The rise of electric Boats

[valhalla360]

Originally Posted by Adelie

What boat? LWL and lightship displacement?

The Uma folks make 3.0-3.2kt using 1.2kW.
Pearson 36, 13,500lb, 29.16’lwl

You avoided the question. It was how much to do 5kt or 8kt.

Of course, that 1.2kw number is based on dead calm conditions. Any kind of head wind and they won't be making 3kts.

[Adelie]

Originally Posted by valhalla360

Somethings not adding up. 1500w might get a small cat in calm conditions doing 2.5kt but 1500w of solar panels isn't going to put out 1500w for 24hr. Plus there are house loads to consider.



If you get 5nm/d out of it you would be doing well on a small cat. A big cat, overcast, waves or even a modest head wind ...and that likely dwindles to nothing.

I want a Cal 34. 500w will push the boat 2.5kt.

If I’m getting 1000w out of the panels half goes into the motor and half goes into the battery bank.
There will be losses going thru the battery and I won’t get full output all day long so I said 1500W. Since I will be arranging to put a significant amount of panels on a tracking mount I expect to get near 1500W for the whole day if I can mount as much as I hope.

House loads will be handled with permanently mounted panels.

SeanD pushed his 30’ Tri at 1.2kt using 70W.

Yes if it’s not calm speed will decrease. If it’s overcast speed will probably drop to about 1kt.

Why are you bringing up headwinds? It’s a sail boat, sails go up and I go on my merry way.

[Adelie]

Originally Posted by valhalla360

You avoided the question. It was how much to do 5kt or 8kt.



Of course, that 1.2kw number is based on dead calm conditions. Any kind of head wind and they won't be making 3kts.

I didn’t avoid the question, I asked for information necessary to provide the answer.

And then I provided an example of what it takes to go a give speed for a give length and weight boat.

Headwinds are a moot issue, wind comes up start sailing and turn off the motor.

[Narfi]

Originally Posted by valhalla360

Having done the Great Loop on a 34ft cat, a 50mile run is going to need around 10kw to maintain 6miles/hour for just over 8hr...so 80kwh of battery bank...round up to 100kwh as you don't want to run them down to 0% charge. Probably around 1400lb of batteries on an 8,000lb boat.

To recharge 80kwh with solar, you would need around 20kw of solar panels (they don't put out power 24/7). Pretty hard to find the space for that on a 34ft cat.

If you reduce the speed, you can reduce the daily draw and battery bank size but now you start to run into some practical issues. On the river system, it's strongly discouraged to run at night because there's a lot of floating debris (including hole trees). If you are going to limit your speed to say 4mph, that's a 13-14hr day...in the fall when days are getting short, you may not have that many hours of daylight.

Also, what happens when you turn up the Ohio River and are fighting a 2mph current for 60miles doing only 4mph? Now you are looking at probably 3-4 days to make it to Kentucky Lake.

This isn't to say you can't do it but solar wouldn't be the primary source of power. Stopping at marinas and plugging in and adding a generator to supplement power generation on the longer stretches really is needed from a practical point of view.

My thought process is size it so that you can go 50 miles in one day on 3 days worth of sun in IDEAL conditions, all other conditions you would run the generator for part of the run, or wait an extra day, etc....
Size the motors larger than minimal so that they can push the speed when needed to fight current, fully understanding that you will be running your generator to cover the extra draw.

10kw for your boat gets you (34ft cat) (I was asking about a 40 but lets go with yours since you have real numbers). IF(big if) you can get 5kw of actual solar production off of your roof then you need enough battery to cover the extra 5. So in PERFECT conditions you could get your 50 miles 'burning' 10kw with a 40(usable)kwh battery bank and 5kw(usable) solar array. Again in PERFECT conditions the following two days should allow you to replenish your 40kwh bank with your 5kw array and be ready to start all over again the 4th day.

Expecting that a majority of travel days will still require the generator to run some to make up for cloudy days, current, etc......

I suspect that the way squares and cubes work the larger the catamaran(what I am interested in) the more feasible (weight and ft2 of roof) the solar and battery requirements become.

With hard numbers on kw needed to motor a range of speeds you could easily calculate the best speed for range and time vs different conditions including cloud cover and current speeds.

On the powerboat I built I have a brand new Mercury 4stroke and it interfaces with my MFD with real time mpg readings so it is fun to play with speeds for economy and range.

