Solar boating

Tad Roberts,

Solar panels are down to $1 per watt. When I bought mine 25 years ago I paid $5 per watt and they still produce rated output. When you figure just 1500 watts of panels can push a light, efficient hull 65 nm on 5 hours of exposure in a 24 hour run with average speed of 2.7 kt, the math says it will have a quick payback on the added investment. Lets say you used every watt produced by $1500 worth of panels, stored in $5000 worth of lithium cells to power a $2000 motor and controller for propulsion, you would be ahead on savings over diesel fuel in short order. One year, 24,000 nm on solar vs 8000 gallons of diesel at 3 nmpg. I know I picked a very slow cruising speed to make my point (2.7 kt) but as you know, to double your speed in water requires and 8 fold increase in power. So at a more real speed of 5.4 kt, then 12 Kw of panels needed. The Solar 21 crossed the Atlantic with 10 Kw of panels and heavy lead acid AGM batteries with a reported 5.5 kt average.

The Greenline website uses the term "superdisplacement" for their highly advanced hull design, thereby invoking thoughts of efficiency. One of the models is listed at 22 knots with a pair of diesels. The photo above shows hard chines with flat surfaces aft. Superdisplacement, indeed.

I look forward to seeing what you come up with for that Loop project Tad.

skidgear said:

The Greenline website uses the term "superdisplacement" ...

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Bottoms up!

Marin said:

Now I'm sure the boat had to meet whatever stability requirements are set by whatever regulatory agencies set them-- the USCG, I suppose, in the US---

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With the exception of pontoon boats, there were and are not currently any stability or capacity standards for pleasure boats over 26' in length in the US.

Tad Roberts said:

With the exception of pontoon boats, there were and are not currently any stability or capacity standards for pleasure boats over 26' in length in the US.

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Thank you for the clarification. I am amazed that there are no standards or requirements for larger boats. Perhaps I am influenced by the industry I work in where you can't change the type of fastener or wire tie used without getting approval from the FAA, JAA, and all the other aviation regulatory agencies around the world.

What is the rationale-- if there is any--- for having standards for boats under 26' feet but not over 26 feet?

Commercial versus private applications. Careful what you wish for...

The Great Circle boat is not yet ready for the light of day. But we have another that may fit the conversation. As there are so many variables I think having a specific boat to consider might help.

This boat is under construction so all data are guesstimates at this point. She is a family weekender for Georgia Strait. Length is 40' overall and waterline. Beam is 8', displacement is 5400 pounds. Power is a 29HP Volvo MD2030 (weight 335LBS) diesel with 2.37:1 reduction turning a 16" by 16" three bladed prop. Construction is 3/4" red-cedar strips sheathed with glass inside and out, the deck and cabin top are foam cored. If the builder can maintain design weight she will manage around 11 knots top speed and cruise in the 8-9 Knot range. 20 US gallons will give her 600 miles at 7.5 knots. At a little over 9 knots she'll burn .54 usg/hr and go 345 miles on 20 usg. That's about a season's usage......

As you can see she is very, very basic to keep weight at the minimum. Her open forward cockpit is an empty well with a hatch access to the fore cabin. Her stateroom under the foredeck is a tunnel with a bunk P&S, nothing else! The deckhouse contains a settee, big dinette which makes a double, galley, helm, and private head against the aft bulkhead. The engine is in a box outside in the cockpit. Solar panels will go on the roof.



So switching her to pure solar, how much does weight go up and range decrease? Besides the fact that here in the PNW (Periodically Not Wet) solar is questionable at best......

Tad, that is great efficiency and I agree that the PNW is not too solar suitable. Your kind of range on diesel combined with lack of sunshine for your boating area makes that design a winner. Good luck with it and can you keep us posted on it's development?

BTW since I'm new to the forum, are you THE Tad Roberts of Tad Roberts Yacht Design?

deckofficer said:

BTW since I'm new to the forum, are you THE Tad Roberts of Tad Roberts Yacht Design?

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apparently........

Although it seems redundant to say Tad, I love the lines of that boat.

You state an 8' beam. Was trailering a consideration in that design? It certainly has the weight right for it if not.

My guess would be a narrow beam for efficiency.

Tad,

Many years ago during my CMA days I seem to have picked up that on displacement hulls if you double your speed it requires an 8 fold increase in power. Did I remember right, or had it wrong all these years?

Marin said:

What is the rationale-- if there is any--- for having standards for boats under 26' feet but not over 26 feet?

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Probably someone from the US could answer better than I......But......I'll guess it's a combination of many issues. Smaller boats are more likely to be open (un-decked) and subject to swamping. The crew load is a larger factor in overall loading for a small boat, thus smaller boats are more likely to be overloaded (thus becoming unstable and/or unsafe). And the large boat manufacturers lobby managed to stave off regulation......

