serious discussion about electric power in large boats

[wingssail]

Originally Posted by CatNewBee

...Assume a gale and lee shore situation where you need power to get outa here...

Some people would insist that their boat be able to sail off a lee shore, even in gale conditions.

[Dockhead]

Originally Posted by danstanford

So how about another way to look at the issue, and admittedly it may not connect with those of you talking about cruising with larger boats on electric power....but I think it would work for UMA, and me.
99% of the time the range of the battery bank is way more than I need since I just need to get from my dock out into the lake for race time or some day sailing. Having said that, I am really concerned about the time that I decide to cruise somewhere 50 nm away and end up having to come home with no wind or wind in the face. So the 1% controls my thinking and I cannot get away from it.
What about a stern hung outboard bracket that you only put the outboard on when you go on a longer trip? In the perfect world you are dragging around an outboard and a gas tank for no reason and when you get home you haul off the outboard and the fuel tank and go back to your solar/electric solution.
Is it a workable solution?
In my case the situation is caused by the fact that the boat is a factory issued Oceanvolt boat that I like a lot. This, for me, might be a solution I could live with where I don't think at this time I see the wisdom in taking out a diesel to run on solar.
Dan

CatNewBee has very well explained the limitations of electric propulsion for cruising boats, which I agree with entirely.


You, however, sir, are a poster boy for one of the few use cases which electric propulsion, in its present state of development, is perfect for.


If you can store enough cheap power from a shore power connection, to do what you require from your propulsion, then electric is fantastic.



If you are worried about occasionally cruising 50 miles away and not being able to get home in a calm, then I think your outboard idea is fine. A surprisingly small outboard will push a smallish sailboat just fine -- provided the weather is reasonable. One issue you will have is that you need a long shaft outboard in order not to have the prop coming out of the water constantly in a seaway, and your dinghy outboard is a short shaft one. But if what you are really worried about is calms, then even that ought to be ok -- but try it out before taking my word for it -- YMMV.


What you WON'T be able to do is motor off a lee shore, motor home against a strong headwind, motor for hundreds of miles at a reasonable cruising speed -- all modes of operation which most of us demand. For that, there is so far no substitute for inboard diesel. But if you are happy without that capability, if you only go long distances rarely, and can pick a weather window for a good sailing wind, then you should be fine.


If 99% of the time you are just motoring to get off the dock to go for a day sail, then electric should be a dream

[Pete7]

Originally Posted by Adelie

Is that 2.5, 4 or 6hp outboard?
Looks like 2.5hp.

Little 2.5hp 4 stroke I believe. Actually might be better with this a silver century Seagull which has a much bigger slower turning prop but that's another story.

Pete

[GrowleyMonster]

Originally Posted by danstanford

So how about another way to look at the issue, and admittedly it may not connect with those of you talking about cruising with larger boats on electric power....but I think it would work for UMA, and me.
99% of the time the range of the battery bank is way more than I need since I just need to get from my dock out into the lake for race time or some day sailing. Having said that, I am really concerned about the time that I decide to cruise somewhere 50 nm away and end up having to come home with no wind or wind in the face. So the 1% controls my thinking and I cannot get away from it.
What about a stern hung outboard bracket that you only put the outboard on when you go on a longer trip? In the perfect world you are dragging around an outboard and a gas tank for no reason and when you get home you haul off the outboard and the fuel tank and go back to your solar/electric solution.
Is it a workable solution?
In my case the situation is caused by the fact that the boat is a factory issued Oceanvolt boat that I like a lot. This, for me, might be a solution I could live with where I don't think at this time I see the wisdom in taking out a diesel to run on solar.
Dan

It will be a long time, if ever, before it is a good idea to take out a diesel that still runs, and repower with electric. I could only recommend it if the diesel was beyond repair and the boat is not worth a new diesel. Even then, it is not for everyone due to the technical requirements vs real world demands.


An outboard is another technology with severe limitations. For inland or perhaps some coastal cruising, an outboard could serve, on the right boat with the right mount. Also fuel efficiency is an issue. Plus there is the gasoline thingy and the explosion/fire thingies. Outboards, being all the way aft on the transom, get lifted out of, and plunged into, the sea a lot. A drowned outboard is gonna be hard to start or even to keep running. For a day sailer who occasionally ventures beyond his practical electric range, an outboard can be pretty handy. On boats over 35' they quickly become less practical. For a 30' boat used in local waters, maybe an outboard will work well for you. Plenty of boats out there that are basically outboard boats. It saves a lot of space below, too.