Perhaps on a 40ft cat you would need 15kw to the motors and a 10kw array with same size battery to compare with the same leg vs. the theoretical day on yours. I don't know, but I would like to start learning and figuring out some of those realistic numbers to see what I can play around with in my head for when I get to the stage of needing to decide on propulsion for the boat I build.(haven't even nailed down the plans 100% yet so I have time)

[zstine]

Originally Posted by valhalla360

You avoided the question. It was how much to do 5kt or 8kt.

Of course, that 1.2kw number is based on dead calm conditions. Any kind of head wind and they won't be making 3kts.

Using Gerr's SHP prediction we can check the 1.2kW @ 3knt on 29ft and 13,500lb.
Gerr Method A is 0.77kW, Method B is 1.94kW (more realistic)
at 5 knts the method B power prediction is 3.95kW (5.3hp)
at 6 knts its 6.07kW (8.14hp)

at 7 knts its 10.03kw (13.5hp)

at 8 knts the prediction is 18.32kW (24.6hp).. NOTE this is OVER hull speed of 7.22knts and you should never motor at this speed.



if the seas are not flat, then there's probably wind to sail!

[Pete7]

Originally Posted by Narfi

10kw for your boat gets you (34ft cat) (I was asking about a 40 but lets go with yours since you have real numbers). IF(big if) you can get 5kw of actual solar production off of your roof then you need enough battery to cover the extra 5. So in PERFECT conditions you could get your 50 miles 'burning' 10kw with a 40(usable)kwh battery bank and 5kw(usable) solar array. Again in PERFECT conditions the following two days should allow you to replenish your 40kwh bank with your 5kw array and be ready to start all over again the 4th day.

How about putting the sails up? Then using say 1/2kw to get moving in the morning and the same with the arrival. That should leave 9Kw to run the electric hob cooking dinner.

[valhalla360]

Originally Posted by Adelie

I want a Cal 34. 500w will push the boat 2.5kt.

If I’m getting 1000w out of the panels half goes into the motor and half goes into the battery bank.
There will be losses going thru the battery and I won’t get full output all day long so I said 1500W. Since I will be arranging to put a significant amount of panels on a tracking mount I expect to get near 1500W for the whole day if I can mount as much as I hope.

House loads will be handled with permanently mounted panels.

SeanD pushed his 30’ Tri at 1.2kt using 70W.

Yes if it’s not calm speed will decrease. If it’s overcast speed will probably drop to about 1kt.

Why are you bringing up headwinds? It’s a sail boat, sails go up and I go on my merry way.

Maybe with a strong tailwind you are doing 2.5kt. Had a 5hp auxiliary that could be deployed on our 34ft cat and maxed out in calm conditions was 3.0kt in testing.

Even so, 0.5kw for 24hr is 12kwh. 1.5kw of solar panels will only be expected to produce around 6kwh/day if everything is operating ideally and there are no house loads.

Headwinds...I'm talking about 5kts headwind can bring the boat to a halt with as little power as you are suggestin.

[Narfi]

Originally Posted by Pete7

How about putting the sails up? Then using say 1/2kw to get moving in the morning and the same with the arrival. That should leave 9Kw to run the electric hob cooking dinner.

For 20+ years of the life of my boat that is what I expect to do, however for the 1 year we do the Great Loop(unless we like it enough to repeat some day), I do not think that is practical, perhaps I am wrong?

It is a thought exercise for me, I love the idea of electric but do not think it is likely practical. But while I sit through a cold winter what does it hurt to run numbers?

For those of you who have done the great loop, what % of any given day can be practically powered under sail instead of prop? (my assumption was that it is a negligent number)

[valhalla360]

Originally Posted by Narfi

My thought process is size it so that you can go 50 miles in one day on 3 days worth of sun in IDEAL conditions, all other conditions you would run the generator for part of the run, or wait an extra day, etc....
Size the motors larger than minimal so that they can push the speed when needed to fight current, fully understanding that you will be running your generator to cover the extra draw.

10kw for your boat gets you (34ft cat) (I was asking about a 40 but lets go with yours since you have real numbers). IF(big if) you can get 5kw of actual solar production off of your roof then you need enough battery to cover the extra 5. So in PERFECT conditions you could get your 50 miles 'burning' 10kw with a 40(usable)kwh battery bank and 5kw(usable) solar array. Again in PERFECT conditions the following two days should allow you to replenish your 40kwh bank with your 5kw array and be ready to start all over again the 4th day.

Expecting that a majority of travel days will still require the generator to run some to make up for cloudy days, current, etc......

I suspect that the way squares and cubes work the larger the catamaran(what I am interested in) the more feasible (weight and ft2 of roof) the solar and battery requirements become.

