Trying to design my own cat.

Fanie
I have the tape. I like that boat. I live 60m above water level so once the ice caps melt the best forecast make my property a water frontage. I figure the Solar-Wind boat will be the perfect way to do the grocery shopping across the bay. Unlike you I will be able to shop any time. The oil will be all gone so your big outboards will only be useful as anchors and you will have to wait for the wind before you can get to the shop. Hence the method in my madness.

Rick W.

 

I like the idea of not being dependable on costly resources like fuel, so I'm with you on this one. Since I can fish, I won't be doing any shopping though. Don't have a bay in any case. There are quite a few places in SA where there should have been water, instead it's empty

 

Rick, my brother Andrew was talking to me some time ago about "why the hell don't we have electric powered multihulls".....batteries have come a long way now, as I'm sure you are aware. apparently there is a new battery called the carbon nano tube. It holds twice the charge of conventional lithium ion batteries.
My brother thinks the solar panels and windmill are good to have but most of the recharging could be done from home (particularly for a commercial model).
I personally find the idea of having a super quiet electric motor very appealing. When the wind dies down I can flick on the electrics and still feel like I am 'sailing'. Andrew thinks it's important to use a kind of double glazing to maximise the quietness because this is the elecctric motor's biggest advantage.
This is definitely something I'm thinking about for my design.

- Richard.

 

Batteries may have come a long way but we're not there yet ! With electric motors you're still limited very much to smaller boats if you want to get anywhere. The distance you can travel is very limited as well. Sails are just as quiet (or can be) and fiddling with the ropes keeps you from smoking so much

 

Richard
My aim is to have a long distance, sea worthy coastal cruiser that I can operate single handed without fuss and park in my garage when I am finished for the season.

There is a whole lot of reasoning behind the design of my proposed boat. I have spent about 5 years working on hull and propulsion efficiency. The validity or otherwise will be in actual performance once built.

The batteries I have proposed provide ballast and will allow around 10 hours operation at 7kts. So battery range only 70nm at 7kts. It will go up quite a lot if I go slower but I think a capable cruiser needs to do at least 7kts.

I am hopeful that a bit of wind once the sun goes down will avoid regular deep cycle. Either solar or wind power would provide enough energy to cruise at 7kts but solar will only be useful for a limited period.

If your intention is to do day cruises within range of safe harbour then a battery powered cat would make a lot of sense. Much easier to handle and operate than a sailing boat. Batteries and motor probably cheaper than sails and rigging. Hull loads could be lower as well. These days it is likely to be cheaper to operate than petrol outboards and more planet friendly given NZ source of power. Sailing boats are extremely difficult to use for serious day sailing unless they have auxiliary power. So you need this as well as sails.


Rick W.

 

Hi Rick and Richard,

I'm not trying to put your idea down, there are downs to it, I'm talking of years of experience using electric trolling motors on our boats. Keep in mind we charge the batteries from mains power every night if we are to go out the next day.

I suggest you do a couple of experiments with a small boat and a trolling motor... see how things hold up.

 

Fanie
The sales pitch for trolling motors is based primarily on thrust. This is nonsense and has nothing to do with performance unless you want to have tug-of-wars with the motors. If you looked realistically at the energy that you put into the batteries in relation to the energy required to push the hull a given distance at a reasonable speed with a trolling motor, the efficiency would be under 25%. My aim is to get more like 70%. Applying that energy recovery to an easily driven hull equates to good range.

I have been doing some testing with batteries on one of my old boats and they seem better at present than their rating.

The tesing is on an old hull nowhere near my most efficient. The initial testing indicates I can get 15km from two tiny VRLA batteries at a cruise of around 6kph. The assembly of parts were simply what I had laying about and not in any way optimised. This is the data I posted last week:
http://www.boatdesign.net/forums/showthread.php?t=20445

I try to isolate and reduce all sources of loss so I can get the most efficient and still practical way to achieve the objective. Your experience with the trolling motors confirms my assessment that they are not designed for efficiency. You can buy more efficient electric outboards but they are more expensive. These are still less efficient than I am aiming for. Here is an example that has some interesting commentary and experiences:
http://www.rayeo.com/news.htm#1

So the combination of easily driven hull/hulls and efficient drive system will give very good range on batteries.

Any experience you have with trolling motors is not particularly applicable to what I am aiming for.

Rick W.

