Optimal hull and keel shape for electric propulsion

[Adelie]

Originally Posted by argosail

Well I did see an awesome outboard electric provider at the show called "electric paddle" but of course they're all out of stock... I haven't look at Hobie, maybe worth an idea but being so light I wonder if it would be an OK ride from Philadelphia down to the Caribs. I like an exciting ride and weather helm doesn't both me much but sailboatdata says they are really really uncomfortable if one believes their ratios (which I know are not always based in reality). The headroom is 44 inches which I can't imagine is fun long-term. I've been cooped up in tugboats a few time but it was never fun.

ElectricPaddle is geared towards powering dinghies and kayaks, not enough power for a bigger boat.

ePropulsion & Torqueedo are better candidates but are overpriced for what you get. They are still geared somewhat towards tenders rather than motherships.

I would look at Elco which has made electric propulsion for about 100yr. Or get an off-brand electric outboard off of Amazon or Ali express.

If you wanted to dip you toe into this without spending a lot I would get 4 deep-cycle batteries as a house & traction bank and a cheap electric outboard from Amazon. Play with it for year and see if it suits you.

Regarding electric outboards. Do not get one where the motor is in a pod in the water. There is a very small efficiency gain by doing this but reliability goes in the toilette. Whenever the shaft seals fail, even a little bit, water will be in the motor and it will short out. While trolling motors use a podded motor, they also don’t tend to be immersed nearly as much. The electric motor needs to be at the top of the installation out of the water.

You don’t want the Hobie, it has no standing headroom anywhere below. That’s OK for the short term but tough to live with long term.

The Mega-30 has standing headroom under the bubble at the aft end of the cabin and slightly better headroom than the Hobie elsewhere. The Mega-30 has an additional advantage over the Hobie, it can be sailed with the keel partially retracted, the Hobie can not. This is a huge advantage.

Also the Hobie draws 5.5’ vs 5.0’. At the south end of the ICW a 5.5’ draft can be marginal in places, you will be touching bottom occasionally, even becoming aground when the tide is very low.

[Rumrace]

When you go out the Western Gap in Toronto there is a Mc Gregor on a pin. I thought I saw a huge outboard on the back in some weird stern. Another time it finally had occupants and I noticed the couch roof was raised up!
Near the end of the season I see the same boat jumping wake full boogie out past the Dufferin pin. I checked my blood alcohol levels. Amazing ! I’d guess it was around 20n.

[Adelie]

Originally Posted by Rumrace

I saw a McGregor on plane. Wow
It’s a water ballast boat ?
Wouldn’t a centre board with a nice brow or swing keel be best?
The optimal hull for power doesn’t include many Sailboats if any.

Water ballast is useful for certain intended uses because the water ballast can be dumped vastly lightening the boat for trailering or for better motoring.

The valving for a water ballast boat is such that you can apply power and open the valves and the water will drain out slowly lightening the boat until all the water is gone.

Optimum depends on what you are optimizing for and if there are any secondary considerations.

If you are optimizing for lowest power requirements that’s a rowing shell. But then you are restricted to flat water only and the are no living accommodations.

If you want 6kt max speed and 2.5kt economy cruising speed using electric power and accommodations and ability the be out in heavy weather then sailboats are the place to look, a trimaran would probably be OK but accommodations would be minimal and storage volume and especial storage weight would be limited. But there would be plenty of room to mount solar panels.

I can’t think of any existing powerboats that would be more than adequate for the conversion to electric propulsion. Power vessels are designed to maximize accommodation and generally have an excess of power available so there is no need to optimize the hull for low drag.

Sailing involve using a low power propulsion source so sailboats tend to be optimized for low drag at the expense of living space.

[Moontide]

Not sure on the motor size issue or how much it draws at cruising speed, but 300 watts of solar seems way short if you are going to be using the motor at all. That will get you maybe 100 ah a day in summer with pretty clear skies. Guessing it wouldn't take long to use that if powering. The supplier should be able to get you specs on that so you can do your own calcs.

[Adelie]

Both the Hobie and the Mega would use about 600W motoring at 3kt.
A 33’, 10,000lb would use about 1,000W at 3kt and 500W at 2.5kt.

If the goal is to go long distances in calms then a lot more solar is needed.
If the goal is occasional use of the motor to set and retrieve the anchor, get in and out of harbors and marinas, to avoid a collision and to help thrust tacks in heavy weather then 300W may be just fine depending on house loads.