With hard numbers on kw needed to motor a range of speeds you could easily calculate the best speed for range and time vs different conditions including cloud cover and current speeds.

On the powerboat I built I have a brand new Mercury 4stroke and it interfaces with my MFD with real time mpg readings so it is fun to play with speeds for economy and range.

Perhaps on a 40ft cat you would need 15kw to the motors and a 10kw array with same size battery to compare with the same leg vs. the theoretical day on yours. I don't know, but I would like to start learning and figuring out some of those realistic numbers to see what I can play around with in my head for when I get to the stage of needing to decide on propulsion for the boat I build.(haven't even nailed down the plans 100% yet so I have time)

If on a 3 day cycle, 20kw of solar becomes 6.7kw of solar (roughly). Of course, you have to include some margins for error so probably more like 7.0-7.5kw of solar...way too big for a 34ft cat even if you ditch the mast.

Now realistically, shoot for 30-40 mile range at cruise speed with a generator to cover longer days or multiple travel days in a row (keep in mind sometimes the weather makes it nice to travel 2 or 3 days in a row before things get nasty based on the forecast) Drop the solar recharge back to something more reasonable (maybe 1-2kwh if no mast) and plan on charging at marinas as a more reasonable approach.

You can play with speed a bit to extend range but it can quickly become impractical (see comment from someone about 1.2kt at 70w). Eventually it starts causing other practical issues to come up.

You can run some estimates based on scaling up to a larger boat. It's possible, just don't get caught up in the magic electric HP ideas. Set realistic range and power requirements for the design.

[valhalla360]

Originally Posted by zstine

Using Gerr's SHP prediction we can check the 1.2kW @ 3knt on 29ft and 13,500lb.
Gerr Method A is 0.77kW, Method B is 1.94kW (more realistic)
at 5 knts the method B power prediction is 3.95kW (5.3hp)
at 6 knts its 6.07kW (8.14hp)

at 7 knts its 10.03kw (13.5hp)

at 8 knts the prediction is 18.32kW (24.6hp).. NOTE this is OVER hull speed of 7.22knts and you should never motor at this speed.

if the seas are not flat, then there's probably wind to sail!

That doesn't sound too far off from what I would expect but the point was to provide real life examples.

[Pete7]

Originally Posted by Narfi

It is a thought exercise for me, I love the idea of electric but do not think it is likely practical. But while I sit through a cold winter what does it hurt to run numbers?

Oh absolutely, btw I have been doing the same thing this winter, nought else to do in lock down

The straight answer your accountant would give is buy a bloody diesel and be done with it, it will out last you. However, I don't want to listen to a diesel chugging away and with a fat stern we sometimes do get fumes coming back into the cockpit.

Pete

[valhalla360]

Originally Posted by Pete7

How about putting the sails up? Then using say 1/2kw to get moving in the morning and the same with the arrival. That should leave 9Kw to run the electric hob cooking dinner.

Doesn't work so well when the mast is strapped to the deck to get under the low bridges from Chicago to Mobile.

[valhalla360]

Originally Posted by Narfi

For those of you who have done the great loop, what % of any given day can be practically powered under sail instead of prop? (my assumption was that it is a negligent number)

Depends how stubborn you are.

If you are really stubborn, you might get up to 50% under sail but you will have many more travel days

Typically, it's more like 10% for sail boats on the loop.

[newhaul]

Originally Posted by valhalla360

Doesn't work so well when the mast is strapped to the deck to get under the low bridges from Chicago to Mobile.

Kite sailing ?
No mast required

[Narfi]

Originally Posted by valhalla360

If on a 3 day cycle, 20kw of solar becomes 6.7kw of solar (roughly). Of course, you have to include some margins for error so probably more like 7.0-7.5kw of solar...way too big for a 34ft cat even if you ditch the mast.

Very rough generalization shouldn't you get roughly 1/4 of your cats footprint as roof space for potential solar? (not counting purpose built full length solar arrays that look butt ugly imo)

34x16(i dont know your beam) = 544 / 4 = 136ft2
Randomly googled some marine solar panels and found 18w/ft2
136x18 = 2448

(same numbers ran on a 40x18ft boat = 3240)
(same numbers ran on a 60x26ft boat = 7020)

back to yours, of that 2448 potential per perfect sunlight hour, what do you get in a day? I would think that would be getting pretty close to your 7.5kwh?

Purpose built with a larger roof say 1/3rd instead of 1/4th would change the numbers enough to potentially tip the scale without ending up 'too' ugly?

34x16 = 3264kw
40x18 = 4320kw
60x26 = 9360kw