serious discussion about electric power in large boats

[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

[ramblinrod]

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

Before you pull the trigger on the electric boat with the O/B back-up. Ask 30'+ boat sailors who have outboards as main propulsion (because they couldn't afford to repower an inboard) what they think of it when Lake Ontario kicks up and then the wind dies off, leaving 2-3 m waves the wind won't support to sail back home.

Of course a retiree can often wait for more suitable conditions. Someone who has to be back to work tomorrow? Outboards on keel boats are OK for small lakes, big water, they suck (and I sailed trailerables with O/Bs on big water for over a dozen years).

[ramblinrod]

Originally Posted by Auspicious

It doesn't exist in any meaningful way.


Hull speed or speed-length ratio was used hundreds of years ago when all hulls were very similar in form and there was no repeatable way to measure power from sails. We could measure approximately hull resistance (recognizing scaling effects - see Froude, Reynolds, et al) but not power. As hull forms advanced the constant factor in speed-length ratio was modified. When I was in college we inherited nomographs, all empirically derived, to determine what constant between 1.05 and 1.5 to use in calculating "hull speed" the only purpose of which was to compare similar hulls. By that time the value of speed-length ratio was more in the constant than the "hull speed" number. In that same time frame numerical models began to develop which barely kept up with more and more variations in hull forms.



From the beginning professionals realized (or had it beaten into us with splines) that the numbers were only representative and did not provide any meaningful absolute value.



The clearest demonstration of this is to look at a simple speed-power curve that shows speed as a function of power (you can use fuel consumption vice power for a particular engine if you like). What you'll see is a curve that is more or less linear (there is a slight bow to the curve) from zero (0) speed to some point where the curve starts to bend upward a good bit over a range of speed after which it becomes mostly linear again with a slight bow. In the early portion of the curve hull resistance is dominated by static effects (wetted surface area and windage). In the last portion of the curve hull resistance is dominated by dynamic effects, principally wavemaking resistance. The transitional region--and it is a region not an inflection point--is more or less correlated with the waterline length approximating the developed wave length, which is itself dependent on both dynamic effects of the hull moving through the water and environmental conditions. The flat water curve is different from one in fully developed seas. Regardless it is a region and not a point and in fact is quite a broad region. See Figure 7.4 of https://www.usna.edu/NAOE/_files/doc...hapter%207.pdf and tell me just where the hull speed is?



In the transitional region for any fixed increase in speed the required marginal increase in power gets larger. For a moderate sized recreational boat the transition region is likely to be on the order of 20% the achievable speed range for the hull. That transitional region makes the concept of "hull speed" really silly. It's pure and simple marketing and nothing more.



There are of course contributing effects. One is fuel consumption curves in modern engines. These will, I believe, tend to compress the speed-power curve transition region when reflected as speed-fuel consumption. This isn't significant and the whole curve is truncated by the maximum power output of a given engine. At some point you can keep pumping more fuel through the engine and it won't generate more power. *grin* Second is changes in lift and drag under sail as a boat heels over. These are deterministic effects and for modern hull forms are why you generally go faster if you don't heel the boat more than about 15 degrees. Specifics of course vary with hull form. Lets not squabble over +/- 2 degrees okay?


In the real world there are other effects that contribute to how fast a boat will go. The "stuff" cruisers strap above deck creates windage. Drag from furled sails. Sail trim ability. Seakeeping thresholds. Sail condition.



It is worth noting that modern sail plans (and I should note that as a naval architect I look back of a great deal of history, so let's say modern sail plans cover the last fifty years, and modern sail materials cover the last twenty years) generate a prodigious amount of power when trimmed well. THAT is why you exceed the "hull speed" under sail, not because you're surfing the boat. Sail power on most boats can drive you well into and even through the transition region. That isn't surfing. It's pure power.



Still in the real world and for a moderate size boat (say 40-48 feet) and a modern engine like a Yanmar 4JH or a Volvo-Penta D55 or any other high speed diesel engine with power output between 55 and 75 HP (naturally aspirated or turbo) you end up with a "sweet spot" around 1800 HP where speed, range, and fuel cost are more or less optimum. That's a subjective choice of course - I've had customers who burn twice the fuel to arrive 35% sooner, or 50% more fuel to arrive 15% sooner. How deep is your wallet.



