Optimal hull and keel shape for electric propulsion

[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 boat show">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.

[Chotu]

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.

Long, thin, narrow hulls are the most efficient displacement hulls. Think “kayak” in terms of shape. Think of one hull of a hobie cat. Think those sculling boats they row as a team. The more your boat looks like these, while also having the least amount of hull underwater, the less resistance it’ll have.

What’s a 10ah system? Details?

What’s the 300 watt solar panel for? Lights and refrigeration? I may keep up with those. Depending on where you live.

[argosail]

Thanks Chotu!

Yeah sorry 10kw electric propulsion motor to replace the inboard!

Guy quoted me about 15k for that with a huge lifepo battery bank. I found their info, its a company called Electric Yacht, their 10kw system is below, idk what they mean by amp-hours (I'm still new to electric and can barely figure out the difference between 12v and 110v etc).

///
The QuietTorque™ 10.0 Sport is a cost effective 10kW electric propulsion system designed for the day sailing and coastal cruising sailboats up to 35’ (LOA) and 12,000 lbs displacement. Typically programmed and sized to push boat at cruising or harbor speed.
\\\

The above is $5500, then the lifepo batteries, and the solar + controller.

So with 300w (so 2 larger solid solar panels (flexible loses cell life quicker)) to charge the house batteries and the propulsion, enough to get into and out of marinas, and maybe a few hours more at 3 to 4 knots if needed.

This was quoted basis a 26ft Nonsuch which is about 8500lbs displacement with more of a flat and beamy bottom and fin keel.

So for something more V-shaped and 7500lbs displacement, might be more efficient as you said?? Wondering how big a difference it would make...

[hlev00]

From a hull efficiency a trimaran would seem ideal. A cat is okay but then you normally have two engines.



But to your question about monohulls, I trust you have seen YouTubers Sailing Uma. If not, check theirs out. They did essentially what you are doing, though with a 36' or 38' monohull. They started with a DIY solution then upgraded ( maybe sponsorship) to a purpose built marine electric motor. In the process the also went from a shaft mounted propeller to a saildrive.

[argosail]

Thanks Hlev, no I have not! I will check out their page.

I haven't thought of sail drives because one concern with the sail-drive, from what I've heard, is that boat has to be on the hard to do any kind of servicing...but electric yacht also has their own saildrive starting at 10kw but about twice the price (so 11K).

[shrspeedblade]

One of the most important factors to consider if you want to go electric is that you have to be of the mindset that the motor, whatever it is, is an auxiliary and its primary purpose is to maneuver in tight spaces (marina, harbors) or to get you out of a pinch for a limited time.

If you don't have the attitude that it is, first and foremost, a sailboat then it probably isn't a good move.

The other two important factors are battery capacity and recharge ability. The larger the battery capacity the easier all other aspects will be. Cram 1000 amp hours into the boat you'll probably rarely look at the gauge!

Its more important for cruising, but the ability to replace charge quickly is also certainly a factor, especially if you have a lot of electric draw on the boat besides the motor.

The Sailing Uma channel is a good suggestion. You also need to be very honest with yourself about what kind of sailor you want to be?

[Adelie]

Welcome.

I would suggest updating your profile with your general location and your boat make & model in the "Boat" category. This info shows up under your UserName in every post in the web view. Many questions are boat and/or location dependent and having these tidbits under your UserName saves answering those questions repeatedly. If you need help setting up your profile then click on this link: https://www.cruisersforum.com/forums...ml#post3308797

I would happily help more if the link above is not enough.

The location you’ve given is so specific only locals would know without Googling it.

Watts is a rate of energy flow: 1 Joule per second
10kW is 10,000Watts.

For electricity Volts x Amps = Watts.
Volts is analogous to water pressure and Amps to gallons/second.
Most recreational marine electrical systems run at a nominal 12v, a few at 24v, electrical propulsion on recreational vessels mostly at 48v. There are functional advantages to using higher voltages but at 60v the system is not longer considered low voltage and safety requirements increase as does liability.
For systems with fixed nominal voltages energy storage is usually done in Amp-hr. So Amp-hours is a shorthand proxy for the amount total amount of energy (Joules) that is stored.

This little explanation is undoubtably leaving you boggled. Don’t worry, you’ll understand it better when you’ve played around with it for a while.

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.

[argosail]

Originally Posted by shrspeedblade

One of the most important factors to consider if you want to go electric is that you have to be of the mindset that the motor, whatever it is, is an auxiliary and its primary purpose is to maneuver in tight spaces (marina, harbors) or to get you out of a pinch for a limited time.

If you don't have the attitude that it is, first and foremost, a sailboat then it probably isn't a good move.

The other two important factors are battery capacity and recharge ability. The larger the battery capacity the easier all other aspects will be. Cram 1000 amp hours into the boat you'll probably rarely look at the gauge!

Its more important for cruising, but the ability to replace charge quickly is also certainly a factor, especially if you have a lot of electric draw on the boat besides the motor.

