several day sailors recently but the much larger mounting footprint and the separate large control box were major drawbacks over the Torqeedo for me.
Cost wise, the motor, batteries, cables and charger totaled about $6500.  Miscellaneous parts added a couple hundred but the total, not counting my labor, was still considerably less than the diesel engine option (but much more than an outboard).
On raising or lowering sail, just head into the wind, drop hand to the throttle for a little headway, engage tiller clutch or autopilot, tighten lazy jacks and grab the halyards!