Optimal hull and keel shape for electric propulsion

[Rumrace]

Quoted from this forum right under Rand Boats in my google search to pull up their web site. Assumptions and fast math?

We should beat up cool companies with facts not discount thousands of RD hours from folks really doing the work.

[belizesailor]

Trimaran with narrow hulls: minimizing wetted surface and weight.

[Rumrace]

Who thinks Hinckley is a stupid boat company. I mean who puts a kitchen up front anyway, except Jeanneau 60.

https://www.hinckleyyachts.com/models/concept-models/dasher/

[GrowleyMonster]

Originally Posted by argosail

My idea is a 27ft aft cabin. Take out holding tank for compost head, run vessel manual, hot water not need for running in mid-lats, tiller steering, use EP only in becalmed seas at 2-3 kts and for house batteries. Extra batteries in aft cabin, holding tank space, solar panels on bimini (300wt total), a course in electrical too!

I suppose going down to 5kw would be much easier but now wonder if even that is doable :/

No, you get nothing for reducing motor and controller rating from 10kw to 5kw. It's not how much power you have available, it is how much power you use. A 10kw motor ran at 48v and 20a uses almost exactly the same power as a 5kw motor ran at 48v and 20a. There is almost no penalty for a bigger motor running at low power, unlike with an ICE. The motor weighs about 10lbs more, and costs about $200 more, lasts longer, and has all that extra power available for those rare occasions when you actually need it. So actually you WANT the bigger motor.

The thing is, you are putting the cart before the horse. LEARN FIRST. Then when your already owned boat, one that is not worth the expense of a new or rebuilt diesel but needs repowering because the existing engine can no longer do its job, THEN repower.

Your head doesnt matter. Nothing wrong with a holding tank, if you maintain it properly. Composting heads are both rather well liked, strongly disliked, and laughed at, depending on who you ask. Has nothing to do with propulsion. Solar will not give you significant recharging capability. Not 300w, anyway. And you will not get 300w out of your 300w panel, on a sailboat, except under very rare conditions. Your sails, mast, even stays and shrouds and antennae will reduce output, and you only get peak output for a few hours a day, anyway. With a small boat, you don't get much regen, either. If you can sail at 10kts then regen is significant. At 5kts, it isn't. A wind turbine generator, likewise, creates insignificant charge power when you are charging a 10kw/hr bank. Without a generator, shore power charging is pretty much all you got. Unless you install a generator.

If you are determined to mess with EP, here is my suggestion, one that should keep you very busy and mostly out of trouble. Find an old long shaft outboard with a bad engine. With a bit of machining with hobby lathe, Dremel, and file, you should be able to mount a PMAC/BLDC motor in place of the power head. Mount the motor controller over the motor. Mount the throttle potentiometer on the end of the outboard tiller, and be sure to flash "stick shift" firmware on the controller so one control gives you both speed and FWD/REV. Now only B- and B+ cable connections are needed. There. 48V electric outboard. BTW, lose the waterpump, it is just parasitic load, anyway. To power it, buy a couple of 20AH 48V Li-Ion electric bike battery packs. They will cost you around $500/ea for good ones. Build a battery box that hangs on to your transom so in the (rare) event of a thermal runaway battery, hopefully it will burn itself away from your boat and plunk down in the water instead of set the whole boat afire. In fact I would secure it with yellow poly rope because it melts in a hurry. These packs have a built in BMS and seem to be reasonably safe and reliable. Put a good quality heavy duty spring assisted outboard mount on your transom, mount your electric outboard, and you can cruise for about 5 miles really slow on EP. Works for your dinghy, too. As a bonus you can build an e-bike and you already have the batts along with the standard 6a mains charger.

Bare bones EP... I made a prop and shaft for a cordless drill, and pushed a pirogue around with it. That was fun.

[GrowleyMonster]

Originally Posted by Rumrace

Congratulations this thread has started false assumptions about Rand Boats on the Internet. The Company called Tesla on the water.
Range 140nm
22 nm top cruise with base package base batteries.
Pending slander suit on the accountants again. Oh shucks

kph? Doesn't sound like experienced boaters are their market, or that they are very experienced in the industry. I am doubting their data, too, at least under real world conditions. But whatevah. Still, looks pretty cool if you happen to have $42k burning a hole in your pocket. They might be good, even very good, at what they are doing, but they certainly aren't making a very believable case.