The Sailing Uma channel is a good suggestion. You also need to be very honest with yourself about what kind of sailor you want to be?

I would run a minimal electric draw. Composting head so holding tanks out and in place either storage or more batteries, use the thru-hull for salt-water intake to the sink. I would try to make manual everything, solar shower or heck even a Joy shower. Only draw should be for charging i-pad for ICW navigation. Wouldn't need much electronics except for AIS but there's an app for that! Might look into Starlink once the marine version comes out? Possibly radar... might look into a windvane for self-steering.

I don't want to be a motorsailer, I want a simple setup so I can spend more time sailing than fixing things.

[argosail]

Originally Posted by Adelie

Welcome.

I would suggest updating your profile with your general location and your boat make & model in the "Boat" category. This info shows up under your UserName in every post in the web view. Many questions are boat and/or location dependent and having these tidbits under your UserName saves answering those questions repeatedly. If you need help setting up your profile then click on this link: https://www.cruisersforum.com/forums...ml#post3308797

I would happily help more if the link above is not enough.

The location you’ve given is so specific only locals would know without Googling it.

Watts is a rate of energy flow: 1 Joule per second
10kW is 10,000Watts.

For electricity Volts x Amps = Watts.
Volts is analogous to water pressure and Amps to gallons/second.
Most recreational marine electrical systems run at a nominal 12v, a few at 24v, electrical propulsion on recreational vessels mostly at 48v. There are functional advantages to using higher voltages but at 60v the system is not longer considered low voltage and safety requirements increase as does liability.
For systems with fixed nominal voltages energy storage is usually done in Amp-hr. So Amp-hours is a shorthand proxy for the amount total amount of energy (Joules) that is stored.

This little explanation is undoubtably leaving you boggled. Don’t worry, you’ll understand it better when you’ve played around with it for a while.

Thanks for the info! I see typical house/starter batteries are 12V and if you run 4 of them in series then that should power the 48v electric motor, and if there is space add some more?

[Rumrace]

Deep V entry flat stern At least two chines and a step if you’re going for speed.
We’ve designed a few in 3D for RC. At speed the flatbottom is out of control.
Check out Delhi Yachts in Poland ( Another Beneteau making large long range electric yachts and Rand Boats for ideas.
Don’t call the combustion engine dead Japan has great Hydrogen engines coming

[valhalla360]

I suggest taking a class or researching electrical systems before buying into anything the salesman suggests.

10kw is roughly 13hp. Your average 27-30ft monohull is going to have a 20-30hp engine, so you are starting out at a disadvantage.
- With cars, the engine size is driven by the need to accelerate from a standstill with the engine at low RPM. RPM* Torque = HP, so the max torque available from zero RPM with electric means they can get similar performance with a lower HP electric motor.
- With displacement boats, that doesn't hold true. The prop can slip allowing RPM to increase and you max out around 6-7kts, so acceleration isn't a big consideration. HP needs are driven by the power needed to maintain speed against adverse conditions after the motor is up to speed. HP = HP. Don't believe in magic electric HP, it's not real.

10ah batteries is a nonsense rating unless the voltage is specified. Assuming it's standard 12v, that's basically 1 small lawnmower starting battery. Ask for ratings in KWH and make sure it's the usable amount (lead acid are only good for about 50% of the rating and lithium are only good for around 80% of the rating). If you just want to get in and out of port, I wouldn't want to go below 4-5KWH of usable power in the battery bank.

You have a 10,000w (10kw) motor being fed by 300w of solar. 300w of solar will generate about 1200w-hr per day...that's about enough for typical house loads. If reserved strictly for propulsion will give you about 7min at 10kw output per day if none is used for house. Of course, you might not need the full 10kw but at 5kw output, it's still only 14min of power per day. You need to be looking at 8-10times as much solar if you want it to provide for propulsion and even that is pretty limiting. Kind of hard to put that much solar on a little 27-30ft sailboat (keep in mind, solar hates even tiny amounts of shade which can drastically reduce output...guess what the mast, boom and rigging do)

As far as efficiency, a typical monohull sailboat is about the best unless you go to multihulls. Avoid hard chines or any sharp angles. Those are areas that create drag. If you can find a suitable catamaran or trimaran, you will be better off for efficiency motoring. Sailing may or may not be better depending on what the boat was designed for...hint, high performance multihulls tend to have poor living spaces.

In calm conditions, 13hp is probably fine. If you just want it to get in and out of port, should be fine (300w solar will still be problematic). If you ever expect to motor or to go up a channel against a current, it quickly can become a problem.

[valhalla360]

Originally Posted by Rumrace

Deep V entry flat stern At least two chines and a step if you’re going for speed.
We’ve designed a few in 3D for RC. At speed the flatbottom is out of control.
Check out Delhi Yachts in Poland ( Another Beneteau making large long range electric yachts and Rand Boats for ideas.
Don’t call the combustion engine dead Japan has great Hydrogen engines coming

Huh?

