electric C-Dory 22

T

Tom Hruby

Member
Hello everyone,
I just want to introduce myself. I have commissioned a C-Dory 22 cruiser from NMI in Bellingham. I will be powering this boat with two electric E-propulsion Navy 3.0 motors. I am not a speed freak and will be cruising at hull speed. With 48 V 400 AH I expect a range of about 40 miles. I will post real data on this site next spring when I get the boat in the water.
FYI I have been cruising electric on Puget Sound for 26 years in home built 26ft St. Pierre Dories. This will be my first experience in adapting a commercially built boat to electric.
For those interested, I wrote a book on converting to electric propulsion that is available at Duckworks in Port Townsend.
Tom Hruby
 
Tom Hruby":niczg6yv said:
Hello everyone,
I just want to introduce myself. I have commissioned a C-Dory 22 cruiser from NMI in Bellingham. I will be powering this boat with two electric E-propulsion Navy 3.0 motors. I am not a speed freak and will be cruising at hull speed. With 48 V 400 AH I expect a range of about 40 miles. I will post real data on this site next spring when I get the boat in the water.
FYI I have been cruising electric on Puget Sound for 26 years in home built 26ft St. Pierre Dories. This will be my first experience in adapting a commercially built boat to electric.
For those interested, I wrote a book on converting to electric propulsion that is available at Duckworks in Port Townsend.
Tom Hruby
Click to expand...

Are those two motors going to have enough reserve power to get you out of sticky situations? I would be more comfortable with the Navy 6 motors for a 22. It's better to have extra power and not use it vs. having no choice in the matter.
 
It appears that the Navy 3 is 6 hp and the navy 6 is 9.9 hp. I have ordered the book, and am fascinated with the concept. I probably would have also ordered the higher hp. I have written about this before, but my father had a 26' fin keel sailboat which had about the same freeboard and an arc bottom similar to the C Dory 25. We used a 1931 Johnson 5 hp for many years for propulsion, including hundreds of trips to Catalina. The speed of the old 5 hp onboard would drive this boat at about 5.5 to 6 miles per hour. I have carried the 3 hp Torpedo for my dinghy for at least 10 years, and used it as a "kicker' on the 22 and the 18' Caracal Catamaran that I use primarily for fishing and as a bay boat. For the Caracal,it will move it at a little over 3.5 mph, The 22 also about 3 miles per hour, and the 25 slightly less.

I lost power in my 62 foot ketch just as we were entering the harbor at Brest France. I put our dinghy in the eater, and we moved the back 62' 35 ton boat at 2.5 miles per hour with 4.5 HP!!! That was enough to have steerage way.

Why did you choose the "Navy 6" over other brands. What will you use to charge your batteries, and how long will that take with solar?

We cruised the inland passage to AK for 4 seasons (April thru Oct) and wintered our Cal 46 (motor sailor) in Sequim. We usually ran at 6 to 7 knots. At that speed, we were basically limited to one pass per day. With the same trips in C Dory, 22 and 25. with the speed we could do multiple passes per day. with speed in the 18 to 20 knot range.

Looking forward to what you do and how it runs. Thank you and welcome aboard!!!!
 
Thanks for the post. (Following)

Was wondering how your are coming up with numbers that compair a 12 foot aluminum boat (on the Navy spec. sheet) and the weight and windage of a C-dory 22? How are you going to get 40 miles out of two of these motors? My math shows your going to need at least 8 hrs of running time if you make 5 mph good. That's 12,000 watt hrs. of battery power. $$$$
 
Exciting, nice to see people pushing the electrical envelope with a c-dory. Are those motors brushless? I met a guy who built an electric canoe with foils that topped out at 20kn or so.

I’m interested in the Minn Kota Quest brushless 36v bow mounted motor and hope to drop my 9.9 kicker and keep my 150hp main gas.