So yes, given a geosim hull, a 45' waterline boat will be about 5.7% faster in the same conditions than a 40' waterline boat. Absent a geosim (i.e. almost all boat to boat comparisons) there are too many other important factors. A naval architect can look at lines and make an assessment but we'll look at ratios like block and prismatic coefficients but we'll also compare the fullness of sections forward. Non-geometric considerations are important also like tankage, stability (CG and GM foremost), and the use cases. "Hull speed" simply doesn't matter.




No question at all in my mind. I agree. I often tell people with 200-300A service to their homes that they have no idea what conservation is. Live on 30A (or less)--assuming 117VAC, half that for our ROW friends on 220VAC--for a while. Now in fairness most of us do avail ourselves of things like laundry and near-unlimited hot water when we can get them. *grin*


/rant/ We should be looking at unplugging things instead of adopting the IoT. Do you really need a "smart" refrigerator with WiFi that orders milk from Peapod because the 'best-by' date has passed?/end of rant/






Maybe. I would say that working to reduce overall consumption is very good. Some things are easy - unplugging unused devices (any charger that isn't charging, anything in 'stand-by' to be turned on by a remote, anything with an electronic control panel). Some things, including PV solar, require thought and awareness of what we are doing to the planet. I don't have a better solution (well...a 15kW nuclear reactor would be nice) than solar and batteries for a cruising sailboat; I would like to think cruisers realize their solution has a foundation that is neither green nor renewable.

Answer: THS = 1.34 x LWL^0.5.

You seem to insist that for THS to be valuable it must be a definitive single point where any amount of power will not increase speed.

It simple is not, and never has been, not for any boat or hull shape.

It is a simple formula to represent a single point on a curve.

The curve may be acute or obtuse.

It doesn't matter, the THS is still a valuable data point.

Of course the actual speed/power curve is more valuable to understanding the speed/power relationship.

I don't believe anyone here has ever said it isn't.

Because platinum is more valuable, it doesn't make gold worthless, and silver a total waste of time.

[ramblinrod]

Another way of looking at the value of THS.

If I told you my boat LWL could you tell me what the traditional THS is?

If I told you my boat LWL could you draw me a power/speed curve?

Some data, even if accuracy is only +/-20% (arbitrary value), can be far more valuable than absolutely no data at all.

I check weather forecasts everyday. 1 week out, I attribute about +/-10% accuracy, 3 days out = 30%, 1 day out 50%, right now 70%.

I still consider the data valuable, even 1 week out, despite it not being very definitive at all.

[Pete7]

Originally Posted by danstanford

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?
Dan

How fast would you need to travel with the dinghy outboard? I think this was good for 3 knots once it got going in calm water on a 28ft yacht.

Pete

[danstanford]

Originally Posted by ramblinrod

Before you pull the trigger on the electric boat with the O/B back-up. Ask 30'+ boat sailors who have outboards as main propulsion (because they couldn't afford to repower an inboard) what they think of it when Lake Ontario kicks up and then the wind dies off, leaving 2-3 m waves the wind won't support to sail back home.

Of course a retiree can often wait for more suitable conditions. Someone who has to be back to work tomorrow? Outboards on keel boats are OK for small lakes, big water, they suck (and I sailed trailerables with O/Bs on big water for over a dozen years).

Rod, I hadn't thought of the outboard dealing with big waves, thanks. I do know my first sailboat was 25'er with an outboard and I never was afraid of not getting back home and that is principally the risk I want to deal with. If I needed to get back from Brighton to Cobourg on Lake Ontario and it was blowing like stink from the west I guess I would likely start beating for the middle of the lake until I thought I was in range of the electric. I do remember being in bigger waves with no wind one time getting home and it was the only time I have ever felt seasick when I went below to make sandwiches.

