Inboard engines and a changing world

[Statistical]

Originally Posted by newhaul

Ok guys I know this seems really weird from me but is a 6hp 48 volt motor enough for my 9k columbia 29 defender long keel ? May be able to get motor and speed controls for real cheap

6 HP seems a bit low to me. Usually reducing the power of the motor doesn't save that much money. 48V usually has options up to 12 kW (~15 HP). You probably want the high end of that. Even if you normally don't need 12 kW it is better to have more than you need than need more than you have.

[newhaul]

Originally Posted by Mickeyrouse

It will definitely move you in and out of the slip and around the harbor. But punching into waves in a seaway? 6HP is still 6HP, assuming things are properly and consistently rated. Even in something like a river, I wouldn’t expect you to move at hull speed.
Depending on mounts, coupling and controls, if your old engine is coming out anyway I’d be tempted to try it regardless. If you still have the old Atomic 4, remember that’s prox. 25 HP. I can’t imagine a 6HP electric would come close to that, though I’d be surprised if any Atomic 4 would put out its advertised horsepower.

Actually it was rated at 18 and no engine when I got the boat I do have a 12 hp westerbeke 10-2 to install but a 1980 commuta car just popped up needing batteries for a couple hundred on my craigslist .. was either a 6hp or 8 hp 48 volt dc motor in the car. Would be a good donor for project . Expensive part is the lifepo4 server bank battery to run it .

[newhaul]

Originally Posted by Statistical

6 HP seems a bit low to me. Usually reducing the power of the motor doesn't save that much money. 48V usually has options up to 12 kW (~15 HP). You probably want the high end of that. Even if you normally don't need 12 kW it is better to have more than you need than need more than you have.

I'm a cheap SOB pennies count to me
See my post above

[Statistical]

Originally Posted by newhaul

See my post above

Ah you already have a motor. Well yeah hard to beat free. I think it is still going to be light for anything but a day sailor in good weather. Of course it can always be an experiment and later you upgrade to a 8 to 12 kW motor for relatively low cost (<$4k all in).

Depending on the motor max speed you likely are going to need a reducing gear. Most DIY EV setups using ribbed timing belt pulleys because they are cheap and reliable and can transfer a lot of power.

[Adelie]

Originally Posted by newhaul

Ok guys I know this seems really weird from me but is a 6hp 48 volt motor enough for my 9k columbia 29 defender long keel ? May be able to get motor and speed controls for real cheap

So the Defender weighs slightly less than a Cal 34 but also has a shorter waterline.
The following is estimated performance of a Cal-34 in calm conditions using a 48v system.

Kts Amps Watts nm Range (300Ahr-80%DoD)
2.5 10 480 63
3.2 20 960 39
4.0 40 1920 23
4.6 60 2880 18
5.0 80 3840 14
5.4 100 4800 12
5.7 120 5760 11

Is this a 6hp motor which would be 4476W or a 6kW motor which would be 8hp?

Motor, controller and 300Ahr of batteries is about what will fit in the space that an A4 and it's fuel tank occupies.

If you go all in on solar panels you can probably go 2.5kt all day and end up with more energy in your battery than you started with.

A 4500W motor will be good for getting you in and out of the marina and harbor, it will let you set and retrieve your anchor, it will get you out of the way of large ships that are thinking about running you down and it will help you thru tacks in very high winds. It's not going to get you long distances at speed, but you will able to slowly motor straight into wind and waves for short periods, 60-120min. With the electric motor you would have power almost instantly available.


The original Columbia-29 had space behind the rudder for a small outboard in a well. Atomvoyages has videos on how to convert a lazarette to a motor well with the ability to tilt the motor up for minima drag sailing. Whether your Defender has sufficient clearance behind the rudder for this to work would require some investigation.

A 6hp Tohatsu high thrust motor will push an Alberg-30 at 5.5kt in calm conditions.

There is no reason you couldn't run the electric motor and the outboard at the same time it you needed shortish period of very high thrust.

If you go the electric route with the outboard, you will probably find the outboard mpg is about the same as a diesel despite the outboard being gas/petrol. The reason for this is that while the diesel is more efficient at max power than an outboard at max power, you probably run it at 1/2 power or less most of the time and efficiency falls way off. Whereas with the outboard you will probably run it at 80% or more power to get the 5.0-5.5kt cruising speed you are used to and fuel efficiency will be near max and similar to the diesel, perhaps even slightly better.

