Optimal hull and keel shape for electric propulsion

[Rumrace]

For gods sake Rumrace stay on topic.
Copy that. Sorry. Those two innovators are from 2016 season old news like

https://electricyacht.com/

There is a 34C&C making better speed than ever.
An electric sail drive cost a touch more than a diesel. An Yanmar 40hp is about 4500 and the equal saildrive with way more torque is 5200 plus how ever much power you need or can carry I suppose. A division of Beneteau has been working on an electric sail drive for years. It’s in Poland at Delphi Yachts
All fast math and wise old knowledge aside it already happened. They even have a better warranty than diesel by a year on two brands. I’ve seen one with dual motors single shaft to cut draw lower when not needed I suppose. They sure are not sitting around saying Can’t

[Adelie]

Originally Posted by argosail

Yes you have some good points. Being off-the-grid is more of an idealistic dream and I can see how the comparison is moot with electric cars. I was actually in the market for an electric car, but the price and unavailability led me to a highly efficient 4 cylinder instead!

That being said, I did see a dealer at the boat show with electric outboards (and no not torqueedo). He did not have however really long-shaft ones but said they are out there.

So would having a 10hp (6kw) electric outboard xlong shaft on say, a 7k displacement 27 footer, fin keel, lightly loaded, be able to push in a becalmed sea state, and for close quarters /docking-undocking? max speed 4kts but realistically going 2-3 knots? I'm wondering if there is a way to charge at the dock if hopping down the ICW to go island hopping in the Caribs? Otherwise I suppose not enough solar panels...

A 6kW is 8.0hp. Electric motor torque curve can make an a electric installation propel a boat better than ICE so 10hp equivalent is a good assumption.
Let’s assume no advantage. 8hp will still propel a regularly loaded 27’, 7,000lb sailboat to hull speed in flat water with some left over. That’s 6.5-7.0kt.

For distance power cruising there is a very steep power-speed curve, for every extra increment of speed power demand increases dramatically.
For boats using inboard EPin the 32-34’ range
300W - 2.0kt
480 - 2.5kt
960 - 3.2
2000 - 4.0

Using outboard EP I would expect electrical demand to be somewhat higher, the smaller propellers have decreased efficiency.

If you built your own high efficiency EP you could probably go the above speeds on about 1/2-3/4 the power. Such a high efficiency setup would have long skinny prop blades and speed would top out in the range of 3.0-4.0kt.

With an inboard setup 3.0kt is at or near the sweet spot for most people who have chosen EP, the point where speed vs range becomes acceptable to them.

To make EP really work without hitting a marina every evening, you need to go all in on solar:
Panels on the dodger
Panels on the Bimini
Panels on an arch across the stern
Extra panels to toss out on deck whenever you are underway.

All this means cruising the ICW in the US or perhaps canals in Europe, it’s 7hr underway to go 20nm. And it means you are underway every other day to make 20nm or perhaps every day if making 10-12nm hops.

[donradcliffe]

The 5 hp outboard on the Olsen 30 died and we needed to get down the harbor to haul out. Put a trolling motor on it with a 100 ah 12v battery. It made it 200 yards at 3 knots there and back and there was still enough in the battery to do another round trip. We are shopping for a 3 kw electric outboard that will have a five mile range, but the torqeedo at $8k is too pricey even for a DDNK (double doctors, no kids) owner.

[Rumrace]

Stay tuned Adelie. I have a Tesla S with the first of the 100 battery. I ordered it 3 weeks before the Tesla 3 came out so it’s approaching 5 years old. The rebates lack of repairs down time and 9K a year in fuel make it a huge win. Even with dual motors and the full Ludicrous effect its less money than all its peers with gas or diesel.
The Tesla 3 is modest and I know it’s the least expensive car for anyone driving 12,000 miles a year. In Canada we have a Coast to Coast electric highway. Tesla is a very common car in Toronto and Montreal
When Canada Japan and Europe formed a free trade union Toyota immediately announced they were doubling the Cami factory to build 3 new electric vehicles. The Ford Factory in Oakville only build two electrics. Mustang and pickup
In Windsor Canada is putting in a battery factory just to supply the electric car industry which is booming.
We are also encouraging Toyota to bring their Hydrogen boats along with Yamaha and Yanmar.
Ontario Canada as it turns out is lithium rich. It’s scrap from dead silver mines.
I think you can get a Tesla 3 for 40k and a rebate depending where. The old rebate here for an S was 19,800.00 and the 3 was 9,700. No idea what it is now.

[GrowleyMonster]

Originally Posted by donradcliffe

The 5 hp outboard on the Olsen 30 died and we needed to get down the harbor to haul out. Put a trolling motor on it with a 100 ah 12v battery. It made it 200 yards at 3 knots there and back and there was still enough in the battery to do another round trip. We are shopping for a 3 kw electric outboard that will have a five mile range, but the torqeedo at $8k is too pricey even for a DDNK (double doctors, no kids) owner.

