Electric Victor Slocum

[John A. Campbell]

I am now lofting the 15' 10" Victor Slocum inboard motor launch and am interested in using the Minnkota engine-mount electric motor that usually mounts on the lower unit of a big outboard. I would mount the Minnkota on the bottom of the hull at an angle to match the shaft angle of the engine had an inboard engine been installed. I'm looking at the model RT101/EM which develops 101 pounds of thrust at 36 VDC at a maximum of 49 amps......larger units are available at 160 lbs. thrust @ 24 VDC (116 amps) and 202 lbs. thrust @ 36 VDC (98 amps). I would like to have a run time of around 4 - 5 hours varying from 25% to 80% of maximum current drain.

The dry hull weight of the V.S. is going to come in at around 220 pounds (I think) and she appears to be a fairly easily driven hull......she can be seen at http://www.boat-links.com/Atkinco/Utilities/VictorSlocum.html Batteries would be located at the same position where the engine would have been so as to try to maintain hull balance. I have great concern over the weight of the batteries. I have ZERO EXPERIENCE with electric boating......any suggestions would be much appreciated.

[JimD]

Batteries are heavy. No getting around that with current technology. I have a 24 volt minnkota for our sailboat. The batteries make good ballast for a sailboat but darn its a lot of weight if you don't need it.

[dmede]

Interesting idea, I like this approach. I know Atkin was usually very accurate with his drawings per engine weight and water lines so perhaps the battery weight is plus in this case as you would want to keep the spec'd weight of the Baby Husky in order to keep the trim correct.

I forget what the weight of the BH was but I want to say around 200lbs?

Do you have any links to similar installations with this electric motor?

[GregH]

Hello John-

I too have looked at the Minkota EM units- (Engine Mount) The larger thrust units you mention are really simply 2 of the standard units mounted on a bracket which in turn is mounted to the cavitation plate of the outboard/inboard lower unit.

I'm building an 18' catboat, and plan to use the Minkota or similar units- one single motor unit on each side of the skeg. I've contacted Minkota, and surprisingly, they are VERY difficult to get any information from. What they did tell me, however, was that for adequate thrust, you need to figure on 2 lbs of thrust for each 100 lbs of gross boat weight-boat, gear, passengers, etc.

Check out this site for starters-

http://www.solarnavigator.net/electric_boats.htm

It will lead you to many sites on electric boats. Many are in the UK- it seems that British regulations are very strict on gas/diesel powered pleasure boats, so electric power is used extensively there. Good luck!

[Ron Carter]

I'm suspicious of the 2# of thrust per 100# of boat. I'm running a 42# thrust motor on a 14' double ended boat with an inboard well. Not over 500# all up and it is no where near over powered. 4.2 mph at 40 amps which is full speed. Cruises 3.0 mph at 23 amps. This is a 12v system. I matched the wire gage on the motor when I made the control head remote and find that at 40 amps I'm getting some heating and associated line loss. If you are rewiring don't skimp on the wire gage. Electric Propulsion For Boats by Charles Mathys will offer more technical data on motors and props than most of us can digest. I doubt 200# of batteries will give you the range you want. The ideal battery is the 6v golf car type. Put them in series to get the voltage required. At 85# each for 36v you need 510# of batteries and another 50# of wiring and conrtols. Electric is a great evening ride but is slow and heavy.

[RonW]

John, it seems that you decided on electric instead of diesel for the slocum. I take it by mounting the engine mount trolling models that you will still be using your rudder for guidance.

Your figures on amp useage seems high, and the 2 lbs thrust for 100 lbs weight is way to low. You should be quite happy with the 100 lb thrust model at 36 volts.
As I recall, 70 lbs of thrust is approx. equal to one horse, and one horse is roughly 750 watts, and the 70 lb thrust model using 12 volts used approx. 60 amps, so 60 amps times 12 volts equals 720 watts.

So your 100 lb thrust motor at 36 volt should only use about 30 amps on high. Study the trojan battery site.
You can also use 12 volt batteries instead of 6 volt, but they have be deep cycle batteries made to be drawn down in use.
With 3 - 12 volt deep cycles at about 60 lb each, you should get about 3 hours on high at about 180 lbs of batteries.

http://www.trojan-battery.com/Products/RecreationalVehicle.aspx

[John A. Campbell]

Thanks to all for the input...GregH, the listing of electric boat companies has been wonderful reading! I really like the looks of the Pender Launch Co. 16-foot boat...she's 16', 1200 lbs. (about twice the weight of the V.S.), and travels 5.5 mph on 24 VDC (2 12-volt batteries in series) for 3.6 hrs. or 4.5 mph for 6.5 hrs. I'm in contact with them now to get pricing on their 3/4 hp electric drive system. RonW, yes....I decided to forget about the diesel.....too much $$$$, smoke, and especially noise. I want to be able to carry on a conversation with my lady love on one end of the boat and me on the other! Also, I got assurance from Tom Hesselink with Budsin Woodcraft Boats that the 101 lb. Minnkota would be more than adequate for the V.S. His 15' launch weighs 520 lbs., runs 4 hrs. on two 71 lb. batteries (total 24 VDC) and has a 55 lb. thrust motor.

