Hull Design Choices for Very Fuel Efficient Live-aboard

Seems you are considering solar + sail. Having been toying with electric boat ideas quite lately and run a solar installer company a while back, i think you should estimate the implications carefully, and seriously consider choosing between the two.

Solar needs quite a bit of unshaded surface, a mast can effectively block entire strings. Production is lighter than storage, and cheaper too.

A small electric boat should remain fairly light if you actualky want to go places.

And a sailing rig needs stability, which implies weight either in the form of ballast in a mono (and the batteries only go so far because they lack lever), or in the form of additional structure in a multi.

For safety, you either need a really decent rig and a level of lightness and hyd4odynamic efficiency that are rather at odds with a houseboat-ish approach, or fairly low wind resistance to power against the wind - in which case a mast is a huge disadvantage, remember wind is faster up there and turbulence pulls quite a bit on the stays and pole ... or quite a substantial fossil backup engine (not just talking about a classic sailboat "auxiliary engine' there.)

 

All points well taken. My reasons for wanting a sail (auxiliary or otherwise) are (1) I will be in northern latitudes mostly and have concerns about stretches of very cloudy days and short daylight hours, especially in Fall and Winter (also a reason for substantial batteries). (2) Electronic systems can fail and I want some form of propulsion available independent of that, so I need a sail or to refurbish an old gas outboard with no electric starter.

As the sail would not be the primary propulsion, my thoughts about it include: (1) keep total size and aspect ratio moderate, appropriate to light hull; (2) easy to reef quickly single-handed, for safety with a relatively light, shallow draft hull; (3) fold down mast, so that sail rig doesn’t shade solar panels when not in use. As to the latter point, I was thinking to have a gap down the middle between the panels on the fore of the boat, into which the sail rig could be laid down. Of course, when the sail rig is up, even if furled or reefed, there’s going to be a big detriment to solar and windage, so laying it down and raising it would need to be fairly easy. I was thinking it might be reasonable to run a junk rig yawl setup on unstayed mast and without a jib, but will need expert design input.

Although it will limit the waters where I can travel safely, I plan to have very shallow draft and use leeboards (or centerboard) for sailing. I’ll try to keep it as light as I can by using the lightest practical construction materials for cabins and interior elements, as well as keeping cabinetry light and minimal. I’ll try to keep the hull light also, but my budget will prohibit exotic hull materials. I’ve lived for long periods happily using nothing but lightweight camping furniture and can do the same on a boat. Aluminum cabinets are very light and I can keep them to a minimum. No marble countertops.

Because I want to be mostly off-grid, I won’t be able to be too stingy with batteries, water tanks, etc. so that will be a weight challenge. A watermaker might help a little. Black water tankage could be reduced with use of composting toilets or by use of a Type II sanitation system, but both entail some use limitations or issues, so not sure about that.

As you’ve pointed out, it will still be very challenging to mostly travel on a live-aboard with electricity from solar. I found and will save your website to keep up with your progress and see how you decide to approach these issues. Maybe I’ll be able to afford one of your boats.

Thanks.

 

Oh, one more reason I wanted a sail available - there will be conditions where it’s more comfortable to sail than motor (mizzen might also be useful at anchor sometimes).

 

If you're going the folding auxilary rig route, it might also be worth having a look at aft-mast rigs. Something like Pass'Avel on Les bateaux du passeur des îles | Le Passeur des îles https://www.passeurdesiles.com/nos-bateaux could probably be tabernacled.
For Blackwater, enteron® – tom logisch® https://tomlogisch.com/enteron/ makes a tiny no-nonsense sewage treatment plant. Seems these bacteria are quite happy with the gentle motion of boats. The smaller one is sized for a couple, and they aren't into superyacht prices. Needs more careful use than a home toilet (not throwing random stuff into it, mostly), but that should be fine as long as you don't throw huge parties aboard.
For stabilisation, if you aren't familiar with it already, i'd also encourage you to look how the passagemaker folks do it. There are even flopperstoppers that you can use at anchor.