What batteries do they run? I’m debating between a premium SOK marine lipo4 12vX3 or more budget batteries with a good bms and low temp cutoff.

Guys are running 3-400W of solar to keep their trolling motor batteries topped off, but 2-3x as much would likely be ideal.

Appreciate you bringing your wisdom to the community.
 
Thanks for the interest. I will try to answer some of these questions. In doing the research for my book I found an equation in Dave Gerr's book "The Propeller Handbook" that had four variables: speed, Length of waterline, shaft horsepower, and cruising displacement. If one knows any three of these variables the last one can be calculated. I adapted this equation to provide me with how many kW of power I would need for different boats. This equation is for displacement speeds, not planing. I am using it because it matched the data from my electric St. Pierre dory almost exactly (98% at all speeds). I am expecting the cruising weight of my new C-Dory to be 3500 lbs. At that weight I would need 5kW to get to hull speed (5.8 mph) and the 3kW E-propulsion motors (total 6kW) would give a maximum speed of 6.9 mph. The two Navy 6.0 motor would give me 12kW but only bump up my speed to 8.7mph. Doubling my power usage only increases my speed by 1/4. To me that is not worth the difference since the 6kW motors would require 1/0 cables instead of 2 gauge, larger fuses, etc. To cruise at 5mph I would only need about 2.5 kW.

The data I found on the internet suggest that the C-Dory 22 needs 11-12 mph to start planing. To get that speed I would need at least 20-25 kW.

Cruising at hull speed or below one needs to cruise like a sailor- watch the tides and winds, especially here in Puget Sound. That said I have successfully cruised 26 years in Puget Sound. My last dory had two Minn Kota 36 V trolling motors with a maximum power of 1.8kW each, but I usually cruised at 1.2kW each (2.4 kW total). If one is not fighting the tide then wind becomes the most likely threat. My St. Pierre dory had a leeway of 1.5 mph in a 25mph wind. I assume the C-Dory 22 will be similar or less, so the two 3kW motors are more than adequate.

I chose the E-propulsion motors for several reasons. 1: The motor is direct drive and underwater which makes for a quieter ride. The only other common direct drive outboard is the Torqeedo which is more expensive ($3000 vs. $4200). 2: E-propulsion is the only outfit that has a dual throttle and a steering linkage for connecting the two; 3. The warranty is 3 years instead of two (if you get on their mailing list); 4. E-propulsion has been around for a number of years and has dealers around the country.

I hope this answers some of your questions. Please feel free to ask more if you have them.
 
OOPs. I missed some of the other questions:
I will probably add solar panels. I had 540 watts of flexible panels on my dory and that would give me about 2.8 mph in direct sunlight or four hours of sunlight were needed to run one hour at 5 mph. At most the panels were putting out about 320 watts.

Also, don't be confused by the hp rating of electric outboards. The Navy 3.0 is 3 kW which is actually only 4 hp. The numbers provided by E-propulsion and Torqeedo, and all the others are "comparisons with" gas motors. For calculating speed and power consumption one needs to use the actual kWatt rating of the motor; not the hypothetical "gas" equivalent.
 
IME, the true hull speed of my 22 cruise is about 4.3 mph (for a planing hull the speed just below where bow rise starts). The commonly used rule of thumb calculation of hull speed is for full displacement hulls and is the speed at which the wavelength of a vessel's bow wave is equal to the waterline length of the vessel. It doesn't really apply to planing boats.

The 22 cruiser is highly affected by winds. Never measured the leeway of the boat vs. wind speed, but in any sort of crosswind the bow will promptly try to turn downwind when steerage way comes off.

If it were me, I'd get/borrow two 3 or 4 hp outboards, attach them to the C-Dory in the same location as you want to mount the electric motors and give it a try before committing to an electric installation. Test it out in the conditions you expect to encounter. Ballast the boat for the expected weight with the electrical installation.

The small motors should just clamp on. I think it would be a good test.
 