[RonW]

John: sounds like you are beginning to sort things out and get control of the situation. You can recharge those batteries with a golf cart battery charger. It will probably cost you about 25cents in electric.
http://www.evparts.com/firstpage.php

Do report back..

[ddeaton]

John,
I am in the planning stages of converting my Wittholz 17' catboat to electric. I am going to use a wound field motor with an Alltrax model DCX300 speed controller on 36 volts.
http://www.alltraxinc.com/old/
The nice feature of a wound field is that you can reverse direction with the speed controller instead of using a large reversing contactor or switch. Same technology as new golf cart systems. I know someone with a Duffy electric launch that has this system and it will run over 10 hours on a charge and the boat is 8 yrs old. Trojen 6 volt deep cycles are the best for batteries, T105 or T145's. Banks of 6 volt batteries will give you the most amp hour output per # of batteries and weight. I am going to use a 3 or 4 to 1 final drive ratio to the prop. I am trying to figure out how to make battery boxes and what material to make them from. I have 500 lbs of lead ballast in the hull now which I dont mind replacing with batteries. The T105's are 62 lbs and the T145's are 72 lbs. About 400 lbs for my bank with 36 volts.

[Ron Carter]

After looking at the prices on evparts.com I'm certainly going to keep the 45year old Harley Davidson golf car that sits in the shed. The Grand kids run the wheels off of it when they visit but in a few years they will graduate to better rides and I'll have the parts for another "next boat". I've got over $2500 worth of parts by their measure. Charger alone is over $500.

[John A. Campbell]

Many thanks, guys, for all the fine input......I still have a lot of research to do but in the short term, I want to talk with the folks at Pender Harbour Launch Co. about their 16-foot launch and its associated equipment. Their boat is very close in size to the Victor Slocum and is about twice the weight. I'm thinking their 3/4 hp electric drive may be a better option than the Minnkota and so that's what I'm struggling with right now......but I'll look at ALL of your suggestions and keep you posted. I'm doing my lofting on an 18-foot long X 4-foot wide drawing board for profile and half-breadth views and a 6'0" X 4'0" "scrive board" for the body plan......sure beats crawling around on these old knees although took a bit of work & expense to build. I painted the boards white and covered them with 8 X 8 =1" fadeout paper.....can make blue-line copies from this material. They're set and braced at a slight angle to facilitate viewing. I use small 1 1/2" x 1/2" sticks of various lengths, pointed and with notches in the ends and clamped to the board edges with spring clamps to guide the lofting battens......works very well, very easy to see discrepancies (hard spots, etc.), and easy to adjust the battens as needed.

[ddeaton]

John,
I would like to keep up with your research also, as I am not ground in stone yet on my decision. I take from your posts that you are not going to mount the motor inboard, or you havent decided yet? I have another post with no answers yet, trying to figure out how to machine out the keel and deadwood for a stuffing box. I am going with inboard for sure at this point.

[John A. Campbell]

ddeaton, I haven't decided on the motor yet......if I go with something like the electric drive setup as used on the 16-foot Pender Harbour Launch (www.harbourlaunch.com), it will be an inboard or if I go with the Minnkota RT101/EM, it will be sort of a "cross" between an inboard and an outboard in that it will mount on the bottom of the hull in line with and protected by the skeg. For sure I will not have an outboard hanging off the back of this boat. Right now I'm leaning toward something like the Pender arrangement because it swings a larger prop (9" 3-blade) at a lower RPM ( 0 - 1750 max.) which sounds like a better application. I really like the Pender boat......seems like a lot of thought has gone into it......have not been able to get in touch with them yet.

[RonW]

Hey John, all those guys are doing is using a standard shaft and propeller, and then mounting a electric motor in line with it using a v- belt and pulleys for the gear ratio.That is exactly the same set up that is used by duffy electric boats and elco electric launch. In fact both of them will also sell you a complete system.
But a whole lot cheaper is evamerica.com
He sells the same motor that duffy uses, adc electric motor, and everything you need for the entire system.

Glen-l also has plans for a setup where you use the lower unit from a outboard and then a motor setup again with pulleys and belts.
But you don't need the rudder, the lower unit turns for guidance.
http://www.boatdesigns.com/products.asp?dept=474

[John A. Campbell]

I noticed that Pender Habour Launch Co. includes a "prop cage" for their 16-foot launch. This seems like a good idea for the Victor Slocum, powered with the Minnkota EM series of motor to protect the motor from underwater damage. I know the skeg offers a lot of protection but this would seem to be somewhat limited by the thickness (sided dimension is 2 1/4") of the skeg. Comments?

