Displacement designs for solar electric river cruiser, 20 - 25 feet

[Jfitzger]

You could use stock panels and use something like these to make custom panels to use the rest of the available space.

https://www.amazon.com/dp/B081Y4J2Q8/ref=cm_sw_em_r_mt_dp_4YKRP3TPA31SQMXRDATY

I’ve heard good things about Sunpower cells.

I’ll be following with interest. I have long standing fantasy of a solar powered voyage down the Mississippi from my home in Minneapolis. If it ever happens it will probably be a beater pontoon with shanty tent on top.

[cstevens]

Thank you everyone! I was holding off posting here for fear of being overwhelmed by good advice, which I am. Let me try to narrow this down and address some of the issues:

1) Inboard or outboard.
I am planning to use an outboard. The electric outboards around a kW are light weight and easy to manage. They do not take up interior space, no shaft hole to leak, easy to remove for repairs, no rudder needed. One of the problems in the Delta is weeds clogging the prop, they are easy to remove from a tilting outboard. I am happy with the high efficiency 250 W EP Carry on the Walkabout. There is an option to boost that to 500 W, maybe use two to get 1000 W, and the company has a new 1500 W version in the works that might be ready when I am. Planning for an outboard keeps the options flexible.

2) Solar panel area.
The Sunpower 170 W flex panel I am using is 45" by 32" including connector dead space, and provides enough power to run the 250 W rated motor at 150 to 200 W for most of the day (smoothed by the battery). If I scale up the motor to 1000 W (4X) and plan for 1000 W of solar (6X) I think it should provide similar speed and range. Six of the same panels would fit on a roof 6 feet wide by 12 feet long.

3) Catamarans
Chris - I appreciate your outside the box thinking, but the big reason to go for a cat is to get enough solar panel area. Per the estimate above, for my planned relatively low power, I should have enough roof area on a 22 foot monohull to support the needed panels. Escargot is cool too, but my wife did not like the little box shape.

4) Construction method
The only boat I have built so far is the Walkabout, an epoxy glued plywood lap construction that needed no lofting. I am willing to learn some new techniques, but should probably stick to a similar method. I have to say that strip planking has the least appeal to me, it looks like a lot of gluing to wind up with a hull that has to be fiberglassed inside and out as well. Cold molding looks the way to build very light and strong, but it would be all new to me. I like the looks of lapstrake, but not necessary.

5) Steam launches
Steam launch designs are an existing class with hulls optimized for the low speeds of electric, so I am looking at them. Gartside, and Selway Fisher, have a number of designs. They are generally set up as inboards, and usually heavier than I am thinking. I do not see many built examples either, making it hard to picture the finished boat.

6) Sailboat designs as solar electric
This may make sense, especially non-planing sailboats, but are the hulls optimized for this application or does the need to mount masts and resist heeling change things? The Romilly looks slippery, but I would have to change the transom area to take an outboard instead of the rudder.

I like the designs posted so far, many very attractive boats, but the Handy Billy seems the best match to my goals and abilities. I see there is a 21 ' by 5' 10" version at 1300 lb. Construction is batten seam cedar over oak, not plywood. I would guess cedar may be hard to source and fairly expensive, but it is appealing to work with real wood.

That all makes sense to me. And if you can make the solar array work on Handy Billy that would be the way I would go as well.

[rgthom]

I just noticed that Doug Hylan has plans available to build the Handy Billy in plywood, so that is an option. There are images online showing a cabin, but the plans site shows an open boat. I will try to contact Harry Bryan, but does anyone know the story of the cabin version Handy Billy?

[cstevens]

Rick, it looks like that cabin was a custom build by Hylan & Brown. There is more info available on Facebook.

https://m.facebook.com/dhylanboats/p...0905884629261/

[cstevens]

More info... seems that the H&B cabin was inspired by one that Maynard Bray built for his Handy Billy, Constanza. There is a bunch of info on her here:

http://forum.woodenboat.com/showthre...za-Handy-Billy

including a link to a Google Drive folder of photos and other info, here:

https://drive.google.com/drive/folde...3bGOE7hnOeawRi

Annnd.... there is an Instagram post showing a lot of detail on the H&B version of the cabin here:

https://www.instagram.com/p/Bq-WmC6hTtv/

[Clarkey]

I have always rather liked this Selway Fisher Yamato boat at just under 24'. Designed for a 9hp diesel I imagine that the engine box could easily be used to house batteries and an outboard put on the transom or in a well



A solar canopy might take inspiration from this somewhat similar hull form:


ETA: Sorry just noticed that it may be a bit heavier than what you are looking for but I guess that migt depend how he has figured in the weight of engine and ballast?