A 10kw motor even if he could supply it with electricity isn't going to get a 9,000lb boat going fast. With a tail wind, he might get a monohull sailboat up close to hull speed. He certainly isn't going to get even a flat bottom boat up on plane.

[Pete7]

Originally Posted by argosail

Thanks for the info! I see typical house/starter batteries are 12V and if you run 4 of them in series then that should power the 48v electric motor, and if there is space add some more?

Couple of us on here have been collecting stats for electric yachts in the 30-34 foot range like the attached. This is the speed and current in watts needed for this speed. If you have a large battery bank preferably LifePO4 then this will give you the range of the yacht. Assume calm flat water, which is why your are motoring. Rough conditions and you will need far more to motor. The two key points are that at 3 knots, its about 1Kw. At 4.2 knots its 2Kw. So you need to be prepared to motor slowly. Travelling fast takes real power.

The other thing to consider is a 48v battery bank will need 56v to charge. The same thing occurs with 12v were you need 14v plus to really charge well, so it just scales up. Achieving 56v will likely need 2 large panels or more smaller ones in series to reach this voltage. There was a Panasonic 67v large solar panel, but it looks like they have pulled it from the market unfortunately. Series has the problem that shade any part of either panel and you loose a huge amount of power. Parallel will allow one panel being shaded to reduce the power generated but you still have the second or third panel generating power.

Electric Yacht is a complete package. You can source the items and make your own brackets cheaper, but your on your own. Thunderstruck is one such option for a self design and build.

Pete

[Pete7]

Originally Posted by valhalla360

Huh?

A 10kw motor even if he could supply it with electricity isn't going to get a 9,000lb boat going fast. With a tail wind, he might get a monohull sailboat up close to hull speed. He certainly isn't going to get even a flat bottom boat up on plane.

I think he means Delphia Boats, but yes 10Kw is about 13Hp although they are not directly compatible and you won't be motoring fast with an electric yacht conversion in an existing hull. A Macgregor 26x might be interesting

Pete

[argosail]

Originally Posted by valhalla360

I suggest taking a class or researching electrical systems before buying into anything the salesman suggests.

10kw is roughly 13hp. Your average 27-30ft monohull is going to have a 20-30hp engine, so you are starting out at a disadvantage.
- With cars, the engine size is driven by the need to accelerate from a standstill with the engine at low RPM. RPM* Torque = HP, so the max torque available from zero RPM with electric means they can get similar performance with a lower HP electric motor.
- With displacement boats, that doesn't hold true. The prop can slip allowing RPM to increase and you max out around 6-7kts, so acceleration isn't a big consideration. HP needs are driven by the power needed to maintain speed against adverse conditions after the motor is up to speed. HP = HP. Don't believe in magic electric HP, it's not real.

10ah batteries is a nonsense rating unless the voltage is specified. Assuming it's standard 12v, that's basically 1 small lawnmower starting battery. Ask for ratings in KWH and make sure it's the usable amount (lead acid are only good for about 50% of the rating and lithium are only good for around 80% of the rating). If you just want to get in and out of port, I wouldn't want to go below 4-5KWH of usable power in the battery bank.

You have a 10,000w (10kw) motor being fed by 300w of solar. 300w of solar will generate about 1200w-hr per day...that's about enough for typical house loads. If reserved strictly for propulsion will give you about 7min at 10kw output per day if none is used for house. Of course, you might not need the full 10kw but at 5kw output, it's still only 14min of power per day. You need to be looking at 8-10times as much solar if you want it to provide for propulsion and even that is pretty limiting. Kind of hard to put that much solar on a little 27-30ft sailboat (keep in mind, solar hates even tiny amounts of shade which can drastically reduce output...guess what the mast, boom and rigging do)

As far as efficiency, a typical monohull sailboat is about the best unless you go to multihulls. Avoid hard chines or any sharp angles. Those are areas that create drag. If you can find a suitable catamaran or trimaran, you will be better off for efficiency motoring. Sailing may or may not be better depending on what the boat was designed for...hint, high performance multihulls tend to have poor living spaces.

In calm conditions, 13hp is probably fine. If you just want it to get in and out of port, should be fine (300w solar will still be problematic). If you ever expect to motor or to go up a channel against a current, it quickly can become a problem.

Yeah a class might be helpful, but youtube videos until then!

The stock motor is a Yanmar 2GM20, which from my research is 16hp. The boat (Pearson 28-2) is 7,000lbs displacement and a shoal keel, not much displacement. I would never even think of going hull speed on electric, 2-3 knots is ok for me in a flat calm with no winds. Also the weight of the engine is 250lbs and then the transmission. The electric unit is much lighter-weight. I'm not sure however for the weight difference between the batteries and a full fuel tank however.
Of course I might get a honda 2200 gen just in case to act as a hybrid...