[mcdenny]

Here's another power option: http://www.thunderstruck-ev.com/sailboatkit.htm $980 for the motor, controller and all the electric bits. The same motor is available separately from http://www.electricmotorsport.com/PARTS/parts.htm for $399 although its not shown on their web page.


Its the same brushless DC motor Briggs and Stratton are using in their second generation electric outboard and what B&S are now selling into the OEM golf cart market.

These are really 3 phase A/C motors with an electronic black box generating the wave forms from DC current. They have no brushes and are generally smaller than a comparable brushed DC motor for a given power.

A cogged belt drive system is just two sprockets, a belt and a flanged unit bearing available from any industrial distributor - about $300. You might be able to use a v-belt system at less cost.

You would obviously have to use a standard inboard setup. That's a lot more work than mounting a submerged motor but you get the ability to use any prop size imaginable rather than be restricted to one or two sizes designed for 2000# bass boats.

Speed is limited to a function of WL length and weight but I'd think a pretty skinny light hull could go at S/L of 1.5. S/L 1.5 for a 14' WL is 6.7 mph. At 800# weight (200 boat, 300 people, 300 batts) this would take 2.5 hp. Thats 39 amps at 48 volts. Four Gp31 12v batts weigh 275# and have a 20 hr rating of 105 amps. You could probably run 90 min at 2.5 hp and maybe 4 hrs at half power, 5.3 mph. You could get 50% more range with (6) 6v batts (400#) of the same physical size.

If you use AGM batts you can lay them on their side. Looking at the Atkin website, you may be able to get the motor and 4 batts under that wide center seat. It looks like Mr Atkin expected to use a pretty big prop, well protected by that skeg, which is perfect for electric drive. I'd build it just like he drew it.

I'm about half done with a slender light 25' x 5'8" launch which will use this motor and (8) 6v batts.

[John A. Campbell]

Denny, I don't understand what you mean by "S/L of 1.5". Enlighten me, please!

The brushless motor looks good but I'm still leaning toward the Minnkota RT101/EM although I find myself wondering why the electric boat manufacturers haven't started using them. Could it have something to do with blade area versus RPM balanced against hull design? I believe the Minnkota develops its thrust at a high RPM with a highly pitched prop, something akin to the racing model boats. Still, 101 pounds of thrust from the Minnkota should be the same as 101 pounds from a slower turning motor with larger prop......right? "Thrust is thrust".....right?

[mcdenny]

S/L is Speed Length ratio, its the speed in knots divided by the square root of the water line length in feet. An S/L of 1.34 is commonly referred to as hull speed and is commonly thought to be the upper limit of a displacement boats speed with reasonable power. Getting past the 'commomly', displacement boats that are relatively light and narrow for their length can go up to up to S/L of around 2.0 according to Gerr's Propellor Handbook. Any decent kayaker can paddle at an S/L of 1.5 at least for a short time.

I'm pretty new to the electric boat scene but I think brushless DC motors with appropriate controllers have just recently become available at a consumer price point.

Vetus has a very high end electric drive system using a brushless motor.

Golf cart motors are inexpensive and have been around for a long time. That may explain their use in boats.

Thrust is indeed thrust but it is not, IMHO, a very useful way to compare drive systems unless you are making an electric tugboat. Thrust of a motor in a stationary boat (bollard pull) is a function of shaft horsepower multiplied by prop diameter. Therefore you could cut power in half, double prop dia have have the same thrust. The boat wouldn't go as fast, though. Speed is a function of hp, weight and WL length. Prop dia doesn't enter into it. (All these formulas are empirical, they work for 'normal' hulls and motors.)

The trolling motors have low pitch props and are meant to move heavy, designed to plane with 200hp, fishing boats. No one expects them to go very fast, they are looking to maneuver and maybe buck a current. The trolling motor works like a tractor in a very low gear. Lots of pulling power but not much speed. When you put a trolling motor on an easily driven boat it just loafs along, not pulling much current or driving the boat very fast.

A watt is one volt times one amp, 746 watts = one horsepower. If voltage is constant, current (amps) and hp have a linear relationship.

An electric motor has a rpm for each voltage, the harder it has to work to achieve that rpm the more current it draws and power it produces.