[timo4352]

Every time this picture comes up... I just love the look of this boat.




I suggest you look at the Atkin catalog. There are lots of low power requirement boats in there.

[jpatrick]

The Handy Billy, at 21'/5'-10", is outside the lower edge of the OP's brief. But with a modest 10% stretch it measures in at: 23'-1"/ 6'-5". That is very close to Atkins' Ninigret, another low power and low displacement possibility. I have been looking hard at both these boats for my next build. I think both can be easily modified to incorporate a modest shelter without adding too much weight to the total. Also, the addition of a windscreen seems prudent and comfortable.

Jeff

[cstevens]

Another type that would be suitable - St. Pierre Dory. I like this one, from Nexus Marine



(https://www.nexusmarine.com/st_pierre.html)

but there are many similar designs available. Maybe a bit larger than you are looking for though. This one is 27' and 2700lbs. And it might be tough to scale it down much since there isn't much room in a dory to begin with. However they are easily driven and seem well suited to the power parameters you are thinking about. Here is an electric powered St. Pierre, based on a Glen-L design:

https://messing-about.com/forums/top...ic-propulsion/

Regarding the size and displacement... my thought is that larger, heavier boat has some advantages in comfort and seaworthiness. If the power package still works there is no downsize to a somewhat larger boat, assuming that there one has room to build and store it of course.

Also another thought on solar array size and the idea of a stowable array. To some extent it's possible to compensate for a smaller solar array by using a larger battery bank. The amount of power generated by the panels is still a fundamental constraint but a larger battery allows for more flexibility in actual use. So, for example, the target configuration from the original post was:

Motor: 1-3kW (I'll assume 2kW average draw)
Battery: 3-5kWh (assume 5kWh)
Solar: 1kW

giving something like 2.5 hours of run time and ~7-10 hours to recharge, unless running at speeds constrained by available solar power.

if the configuration were something like:

Motor: 2kW (average draw)
Battery: 10kWh
Solar: 500W permanent, 500W temporary (either as a stowable hard array or as a bimini or canopy)

Then there is the option to run at 2kW while charging with the 500W permanent array underway, and then deploy the additional 500W while at anchor. The extra battery capacity doubles the run time, allowing a longer run at a net battery draw, and also makes better use of extended time at anchor by storing more energy when the full array is deployed. The temporary array option might also allow for a significantly larger array when at anchor. Maybe an inflatable raft with a 1kW folding solar array? Could even be towable...

[amish rob]

3AA6257D-F139-4AB6-81DB-2A3928744552.jpg
Bruh...

[cstevens]

^^^ yes!

[rgthom]

Thanks again everyone, all very good recommendations.

Clarkey - I do like that Yamato boat, had not noticed it before. I see a lot of interesting boats on my business trips to Japan, and Douglas Brooks has documented some very traditional types. The plans call for a lot of ballast, not sure how it would perform as a lighter unballasted boat.

Tim - Your Ninigret is truly inspiring, a beautiful craft. I have perused the Atkin catalog, the designs are relatively light as you say but even low power for those designs is more than I will have. The plans notes have a very stern warning not to mess with the designs, so my tiny electric outboard does not match up well to any of the cabin boats which are all inboard. Ninigret may actually be the closest match, but it is a planing hull as you know. Don't suppose you would swap out the gas motor for a small electric and do some tests for me . Just kidding! Of the cabin boats the 21 foot Bamaling looks a lot like the Caprice which Tad Roberts proposed:


Rob - The Redwing 18 is on my list, maybe stretched a bit. Karl Stambaugh is now offering solar plans for this and several of his other boats, and a forum member just converted his to electric motor.
https://cmdboats.com/elec.htm?cart_i...526c92088633be

[rgthom]

Another type that would be suitable - St. Pierre Dory. I like this one, from Nexus Marine



(https://www.nexusmarine.com/st_pierre.html)

but there are many similar designs available. Maybe a bit larger than you are looking for though. This one is 27' and 2700lbs. And it might be tough to scale it down much since there isn't much room in a dory to begin with. However they are easily driven and seem well suited to the power parameters you are thinking about. Here is an electric powered St. Pierre, based on a Glen-L design:

https://messing-about.com/forums/top...ic-propulsion/

Regarding the size and displacement... my thought is that larger, heavier boat has some advantages in comfort and seaworthiness. If the power package still works there is no downsize to a somewhat larger boat, assuming that there one has room to build and store it of course.