The Torqueedo is indeed obscenely overpriced, though I must admit it is a pretty good one. Elco has outboards, and they are available with long or short shaft, tiller or cable steering, integrated controllers, and their little 5hp one runs on 24v which sucks UNLESS your boat already has a 24v house bank. The 9hp 48v model is $2910. https://www.elcomotoryachts.com/prod...ric-outboards/

Yeah when it is slick calm it is amazing what a trolling motor will do. Even a fairly big boat, once you get it moving, a trolling motor will keep her moving along. Just remember it takes just as long to put on the brakes as it does to get her going.

Lots of guys just mate a BLDC motor to an old gas outboard carcass with the dead power head removed, add a 300a controller, and there you go, a 5kw electric outboard for under $1k, batteries not included, some assembly required LOL. You can run one for a short distance with a 48v 20ah ebike battery, just keep the power down to around 500w or so. In fact you could even use a 1kw ebike controller. They run about $75 so with a $500 motor and a free donor outboard, you get your hand in the game pretty cheap. But not as cheap as your trolling motor.

[GrowleyMonster]

Originally Posted by Rumrace

Stay tuned Adelie. I have a Tesla S with the first of the 100 battery. I ordered it 3 weeks before the Tesla 3 came out so it’s approaching 5 years old. The rebates lack of repairs down time and 9K a year in fuel make it a huge win. Even with dual motors and the full Ludicrous effect its less money than all its peers with gas or diesel.
The Tesla 3 is modest and I know it’s the least expensive car for anyone driving 12,000 miles a year. In Canada we have a Coast to Coast electric highway. Tesla is a very common car in Toronto and Montreal
When Canada Japan and Europe formed a free trade union Toyota immediately announced they were doubling the Cami factory to build 3 new electric vehicles. The Ford Factory in Oakville only build two electrics. Mustang and pickup
In Windsor Canada is putting in a battery factory just to supply the electric car industry which is booming.
We are also encouraging Toyota to bring their Hydrogen boats along with Yamaha and Yanmar.
Ontario Canada as it turns out is lithium rich. It’s scrap from dead silver mines.
I think you can get a Tesla 3 for 40k and a rebate depending where. The old rebate here for an S was 19,800.00 and the 3 was 9,700. No idea what it is now.

I actually like Tesla's cars but i'm holding out for the cyber-truck. I am kind of stoked about that one. Mrs Monster is gonna have sticker shock though so I don't know if we will actually get one.

[belizesailor]

Originally Posted by Adelie

Alas Hobie 33's use outboards. The motor the OP discussed at the boat show is a replacement for an inboard.

The H33 is a 4000lb boat so it would take significantly less power to propel than the 7k-9k boats the OP mentioned. https://sailboatdata.com/sailboat/hobie-33

Another option would be a C&C Mega-30 which again uses an outboard.
https://sailboatdata.com/sailboat/mega-30-od-cc

Both of these boats are very light weight meaning less power is needed to propel them to the same speed but they are also weight sensitive which would mean that LFP batteries would be required and you still wouldn't be able to carry as many as a heavier displacement sailboat so range and speed would probably be a wash.

There are electric outboards that could be used but the tradeoff is that they use small propellers which sacrifice efficiency. Given that electric motors are involved it would not be unreasonable to vastly increase the diameter (1.5x-2.0x) of the prop and pitch it up a little to increase efficiency. The motor would not be running at optimum and load and RPM and may die an early death. Hard to tell.

The original H33's have a relatively large OB engine well which could likely accomodate a suitable electric power plant. If not, there is ample space in adjacent stern areas. Ive thought about electric power for my H33. Ive not done the math, but it takes very little to move a H33. Ive not used the clunky old OB set up in years, I just scull off the dock using the rudder. Nothing more than a breath of wind required to sail.

Electric power would be good for the typical H33 use which is daysilaing/racing...only needed to push it out of the marina.

OP doesnt mention intended use that Ive noticed...

[Rumrace]

I have not quit gas combustion. 2 antique bike an old bmw and a crate LS3 with blower and Speedmaster 3 drive.
The LS3 has only been test run on the stand and the Merc drive is clean new gears pump etc Hunting for a Donzi 18 hull.
But my previous boat has consumed $1500.00 in diesel in a day. I did drive a 5 series which are liking gas. I spent average $9,700.00 a year in fuel. I had a 530xit y 309,000 on it and only one bill for a fan relay. I miss the shifter 4 years later I still reach for it. The first Tesla truck designs were pretty much a Chrysler ram body. It’s exactly what Ford and Toyota are delivering. Keep in mind Toyota is sharing patents with Tesla. GM got their greedy asses boycotted in even government fleet in Canada. 287,000 car sales a year we are determined to end. GM borrowed 650m off Ontario in 2008. They never paid 450m back while handing each other bonuses so we don’t care what the thieves build. Yamaha took the top spot during the metal trade wars with Yamaha tariff free and Merc 25% f u back tax. Those things don’t get undone .its also why it’s my first and last Tesla. Now that the pack are catching up I’ll buy a Canadian built one without the Chinese steel.