I agree with ssobol. The easily driven speed is really close to the sq root of LWL, not the 1.34 x sq. root of LWL which is where the boat starts to climb over its own bow wave. The C Dory is probably not as easily driven as a the true "St. Pierre dory" (Tom is cited in the Glen L site.). The St. Pierre dory has a narrower waterline beam and a true flat (rocker) bottom. (I used to row a 16' "Gloucester Gull Dory" 6 miles every morning.). I have never owned or tried to row a 16' C Dory, but suspect it would be much harder to get the same speed, if even possible under oars. (My grandfather had Thol Pins and used to row [standing up and facing forward] his 30' sailing cutter with 18' sweeps when there was no wind)

It would be interesting to compare the easily driven "hull speed" on the C Dory prior to 1987 (which also was a true semidory, with a flat (rocker) bottom. The difference between a semi dory, a true dory is that the bottom of the boat is a flat sheet of plywood which is very narrow aft as well as at the bow for a true dory. The Semi Dory (early C Dory) and a flat wide stern, with no dead rise. The True dory will not plane, and will squat when more power is given than the hull speed.

The C Dory after 1987 used a low dead rise at the stern, to a V of the bottom forward, instead of being flat.

Tom, Ask the moderator (see the "member list" TyBoo) for a photo album, and put some photos of your St. Pierre Dorys. As I understand you initially had the trolling motors in the well, but then moved them out board?

A 3500 lb C Dory 22 will be light and maybe not too far off from actual--but until someone weighs one, we won't know. (Hint). I have used the Suzuki 2.5 hp gas outboard, on both my Caracal cat (currently my kicker there) the 22, and on the C Dory25 I took to Ak. I have compared it to the Torqeedo and the Suzuki will push the boats faster (and for a much longer time.). Full power on the Torqeedo 1003)bdoes not last very long. One article showed: 2.4 mile range at full power (5 knots) on a Caledonia yawl (19.5'; double ended round bottom very light weight) 4 knots the. range increased to 6.3 nm, at 3 knots 9.5nm, and at 2 knots 15.6 nm. From Small Boats Magazine CHRISTOPHER CUNNINGHAM From SEPTEMBER 2015. this is not much different that I found the Torqeedo 1003 pushing my 9.5' high pressure air floor inflatable dinghy.

By the way, the shipping on Tom's book is almost the same as the purchase price. Cost of doing business...
 
Hello everyone,
This is a great discussion and I will try to address some of the questions/issues that have been brought up.
Yes, I should not be using the power equation for displacement hulls. My bad! In going back to Dave Gerr's book on Propellers I found he uses Crouch's equation for estimating power needs on a planing hull. Here are the number I calculated; will have see what I really get during testing because usually this equation is used for speeds above planing speed.
1.5 kW = 4.2 mph 3.8 mph at 4000 lbs
2 kW = 4.9 mph
3 kW = 5.8 mph 5.2 mph at 4000 lbs
6 kW = 8.2 mph 7.6 mph at 4000 lbs
This is very similar to what i was getting for the full displacement hull.
I would need about 13kW (17 shaft hp) to get up to the planing speed of 12mph.

I am using 3500 lbs as my estimate of cruising displacement because the motors and batteries weigh less than a 90hp outboard, full gas tanks, and full water tanks (I won't have a freshwater system on board). The two motors weigh 110lbs together and the batteries I will be using weigh 400 lbs.
I have decided to go with the EPOCH 48V 100AH batteries rather than the E-propulsion ones. They are IP67 waterproof rated and have blue tooth connectivity to a phone. I will be using four batteries for a total of 400 AH and 19.2 kWhrs. They are slightly more expensive than the epropulsion ones but the configuration and size works better for my needs. Also they have an 11 year warranty rather than 3. I will be placing them under seats that I will build along the sides of the cockpit. I am in discussions with Michael at NMI to see how best to do this.