In all other conditions I would be sailing as long as there was wind.
Thanks again for the input, Dan

[CatNewBee]

Originally Posted by danstanford

Rod, I hadn't thought of the outboard dealing with big waves, thanks. I do know my first sailboat was 25'er with an outboard and I never was afraid of not getting back home and that is principally the risk I want to deal with. If I needed to get back from Brighton to Cobourg on Lake Ontario and it was blowing like stink from the west I guess I would likely start beating for the middle of the lake until I thought I was in range of the electric. I do remember being in bigger waves with no wind one time getting home and it was the only time I have ever felt seasick when I went below to make sandwiches.

In all other conditions I would be sailing as long as there was wind.
Thanks again for the input, Dan

What is the range of your outboard, how much fuel you need to store to come back home?

Keeping the inboard diesel and the fuel tank means not to motor all the time and refill every week. We fill our cat (2 x 200l) two times per year, first time when it is half empty, and second time before going to a marina for wintering, we need per season 350...400l of fuel. But we do have an average range on engine of 250h with full tanks, giving us a mororing range of 1000+ nm without sail and refill.

Can't do that with electric. Most of the time we sail, from 6kn of TWS wind aparrent or beam reach and 8kn broad reach. Sometimes we do motorsailing to point higher or to increase the speed to reach the anchorage before dusk.

Power from the engines is always there when needed. Alone the peace of mind is worth the diesel setup. And the fuel can be used for the generator, A/C, heating, toppin up the battery, cooking, watermaker if necessary. We do have 1650Wp solar and 15kWh LFP, no need for the genny during the summer, late autumn, early spring and winter is a different story.

[danstanford]

Originally Posted by CatNewBee

What is the range of your outboard, how much fuel you need to store to come back home?

.

In the past 24 months there has not been a time the electric would not have done the job just fine. I can think of once three seasons ago that I motored for a full day into a headwind going somewhere.
This, for me, is not a question of full time cruising, just everyday use. I probably should recognize that I am writing to cruisers given the name of the forum.

[CatNewBee]

Originally Posted by danstanford

In the past 24 months there has not been a time the electric would not have done the job just fine. I can think of once three seasons ago that I motored for a full day into a headwind going somewhere.
This, for me, is not a question of full time cruising, just everyday use. I probably should recognize that I am writing to cruisers given the name of the forum.

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

[ramblinrod]

Originally Posted by danstanford

Rod, I hadn't thought of the outboard dealing with big waves, thanks. I do know my first sailboat was 25'er with an outboard and I never was afraid of not getting back home and that is principally the risk I want to deal with. If I needed to get back from Brighton to Cobourg on Lake Ontario and it was blowing like stink from the west I guess I would likely start beating for the middle of the lake until I thought I was in range of the electric. I do remember being in bigger waves with no wind one time getting home and it was the only time I have ever felt seasick when I went below to make sandwiches.

In all other conditions I would be sailing as long as there was wind.
Thanks again for the input, Dan

We sailed our current boat out of Newcastle for 10 years (now at Trent Port).

Have made the trip from the Murray to Cobourg many a time, coming back from vacation, and Cobourg to Newcastle even more.

Been many a day I enjoyed have the inboard diesel and would not have wanted to rely on an outboard to get me anywhere.

If possible, I sail. But if the wind won't support the waves, and I can only make a knot to the good, Brighton to Cobourg would take around 18 hours. Better things to do.

Electric or outboard propulsion can be suitable for someone who needs limited propulsion for limited range in fair conditions.

For a cruiser, where significant propulsion may be needed, for significant time, in absolute snot, neither electric nor outboard will cut it. It could mean the difference between the crew being grumpy (diesel inboard), or never setting foot aboard again (electric or outboard).

[Auspicious]

Originally Posted by ramblinrod

Answer: THS = 1.34 x LWL^0.5.

You seem to insist that for THS to be valuable it must be a definitive single point where any amount of power will not increase speed.

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.

Originally Posted by ramblinrod

It is a simple formula to represent a single point on a curve.

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.

Originally Posted by ramblinrod

It doesn't matter, the THS is still a valuable data point.

Nope.

Originally Posted by ramblinrod

If I told you my boat LWL could you tell me what the traditional THS is?

