electric c-dory and speed with kickers

[galiano]

I'm musing/fantasizing about an electric cruiser, and something like a C-Dory 22 seems like one of the few hulls that might be efficient enough for it to work.

Going at planing speeds is just going to be unrealistic with current battery technology, but does anyone have a good sense of how much power it takes to get a C-Dory to hull speed? For folks who have 6HP or 9.9HP kickers, how many mph can you get up to with them?

Avi

[txmntman]

I’m going to say that my 6 hp kicker will move my CD22 about 4-5 mph in calm water, but it has been a while since I’ve run “speed trials” with just a kicker….

[Aurelia]

We once had a 4hp yamaha four stroke based on the same motor as the 6ph unit, and that was mounted up to a few hulls while we owned it and I think is was about the required amount of thrust for making hull speed in a 19/22. I have also used a 2.5hp suzuki on the 19 hull and it doesn't quite get up to hull speed, even at full power. Same for a Torqeedo travel model. So somewhere in the 4-5hp range is likely the minimum (gas) rated power. While something in the 8-10hp range can push the boat to hull speed without working too hard.

Greg

[Karl Konecny]

I have a 5 hp Mercury with a high thrust prop with will push my 22' cruiser at 4.3 knots with is almost 5 mph. That is on a lightly loaded boat (one passenger and a dog)

[ssobol]

For a boat like a CD-22 that is full time powered by about 6hp, is there enough margin for times when things are not that smooth, there is a strong current, or when it gets windy (the CD-22 is quite susceptible to wind)? I would think that 15 or 20 hp would be a better sized motor. Nimble Nomads only go about 7 knots, but they are usually fitted with 40 or 50 hp motors.

Also, I think a CD-22 with enough batteries for a reasonable cruising range with FLA batteries is going to be fairly heavy. Can the boat structure support that weight say when bumping down the road on a trailer? Li batteries would be lighter, but also a lot more costly.

[Karl Konecny]

Any all electric boat the size of 22' cruiser would need Li batteries (unless it was a submarine where you need the extra ballast). And yes, today it would be very expensive unless you only used the boat for short sunset cruises. But in 5 to 10 years, we shall see.

[Karl Konecny]

I also believe that 40 hp (with appropriate prop) would be minimum needed if you wanted to get up on plane and maybe achieve 12 to 15 knots. But with such a motor and the full battery set from (for example) a Chevy Bolt (which has about a 300 mile range on the road), you would completely drain a full charge in about two hours and have a range of about 30 miles.
Otherwise, you are stuck down below hull speed (~6 mph) and about 6 hp. But even there with the Bolt battery pack you would deplete a full charge in about 10 hours and have a range of about 60 miles.
A true cruising boat would need a large, expensive battery pack.
And then there is the charging issue????
I still have hope in 5 to 10 years.

[thataway]

First what is the hull speed of a C Dory 22? Assume that the LWL is 19 feet, and the sq root of 19 x 1.34 is 5.8 knots

Second the C Dory is not a particularly efficient boat at low speeds. It is an efficient boat at planing speeds.

An efficient hull would be like a canoe: a long boat narrow boat, with rounded bilges is far more efficient.

The Torqueedo 1103 (first model) or the Mercury 3.5 hp 2 stroke will push a 22 at about 3.5 knots.

LiFePO4 batteries can be had as low as $350 for 100 amp hours at 13.5 volts DC.. This would probably be as good as you can (would be more efficient if went to 48 volts DC.

In Calm water the 9.9 motor would push the C dory 22 at its theoretical hull speed.

[galiano]

Thanks for all the info folks!

For those who aren't tracking what's out there in terms of electric: I would think something like the ePropulsion Navy 6.0, which claims to be equivalent to a 9.9HP, would be the right motor. It sounds like you could run it at about half power most of the time to get to hull speed (and then have some extra power in reserve for bad conditions). Half power would be a 3000W load on the batteries.

They sell a 9kWh lithium battery pack, so you'd then need one of those packs for each 3hrs of cruise. These packs are about 20" x 20" x 10", weigh 200lbs, and cost $4k.

So if you were willing to add 1000lbs of battery, for $20k, you'd get 15hrs of cruising at hull speed, or a range of, what, 150 miles? (Keeping in mind that you are getting rid of maybe 500lbs of gas motor and fuel... maybe you could add even more?)

In terms of charging, 30A shore power gives you a 1:1 charge time to cruise time, so you could probably recharge most of the way in one night.

You could also mount a light gas kicker with a small fuel tank to beef up your range when you just can't get to shore power.

It feels right on the edge of worth doing... not *quite* there yet but definitely interesting.

[galiano]

Bob, understood re wanting a longer narrower hull. Are there any specific hulls out there you think would make a good base for this kind of project? Something like a modern Monterey Clipper? (Is anyone building those?)

[starcrafttom]

Sorry but other then the 'I did it" feel good what is the point? modern out boards are very clean burning as are modern cars and very quite at hull speeds. Well really quite compared to older two strokes at any speed. So what's the point? If you want reliable slow cruising get a single 30 to 40 hp out board. As bad as most marina power systems are I do not think I would want to try charging an electric boat over night. As oppose to a trickle charger for a starter battery. I know its done for little ferrys/harbor tour boats, but they are using different systems designed just for that use.

If this is for a lake that is only electric then there are better system. Hell there are electric speed boats available in Germany just for that market.

[BillE]

The electric outboards are not all that quiet, either. They are quieter than small gas outboards but the small torqeedos still have a bit of an irritating whine to them and I find their sound less pleasing than a larger outboard running at low rpms, which have more of a soft murmur.
The advantages I see with electric are reduced maintenance, environmental benefits, the total absence of fuel odors, or any possibilities of fire. But I do not see any savings in cost or noise.

[croakz]

I really wanted to use my e-Propulsion Spirit 1.0 Plus as a kicker and was thinking about getting one of these to power it:

https://signaturesolar.com/eg4-wp-lithium-battery-48v-100ah

48V, 5.12kWh @ 85lbs for ~$1700.

But I'm not sure it's powerful enough. Maybe a Navy model would work, but I liked the idea of using my dinghy motor as a kicker.

[starcrafttom]

[galiano]