Solar Panels - Bimini or Davits - Pros and Cons of Both

[GordMay]

Originally Posted by S/V Alchemy

... Putting weight at either end is just like putting fatter kids on a see-saw: the tendency to pitch, and to pitch faster, increases. Depending on your boat it might not be an issue, but I would hesitate to recommend bolting panels two feet off the stern to solve a "weight in the bow" problem.

That's not true. Think pendulum.

Generally, putting weight in the ends, further from the centre of rotation, (thereby increasing the moment of inertia) increases the amplitude of pitch, whilst reducing the period.
A boat with a low moment of inertia (light ends) will pitch less but more quickly; a boat with a high moment of inertia (heavy ends) will pitch more slowly but more deeply.

Hence, Putting weight at either end is more like putting the kids further out (from axis) on a see-saw.

[Mark Johnson]

Good point Gord, and I totally agree! I kept my Trimaran's bow weight as low as possible, I even remove and store my bow anchor in a wing locker when seriously at sea. My aft solar panel was actually less weight and windage than the windvave that was designed to be there. (I opted for an autopilot instead)

Searunners, unlike about all other multihulls, store the VAST majority of their entire payload, including tools, supplies, engine, batteries, and tankage... at or below the waterline, in the middle third or the boat.

It is hard to accomplish this unless it is designed into the boat, but to what ever degree it can be accomplished, it is a good thing.

Monohulls, especially BIG ones, are nowhere near as sensitive as our trimaran to weight out near the extremities, but SOME use the forward V berth as a "catch all" for all kinds of heavy stuff, and use BBB chain that is WAY too large, for the extra cantenary effect! They could go down a size on the chain, but use HT / G-4 chain instead, and go UP a size on the anchor! (OR use a more weight effective design, like the Rocna). This way they could get a couple or three hundred pounds off of the bow, have ground tackle that is just as strong, with even better holding power, and the only penalty would be that they may need to go up a notch on how much scope that they put out.

The benefit is a MUCH nicer motion at sea, and less green water over the decks...
Often the realties of the boat's design, and our needs, just dictates that we do what we do. Like my boat should not have a windlass, but my injured back requires one... So I built the lightest installation I have ever seen.

To what ever degree that we can keep the boat's "optional weight" low and near the center of the boat, (especially off of the bow or way up the mast), the better.

Point well taken though, Mark

[S/V Alchemy]

Originally Posted by GordMay

That's not true. Think pendulum.

Generally, putting weight in the ends, further from the centre of rotation, (thereby increasing the moment of inertia) increases the amplitude of pitch, whilst reducing the period.
A boat with a low moment of inertia (light ends) will pitch less but more quickly; a boat with a high moment of inertia (heavy ends) will pitch more slowly but more deeply.

Hence, Putting weight at either end is more like putting the kids further out (from axis) on a see-saw.

Fine, Mr. Physics, but fatter kids on a see-saw is a funnier image!

[endeavor]

Well we seem to have gone off in another direction with this thread but I guess I started it. I'm heading down to the Caribbean this fall and I just got myself a Rocna 20 (45lb) anchor and now I'm going to be adding all this chain (well maybe not 200' not sure yet). I would think that it would be worse to have all that weight up front and plowing into the waves. I mean there are all kinds of boats out there with chains in the bow and davits/solar panels astern. They seem to be alright.

[jm21]

So, had a related question and trying not to start a new thread....

My wife and I will have much higher than normal power needs, at least so it would appear. We want to try living on a monohull sailboat for a couple years and see how things go. But she wants a big freezer and I would have a virtual office that would require quite a bit of electronics being run for 30-40 hours per week. Calculating things out, it seems like we should plan for somewhere in the neighborhood of 2.5kwh energy use per day on average to be really safe.

The cheapest way to go in the very short term would seem to be a 2kw portable gas generator, but they're noisy as heck and in the long-term, even 2+ years, a very cost-efficient solar setup might be better.

However, it seems like the most cost-efficient solar panels typically measure 65" X 39" and weigh 40ish pounds, which is hard to place on a monohull sailboat.

I am thinking of a setup with a kind of bimini-ish arch-ish davit-ish structure of SS or aluminum that was 1/2 or 2/3 on the boat, then extending out behind the boat (possibly with support poles coming off the transom?). You could fit solar panels to this while at anchor, and when moving the boat long distances, either remove the panels or reduce the number of panels and use it as a dinghy davit. It wouild need to support maybe 300-400 pounds. At least 3 but preferably more 235w panels (the more the better, 6-7 would be ideal as it would allow us to run AC on hot days for a couple hours). It seems like a structure could be made out of basic pipe and fittings for a few hundred dollars. A boxy structure, not like a bimini with bows.