If your diesel still runs fine, it probably isn't worth swapping out unless you are really invested in the idea of going EP.

[newhaul]

Originally Posted by Statistical

Ah you already have a motor. Well yeah hard to beat free. I think it is still going to be light for anything but a day sailor in good weather. Of course it can always be an experiment and later you upgrade to a 8 to 12 kW motor for relatively low cost (<$4k all in).

Depending on the motor max speed you likely are going to need a reducing gear. Most DIY EV setups using ribbed timing belt pulleys because they are cheap and reliable and can transfer a lot of power.

4000 rpm so a 3.5:1 ratio is about right ( didn't do exact math ) the diesel is 2,000rpm and a 1.8:1 fwd and 2:1 Rev. On the hurth.
Not free but an old comuta car for $200 just needs batteries.

[newhaul]

Originally Posted by Adelie

So the Defender weighs slightly less than a Cal 34 but also has a shorter waterline.
The following is estimated performance of a Cal-34 in calm conditions using a 48v system.

Kts Amps Watts nm Range (300Ahr-80%DoD)
2.5 10 480 63
3.2 20 960 39
4.0 40 1920 23
4.6 60 2880 18
5.0 80 3840 14
5.4 100 4800 12
5.7 120 5760 11

Is this a 6hp motor which would be 4476W or a 6kW motor which would be 8hp?

Motor, controller and 300Ahr of batteries is about what will fit in the space that an A4 and it's fuel tank occupies.

If you go all in on solar panels you can probably go 2.5kt all day and end up with more energy in your battery than you started with.

A 4500W motor will be good for getting you in and out of the marina and harbor, it will let you set and retrieve your anchor, it will get you out of the way of large ships that are thinking about running you down and it will help you thru tacks in very high winds. It's not going to get you long distances at speed, but you will able to slowly motor straight into wind and waves for short periods, 60-120min. With the electric motor you would have power almost instantly available.


The original Columbia-29 had space behind the rudder for a small outboard in a well. Atomvoyages has videos on how to convert a lazarette to a motor well with the ability to tilt the motor up for minima drag sailing. Whether your Defender has sufficient clearance behind the rudder for this to work would require some investigation.

A 6hp Tohatsu high thrust motor will push an Alberg-30 at 5.5kt in calm conditions.

There is no reason you couldn't run the electric motor and the outboard at the same time it you needed shortish period of very high thrust.

If you go the electric route with the outboard, you will probably find the outboard mpg is about the same as a diesel despite the outboard being gas/petrol. The reason for this is that while the diesel is more efficient at max power than an outboard at max power, you probably run it at 1/2 power or less most of the time and efficiency falls way off. Whereas with the outboard you will probably run it at 80% or more power to get the 5.0-5.5kt cruising speed you are used to and fuel efficiency will be near max and similar to the diesel, perhaps even slightly better.

If your diesel still runs fine, it probably isn't worth swapping out unless you are really invested in the idea of going EP.

Ok one more time the boat had an atomic was removed by prior owner ( 2 ago) now has an open engine bay . The diesel is on a pallet ready to install ( got 200 invested in it ) .
Currently has a 7.5 evinrude 2 stroke on a bracket on stern .

Just toying with the idea for the next 2 or 3 years before I jump again .

Sold the suzuki 4 stroke for what I paid for the boat . Now a 7.5 evinrude. Good swap .

[Corvidae]

With electric motors, the cost of the motor is the cheap part. A 48v bank is going to cost more than that motor. Guestimate around $2400 for 9.6kwh that you're going to want. You could get AGM's for less, but you really don't want to.

[newhaul]

Originally Posted by Corvidae

With electric motors, the cost of the motor is the cheap part. A 48v bank is going to cost more than that motor. Guestimate around $2400 for 9.6kwh that you're going to want. You could get AGM's for less, but you really don't want to.

Lifepo4 is the only way to go

[malbert73]

I’m hopeful that in the next 5 years I can repower my 17 Boston whaler (with vintage but bulletproof Yamaha 85) with electric outboard + Li. Never run more than 2-3 hours in a day, so a much better use case, and uses a ton more fuel than my sailboat diesel inboard

[Adelie]

Let’s assume you use 40kW to stay on a plane. Ignore whatever brief surge you need to get on a plane, to brief to bother accounting for.