 

For me, the whole point is to have sails. I did a lot of sailing when I was a kid (mostly racing) and so I am used to focusing on trimming the sails and I enjoy doing it.....although I don't know what it's like to do it for 10 hours or so! I just like the feeling of being pushed along by wind and sail.
The battery and electric motor would be ample efficient enough for my purposes. I would use it only when the wind dies and would probably never need to use it for more than about 50km at a time. I like the idea of island hopping around places like catalina island.
But anyway, according to my brother, who is very involved with a few engineering projects (like you Rick), he reckons batteries are up to the play now. I have no idea what VRLA batteries are....so I'm going to do a bit of research on batteries now. bye for now

 

Richard
If I am racing it is not too hard to work for well over 12 hours with a reasonable degree of concetration. An overnighter is my longest race. If you are cruising then you tend to have lots to do if you are short handed. I get tired of steering after about 2 hours so I prefer an autopilot. You then try to trim sails so you have good speed without being pressed. It is usually not as fast as it could be.

I think there will be a whole new dimension with a solar-wind boat. Initially I am thinking that I will not allow the turbine to weathervane. I will have a means of turning it so I can control power. I am aware this might cause some nasty loads on the blades but it is something I intend to experiment with. Also the load on the turbine needs to be mindful of the charging requirement anf thrust limit of the blades so this is something to work out.

The solar cells do best when they face the sun. I do not want to have them movable relative to the boat so am already thinking about how I can heal/trim the boat to partially track the sun.

Anyhow I think there will be a lot of thinking to get the best from it. Maybe a bit different if you were only using charged batteries but even then you have to decide how fast you can go in the conditions and conserve charge to get home. The range of a battery boat is bound to be less than a typical fuel powered boat.

Rick W.

 

Rick, I look forward to seeing your boat working in choppy sea conditions. If you can get it to be a good reliable boat in most conditions....then you will be truely advancing a whole new technology.
I did a bit of research on batteries and it turns out that Andrew was being a bit optimistic. Carbon nanotubes hardly exist at the moment. They are only being used on a small scale for power tools etc. because the cost is between a hundred and a thousand times more than conventional batteries! Some time to go yet.
Conventional lithium ion batteries have their problems too...they don't age well, are dangerous and can have unpredictable charging problems.
From what I can see at this point, maybe VRLA batteries are the way to go as long as they are well ventilated.
- Richard

 

Richard
The thing about a sailing boat is that the whole power system that you have paid tens of thousands for is useless if there is no wind. You go nowhere on those beautiful balmy days unless you motor.

A solar boat will relish beautiful balmy days. Plenty of sun and calm water. I can see myself waking up at anchor; sun getting up, panels firing up and I head off on auto-pilot to the next island while having a leasurely breakfast. Arrive as the wind is picking up in the afternoon and anchor up. The sun and wind continue to charge the batteries while at anchor ready for the next day's run.

So my aim is to travel when the sea is calm and leave the sheets-in-the-teeth stuff to the more heroic types. Unless I really have to be somewhere by an appointed time I will stay at anchor until the weather suits me.

My reading suggests that gel VRLA has superior cycle life to AGM VRLA.

There is still a way to go with batteries. One of the big issues right now is the escalation in lead price. It has risen about 8X in the last 5 years so puts gold and oil in the shade. As the population of cars grow (China expects 10M/yr by 2010) and there is more use of alternate power then lead price will continue to skyrocket. No good having a $50,000 car you have to crank start. So the price of lead batteries will climb strongly.

The lithium nano batteries have such a high demand that they cannot be made fast enough right now and I am not certain that all the bugs have been ironed out for long-term use. I think they will be difficult to charge reliably. Anyhow main issue is the same as lead. There is simply not enough lithium to suport a large population of batteries. The biggest producer is Chilean based but is listed on the NYSE and their share price is strong - rightly so.

Rick W.

 

Rick, there are brushless DC motors with effieciency that could be as high as 80%, maybe more.

 

Fanie
I have priced one that achieves 92%. It weighs 5.5kg and is rated at 3.8kW. The air cooled version has an enclosure rating of IP54. I am having difficulty finding a gearbox that allows best use of the motor as it spins to 6000rpm.

I am yet to find a gearbox that allows me to get the best from this motor. To get overall efficiency around 70% you need all components - batteries, motor, gearbox, controller, prop to be getting efficiencies well into the 90s.

There are a few motors that get up around 90% that spin slower so they may end up a better overall compromise.

My aim for cruise speed is to spin something like a 500mm prop at 600rpm as this will give good prop efficiency. Finding a right angle gearbox that suits the application and will handle a high speed motor is not easy.

Rick W.

 

Do you need a gearbox ? With a decent speed control you could maybe end up much better than with a gearbox. Any drive train stuff, prop shafts, gearboxes takes some energy away.

Have you considered looking at hydro fusion ? Some potential there.

 

Rick, you mentioned operating your boat single handed. Will it be large enough to take an extra person or more?
How would you expect it to perform during a sudden squall....when you say "long distance, sea worthy coastal cruiser" that suggests to me that it needs to be able to handle a bit of unexpected weather.