Hook the motor to 12v and turn it on out of the water. It will spin x rpm and use very little current and producle little hp. Now put it on a small canoe tied to the dock. It will still (probably) turn the same rpm but use a lot of current and produce its max thrust and max hp. Now untie the canoe. As the boat goes faster the propellor is easier to turn (but it won't go faster than x rpm), the current (and therefore hp) drops. As the boat goes faster the resistance increases and the motor power decreases until they balance and that's the top speed of that boat and motor at that voltage. A higher pitch prop will load the motor more, drawing more current, producing more power, driving the boat faster. The limit is how much amperage the motor can handle without overheating.

I'd suggest you decide how fast (pick S/L between 1.5 and about .75) and how far you want to go. With the boat's loaded weight and WL length you can back into the drive system and battery bank you will need. Feel free to email me. I have a spreadsheet to does the math.

[John A. Campbell]

Thanks, Denny, for the input.....I've just now sent you an email for the spreadsheet. Allstar Marine in Dallas (a marine repair facility) says the Minnkota motors are not intended for continous use at a high output....that they usually "melt or break" so I'm leaning now toward the "regular" inboard arrangement with cog belt reduction and using the brushless motor, a golf cart motor, or the so-called E-Tek motor from EVamerica. The Vetus is indeed a very high end product......somewhere around $6000 as I recall. The Electric Launch Co. makes a 24 VDC system that sells for $3280. Pretty pricey stuff and seems like a lot of overkill for my boat.

[RonW]

Hey john, email bob at www.evamerica.com and ask him to mail you by e-mail a catalog. He is a electrical engineeer and can design and layout your whole system and sell you top quality parts, everything, at very reasonable rate.Complete system. I would estimate the entire system to be between $1,500. and $2,000 at most. Problem solved. Do use a double pulley and vee belt on the shaft and motor, they run quiet and smooth for years with no problems, cogged belt systems have problems. Simple works the best.

[John A. Campbell]

RonW, I called Bob Batson at EVAmerica and have printed off their Spring 2006 catalog and their EVA Technical Papers. Bob will also be sending me some stuff on electric boat equipment plus a contact with a fellow in Maine who has built an electric boat of about the same size as the V.S., using EVA equipment (also sending me some photos of the boat). Bob said he can furnish everything for the electric drive (recommends the A004009 motor rated at 4.0 continous horsepower) including the motor mounting hardware for inboard arrangement. At first he suggested the Minnkota and I told him I had heard some bad stuff about running Minnkotas continously at a high output (have since heard even more bad news about that) and wasn't too interested in that so we switched over to discussing the regular inboard electric motor driving a 9" diameter X 8" pitch 2-blade prop recommended for this boat and the Palmer engine by Billy Atkin. I've also posted a "visitor's thread" on www.oldmarineengines.com asking for input as to the weight of the Palmer "Baby Huskie" w/gearbox and the RPM range at the output of the gearbox. My reason is to try as far as practical to duplicate the Palmer engine with an electric drive and still maintain around a 4-hour run time without sinking her from excessive battery weight. If anyone out there in Forumland should happen to know the specs on the Palmer engine, I would like to hear about it in case I don't get a response from the "old marine engine" folks.

Thanks to all for your input !

[John A. Campbell]

I have been thinking about (and it has been suggested) that lengthening the V.S. to 18 feet will improve the efficiency of the boat, i.e. make her more slippery by reducing the rocker. Are there any tradeoffs in doing this? I am somewhat hesitant to do this as I really don't care to tinker with William and John Atkins' work but as I recall there have been threads on this forum which indicated this can often result in an improvement. Comments?

[John A. Campbell]

Forgot to mention that if I did increase the length, it would be done at 13% X the spacing in inches between stations so as to arrive at around 17' 9" feet in total without creating anything other than a stretched version of the original.

[geeman]

I have to say that since the wife and I converted our old plastic boat to electric ,we've not regretted it yet.We cant go fast but we're not in a hurry anyway.But we can go silent and we enjoy the quiet more then we miss the noise and gas costs.Our boat is NOt designed for electric ,its a planing boat,but we have fun anyway.BTW We been out for up to 4 hours and never made a real dent in the number 1 battery.Never yet this summer have we had to use all 3 batteries yet.Our setup is as simple as you can get,keep it simple less chance for screw ups and easier to replace repair parts.I'm not saying thats for everyone but it works well for us.

[John A. Campbell]

My lady friend Barbara and I just got back last night from an 8-day trip through New England and visited Mystic Seaport for a couple of days.....we rode the electric launch "Necessity" several times and I am 100% convinced that electric power for Victor Slocum is the way to go.
Mystic Seaport, Walden Pond, Kankamagus Highway, cog train to the top of Mt. Washington, and all those coastal villages along Route 1 from Bath, Maine to Bar Harbor..................I feel like I've died and visited Heaven......wonderful seafood, scenery, tons of wooden boats, and very friendly people all along the way......we will go back every year from now on......if I didn't have such deep roots in Texas, I'd move there today.