[sailingharry]

Originally Posted by argosail

My idea is a 27ft aft cabin. Take out holding tank for compost head, run vessel manual, hot water not need for running in mid-lats, tiller steering, use EP only in becalmed seas at 2-3 kts and for house batteries. Extra batteries in aft cabin, holding tank space, solar panels on bimini (300wt total), a course in electrical too!

I suppose going down to 5kw would be much easier but now wonder if even that is doable :/

One question that I don't think has been addressed yet is "why." You are looking at spending a big chunk of change. You are likely to find that it will not help resale value (and for many buyers, it will disqualify the boat). You will have significant limitations on much of cruising life (slower motor speeds, smaller range, requirements to pay for a marina, etc, etc, etc).


All of these "costs" can only be justified by understanding the "return" -- the WHY you want electric. To save money? Not going to happen. Even if your engine is dead, you can buy a rebuilt for less. And those marina costs for charge-ups are easily $1K/month, or $12K/year, that those of us who anchor out don't pay. To minimize pollution? Problem is, if you sail your diesel powered boat in the frugal way you would have to sail an EP boat, you already are in the bottom few percentile of boaters. Total environmental impact? Cars recover the environmental impact of the batter construction in a few years -- because they are driven a LOT. Not sure a boat ever balances out.


You are already looking to buy a boat with the intention of converting to EV. If the engine currently runs, you are taking on a project of substantial time and money because you WANT TO, not because you HAVE TO. Even if the engine is dead, you are fixing in the hard/expensive way. You have a reason to do this -- what is it?


Oh, on power consumption. Hot water takes no power (it can't use batteries, so is shore power only). Tiller steering and wheel steering both have no electricity. Manual heads don't use electricity (not entirely sure you'd find the holding tank place suitable for more batteries). Fresh water pumps take almost no power -- but on a 27' boat, there is so little water tankage that manual pumps greatly reduce water consumption. For many boats, electric refrigeration is the most significant power consumption, and if you don't have that you basically don't have refrigeration (finding/getting ice 2-4 times a week is expensive and not super easy). Another big drain is an autopilot -- nearly essential if you single hand, and wind vanes are expensive, fiddly to set up for a 2 mile stretch of the ICW, and don't work in light airs.

[sailingharry]

Originally Posted by Rumrace

Who thinks Hinckley is a stupid boat company. I mean who puts a kitchen up front anyway, except Jeanneau 60.

https://www.hinckleyyachts.com/model...models/dasher/

Rumrace, You are very hyped about EP in runabouts. Cool. Sort of a different universe than what is being discussed here.


First, not sure that many of these, if any, are available for purchase. And I am pretty sure than NONE are flying off the shelf! Their prices are not something many of us here on CF can do more than shake their heads at -- you may be in their market demographic, but most ofu aren't. There are some EP harbor cruisers around, some pretty cool. They go 3 or 4 kts, get 4 or 5 miles, and then get tied up until the next time.



Second, none of those boats are live aboard. Not even the minimal "accommodations" that the OP is willing to consider (start with a place for a single person to lay down out of the rain....). No head, no galley, no storage.


Third, OP is not looking to occasionally go a few miles. He wants to CRUISE! So with EP, that really means SAIL. None of those are sailboats.


Finally, OP is looking for shoestring budget. Buy a '70's boat, put in minimal cost to get a barely functional boat, and go. None of the boats you've talked about are remotely related to the OP's desires.



Most of the negative feedback on this thread is not bashing Hinkley and their ultra expensive yacht, or the super rich who park it in front of their mansion. We aren't bashing the thought that a Cigarette boat can't be electric (we'll hate the idiot in the electric one as much as the idiot in the gas one). We are bashing the idea that for $5K OP can slap in some magic sauce and be happy about the outcome. He's talking about 27' boats that probably can be found for under $10K -- showing him a boat 10 feet shorter for 4 times the price is not really saying....anything.