Also another thought on solar array size and the idea of a stowable array. To some extent it's possible to compensate for a smaller solar array by using a larger battery bank. The amount of power generated by the panels is still a fundamental constraint but a larger battery allows for more flexibility in actual use. So, for example, the target configuration from the original post was:

Motor: 1-3kW (I'll assume 2kW average draw)
Battery: 3-5kWh (assume 5kWh)
Solar: 1kW

giving something like 2.5 hours of run time and ~7-10 hours to recharge, unless running at speeds constrained by available solar power.

if the configuration were something like:

Motor: 2kW (average draw)
Battery: 10kWh
Solar: 500W permanent, 500W temporary (either as a stowable hard array or as a bimini or canopy)

Then there is the option to run at 2kW while charging with the 500W permanent array underway, and then deploy the additional 500W while at anchor. The extra battery capacity doubles the run time, allowing a longer run at a net battery draw, and also makes better use of extended time at anchor by storing more energy when the full array is deployed. The temporary array option might also allow for a significantly larger array when at anchor. Maybe an inflatable raft with a 1kW folding solar array? Could even be towable...

Chris - I was lusting after that Nexus St Pierre a few years ago, even stopped by the shop to talk to Dave Roberts about it. That and Gib's boat would be fantastic, but I think they need a gas motor at that size. I am planning for a boat that runs 4 kts using 1 kW or less, approx 5X scale up from the Walkabout.

[cstevens]

Chris - I was lusting after that Nexus St Pierre a few years ago, even stopped by the shop to talk to Dave Roberts about it. That and Gib's boat would be fantastic, but I think they need a gas motor at that size. I am planning for a boat that runs 4 kts using 1 kW or less, approx 5X scale up from the Walkabout.

i agree that something like Redwing makes a lot of sense. Better space utilization than a dory for one thing. But regarding the power requirements, the electric dory in the link I posted runs at 2kW max draw using trolling motors and the owner claims 3.8kts using one motor running at 1KW. I’d bet that the higher efficiency of the EPC would give you better numbers than that. So i would not eliminate the dory based on power requirements.

[rgthom]

i agree that something like Redwing makes a lot of sense. Better space utilization than a dory for one thing. But regarding the power requirements, the electric dory in the link I posted runs at 2kW max draw using trolling motors and the owner claims 3.8kts using one motor running at 1KW. I’d bet that the higher efficiency of the EPC would give you better numbers than that. So i would not eliminate the dory based on power requirements.

OK, I won't discount a dory yet. I will say I was put off back when McMullen would rail against them at any opportunity - claiming the hull form is unrefined and why use one when so much better designs are now available. Not wanting to start a dory flame war here.....

[cstevens]

OK, I won't discount a dory yet. I will say I was put off back when McMullen would rail against them at any opportunity - claiming the hull form is unrefined and why use one when so much better designs are now available. Not wanting to start a dory flame war here.....

Ha! I was going to say that Redwing will undoubtedly bring out all the flat bottom haters. And the St. Pierre will bring out all the dory haters. And not to say that any of them are wrong, but post any photo of a big, heavy, inefficient, pilot cutter or a Colin Archer ketch or some other workboat-derived design and everyone goes gaga. You won’t find anyone talking about how they are terrible boats and the modern canoe body hull is a much better design. Pretty much every boat on the forum could be “better” with a more modern hull, or layout, or rig, or something. But for most of us that’s not the reason we have wooden boats. Anyway, that’s the end of my rant on the subject.