[Adelie]

Originally Posted by sailingharry

Umm....yes. If your objective is to remove a functioning engine, spend a lot of money, impose severe limitations on your cruising, and claim (in many ways, falsely) that you are an environmental activist by eschewing diesel, then yes. But it still comes back to "WHY."


Yes, you can dock hop down the ICW. Easy peasy. Lots of marinas (well, OK, you aren't going to make it through the Dismal Swamp Canal, but you can go around). $100/night is a good budget. A 30A cord will charge batteries at the rate of 3kW, so for a 10kW motor, 3 hours of charge for each hour of motoring -- if you are pier side for 16 hours, you can get 5 hours of motoring the next day (if you have 50kWH of battery!).


Oh, for those charge times -- it only works for Lithium. Any lead acid is many hours longer to charge, because they start to taper down on charge rate and the last 20% takes many hours no matter how big your charger is.



No, in the Caribbean, from my very limited experience, you won't be charging from shore power -- there aren't many marinas. Almost everything is moorings, so you are 100% solar and any engine powered charging source you have. Count on a week or two of solar charging for each hour of motoring.


A question -- if mass produced electric cars, that have a really solid use-case, and a well developed supporting infrastructure, are too expensive -- why would you think that custom installing a one-off system for a poor use case with no good supporting infrastructure would even come close to making economic sense?

The question of why goes back to personal preference. If you buy a new house and want to repaint it; would you not do so just because the neighbors took umbrage at you choosing to cover a still intact existing paint scheme?

The use case of a 50kW-hr battery and using 10kW when underway is unrealistic. A 50kW-hr battery bank assembled using Battleborn batteries would require 44 batteries, weigh 1364lb and cost over $40k including taxes and shipping. A 15kW-hr bank is more likely weighing 372lb & costing $11k or so.
Also a 27’ boat is not going to cruise in 10kW, that’s emergency power. They are going to toddle along at 3.5-4.5kt using 1.0-2.0kW.

With a 15kWhr bank, 12 is usable. Assuming 4.0kt using 1.5kW that means 8hr of motoring to make 32nm. If they have gone all in on solar then either speed increases, range increase or time to recharge from solar decreases. With 1,000W solar that winds up being 32nm every third day.

If you drop speed to 3.0kt, demand will be about 750W, travel 5hr for 15nm everyday just the solar would be enough to propel the boat with no net draw on the batteries.

Is this a use case you would accept? Doesn’t sound like it. Does that make it a bad use case? No, just a use case others accept and you don’t.

Regarding the Great Dismal swamp. Norfolk to Elizabeth is about 45nm. The canal is less, let’s call it 35nm. That’s a single long day starting with a full battery and motoring in sunny weather. Boat Alexandra and others have sailed it.

[Rumrace]

My Tesla S has better range than its gas peers. Audi S 7, BMW 750m Porsche panamerica S. Takes 20 minutes to charge in a free charge station on the transcanada. Free charge in my office building rebate on home utility. Our government has been focused on spending our carbon tax on infrastructure. We have the biggest electric highway in the world in soon to be the biggest country. All new condos have 220 lines ready for your cars gear. It’s code.
We don’t care where transvesties pee and are not going to rehash who is in charge of your girls body again.

[Seabeau]

Originally Posted by argosail

I'm looking down the line to convert to electric a 27 to 30 ft monohull with displacement around 7k to 9k. From the person I spoke to at the Annapolis boat show, a 10ah system should work with abt 300 watts solar for a good few hours a day.

Now I'm guessing the less wetted surface the better for getting longer range on electric, so I imagine a fin keel would be better than full. Does that make sense?

Regarding the shape, would a flat bottom equal less resistance as well or would a V-shape be more efficient?

Intended vessel would be for coastal cruising eastern seaboard and caribs.

A no keel would be the best for less wetted surface, followed by a lifting keel/centerboard or dagger board.

[Shaneesprit]

Quite interested in what your reason is to go electric without a clue about what it means?
Or at least that’s the way the question appeared. Sorry in advance.

Is it environmentally friendly - probably not.
Even in a classic car they say going EV is environmentally damaging. The conversion it’s self does more carbon damage than could ever be repaid, on a boat it’s going to be worse.
300w of solar is about enough for lights chart plotter and a radio.