[argosail]

Originally Posted by sailingharry

You are already looking to buy a boat with the intention of converting to EV. If the engine currently runs, you are taking on a project of substantial time and money because you WANT TO, not because you HAVE TO. Even if the engine is dead, you are fixing in the hard/expensive way. You have a reason to do this -- what is it?

Yes you have some good points. Being off-the-grid is more of an idealistic dream and I can see how the comparison is moot with electric cars. I was actually in the market for an electric car, but the price and unavailability led me to a highly efficient 4 cylinder instead!

That being said, I did see a dealer at the boat show with electric outboards (and no not torqueedo). He did not have however really long-shaft ones but said they are out there.

So would having a 10hp (6kw) electric outboard xlong shaft on say, a 7k displacement 27 footer, fin keel, lightly loaded, be able to push in a becalmed sea state, and for close quarters /docking-undocking? max speed 4kts but realistically going 2-3 knots? I'm wondering if there is a way to charge at the dock if hopping down the ICW to go island hopping in the Caribs? Otherwise I suppose not enough solar panels...

[nmccubbin]

Our 7 kW outboard moves our 47 ft 15 ton boat at 3 knots in calm
5kW would do fine for the conditions you mention, while saving weight, space and money
I am not a fan of composting heads, but definitely consider that traditional heads should be manually operated, not electric

[nmccubbin]

I have run the ICW a couple of times. A lot of motoring is required, so electric with 300 watt panel would be incredibly slow
300 watts = 1/3 HP. Effectively the panel will run a 1/4 HP motor continuously, at the height of the noonday sun in the tropics
In my experience solar panels put out about 20% of rated peak, averaged over 24 hours, or 60 watts.

[sailingharry]

Originally Posted by argosail

Yes you have some good points. Being off-the-grid is more of an idealistic dream and I can see how the comparison is moot with electric cars. I was actually in the market for an electric car, but the price and unavailability led me to a highly efficient 4 cylinder instead!

That being said, I did see a dealer at the boat show with electric outboards (and no not torqueedo). He did not have however really long-shaft ones but said they are out there.

So would having a 10hp (6kw) electric outboard xlong shaft on say, a 7k displacement 27 footer, fin keel, lightly loaded, be able to push in a becalmed sea state, and for close quarters /docking-undocking? max speed 4kts but realistically going 2-3 knots? I'm wondering if there is a way to charge at the dock if hopping down the ICW to go island hopping in the Caribs? Otherwise I suppose not enough solar panels...

Umm....yes. If your objective is to remove a functioning engine, spend a lot of money, impose severe limitations on your cruising, and claim (in many ways, falsely) that you are an environmental activist by eschewing diesel, then yes. But it still comes back to "WHY."


Yes, you can dock hop down the ICW. Easy peasy. Lots of marinas (well, OK, you aren't going to make it through the Dismal Swamp Canal, but you can go around). $100/night is a good budget. A 30A cord will charge batteries at the rate of 3kW, so for a 10kW motor, 3 hours of charge for each hour of motoring -- if you are pier side for 16 hours, you can get 5 hours of motoring the next day (if you have 50kWH of battery!).


Oh, for those charge times -- it only works for Lithium. Any lead acid is many hours longer to charge, because they start to taper down on charge rate and the last 20% takes many hours no matter how big your charger is.



No, in the Caribbean, from my very limited experience, you won't be charging from shore power -- there aren't many marinas. Almost everything is moorings, so you are 100% solar and any engine powered charging source you have. Count on a week or two of solar charging for each hour of motoring.


A question -- if mass produced electric cars, that have a really solid use-case, and a well developed supporting infrastructure, are too expensive -- why would you think that custom installing a one-off system for a poor use case with no good supporting infrastructure would even come close to making economic sense?

[argosail]

Originally Posted by sailingharry

Umm....yes. If your objective is to remove a functioning engine, spend a lot of money, impose severe limitations on your cruising, and claim (in many ways, falsely) that you are an environmental activist by eschewing diesel, then yes. But it still comes back to "WHY."


Yes, you can dock hop down the ICW. Easy peasy. Lots of marinas (well, OK, you aren't going to make it through the Dismal Swamp Canal, but you can go around). $100/night is a good budget. A 30A cord will charge batteries at the rate of 3kW, so for a 10kW motor, 3 hours of charge for each hour of motoring -- if you are pier side for 16 hours, you can get 5 hours of motoring the next day (if you have 50kWH of battery!).