[valhalla360]

Originally Posted by Adelie

I can’t think of any existing powerboats that would be more than adequate for the conversion to electric propulsion. Power vessels are designed to maximize accommodation and generally have an excess of power available so there is no need to optimize the hull for low drag.

If you are looking for actual propulsion rather than just getting in and out of the marina, some of the low speed single engine trawlers could be suitable.

Even better would be a sail catamaran with the rig removed.

Either option would allow for substantial solar arrays (like 2-4,000w) which would get up in the range of allowing for some more realistic speeds.

Say a 10kwh battery pack with 2kw of solar.
- That will generate around 8kwh.
- Around 4kw will get you up around 5kts on the 30-35ft sail cat hull.
- That's good for 4.5hr at 5kts (22nm) if you start with a full battery bank.
- The next day, you only have 2hour of run time starting with an empty battery bank and waiting for the sun to get high enough to start charging but hang out for a couple days and you can refill the battery bank while living comfortably not having to worry much about house loads.

Speaking of which, house loads is where this would really shine. If you bump up to say 15kwh battery bank and 3kw solar array, you could viably run air/con at anchor in moderately warm conditions.

In theory a 34x14ft cat could fit 7kw of solar (assuming 15w/sft) but figure more realistically 5kw producing around 20kwh per day.

Feed that into 60kwh battery bank (about the size of a nissan leaf base battery).
- That would give you 10hr at 4kw output and you end the day 20kwh in the bank plus 20kwh generated by the solar after covering 50miles.
- Now you have 40kwh to cover house loads over night and get you going in the morning until the solar kicks in and gets you another 50miles the next day.
- Mix in an occasional marina stay if trying to make miles or anchor out for a couple days and you top up the batteries.

That is getting viable for comparison to current cruising boat capability. It's a bit less but not an unrealistic 2-3kts which is really only useful for getting in and out of port (a mile or so before putting up the sails)

Assuming it's a 15kw motor (you don't have to run at peak output most of the time and there is little efficiency penalty putting a bit bigger electric motor in), it will usually be able to get you out of a jam when conditions turn against you and those 2-3kt systems are giving you 0 to negative 1-2kts.

Really though it would be best if the boat was built from the ground up with a solar/battery/electric propulsion system. Retrofitting 5kw of solar on a small catamaran is going to be difficult to do without it being really clunky.

[fred4936]

Our old boat was a Tartan 27-2 that I converted to electric. We had the boat for 9 years and it worked very well. We may convert our present boat, a Pearson 34-2 to electric, but after we do the Great Loop. Our kit made about 5kw, and liked to motor at around 4.5 kts. It worked very well for us, with a FLA battery bank.

[argosail]

That's awesome, what kind of load were you running for your house needs (electronics, electric head, galley, etc) ?

I was told that 10kw was necessary, 5 can do it? I would go manual water pump, compost head, tiller steering, alcohol stove. No a/c because of opening ports breeze and we survived thousands of years without it.

How much running time around 4.5kts a day in the florida sun?

I was looking at Tartan 27-2 but I like the Pearson 27-2 in that range for the mini-aft cabin. Not full keel but it has a transom hung rudder with tiller so better than a spade, I think...

[GrowleyMonster]

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.

I designed and built an electric propulsion system for my last boat, so I know what I speak of.

Repowering a 27 to 30 foot sailboat with EP is very smart. Under certain circumstances.

1. You already own the boat.
2. It has a dead or dying ICE engine.
3. You use the boat mostly for day sailing, weekending, and marina hopping coastal cruising.
4. You don't like to motor very much and you do not have to motor very much.
5. You know quite a lot about electricity, electronics, motors and controllers, wiring, particularly wiring that must be able to carry very large current, and BATTERIES. Don't mess with this if you are not a reasonably competent engineer, even with a turnkey system.

I am not seeing how you are checking all of those boxes. If you just want to go EP because it is cool, don't. The novelty will wear off and there you are.