(Cocoon stalled unfortunately, it's not exactly an easy environment for such cosmopolitan projects these days, and the key partner had a lot of new stuff to care about on the personal side. It was a fast sail & fossil fuel boat though, with solar only for the hotel loads. And bigger than what you have in mind - hardly doable under 60', and requiring some half-fancy carbon parts. Perhaps i'll come up with a freak electric concept in a few months, but that is more cruising than liveaboard .. not quite the fit either i fear but thanks for taking interest )

 

Everything is a trade off in boat design.

You’ll need to decide what is most important for your needs and desired experience.

With respect to the question of why Multis seem to be the popular choice for solar electrification, one of the reasons is also the reason some prefer them as sailboats -stability.

At rest and while underway many feel them to be more comfortable, so if you are looking to build a live-aboard this might be important to you.

And one benefit of this in relation to solar is flatter “sailing” should provide more consistent harvesting versus a mono which might roll quite a bit.

Have you considered a kite instead of an auxiliary sail rig?

A kite would create less shading.

I agree with the above statement about power generation from solar being the better choice over battery power.

I see a lot of builds with an imbalance in power output and storage versus input where more solar could have been incorporated.

It you haven’t already seen the YouTube channel of guy traveling around on his solar electric powered Helios mono, you might want to as he has developed some opinions on hull shape and application of various systems and power demands through real world experience of cruising his boat while collecting and analyzing the data and applying it to how he uses his boat.

 

Thank you for those links. The new boat in that Breton ferry boat fleet, Pass’Avel (photo below) is interesting to me for several reasons. It’s very similar in length and beam to what I was thinking of and it’s operating environment is fairly similar to my “needs.” If my reading of French was correct, the hull is built in aluminum while the cabins, etc. up top are of wood, which is a sort of mixed approach I’m seriously considering, with a professionally built hull and largely self-built topsides. The sail is certainly interesting. As you said, it’s rigged aft mast. What I expected to see was an aft mast with a sail unfurled further aft. In this case, the foot or whatever it’s called is attached forward, so the triangular sheet is reversed fore-to-after by comparison to a typical sail. I’ve never seen one like that. Is it being used in the manner of a jib or mainsail? In the latter case, I’m not comprehending how it functions as a wing. Maybe you or someone else on here will explain how it works.

Youre right, I was planning a mainsail forward and pilothouse aft, thinking it good to have all or most of the mainsail visible from the pilothouse, but I hadn’t thought of a sail configured like this with mast aft and sail rigged forward.

I’ll look at the sewage treatment site also. I hadn’t run across that company. Type II devices for boats this size seem pretty uncommon.

Thanks again and good lick getting something new going.

 

@SolGato Thanks for your response. I hadn’t thought of the possible utility of a cat in heeling and/or rolling less and keeping the solar panels pointed more consistently upward. If a monohull is very beamy and flat-bottomed/hard-chined that difference may be less severe, but something I need to consider.

I have indeed investigated the kite sail idea. I think I might be able to make good use of it in coastal environments and in the Great Lakes. I’m wondering if it would be difficult to use successfully in the US inland waterway system of rivers and reservoirs where space can be limited and surrounding banks can be forested and/or rise steeply. Nonetheless, definitely worth serious consideration as it would be much easier to integrate with a solar powered electric motor design. Do you have any experience using kite sails in this manner?

The optimum balance of solar generation and storage is an important subject for careful analysis in this case. I’m planning to have lots of roofed cabins and pretty limited uncovered deck to maximize space for mounting solar panels on top. Also, not planning to have any seating up on top and will keep perimeter walkways narrow.

If the Helios boat you’re referring to is the home-built black monohull that started up in Scandinavia and is now down in the Mediterranean, I’ve been watching it on the True North Yachts channel on YouTube. I thought that his very lightweight, long, skinny cork of a boat would get thrashed once he got out of the rivers and canals and into the Med, but with what I saw so far, he was doing pretty well in that environment. I haven’t seen the past several weeks.

Thanks again.

 

If using light weight aluminium furniture etc. in a cold humid environment, you may also need to run a dehumidifier to reduce condensation making life inside a bit cold and wet to the touch. Have no exposed metals showing from the roof lining. Cold drips of condensation can be annoying and inconvenient. One cabin I had with an exposed aluminium beam over the berth was not fun, getting dripped on while asleep.