[rgthom]

There's a theme in many of the responses I'm getting from knowledgeable boat folk: Designer Tad Roberts proposed a canoe hull, double ended and narrow at the waterline. Designer Francois Vivier advised against one of his motorboats, instead a scaling up of one of his rowing designs (he is too busy to work it up at the moment). Designer John Welsford advised going with a stretched Long Steps, already a scaled up version of the double ended (at the waterline) Walkabout. Chris Stevens here posted the Energy 48, a very much enlarged Alden ocean shell rowing boat. For low power electric motor, it seems the right idea is to scale up a rowing boat.

[rgthom]

I've made some sketches, just to get an idea of looks and scale. The guy on these boats is my close cousin, adjusted to my 6' 4" height.

This is Long Steps, stretched in length only by 15% out to 22 feet. John Welsford has hinted a stretch should be OK. It looks a bit like Clarkey's Yamato boat:




This looks too small in the cabin, and beam maintained at 5' 6" would could be tight quarters for two.


This sketch is Long Steps expanded in all dimensions by 15%, a 50% bigger boat, plus a bigger cabin. Beam would be 6' 4". JW has seen this but made no comment, I have not asked directly for approval.



This should be enough room. Tweaked up by a skilled designer it might work. Any comments?

[stromborg]

It's an interesting engineering problem. Minimal wetted surface area to minimize drag but stable enough for an above-decks surface large enough to support a suitably sized solar array.

[Clarkey]

I suppose 'scaled up rowing designs' might hint at something like a St Ayles Skiff as a basis? Probably lacking a bit of primary stability bit that might be compensated for by using the battery bank as ballast (not that the batteries will actually be that heavy these days)? To be honest though I would love to see what new design John Welsford might come up with for this brief rather than a stretch of Long Steps.

[timo4352]

I've made some sketches, just to get an idea of looks and scale. The guy on these boats is my close cousin, adjusted to my 6' 4" height.

This is Long Steps, stretched in length only by 15% out to 22 feet. John Welsford has hinted a stretch should be OK. It looks a bit like Clarkey's Yamato boat:




This looks too small in the cabin, and beam maintained at 5' 6" would could be tight quarters for two.


This sketch is Long Steps expanded in all dimensions by 15%, a 50% bigger boat, plus a bigger cabin. Beam would be 6' 4". JW has seen this but made no comment, I have not asked directly for approval.



This should be enough room. Tweaked up by a skilled designer it might work. Any comments?

Those two look like vastly different boats to me.

[amish rob]

Thanks again everyone, all very good recommendations.

Clarkey - I do like that Yamato boat, had not noticed it before. I see a lot of interesting boats on my business trips to Japan, and Douglas Brooks has documented some very traditional types. The plans call for a lot of ballast, not sure how it would perform as a lighter unballasted boat.

Tim - Your Ninigret is truly inspiring, a beautiful craft. I have perused the Atkin catalog, the designs are relatively light as you say but even low power for those designs is more than I will have. The plans notes have a very stern warning not to mess with the designs, so my tiny electric outboard does not match up well to any of the cabin boats which are all inboard. Ninigret may actually be the closest match, but it is a planing hull as you know. Don't suppose you would swap out the gas motor for a small electric and do some tests for me . Just kidding! Of the cabin boats the 21 foot Bamaling looks a lot like the Caprice which Tad Roberts proposed:


Rob - The Redwing 18 is on my list, maybe stretched a bit. Karl Stambaugh is now offering solar plans for this and several of his other boats, and a forum member just converted his to electric motor.
https://cmdboats.com/elec.htm?cart_i...526c92088633be

Yeah, I knew he already had plans for longer ones, but I had no idea about the electric part. I think a Redwing style hull with a hard awning top (foam sandwiched with ply for insulation and light weight) would be slick. Some roll down curtains to make the cockpit a tent, and you’re good to go.

Especially if the hard awning were supported by telescopic legs, so you could lower it to trailer...

This project is going to be cool, no matter what you decide!

[cstevens]

The thing about the scaled up sail-and-oar designs is that they are good candidates for solar power because they are light and easily driven but I’m not sure that any of them would make great cruisers. That scaled up Long Steps, for example, still looks like a tiny boat for the length to me.

The factor that makes a good pulling boat is a long, narrow, light displacement hull. But that’s not a great thing in a cruiser as it puts a major constraint on space. If you just want a “Walkabout for two” it might do, but I think you can do far better than that given your power targets.

My suggestion is that instead of looking at designs that will give you the smallest, lightest possible boat that you can possibly fit into, you should nail down your power parameters (1kW for 4kts, for example) and choose the best cruiser that will fit that constraint.