Is this just a dumb idea or....? I know it would be ugly as sin, but that's OK with us.

[sww914]

Mine form a cover over the cockpit like a bimini, I love it love that unless it's cold and cloudy. I have about what you describe, 3 200 watt panels. It's plenty of electricity and we are electronics junkies. The best way that I've found to have an adequate supply is to reduce consumption a bit, it's been a lot easier than I imagined. You'll get used to not having a huge freezer right away, I was really worried about that but it's been a non-issue except for a lack of ice cream storage. We make our own now, it's better.

[Pete7]

Originally Posted by jm21

Is this just a dumb idea or....? I know it would be ugly as sin, but that's OK with us.

Sorry JM, but you are going to have to re-think your plans. 400lbs on the stern on a mono isn't a good idea. I just can't see 7 x 235AH panels on a mono either which would only produce a ball park figure of 550AH per day.

Requiring 2.5kwh per day is going to be a diesel generator. However, if your working and living on board and yacht is big enough, then why not have a genny as part of the cost of running the business.

It's the large freezer that's going to be your problem, whilst nice to have ashore do you really need it on a boat? worth thinking about.


Pete

[Cotemar]

jm21,

If you buy better panels they will be smaller, lighter and put out more power.
SunPower makes a 240 watt panel that is 61" x 31" and 33 lbs.
They also make a 327 watt that panel that is 61" x 41" and 41 lbs

Sanyo makes a 237 that is good also.

Cheap panels are big and heavy. For a few hundred dollars more you get the top of the line.

[jm21]

Well, what I was thinking of was that it could alternate between being used as pure solar storage when at anchor (130ish pounds for 3 panels up to 260ish for 6), and when moving the boat just hold 1-2 panels and a hard bottom inflatable hanging off it, which I was guesstimating close to 400 pounds.

I got the idea reading some posts about designing hard top biminis that you could walk on. I started thinking "hey, if they can hold a hard fiberglass top and a person...why not a crapload of solar panels?"

So maybe just a place for holding panels and if we want davits do something else.

None of the boats we've looked at have diesel generators and they appear to be quite expensive to buy...I've been looking at gas generators but once you take the cost of fuel into consideration it's not all that much cheaper. Would be about $1k/year in gas. And cheap gas generators are noisy as hell. If you buy a nice quiet gas generator, in two years the gas system would have cost the same as the initial cost of a 6x235w solar system and you'd still be buying gas.

Maybe 3x solar panels, a bit fewer batteries, and a small generator for cloudy days? Or maybe a really good alternator?

For panels, we were looking at some sharp panels that were 235 and 44lbs which didn't seem too bad. $310 shipped I think. I will check out some of those other panels though.

The freezer is a headache, but it's a big deal for me and a bigger deal for my wife. We've got about 10 cubic feet freezer space at our house, but it's all vertical. Going to a top loader we could probably fit more in a smaller space, and we would be downsizing overall, but I don't think we could go down too much below 3 cubic feet. Could save a little bit of space with one of those vacuum sealing tools. 3 cubic feet would basically be enough to hold a decent variety of frozen meat and not much else. We would plan on only re-supplying once every few weeks. I know there are a ton of alternative options but we like good meat and a decent variety...and would be nice if we caught a big fish to be able to store it somewhere...and I just can't see canning a good steak...

It is really hard to find decent information about energy usage for different types of freezers. Can find some information for some of the big brand ones like Engels but that's about it.

[Caribsailors]

Here's My set up 2 x 150 watt

[OceanPlanet]

Here is a recent installation of SolbianFlex panels (1 x 125W, 1 x 80W) on a bimini...installed with zippers on the edges so they zip directly on to the canvas.

[COLINFLTENG]

Originally Posted by OceanPlanet

Here is a recent installation of SolbianFlex panels (1 x 125W, 1 x 80W) on a bimini...installed with zippers on the edges so they zip directly on to the canvas.

What MPPT controller did you use
Colin

[Ashura]

oh wow. I did not know how much flexible solar panels were! They are like 10x the fixed panels...

[COLINFLTENG]

Yes you pay for what you get

[sailinglegend]

Originally Posted by endeavor

.... I am torn between installing them on the bimini or on the davits. .....

Neither - instead use semi flexible panels mounted on the deck.

Arches to mount fixed panels can be expensive, it may be better to invest in the less efficient semi-flexible panels that can be walked on and can be permanently stuck to the deck. They are light enough to be mounted on biminis or sprayhoods and can be moved to follow the sun angle.