So 40kW for 3hr is 120kWhr.

You only want to use 80% of battery so

120kWhr / 0.80 = 150kWhr =150,000Whr installed capacity.

Currently the best generally available Li-ion batteries are 260Whr/kg.
There’s something entering the market claiming 500Whr/kg. Probably cost you an arm and a leg and your first born.
Let’s assume that the technology pans outs and in 5yr the prices come down to something reasonable.

150,000Whr / 500Whr/kg = 300kg = 660lb.

My guess is that in 5yr or so we’ll be getting specific energies around 350Whr/kg.

150,000/350=429kg=942lb.

For a 17’ powerboat a thousand extra pounds of dead load would be hard to accept. 300-500 probably would be fine.

That means cutting max run time on a plane to 1hr and change.

What I expect to happen in 5-10yr is for the best Li-ion batteries to be around 400-600Whr/kg but still so expensive there only have niche uses.
I expect sodium ion batteries which are currently at about 160-180Whr/kg to make it up around 200-300Whr/kg (where Li-ion is now) but cheaper than any Li-ion is now.
So NA-ion batteries take over the EV & EP markets due to cost.

[newhaul]

Originally Posted by Adelie

Let’s assume you use 40kW to stay on a plane. Ignore whatever brief surge you need to get on a plane, to brief to bother accounting for.

So 40kW for 3hr is 120kWhr.

You only want to use 80% of battery so

120kWhr / 0.80 = 150kWhr =150,000Whr installed capacity.

Currently the best generally available Li-ion batteries are 260Whr/kg.
There’s something entering the market claiming 500Whr/kg. Probably cost you an arm and a leg and your first born.
Let’s assume that the technology pans outs and in 5yr the prices come down to something reasonable.

150,000Whr / 500Whr/kg = 300kg = 660lb.

My guess is that in 5yr or so we’ll be getting specific energies around 350Whr/kg.

150,000/350=429kg=942lb.

For a 17’ powerboat a thousand extra pounds of dead load would be hard to accept. 300-500 probably would be fine.

That means cutting max run time on a plane to 1hr and change.

What I expect to happen in 5-10yr is for the best Li-ion batteries to be around 400-600Whr/kg but still so expensive there only have niche uses.
I expect sodium ion batteries which are currently at about 160-180Whr/kg to make it up around 200-300Whr/kg (where Li-ion is now) but cheaper than any Li-ion is now.
So NA-ion batteries take over the EV & EP markets due to cost.

What vessel are you looking at? My rib fishing boat has a 15 hp ( 11kw ) tohatsu and planes on just over half throttle.

[AKA-None]

Originally Posted by newhaul

What vessel are you looking at? My rib fishing boat has a 15 hp ( 11kw ) tohatsu and planes on just over half throttle.

I believe it was mentioned as a Boston Whaler

[newhaul]

Originally Posted by AKA-None

I believe it was mentioned as a Boston Whaler

On that 17ft whaler yes agreed .

[Adelie]

Originally Posted by newhaul

What vessel are you looking at? My rib fishing boat has a 15 hp ( 11kw ) tohatsu and planes on just over half throttle.

The 17' Whaler in the post just before mine.

Regarding your RIB with the 11k motor. Lets say it takes 4kW to stay on a plane. This jives with a previous survey I did about how many people could get on a plane with a particular sized motor and a particular size and type boat.

Once again, getting on a plane requires a lot more power but for a very brief period and once on a plane you can throttle way back. As with ICE engines, the more people and the more gear you have on the boat the more power required to get on a plane and to stay on a plane. Lets assume the minimum of 4kW.

So for 1hr on a plane, you need 4kWhr.
For 80% usable capacity you need 5kWhr = 5,000Whr of capacity.

A Battle Born battery has about 1250Whr in it and weighs 29lb.

5000Whr / 1250Whr per battery = 4 batteries.

4 batteries x 29lb = 116lb = 53kg.

Barely planing speed will be about 10kt. So in 1hr you can go about 10nm.

If you don't plane, but are content to motor at about S/L -1.0 or about 3.3kt you will use about 200W.

4,000Whr / 200W = 20hr. --> 20hr x 3.3kt = 66nm.