If you are going to have a gasoline outboard as a backup to electric, you might also consider a 2k lunchbox generator as well.



Just my opinion but for a bigger boat I would shy away from outboards, even more so than EP. Unless you are very sure that it would work well for you due to a specific set of operating parameters that you will not often exceed. In a boat with a dead diesel, that isn't worth repowering with diesel, and that will not really require the range and efficiency of diesel, maybe go EP or outboard or both might be indicated. Remember though, that on larger boats, FLA batteries become less practical and the bank is gonna cost a lot more, making the whole system not much cheaper than a diesel. It is a whole nother world from the 25' to 32' range of boats.

[ramblinrod]

Originally Posted by Auspicious

Correct. That is what I maintain. If you don't think errors in excess of 20% in a number isn't meaningful I don't know what to say.



If you don't think the technical description of a naval architect is not helpful perhaps you shouldn't go sailing any more.



If you don't think understanding the speed-power curve is not useful to recreational boaters who cruise or have aspirations to cruise I just don't know what to say.





We've been through this before in this thread. The curve moves and the point on the abscissa does not. Therefore it is useless. Read my earlier posts. Look at the numbers. Go out on four different hulls with the same LWL and tell me how "hull speed" has any benefit.





Nope.





Yes.






No. Give me the lines and I can get close. Give me the boat and I can hit it.



Your question is tantamount to "do you still beat your wife."



For real-world application "hull speed" is useless.






Not arbitrary. I showed the numbers above for 22% (+/- 11%) for one boat.


Your analogy of weather forecasts is specious. We can get something useful from weather forecasts given their accuracy. There is nothing useful in hull speed.



Give me something specific you can use "hull speed" for. You might want to reread my posts first.

I think you need to give this a rest to maintain any credibility.

[GrowleyMonster]

Are we still talking about EP?

[Auspicious]

Originally Posted by a64pilot

See, I think and have thought so for a long time that for the vast majority of boats, electric propulsion is very viable, that’s because they don’t often go anywhere and when they do it’s very often just to day sail and then back or the Marina and plug back in.

Agree. Day sailing for which you don't go out if there isn't wind and plug back in at the dock is perfect for electric.

Originally Posted by a64pilot

A few people cruise with no motor at all, so it’s possible, but they are very rare. I’ve not run into one myself yet.

I can think of one in particular. I've got six cases of her books in my basement waiting for her to show up for the Annapolis Boat Show. *grin* Autographed copies....

[danstanford]

Originally Posted by CatNewBee

So you must recharge / top up your battery every day back in the marina plugged in after using your engine.

Yes, that would be the model. Do you think this would be a problem?

Most everybody in every marina I have been in come back into the slip and plug in and then MOST of the time unplug before they attempt to leave!

It would appear based on the battery capacity that they claim, I could quite easily go 10 trips or about a month before I would need to re-charge if I chose to do that. Knowing me, I would charge her up full every time I returned though.

I can see how this would not work on a mooring unless you had some solar.
Dan

[john61ct]

Originally Posted by danstanford

Yes, that would be the model. Do you think this would be a problem?

Each person's use case is different.

If you want a serious discussion about viability of EP for yours, best to start a new dedicated thread, and try to discourage others from derailing the specific questions **you** need to clarify.

[danstanford]

Acknowledged.

Hopefully no one thought I was being sarcastic or disruptive when I asked if this would be a problem, it was a genuine question.

[john61ct]

Yes, and there are several variables involved, which I reckon will be much easier to address if you start a new thread,

lay out as much background info as to your use case in the OP, do not assume anyone has read this thread,

but perhaps link back to it for general reference so people don't feel the need to repeat its general consensus points.

[SieveSailor]

I've attached data I took yesterday, if anybody finds it helpful.

[Auspicious]

Originally Posted by SieveSailor

I've attached data I took yesterday, if anybody finds it helpful.

Interesting. I especially like the curve fit. *grin* Flip the axes and you'll see the conventional speed-power curve!

[Montanan]

Originally Posted by SieveSailor

I've attached data I took yesterday, if anybody finds it helpful.

Thank you, very beneficial to have actual empirical data.

[StuM]

Originally Posted by SieveSailor

I've attached data I took yesterday, if anybody finds it helpful.

Thanks for that, it shows what a lot of people here have been saying.


Regardless of whether you are driving the prop with diesel or electricity, power requirement roughly doubles for every knot increase in boat speed once you get past idle.