One tool I have found particularly useful in thinking about solar power is this displacement hull power calculator:

https://www.kiwiprops.co.nz/cms/inde...esselspeedcalc

It’s especially interesting to play with length and displacement numbers. Increasing the waterline length even a little bit for the same displacement makes for a pretty big reduction in the power requirement. I also think you will find that your 1000lb displacement target is really low given your power parameters. For example the Redwing 21, a much more substantial design than your “Giant Steps”, would take less than 1kW to go 4kts. The Nexus dory would require just about exactly 1kW for 4kts. Both of those designs seem like they would be far more comfortable than a big row boat.

[Clarkey]

Michael Storer has some background in solar electric boats - his 23 footer could provide some food for thought? The flat bottom might not be what quite what you are looking for but Michael does put a lot of consideration into the handling and structure of his designs.

https://www.storerboatplans.com/boat...rd-motor-boat/

[jpatrick]

Storer seems to think rather highly of his flat bottom boats. Says they take short steep waves with little pounding while staying dry. But if this were always the case, we'd see many more flat bottom boats. But we don't... so Why not? Now, I'm not trying to derail this discussion by bringing out the "flat bottom haters." But the boats being discussed seem to fall into the two groups.

Does the long and lean rule for achieving efficiency apply to all hull types?

Jeff

[rgthom]

The thing about the scaled up sail-and-oar designs is that they are good candidates for solar power because they are light and easily driven but I’m not sure that any of them would make great cruisers. That scaled up Long Steps, for example, still looks like a tiny boat for the length to me.

The factor that makes a good pulling boat is a long, narrow, light displacement hull. But that’s not a great thing in a cruiser as it puts a major constraint on space. If you just want a “Walkabout for two” it might do, but I think you can do far better than that given your power targets.

My suggestion is that instead of looking at designs that will give you the smallest, lightest possible boat that you can possibly fit into, you should nail down your power parameters (1kW for 4kts, for example) and choose the best cruiser that will fit that constraint.

One tool I have found particularly useful in thinking about solar power is this displacement hull power calculator:

https://www.kiwiprops.co.nz/cms/inde...esselspeedcalc

It’s especially interesting to play with length and displacement numbers. Increasing the waterline length even a little bit for the same displacement makes for a pretty big reduction in the power requirement. I also think you will find that your 1000lb displacement target is really low given your power parameters. For example the Redwing 21, a much more substantial design than your “Giant Steps”, would take less than 1kW to go 4kts. The Nexus dory would require just about exactly 1kW for 4kts. Both of those designs seem like they would be far more comfortable than a big row boat.

Thanks for that link, very interesting to play around with. It does not include any adjustments for the hull shape, though, so any boat of the same length and displacement calculates out to the same power for a speed. I went back to my measured data from the calm water tests of the Walkabout and put in Gerr's calculated power to compare. At 600 lb displacement, 16 foot waterline, this is what plotted up:



Measured power is significantly less than calculated, except the measured curve gets even steeper at a hull speed around 4.3 kts. So either the hull shape of Walkabout takes less power to drive, or maybe the EP Carry is more efficient than the type of motor Gerr used for calculations.

[rgthom]

Michael Storer has some background in solar electric boats - his 23 footer could provide some food for thought? The flat bottom might not be what quite what you are looking for but Michael does put a lot of consideration into the handling and structure of his designs.

https://www.storerboatplans.com/boat...rd-motor-boat/

Well, that's not bad looking and an interesting idea for an easy to build river cruiser. Take a flat bottom boat, chop off the stern so you have only the bow, and you have an easy cruising boat if the waves are not ocean size. Storer specs a 10 hp high thrust motor, maybe electric would work.

[cstevens]

Thanks for that link, very interesting to play around with. It does not include any adjustments for the hull shape, though, so any boat of the same length and displacement calculates out to the same power for a speed. I went back to my measured data from the calm water tests of the Walkabout and put in Gerr's calculated power to compare. This is what plotted up:

Measured power is significantly less than calculated, except the measured curve gets even steeper at a hull speed around 4.3 kts. So either the hull shape of Walkabout takes less power to drive, or maybe the EP Carry is more efficient than the type of motor Gerr used for calculations.