 

True North yes, couldn’t remember channel name.

He seems to be leaning toward a Multihull design for his next scaled up build for some of the reasons I mentioned.

I think he has also learned the lesson that lightweight doesn’t always necessarily translate to the best efficiency when you’re out in ocean energy with a fair amount of windage and not a lot of ballast.

 

"Hull Design Choices for Very Fuel Efficient Live-aboard"

An engineless sailboat, seriously.
But why the obsession with efficiency?
I think you may have your priorities mixed up.

 

Since I don’t know what specifically you envision my priorities to be or in what particular way you think they are mixed up, I can’t get the benefit from your response, if some was intended.

I see great value in sails for the ability to use free wind to move and their ability to fully function when no electric instruments or hydrocarbon driven machinery is available/operational.

I also see value in means of propulsion that require less constant and immediate attention to detail than sails, so my focus on propulsion can be kept to a minimum much of the time and I can direct more of my attention elsewhere. I think motors would help with that in many conditions. Also, sails may be challenging to use for propulsion in a river with steep, forested banks on either side or anywhere when no wind is present.

Finally, although I’m a geoscientist whose job is to find hydrocarbon reserves buried in the earth so they can be recovered and used for energy (and other things), I would prefer not to rely much (or at all) on hydrocarbons on my boat because I value having as much quiet as possible, not having any oil in my bilge, not producing emissions from burning gas or diesel to move my boat, etc..

How to balance and minimize conflict between these and other priorities (shallow draft, a place to sleep, a place to cook, etc.) is definitely a challenge. I thought the impact of hull design on the energy required to move it from one place to another would be an important matter to consider and seek input on.

 

What do you think about post below. About Philippines boats ?

 

A moderate monohull, say 48 x 10 ft, will get you 6 knots easily with less than one horsepower per ton of displacement. Proper choice here equates to a relatively large propeller at low RPM, as that is going to give far better propulsion efficiency than typical smaller props at typically far greater horsepower. Given that you will usually drive the prop with a solar powered electric motor, then the logical IC engine setup is to have electric generation via the engine, energizing the main propulsion motor. Better yet, have the IC engine directly turn the propulsion motor and prop through a clutch. That arrangement is far more efficient (direct drive) than using an electric generator to drive an electric propulsion motor. Motor-generators are common, and the clutched IC engine setup allows reasonable solar-electric, as well as IC engine power for main propulsion, or split for propulsion as well as battery charging. Of course a moderate sail rig can be setup to propel the boat as well as reasonably generate electric charging current thru the electric propulsion motor acting as a generator. In my view, any solar powered boat needing extended range should have these features incorporated.

In a practical sense, considering the expense for all this machinery, vs the simple direct small diesel driving a slow big propeller, you can get plenty of fuel and range at a great saving of capital outlay. A 15 horsepower Diesel, drinking one gallon of fuel per hour, will allow more than 1500 miles range with a typical 275 gallon home heating fuel oil tank. Think of a miniature cargo ship design, they all use this setup, with Length/Beam 5 or more, a single screw of proper size, and a Diesel with great reliability. The real world does it this way, and with good reason.

 

I take it you’re referring to the thread on “Phillipines Banka modifications.” Insofar as much or all of my use will be in northern latitudes far from the equator, I don’t think that sort of very open design would be appropriate.

A trimaran, in general, could potentially work. I may misunderstand, but my thought would be that with the small amas like that, the boat would be constantly rolling back and forth if not heeled firmly to one side under sail. I’d be motoring a lot of the time.

 

Thanks for the ideas. My first thought would be that, relying on internal combustion (that’s the “IC” right), whether diesel generator or diesel engine for propulsion, might be noisier than what I hoped for with electric motors. However, you’re describing extremely low horsepower, so I’m guessing diesel engines of that size may be very quiet.

You’re talking about LWL/BWL of 5/1 or more. Do you think one could get achieve a moderately comfortable ride in a hull of thos proportions while cruising coastal waters at the modest speed of 6 knots or so that you’re discussing? To get a decent ride in imperfect conditions with those hull proportions, what sort of stabilization do you think would be required, if any?