Oh, for those charge times -- it only works for Lithium. Any lead acid is many hours longer to charge, because they start to taper down on charge rate and the last 20% takes many hours no matter how big your charger is.



No, in the Caribbean, from my very limited experience, you won't be charging from shore power -- there aren't many marinas. Almost everything is moorings, so you are 100% solar and any engine powered charging source you have. Count on a week or two of solar charging for each hour of motoring.


A question -- if mass produced electric cars, that have a really solid use-case, and a well developed supporting infrastructure, are too expensive -- why would you think that custom installing a one-off system for a poor use case with no good supporting infrastructure would even come close to making economic sense?

Yes I'm well aware that would need lithium batteries and would rather have these even with a conventional diesel setup (lithium house and starting batts).

Please note I did not mention anything environmental in my posts so don't use me as your political pivot point or whatever. I am trying to make a self-sufficient off-the-grid minimalist boat so to speak. I don't need 5 hours of motoring, I am not in a rush to get anywhere, certainly nothing like a cigarette boat on electric. If I go with electric outboard I would keep the diesel, have redundancy makes sense, just like having a generator backup in case of switching the engine to EP. This will depend more on what sweet deal I can find for a dead boat or a boat with a rrrrealy poorly maintained engine about to become dead. If I find a good deal with a good engine, could go electric outboard, could also put the electric outboard on the dinghy. Having a full electric inboard EP without diesel may be an idealistic end but will be hard to find an affordable way to do this, unless there is a project boat or something out there. Who knows? Just weighing options. If I can't fit this project into my budget, I would just start start slow with changing batteries to lithium and figure out things down the road. I appreciate all advice but not sure how many times I have to say my plans.

[sailingharry]

Originally Posted by argosail

Yes I'm well aware that would need lithium batteries and would rather have these even with a conventional diesel setup (lithium house and starting batts).

Please note I did not mention anything environmental in my posts so don't use me as your political pivot point or whatever. I am trying to make a self-sufficient off-the-grid minimalist boat so to speak. I don't need 5 hours of motoring, I am not in a rush to get anywhere, certainly nothing like a cigarette boat on electric. If I go with electric outboard I would keep the diesel, have redundancy makes sense, just like having a generator backup in case of switching the engine to EP. This will depend more on what sweet deal I can find for a dead boat or a boat with a rrrrealy poorly maintained engine about to become dead. If I find a good deal with a good engine, could go electric outboard, could also put the electric outboard on the dinghy. Having a full electric inboard EP without diesel may be an idealistic end but will be hard to find an affordable way to do this, unless there is a project boat or something out there. Who knows? Just weighing options. If I can't fit this project into my budget, I would just start start slow with changing batteries to lithium and figure out things down the road. I appreciate all advice but not sure how many times I have to say my plans.

I was adding environmental, because that is the normal driving force. The problem with providing feedback and suggestions is that we (or at least I) don't understand the objective, and have to assume. It surely is not financial, as financially EP almost never makes sense on a boat. You have your reasons, and they work for you.



So, yes, everything you say is true. A small electric inboard or outboard will provide you with a small amount of speed in calm waters for a small amount of distance with a recharge that is dependent on power sources, battery size, and battery state of charge. All true. Since the reason for doing this is unclear, the cost/benefit analysis can only be done by you. Not sure what you are looking for from the forum.

[GrowleyMonster]

Look... if you want to do it, then do it. I think you will end up with regrets because you are not an engineer or even an electrician. You don't know anything about batteries and you think Lithium batteries are the way to go for EP. Your solar charging expectations are unrealistic. I don't think you understand what it is like to motor from sunup to sundown and only put 6 or 7 miles behind you, or run your batteries dead stemming a current or tide and still not getting where you need to be. I doubt that you are sailor enough to know how to work around the limitations through superior voyage planning and piloting. But if you insist, then just have a go.