With some notable exceptions, stability or lack thereof is not a huge safety issue with US pleasure boats. Sad exceptions are horrors like last years capsize of a 34' powerboat on July 4th (at night) on Oyster Bay NY. Boat was wildly overloaded with 29 people aboard.....

CPseudonym said:

Although it seems redundant to say Tad, I love the lines of that boat.

You state an 8' beam. Was trailering a consideration in that design? It certainly has the weight right for it if not.

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Thank you for your kind encouragement, it's always welcome

Actually trailering was not a consideration at all. The beam may be 1.5" greater than 8' above waterline midships. The main criteria was to keep the molds and bulkheads (NC cut) to one sheet of plywood.......saving money.....

I remember that accident. OK to overload a bit with guests at anchor, a different story when underway. This is a 8500 lb PDQ 36 with a bit of a deck load.

Tad Roberts said:

Thank you for your kind encouragement, it's always welcome

Actually trailering was not a consideration at all. The beam may be 1.5" greater than 8' above waterline midships. The main criteria was to keep the molds and bulkheads (NC cut) to one sheet of plywood.......saving money.....

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So long and lean wasn't part of the equation but rather maximizing material yield?

deckofficer said:

Tad,

Many years ago during my CMA days I seem to have picked up that on displacement hulls if you double your speed it requires an 8 fold increase in power. Did I remember right, or had it wrong all these years?

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That may hold true for a particular ship type, but resistance is not a linear function. It's a curve that becomes almost vertical at some point (popularly over the S/L 1.34). So the difference will depend on where on the curve you are comparing. For instance just looking at the boat I posted above, the difference in required power between 6 and 12 knots is 13 times as much, from 1.6HP to 21HP (Theoretical).

Thanks Tad. I've always used it as a rough rule of thumb. When I come across a new hull design that is touted as efficient, I take its top speed and hp required and start reducing speed to see what speed electric would start to be viable. For example the new Aspen C90 will run 20 kt on 150 hp, so if my rough rule of thumb holds true, then 5 kt would only require 2.5 hp.

deckofficer said:

... One year, 24,000 nm on solar vs 8000 gallons of diesel at 3 nmpg. I know I picked a very slow cruising speed to make my point (2.7 kt) but as you know, to double your speed in water requires and 8 fold increase in power. So at a more real speed of 5.4 kt, then 12 Kw of panels needed. The Solar 21 crossed the Atlantic with 10 Kw of panels and heavy lead acid AGM batteries with a reported 5.5 kt average.

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Bob: 24,000 nm in one year at the speed you mentioned? We cruise full time and in the last 5.5 years we have covered between 2500 to 3000 miles per year. When we cruised on our sailboat (7+ years) we averaged ~6000 miles per year but we were crossing oceans then. I don't think these number are out of line with the average cruiser. I'll be the first to admit though, I'm a better travel than I am a sailor. The boat is the instrument to get us to where we want to go.

Larry,

I just used those numbers as an extreme example of maximizing all collected solar for propulsion. Like you, when I cruised, it was a passage followed by a lot of time at the new anchorage. Plus if you go with electric galley and electric dinghy, then that collected solar will be used for more than just propulsion.

Tad: I am infatuated with your 40 footer. She reminds me of the Martin's Energy 48 - long and lean.

The heaviest part of solar is the battery. I just installed a 1,000 ah/48v one at 1,250# or so.

If you used the PV panels w/o frames glued to a grid if red cedar you could eliminate the weight of the wood and glass to sheath the cabin top. Not a lot of area, but enough for what I feel is a spartan cruiser.

I have been looking for low HP modern common rail diesels so you don't need to use an inefficient old-fashioned one. The Smart Car in Canada has a diesel option - maybe find someone to marine e for you. This motor was the building block for the 25kw generator that Glacier Bay was using for their diesel electric system - never made it to market.

FNM uses Fiat diesels as low as 75HP in a parallel hybrid system. Still bigger than you need.

Dave Westphal, a Miami legend in sailboat circles has recently build two long lean day boats with plug in electric power.

I'd love to you post more on your design? Renderings? Plans? I love the idea of designing her to an 8' beam since that's the length of a sheet of plywood. The late Phil Bolger had a similar practical streak evidenced in his easy to build from readily available materials.

Reuben,

I thought I asked you this but couldn't find it in my PM box, so maybe I asked Larry Graf @ Aspen. Do you have an opinion on the 36 hp 80 kg turbocharged Steyr diesel?

Not sure the small Steyr is a shipping product? A quick look at the website shows an unusual configuration (unless I'm mistaken?).