Yes.

Originally Posted by ramblinrod

If I told you my boat LWL could you draw me a power/speed curve?

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.

Originally Posted by ramblinrod

Some data, even if accuracy is only +/-20% (arbitrary value), can be far more valuable than absolutely no data at all.

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.

[a64pilot]

Originally Posted by danstanford

In the past 24 months there has not been a time the electric would not have done the job just fine. I can think of once three seasons ago that I motored for a full day into a headwind going somewhere.

This, for me, is not a question of full time cruising, just everyday use. I probably should recognize that I am writing to cruisers given the name of the forum.

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.

An electric motor doesn’t need fuel tanks, fuel filters, fuel pumps, doesn’t need any thru hull, exhaust system or cooling system, it doesn’t need it’s oil changed or heat exchanger cleaned, or the pump impeller changed, doesn’t need a starter and on and on.
Pretty much either works or it doesn’t. Is silent, doesn’t need warming up, won’t stall on you coming into dock.

So if you don’t need range, it’s excellent I would think.

One manufacturer puts what looks like a trolling motor in the rudder, that way it makes it very maneuverable because you can steer the thrust too.
Imagine how much space you would free up if the engine compt. Didn’t exist anymore.

Something like a school boat to teach sailing,it would seem to be ideal.

Just unfortunately not the average cruiser who wants to be able to motor down the ICW day after day, sometimes.

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.

[CatNewBee]

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.

An electric motor doesn’t need fuel tanks, fuel filters, fuel pumps, doesn’t need any thru hull, exhaust system or cooling system, it doesn’t need it’s oil changed or heat exchanger cleaned, or the pump impeller changed, doesn’t need a starter and on and on.
Pretty much either works or it doesn’t. Is silent, doesn’t need warming up, won’t stall on you coming into dock.

So if you don’t need range, it’s excellent I would think.

One manufacturer puts what looks like a trolling motor in the rudder, that way it makes it very maneuverable because you can steer the thrust too.
Imagine how much space you would free up if the engine compt. Didn’t exist anymore.

Something like a school boat to teach sailing,it would seem to be ideal.

Just unfortunately not the average cruiser who wants to be able to motor down the ICW day after day, sometimes.

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.

There are small recreational boats that can be rented on lakes, running 3...4kn at full speed about 4 hours and then must be quick-recharged for 2 before can be rented again, they stay at the charge station over night. Feasible.

Also feasible as outboard for the dinghi, it is a short range to get to shore when at anchor, so a charge for 3..4 hours shall be sufficient, you don't race them, nor do you waterskiing with them.

For a silboat and offshore cruising it is a bad idea, assume your mast break or your sails ripp, you must be able to get to shore instead of drifting to the ocean. Assume a gale and lee shore situation where you need power to get outa here. Bad idea with electric only. With a generator as range extender doable, but then you can use a real engine instead.

You are talking all the time about the simplicity of a electric motor, thats true, but add addequate batteries for storage, a battery management system to keep them alive, decent chargers than can quick charge them over night, propper cabling and all the control electronics and you end up in the same complexity, weight, storage requirement, price point, you name it. Batteries do not live forever, so there are your maintenance chores and expenses.

Consider a lightning hit, a simple diesel will survive, I am not sure about the electronics in a electric setup.

[Adelie]

Originally Posted by Pete7

How fast would you need to travel with the dinghy outboard? I think this was good for 3 knots once it got going in calm water on a 28ft yacht.



Pete

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

[wingssail]

Originally Posted by jmh2002

I don't particularly want to enter into this debate, but just wanted to add an interesting note that seems to be contrary to your tests - my consistent experience on large fast (planing) motoryachts was generally always that the faster we went the more fuel efficient the vessel was vs boat speed.

My experience with medium sized inboard powered deep v planning boats is that the best miles per gallon is at slower displacement speeds.

Once the throttle is advanced the next best MPG is just after planning is achieved. After that the mpg declines as speed is increased. It is linear to maximum speed which was about 50MPH.

I am surprised to hear than any planning powerboat gets better mileage as the speed is increased.