electric outboard for 28ft catboat.

[gschuld]

Hello fellas.

I have a question for the electric propulsion over achievers hanging out around here. Here goes ...I have a 1924 28ft racing catboat (wooden)that I am interested in installing an electric motor on. Any kind of inboard installation would be out of the question. The class rules forbid it, I would know, I wrote them!
I would like to keep the boat at my house which is on a man made lagoon that is roughly 600ft. from open water (and the race course). I have no intention of cruising mile after mile a 6knots or anything here. I would like though to be able to simply power out of the lagoon and back from sailing to be able to make "lagoon living" more reasonable for my boat. And if I happened to be out for a night sail and the wind dies on me, I'd like to know that I could get back fairly easily from a say 1-1.5 mile max distance from home. I would like to be able to atleast make some headway into a 10knot or so breeze for short bursts.
The boat is carvel planked, very smooth (hauled and scrubbed bi-weekly), and the class has a minimum weight of 4700lbs. ready to sail without crew. The max crew weight allowed is 1600lbs. (oh yeah...lots of live ballast...did I mention 650sq.ft. of sail area and no ballast other that crew..fun stuff). If you would like to see the boats I am talking about go to bayhead.com and look at any PM BBYRA races. So with a full load of crew the total weight is about 6300lbs max.
My boat's natural weight leaves me with the ability to run about 160 lbs or so of battery weight to "make weight" in the class. I checked with the rules committee and got the OK to use batteries in place of the usual lead that I have been carrying as long as I'm up to the 4700lb. weight and it's placed in the same place.
Since bilge pumps and a relatively powerful marine cd player are regularly used, I'd also like to be able to rely on the extra 12 volt power available to me. I realize that 24 or 36 volt power might be a better power source solution for propulsion, but I'd like to stay with 12volts if possible. The only reasonable propulsion unit that I could come up with is a trolling type motor that can be easily dismounted and stored below. The weight of the unit would be somewhat important as the trolling motor would not be considered part of the boat in the eyes of the rules and so would be extra weight beyond the 4700lbs. necessary. Anything in the trolling motor size would not be an issue to me weight wise. Recharging would be no problem as I have a power source for a battery charger where I'll keep the boat.
Any thought as to whether 4 fresh deep cycle batteries (in 12 volt form) would be sufficient to propel my craft given my performance desires?

Would 24 or 36 volts be a significant improvement over the 12 for my situation?

Thanks in advance,

George

[gschuld]

Oh yeah. Any recommendations as to trolling motor models, thrust ratings, battery types, etc?

George

[Fanie]

24V or more voltage trolling motors are much more efficient than a 12V one. If the batteries weight doesn't worry you, you could install a trolling motor. An 8m boat to be drawn by a trolling motor will work, however in strong winds you may pick up problems. Also if the wind dies on you you and you're out somewhere you could expect only so many hour's life from the batteries depending on battery size. It also means carefull maintenance of the batteries when not used, you have to charge them properly after each use. If you do get the trolling motor, get the biggest one you can afford. Minn Cota and Moto Guide makes nice ones, I prefer the Moto Guide. You can google for them.

I would suggest you do get the baby outboard and store it below - just for real emergencies.

[Rick Willoughby]

Fanie is right if you want to push a boat your size with some conviction. I would recommend something like this:
http://www.rayeo.com/motors.htm

I am looking at an application using an Etek motor and Sevcon controller but I will make my own drive leg. Briggs and Straton offer an outboard with the Etek motor but I have not found a distributor.

I have two small Fullriver VRLA betteries for doing some scale trials and I would recommend you use VRLA type rather than flooded batteries. The gel version are supposed to give better cycle life than AGM version. I have so far looked at Surrette, Haze and Vision VRLA gel batteries. The Surrette site has some useful information on battery life and care.

Thrust does not mean much unless you have a tug-of-war or simply want to tether the boat to a jetty and see what load you can pull. That is what is being measured. It is power that matters from the perspective of actually making way. A large diameter slow revving prop will yield higher efficiency and higher speed against a breeze than small diameter prop turning fast.

So a trolling motor will move the boat but if you want to make a fair speed in moderate conditions then you should be thinking about 4 to 5HP for the size of boat you have.

Rick W.

[FAST FRED]

Briggs and Straton offer an outboard with the Etek motor but I have not found a distributor.

There may be old British Sea Gull engines in your area , some were geared to swing a rather large prop to move good sized sailboats , so the down leg might be suitable.

FF

[gschuld]

Thanks for the feedback fellas.

I would really prefer to use the standard trolling type drive system. The boats I sail use underhung barn door type rudders that are 4 1/2 feet long and extend 18" aft of the transom and the rear upper edge sits above the waterline by about 4 inches. Believe it on not I would prefer to be able to mount the motor/prop end of a higher thrust motor/prop combo to a fixture that clips right on to the aft edge of the rudder itself. I am a boat builder with lots of experience making custom bronze hardware so mounting though unorthodox won't be a problem. So simply the power wire would be connected to the boat with controls mounted inboard. This way the docking control would be great since the driving force would be inline with the rudder. To remove it would mean reaching down, disconnecting it from the rudder, and unplugging the wiring from the top aft edge of the deck from it's water resistant plug. Nutty idea right. Theory seems feasable, though admittedly complicated. I doubt that I would ever need more than 15 minutes worth of run time at a reduced power setting. Sticking with 12 volts as a power source would be very helpful if possible. Does anyone think 4 batteries hooked in 12 volt would work well enough with a trolling (motor in water) type gear foot? If I went to 24 volt, I would only be able to use 2 batteries as I need at least one in 12 volt to run other things. If I went to 36 volt, I could probably run 3 batteries. Sticking with 4 (12 volt) bateries would be preferable though if not unrealistic.

Thanks,

George

[Fanie]

George, between the same thrust 12V and a 24V trolling motor the 24V motor would outlast the 12V motor by quite a bit. 12V is very unefficient. I had both in the past, and have a 24V on the moment. (sigh) If my father didn't have such a poor son I would have had one of those 110lb thrust remote jobbies on my boat. Too many nice to have's to afford them all. In theory the 36V would last about 25 to 30% longer than the 24V.

To give you a 12V / 24V effieciency idea, the 12V neon lights we make draws 800mA, while the same (24V model) light draws only 200mA off 24V.

[gschuld]

Bummer,

If I go outside 12 volts, it would likely be 3 batteries in a 36 volt configuration.

George

[Fanie]

You could use mains as well. Just needs a long power cable which reminds me... Nothing prohibits you to put a fueled generator on board.

[gschuld]

I don't think a generator would be a good idea. Trust me it is not that kind of boat. Check out the bayhead.com website under A-cats. Great pictures

Thanks for the thoughts though

George