I repowered a Cal 2-27 for well under $3k, including batteries. I had been thinking about it because I was not exactly in love with my Atomic 4 gasoline engine. However, I could not justify it as long as the Atom Bomb still ran. When the fuel tank sprang a major leak and spilled 15 gallons of gasoline into the bilge, something had to be done. In order to remove the fuel tank I had to either cut a huge hole in the boat, or pull the engine. I pulled the engine. While it was out, I started thinking about simply repowering. I had already done a lot of research and had a pretty good idea of what components I would want and how to make them all play nicely together. So I cleaned everything up, got rid of all wiring, hosing, and piping related to the engine, sold the old Atomic for $400 which actually brought the total cost down even more, and went ahead. I ended up with over 10kw/hrs storage and a 10kw motor that pushed the boat nicely, at a brisk pace for a short time, or at a very sedate pace for long enough to cross Lake Pontchartrain under power. You can have a reasonable size bank. You can have low cost. You can have high speed. You can have long(ish) range. You only get one or two of those, not all. The main limiting factor is the batteries, which are your fuel tank. After studying the matter carefully I decided that GC-2 size golf cart batteries, 220ah capacity, bought from Sams Club for $85/each, were the best solution for me, for too many reasons to list here. Motor was Motenergy, originally a 5kw unit, later a 12k one. Controller was Kelly, originally square wave, later upgraded to a sine wave unit. Reduction gear was a fully enclosed gearbox but if I had to do it again I would do what most do, and use a belt drive.

I find turnkey systems horribly overpriced, and even having it installed professionally still elaves you with a propulsion system that you do not understand, and do not know how to maintain, troubleshoot, or even operate properly, if you are not well read in the subject.

EP repower is a great way to rescue an old 70's built fiberglass boat like what I had. Lots of these boats around being practically given away, with dead diesels or A-4's. EP offers tremendous advantages for small boats where motoring is not a priority and shore charging is readily available. A resourceful DIY-er can do the conversion for about 1/3 what a new Beta diesel costs. No fuel to buy, smell, or spill. Quiet. Some systems are VERY quiet. No minimum idle speed, so you can ghost into your slip at just a few dozen RPM, or glide by a placid shoreline and observe wildlife. Instant on, no warmup. No complicated start sequence, or crossing your fingers. The big bank necessitated by the propulsion motor can be quite useful for other things. Recharging such a big bank with 300w of solar isn't going to happen. But when you can just go out for a day of sailing or an overnight, return to your slip, and plug in, that is a sweet deal.

If you want to go electric, first of all learn about electric. There really is a lot you should know, particularly about batteries. For instance, do you know how to manually equalize your FLA batteries? Probably not. It is rumored that there are smart chargers that will equalize, but I have seen NONE, ZERO, NADA, that will charge at the proper equalizing voltage. None. So you need to know how to do this manually. You need to know about charge algorithms, how to do Peukert calculations, how to water your batteries and why you don't want batteries that you don't have to water. You need to become an engineer, basically. Then think about taking the plunge. Until then, you are quite frankly better off with a good outboard mount and a long shaft Tohatsu or Mariner on your 30' boat with the dead engine. Even so, you really need to know a few things about gasoline safety as well as outboard operation and maintenance.

The more you know, the less you fail. Learning from your failures is hard, frustrating, and expensive, so learn as much as you can without the trial and error process before you play for keeps.

I like EP and have no regrets at all with the repower, but it is not for everyone, and there are a lot of ways to screw up in designing, installing, or using it. The diesel is mature technology and very well engineered, with plenty of competent service people, and lots of excellent books about them. EP has been around in a big way for about 140 years but still has not achieved the same status that the infernal combustion engine enjoys today. Be aware that it is a fringe technology and there are reasons why all boats are not electric. Outboards are very practical in the same set of circumstances that allow EP to shine, and they are like the diesel, familiar technology. Well, that is, if you are familiar with them.

Study, do your homework, and instead of looking for a boat to repower, just wait until you happen to own one that would be a good candidate. All standard sailboat hulls are of good shape for pushing with electric, so no worries about that.

[sailingharry]

Like Growley said, it's good FOR THE RIGHT CONDITIONS! Like everything, it has pluses and minuses. Everyone talks the pluses. The minuses are there, even if you don't talk about them. Just go eyes open.
* Power. My 34' Sabre had 27HP. In bad conditions, that wasn't enough. Sure, it's a sailboat. You have to WANT to sail upwind 10 miles with seasick crew in 20-30 with 4' seas to do it under sail.
* Power/Range. Our 43 foot has a large diesel. Last year we did New Jersey, Atlantic City to Sandy Hook, 80 miles each way, both up and down the coast. We had a dog to take ashore, so needed to do it fairly fast. 12 hours at about 90% max RPM. Solar would have been painful!
* Range. It's great (Really, GREAT!) if you day sail out of a harbor and want to go in and out and can charge every night.
* Speed. Speed is a serious trade off. Double the speed, half the range. It's easy to say your are OK with 2-3 kts. We usually turn on the engine when we drop below 5. If you have someplace to be, 2-3 kts is amazingly slow. 30 miles to the next harbor, you were going to do it in an easy 6 hours at 5 kts, and now you are looking at closer to 12 (actually, even at 2-3 kts, you won't make 12 hours....)