You are going to spend between $3k and $15k on your entire EP system including batts but not counting solar, because it quite honestly has no place in an EP sailboat's propulsion/storage/charging system design. IOW, going electric will cost somewhere between the cost of a used diesel pulled from a 30' boat and maybe wanting a rebuild, to a nice new diesel, professional installation included.

You are going to end up with a boat that because it has no diesel, will be hard to sell. And so, I suggest you buy a boat with no diesel or a totally dead diesel to start with. That way your repower does not materially reduce its resale value. If you pull a working diesel to install EP you are reducing resale value significantly. So buy one that ALREADY is cheap because it has no diesel.

Look for a 70's built mass produced fiberglass boat, keep your purchase price below $3k. Make sure the decks are not spongy and if the keel is external, it is solidly attached, you have no termite damage or major dry rot, your chain plates are solid and solidly attached, mast and boom are good, and you have at least one full set of GOOD sails in addition to any old rags in way of spares, and your storm sails. Figure on new stays and shrouds all around at that price. Extra points for a shaft that has had its zinc renewed regularly, and a good fixed prop. You do not want folding for EP. You don't need a special place for your batteries. Mine were right there on the cabin sole in a DIY battery box holding all 8 of them. You stepped down through the companionway and then on the top of the battery box. My bilges were way too shallow to put batts below the sole.

Hull doesn't matter enough to worry about. You are going to be so far from optimization that the fraction of a percent available by cherry picking your hull will be best ignored.

When you look at a boat that seems like it would check all the boxes, SAIL it. Give the PO enough to make it worth his while to take you out for a couple hour sail. Make sure you get reasonable performance under sail and she will point reasonably high. Reduce the amount of motoring that you will have to do, by only considering a good sailer.

Start right now, educating yourself, especially about batteries. Figure on using golf cart batteries, and learn how to make them last as long as possible.

Motenergy 10kw or 12kw motor. Kelly SINE WAVE 500a controller. No, you will never use 500 amps. There are reasons to overspec the controller. Kelly, because you can program it yourself and optimize for your motor. Curtis controller only if you buy it in combination with a motor and it is set up for the motor, and remember you want sine wave, and you want single control, "stick shift" firmware so you can set FWD/REV and RPM with a single knob or lever.

Belt drive, with heavy duty pulleys and belts. Belt drive allows easy change of reduction ratio in small incrememts. For the typical 30' boat and 48V system, start with 2:1 ratio and the biggest prop that still gives you about 15% hull clearance, pitch about 75% if diameter to optimize for 2-3kts cruise, 100% to optimize for 5kts. Good belts and pulleys. A single vee belt is woefully inadequate, don't even think about it. vee belts are cheap but you would need about 3 or 4 of them. Make sure you have a thrust bearing to keep the prop shaft from just pushing up into the boat when you turn the prop. Never go direct drive without a thrust bearing because the motors are NOT rated for an axial load, and especially with an axial flux motor, you will destroy it almost instantly, in most spectacular fashion.

There are so many more ways to screw this up. You NEED to do your homework and do not rely on a vendor to set things up properly or teach you how to operate or maintain properly. Remember, he wants to sell you stuff. Ideally, he would love to sell you the same stuff all over again after you destroy it the first time. Turnkey systems have advantages but make sure you UNDERSTAND the system. By understand, I understanding each component, how it works, why it works, and how it is optimized for the application, how the components interface with one another, how to best operate and maintain each part and the whole system, and so on. This is fringe technology. Never forget. You must be your own engineer. At the moment you are not even close.

But yeah if you are determined, just do it. Take my advice or not, whatevah. Be sure and post your results. I'm done here.

[argosail]

Originally Posted by GrowleyMonster

Look... if you want to do it, then do it. I think you will end up with regrets because you are not an engineer or even an electrician. You don't know anything about batteries and you think Lithium batteries are the way to go for EP. Your solar charging expectations are unrealistic. I don't think you understand what it is like to motor from sunup to sundown and only put 6 or 7 miles behind you, or run your batteries dead stemming a current or tide and still not getting where you need to be. I doubt that you are sailor enough to know how to work around the limitations through superior voyage planning and piloting. But if you insist, then just have a go.