[valhalla360]

Originally Posted by Adelie

A 6kW is 8.0hp. Electric motor torque curve can make an a electric installation propel a boat better than ICE so 10hp equivalent is a good assumption.

No, there is no magic electric HP for displacement boats.

As explained in a prior post, it does work for cars because the engine size is largely driven by the ability to accelerate.

Take a 1974 VW bug
- Peak HP is 50hp around 3750rpm.
- Peak Torque is around 80ft-lb at 2750rpm with around 35hp being generated.
- At 1000rpm torque is around 25ft-lb resulting in around 5hp being generated and there are losses related to engaging the clutch.

If you put in a 50hp electric motor with the same 80ft-lb peak torque, it can generate peak torque at any RPM...so at the equivalent 1000RPM in 1st gear, it can generate around 16hp or over 3 times as much HP even though it still has the same max HP.

Once you are up to highway speed, they will both still be dogs as they will both be using pretty much all the available HP to to fight aerodynamic drag.

This is why you see even econoboxes spec'd with 150hp ICE motors, so they have enough HP off the line at low RPM to be peppy. They will pretty much never generate the max HP rating as it only takes 40-60hp to keep your average econobox doing 60-70mph. In normal use, there simply never is a situation where you will get the econobox generating max HP.

EV cars can downgrade the max HP so long as they can generate more low RPM torque and therefore HP, so long as they have enough to maintain good high speed performance which 150hp is overkill, so dropping back to 80-100hp still gives a peppy feel accelerating at low speed but plenty to maintain freeway speeds.

With a displacement cruising boat it's a much different situation.
- Acceleration is rarely a consideration. Unless something has gone horribly wrong, you almost never give the motor more than a slight goose while docking.
- Even if you do need to give it everything, unlike with a car where you have to accelerate 3-5,000lbs of the car to build RPM (assuming the wheels don't spin which hurts acceleration anyway)...with a boat, the prop will slip in the water allowing the engine to quickly build RPM and get up in the range where it's putting out good torque (and therefore HP).
- The thing that drives engine sizing in displacement boats is the cruising/peak speed, potentially with adverse wind or current considered. In that case, it's HP vs HP and both ICE and electric HP have the same definition.

Before someone says electric motors of the same HP have higher torque, since HP = torque * RPM, you can simply add a reduction gear if you need more torque at the prop shaft and other than a couple percentage points for efficiency losses, the HP that reaches the prop shaft will be the same. You can turn the same prop at the same RPM.

[valhalla360]

Just a quick follow up to my long post:

If you are willing to accept 2-3kts, you could get a 1-2hp ICE (maybe 5-6hp if you want overkill) and achieve the same thing in a 27ft boat. Biggest issue is finding one that's drop in replacement as very few people would accept a 2-3kt cruising speed, so there is no demand.

[sailingharry]

This EP thread, like most, focuses on the slow speeds, inability to power in heavy conditions, range, recharge times, and huge amounts of solar required. But I got to pondering another question. We talk about marina stops as "the easy top up."


Run some numbers, it's interesting.


A 200A charger (that's a beast!) is about the most you can pull from a 30A shore power cable (it draws close to 25A, so not a lot of room left). 200A @15V, is about 3kW. If you are down 15kWh, that's 5 HOURS at full charge capacity (that's with Lithium, lead acid won't take it and backs way down, taking longer). If you get one of Rum's go fast boats, the banks are a lot larger and the charge is a lot longer (although they probably take 50A 240V, or close to 10kW charge rate). Yes, well configured you can get a full charge overnight -- but it's going to take some engineering to make that happen. Kind of shocked me that it takes that long.


And, unless like RUM you are using tax dollars to charge your boat (haven't seen any free charge stations at private docks, and the marina charges a premium for power), you have to pay for that. Consider a 20HP power (pick any other number and it will work out the same). I'm recalling my Sabre 34, which had a 27 HP diesel but at cruising throttle, probably 20HP, it burned about 1/2 gallon per hour, maybe a touch more -- so at today's prices, about$3/hour or a bit less. 20HP is 15kW, so it burns 15kWh/hour. My electric here at home runs about .012/kWh, so that's $1.80/hour. Not the savings I expected -- I really expected to see numbers better than 50% savings. (yes, you could re-run these numbers with a 2kW motor, but I don't have diesel consumption rates for a 5HP diesel running at 60% load).


My house bank is 800 Ah of AGM's. I rarely drop below 50%, so I can be down 400Ah, or 5kW when I pull into a marina (very rare event) and power up my 160A inverter charger. These calculations are actually a bit relevant to my personal power situation! And even more so the end of next year when 800Ah of AGM magically turns into 600Ah of Lithium.....