Steyr is a "boutique" manufacturer with high end, specialized, uni-block diesels. Their motors can run on bio-diesel and maintain 1,500 RPMs with NO cooling. The turbo models get high HP/pound.

You can eat off the factory floor!

rjtrane said:

I'd love to you post more on your design? Renderings? Plans? I love the idea of designing her to an 8' beam since that's the length of a sheet of plywood. The late Phil Bolger had a similar practical streak evidenced in his easy to build from readily available materials.

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Phil taught me many things, perhaps the most important concept is that much is possible with little.

Since you asked......

This is very much a collaborative design worked out over years of conversations with the owner/builder. As such the design is in flux until it's built and the rough drawings are only a guide. I supplied the hull lines and NC data for the molds/frames/bulkheads which are spaced 2' apart throughout her length. So the aft cockpit is 12', the deckhouse is 12', the foc'sl is 8' and the forward cockpit/anchor locker is 8'. The actual layout is the owner's wish.

No decision on how the transom will be done, I like open so small boats can come aboard easily, I think Ron wants it closed so kids and dogs stay
aboard.

The bottom is almost flat at the transom, but only immersed about 2" so she should slide right along. I'm concerned there's not much grip on the water (low-speed control might be iffy) but we'll address that after first trials. A centerboard, some fixed fins, or something.......She is an experiment, mainly I'm hoping to illustrate how light we can build, but we'll see.

Very interesting boat with very nice albeit simple lines. I hope we'll see it sometime up in BC waters. Do you know yet where it will be based out of?

Did you consider a sail drive? Get the motor out of the way?

I had Bolger design my 28' Summer Hen. We built her the same - strip built with glass outside (none inside). Similar proportions - 7' beam - 9" draft board up. We never tooled or produced her though.

Did you make a towing model?

Marin said:

I hope we'll see it sometime up in BC waters. Do you know yet where it will be based out of?

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She's under construction in the owner's shop close to Halfmoon Bay, Sunshine Coast. Home waters will be the mouth of Jervis Inlet to Desolation Sound.

rjtrane said:

Did you consider a sail drive? Get the motor out of the way?

I had Bolger design my 28' Summer Hen. We built her the same - strip built with glass outside (none inside). Similar proportions - 7' beam - 9" draft board up. We never tooled or produced her though.

Did you make a towing model?

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I've been warned about sail-drives so often I never consider them any more. As far as I can tell the main reason to have one is to reduce installation man hours and required skills. That's not the case in a home build. In BC you would still have to build a keel/guard forward of the leg to protect it from drift. And I know that a straight shaft with a bearing and stuffing-box is rugged, reliable, and cheap to buy and maintain because they are everywhere. While I agree a Z-leg could get the engine a bit further aft, I actually wanted it further forward to reduce rotational moment (pitching). But the owner/builder already had this powerplant (the boat is an attempt to get the most from this engine) and the boat was designed around it. We'll see if we were right when she's launched.

I'll have to look up the Summer Hen, it's a vague memory......

No model, the form is actually a high-speed motorsailer that I stretched and tweaked. It's closely related to an old (light-displacement, narrow beam) Maine LobsterBoat form. The prismatic and LCB are correct for the design speed, beyond that only tiny improvements are possible given the length, beam, weight, and speed. This is full sized testing, if this one works as advertized the follow up will be about 30' and half the weight with small outboard power.......I am thankful for an owner willing to put money and effort into an experiment.....

deckofficer said:

For the Nissan Leaf, Ford Focus electric and the GM Spark and Volt, which are all electric drive, they use lithium.

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While technically correct, there is a dirty little secret, CA driven, going on here. It is called COMPLIANCE..

An interesting read in USA May 9th issue, in summary.

CA mandates that if you sell more than 60,000 vehicles per year in CA the manufacturer must sell for a competitive price, a purely electric drive vehicle. Hybrids like the Prius don't count nor do CNG vehicles. So Ford makes the all electric Focus selling something like 560 of them last year and only because of the over $10,000 of rebates from the govt and Ford. Ditto the Leaf, Spark, Volt and Toyota RAV. Guess who is paying for this largesse? Fiat estimates their little electric 500 will lose $10,000 per vehicle, all out of Fiat's pocket

Tesla just reported an $11M profit for the quarter, but wait a minute. Tesla gets govt ZEV credits that can then be auctioned to other automakers to offset their non ZEV vehicles. The company income from such sales came to $68M in the quarter or 12% of revenue.

Of course CA won't allow any new power plants to be built to supply ready kilowatts for these all electric vehicles so the CA environment is really saved now! And the State wonders why it is in hock.