I really can't address how the rocker would impact performance. In my experience, the narrow flat bottom, strong rocker and sharp angle to the sides created a lot of turbulence in even small waves and impacted the speed. We were pounding in waves as small as 1 to 1.5 ft at 4mph. The bottom is flat from side to side but not from bow to stern. The bow and stern are about 12 inches higher than the low point amidship on the St. Pierre Dory.
And, yes, I have built three electric St. Pierre Dories. The first was powered by a 36V forklift motor and 6 golf cart batteries and a 16x16 prop cruising at about 500 rpm (1996-2006). The second was powered by two Motor Guide 36 V trolling motors in an outboard well in the cockpit (2006 - 2011). It took me five years to figure out that the throttles can be removed from the shaft and the motors hung on the sides to eliminate the well. In trolling motors there are only wires running down the shaft and these can be extended. My last dory (2012 - 2023) was powered by two Minn Kota 36V motors.

With regards to windage: I think the C-Dory will be better off than my St. Pierre Dories. The distance of the bow and stern from the water on the latter was close to 5 ft and with the with enlarged cabin I had a lot of windage.

I will try to get some pictures of my dories posted, but I am not too computer savvy. There are pictures of my boats in the book. I am sorry that shipping costs are what they are. I am selling my book to Duckworks at cost and they are making only a small profit on it.

The Torqeedo 1003 is only 1.1 kW maximum with 500 W at the prop. And the batteries they provide with these motors is not really suited for long term cruising. The actual kWhours they provide with the motor is very small. You would need additional batteries.
 
Oh wow,19.5 KWH for battery power. So you can run one Navy 3.0 outboard at 2 KW 9.6 hours, run two motors at 4 KW 4.8 hours.

Going to need a-lot of roof space for solar panels to recharge it up in five hours for the next day. Even if you’re able to put 5000 watts of solar on the roof of a c-dory 22 under perfect conditions.

What are you using for a AC shore chargers?
 
I might get 500W of solar panels on the top not 5000W. The panels will be only for emergencies. We usually cruise from marina to marina and recharge with shore power overnight. We like to pace ourselves and don't travel more than 3-4 hours a day. Luckily marinas are spaced at most 15-20 miles apart. Our longest day is from Olympia to Gig Harbor but we can save an hour or two by catching the tide in the Tacoma Narrows. In the past we have trailered the boat to a launching ramp (usually Tacoma, Manchester, Oak Harbor, Roche Harbor via the ferry, and Shilshole) and cruised in that neighborhood.
 
Sam Devlin has built two solar electric boats (approx. 30' and 50') that come regularly to the Port Townsend Wooden Boat Festival. These are powered by pod motors. The owner of the 30 footer told me that he was inspired to have Sam build him one after seeing my electric St. Pierre Dory at the boat festival. Unfortunately, the C-Dory is fiberglass so I won't be able to show it at the boat festival, but I hope to collect a lot data this spring and present it at my talks on electric propulsion at the festival.

P.S. Sam's workshop is just a few miles from where I live, and I have known him for many years.
 
Tom, I will be very interested in the data you develop, particularly comparing a 22' planning dory, below hull speed (dragging its transom) with a heavily rockered double ender like the St. Pierre. I have owned one St. Pierre with a one cyl. Sabb (not Saab!) diesel, and it was very easily driven. Like Dr. Bob, I also have a lot of hours at the oars of a Gloucester Gull dory--the streched 20' version--which rowed with hardly any effort, compared, say, with a 12' planing skiff which (like, I imagine, the c-dory 22) tried to pull the ocean behind it dragging its transom. Your results will be very interesting. Could you share with us why you decided to fit out a C-dory, rather than a displacement hulled boat, for this project? Please keep us posted--I will follow this with interest. I have been considering a small backwater-cruise charter boat with electric power--like a Bolger Champlain or similar--for many years, but have never gotten past the dreaming stage. Sam
 
Back
Top