* Recharge. Solar really won't do it. First, that 300W won't handle house loads. Really, it won't. We have many more loads than you do, and with the 600W we now have, I hope we will be closer to autonomous this year. But 300W won't do house loads even with your light loads. Power for the engine? NEVER! Maybe with 1.5KW, if you can install that on a 30 footer. If you marina hop ($2-3/foot/night, plus $10 for shore power) you can recharge every day, that helps. But if that's too much money ($2K/month) you are back to solar. Last summer, we literally went 60 days without a single shore power connection -- marinas with docks north of Cape Cod are scarce and expensive.
* Battery life. A battery may be $2-$4K. It may last 10 years. If you are doing electric, you don't motor much. If you don't motor much, you burn, what, 50 gallons of diesel a year? At $5/gallon, that's $250/year, or $2.5K in 10 years. Do that math.... Unlike electric cars, where the math rewards high mileage users who burn lots of fuel every day (and there's a great environmental return), electric boats work for those who use very little diesel to begin with, and are returned with very high costs and limited environmental goodness.



I used to race against a Harbor 20. It came with a factory implementation of a modified Torquedo. Pretty damn slick! He motored 1 mile to the race, 1 mile back (more if the wind died half way through the race) and then plugged in when at home. SLICK! That's a WAY COOL solution!


Oh, and watch Sailing UMA and realized that while it works FOR THEM, they do not represent the more common cruising lifestyle (and finances).

[CarlF]

To summarize some of the advice you are getting - your problem is not the motor or the hull or the batteries. Your problem is how to charge enough to support a 10kw motor (10,000 watts). All your other loads (often called hotel loads) might average 100 watts. They are nothing.

On a 27 monohull you’ll be lucky to have 100 watts of solar due to shading from the rig. You will have to solar charge for a month to motor for an hour.

If you can plug into a dock every night, this can work well. Otherwise you will need a genset which defeats your whole purpose and is prohibitively expensive on a 27ft boat. (and a Honda generator isn’t big enough)

[ron17571]

Originally Posted by CarlF

To summarize some of the advice you are getting - your problem is not the motor or the hull or the batteries. Your problem is how to charge enough to support a 10kw motor (10,000 watts). All your other loads (often called hotel loads) might average 100 watts. They are nothing.

On a 27 monohull you’ll be lucky to have 100 watts of solar due to shading from the rig. You will have to solar charge for a month to motor for an hour.

If you can plug into a dock every night, this can work well. Otherwise you will need a genset which defeats your whole purpose and is prohibitively expensive on a 27ft boat. (and a Honda generator isn’t big enough)

yeah, what he said. Maybe a smaller unit with the batteries and solar sized to match. Sail as much as possible.

[nmccubbin]

Given your comment that you do not fully understand Amps, Volts and Watts, be VERY careful
Most electric propulsion salesmen make atrésies used car pedlars look like saints
There is some good stuff written by other posters, so I will not repeat it.
My own feeling (I am an engineer who has built two 40 ft plus sailboats) is that electric drive is a mistake. The laws of physics and limitations of current and foreseeable equipment are incompatible with success. I would happily buy one of the recent electric cars. Electric drive for sailboats is aLONG WAY OFF

[argosail]

My idea is a 27ft aft cabin. Take out holding tank for compost head, run vessel manual, hot water not need for running in mid-lats, tiller steering, use EP only in becalmed seas at 2-3 kts and for house batteries. Extra batteries in aft cabin, holding tank space, solar panels on bimini (300wt total), a course in electrical too!

I suppose going down to 5kw would be much easier but now wonder if even that is doable :/

[Rumrace]

Congratulations this thread has started false assumptions about Rand Boats on the Internet. The Company called Tesla on the water.
Range 140nm
22 nm top cruise with base package base batteries.
Pending slander suit on the accountants again. Oh shucks