You are going to spend between $3k and $15k on your entire EP system including batts but not counting solar, because it quite honestly has no place in an EP sailboat's propulsion/storage/charging system design. IOW, going electric will cost somewhere between the cost of a used diesel pulled from a 30' boat and maybe wanting a rebuild, to a nice new diesel, professional installation included.

You are going to end up with a boat that because it has no diesel, will be hard to sell. And so, I suggest you buy a boat with no diesel or a totally dead diesel to start with. That way your repower does not materially reduce its resale value. If you pull a working diesel to install EP you are reducing resale value significantly. So buy one that ALREADY is cheap because it has no diesel.

Look for a 70's built mass produced fiberglass boat, keep your purchase price below $3k. Make sure the decks are not spongy and if the keel is external, it is solidly attached, you have no termite damage or major dry rot, your chain plates are solid and solidly attached, mast and boom are good, and you have at least one full set of GOOD sails in addition to any old rags in way of spares, and your storm sails. Figure on new stays and shrouds all around at that price. Extra points for a shaft that has had its zinc renewed regularly, and a good fixed prop. You do not want folding for EP. You don't need a special place for your batteries. Mine were right there on the cabin sole in a DIY battery box holding all 8 of them. You stepped down through the companionway and then on the top of the battery box. My bilges were way too shallow to put batts below the sole.

Hull doesn't matter enough to worry about. You are going to be so far from optimization that the fraction of a percent available by cherry picking your hull will be best ignored.

When you look at a boat that seems like it would check all the boxes, SAIL it. Give the PO enough to make it worth his while to take you out for a couple hour sail. Make sure you get reasonable performance under sail and she will point reasonably high. Reduce the amount of motoring that you will have to do, by only considering a good sailer.

Start right now, educating yourself, especially about batteries. Figure on using golf cart batteries, and learn how to make them last as long as possible.

Motenergy 10kw or 12kw motor. Kelly SINE WAVE 500a controller. No, you will never use 500 amps. There are reasons to overspec the controller. Kelly, because you can program it yourself and optimize for your motor. Curtis controller only if you buy it in combination with a motor and it is set up for the motor, and remember you want sine wave, and you want single control, "stick shift" firmware so you can set FWD/REV and RPM with a single knob or lever.

Belt drive, with heavy duty pulleys and belts. Belt drive allows easy change of reduction ratio in small incrememts. For the typical 30' boat and 48V system, start with 2:1 ratio and the biggest prop that still gives you about 15% hull clearance, pitch about 75% if diameter to optimize for 2-3kts cruise, 100% to optimize for 5kts. Good belts and pulleys. A single vee belt is woefully inadequate, don't even think about it. vee belts are cheap but you would need about 3 or 4 of them. Make sure you have a thrust bearing to keep the prop shaft from just pushing up into the boat when you turn the prop. Never go direct drive without a thrust bearing because the motors are NOT rated for an axial load, and especially with an axial flux motor, you will destroy it almost instantly, in most spectacular fashion.

There are so many more ways to screw this up. You NEED to do your homework and do not rely on a vendor to set things up properly or teach you how to operate or maintain properly. Remember, he wants to sell you stuff. Ideally, he would love to sell you the same stuff all over again after you destroy it the first time. Turnkey systems have advantages but make sure you UNDERSTAND the system. By understand, I understanding each component, how it works, why it works, and how it is optimized for the application, how the components interface with one another, how to best operate and maintain each part and the whole system, and so on. This is fringe technology. Never forget. You must be your own engineer. At the moment you are not even close.

But yeah if you are determined, just do it. Take my advice or not, whatevah. Be sure and post your results. I'm done here.

Thanks yes, this explains quite a lot for me along with everyone else's info, thanks as well.

I might just have to put my ego aside and with occam's razor call it quits. I will keep a close watch on sailing uma and look for a dummy's guide to electrical engineering (if that exists) but all the info has been definitely helpful so far.

I have an electric bicycle belt drive so maybe I will start tinkering with that just to get a vague idea of a fraction of the complexity of a vessel EP system. It was $1,000 new so not a catastrophic loss if I short-circuit something or whatnot, nothing like a brand-name ebike which costs 4,000 to 5,000. At least to help shape my thinking which so far seems like trying to fit a square into a circle if that makes sense!