Yes, the 10.665 coefficient is doing a lot of work in that formula, and one of the things that it does is to build in some assumptions about hull form. A NA would actually calculate real coefficients for a given hull design based on sectional areas. Or these days they would have the computer do it for them I'm sure. There is a pretty decent overview of that formula (as well as a bunch of others) in this document:

https://www.ericwsponberg.com/wp-con...ign-ratios.pdf

You could probably get a good approximation of the number for the Walkabout by adjusting it until the predicted curve matches your measured curve. You can also really get lost in the weeds over on boatdesign.net if you want to, for example:

https://www.boatdesign.net/threads/l...er-boats.5073/

On another note: Regarding the Michael Storer river camping boat design shared above, Storer's assessment of the design (linked in the post) is really interesting as it shows how an initial design constraint - in this case the goal of production efficiency for an anticipated run of 50 boats - cascades into a set of design decisions that result in a boat which is ideally suited to a certain use and not some other use. And it illustrates something that I have been thinking about regarding this thread, and the idea of adapting an existing design to create a low-powered, efficient river cruiser. Which is that starting with any existing design means that you inherit all of the initial design decisions and constraints, And then you add others during the process of adaptation. If you get too far away from the original design goals then it's difficult to arrive at something that is ideal for any purpose at all.

Long Steps is a superlative sailboat (by reputation, I have not sailed one myself) and is the result of a thousand design choices that John Welsford made in order to create that particular design with those capabilities. A scaled up Long Steps would probably make an ok solar river cruiser but it will be compromised in many ways that will make it less than ideal for that purpose. If JW could be induced to design a suitable boat I am pretty sure it would differ significantly from Long Steps in hull form, layout, and many other areas other than just size.

My personal opinion, but I think the best options here are to either a) choose an existing design that meets the general use and power criteria (Redwing 21, St. Pierre Dory, likely others), or b) commission a custom design from a clean sheet of paper, as Tad has proposed with his solar Caprice.

[Clarkey]

I'm inclined to agree. Although it is interesting to speculate what characteristics of existing designs might be adapted to this brief the reality is that this is an exciting new cruising type and it would be great to see how talented designers approach it from scratch.

[rgthom]

Hmmm, anyone want to chip in on a commission for the new design? Just kidding, I'm not retired yet and at least a year from starting. As of today I am torn between the already tested designs of the Redwing 18 (maybe stretched) and Handy Billy 21, vs a new design by Tad Roberts or John Welsford. This picture of the Handy Billy has just about everything I'd want, in a great looking design. I like the removeable cabin, the V-berth under, the helm station, and the simple configurable layout. If a small electric motor could be transom mounted to eliminate the motor enclosure and open up the full cockpit it would be even better. I hope a solar roof would not detract too much, if done right. I will try to contact Harry Bryan for his opinion.

[cstevens]

Actually I think the idea of finding a group of people who are interested in a solar cruising design to go in on paying the cost of a commission is a great idea. While I don't know when, if ever, I would ever build such a boat I might be interested in participating just to see it happen. I expect there are others who would do so as well. But at the same time I think a solar Handy Billy would be a wonderful thing to see as well. I don't think you can go wrong either way.

[offbelayknife]

I would certainly be interested in participating. As I've been studying various designs and dreaming up ideas on what to build, it's hard to make a 'recreational' case for any fossil fuel use. Even if I didn't build one myself, helping get more solar electric designs out there, especially one from whole cloth, is worthwhile. An electric-solar Roan Mhor keeps whispering to me.

[stromborg]

If I was going to build a motorboat it would be this one.

I might have to do it just because it's so pretty...totally trailerable, right?

[Timo_N62.9_E27.7]

etusivu_2020-11-07_200px-768x512.jpg

This is an easily driven electric powered boat. Not solar though but might be adaptable.

http://www.elwood.fi

[Clarkey]

I would certainly be interested in participating. As I've been studying various designs and dreaming up ideas on what to build, it's hard to make a 'recreational' case for any fossil fuel use. Even if I didn't build one myself, helping get more solar electric designs out there, especially one from whole cloth, is worthwhile. An electric-solar Roan Mhor keeps whispering to me.

Me too, I just can't really consider the idea of burning fossil fuel for recreation anymore. I would be happy to commit to a set of plans.