Rick, This has been very interesting and thanks for the links and pictures.
"The linked photo shows Twin-8 as a light hull sitting on the water.:
It has a concave keel line. Again the shape is a product of 30,000 to 40,000 iterations to target minimum drag for its design displacement and speed. One of these hulls is being paddled as an OC2 and the owner believes it is the fastest OC2 he has ever used but has not raced it yet"
I think you mean convex, I had a surf ski like that, with no rocker though. That was the thing about surf skis they were like paddling on a pole almost impossible to turn very fast though.
"Hulls designed for high speed have hard chines. Boats designed for low speed have round chine - simple. A soft chine maintains attached flow whereas a hard chine causes flow separation. On a long slender hull with a tiny degree of rocker I can see no benefit in maintaining attached flow over the chine. If the hull moves fast enough to lift the foot of the stem clear then the hard chine has a distinct advantage because water does not stay attached to get forced up the sides of the hull as seen here:
There is power lost in lifting the water. That power could be directed at lifting the hull if the flow was directed sideways by a hard chine. Beamier hulls usually have spray rails to detach flow but my hulls are so narrow that slamming is not an issue so I can use the flat bottom and hard chine to achieve the same result."
As far as I can see the bow is forcing the water up the sides not the chine. But what you are saying about attached flow is the complete opposite to my understanding of drag and fluid flow. Attached flow has much less drag than separated flow as an example look at the Americas Cup hulls.
Solar racers are usually not permitted large batteries. A small battery is usually required to stabilise voltage. The E340 race has no restriction yet on battery size or solar array. There are talks of setting limits to prevent high speed boats and keep costs down. Solar cells are extremely light so pack a lot of power to weight. The 2.2kW panels on the E-340 boat weigh 40kg and when/where the race is run, average sunlight day is equivalent to 7.5 hours full sun. This results in 410Wh/kg over the day. A good lithium battery gives about 100Wh/kg for a single charge so it is better to get more solar panels than battery if going long distances.
That is a whole lot lighter than the 140 watt kyocera's that I have (13kg each), but I suppose most of that weight is in the glass and the frame, Five times heavier in fact. Of course the thin film solar panels are 5 times the cost, there must be a correlation there. Is it really $800 for a 60 watt panel or $30,000 for 2.2KW? 3 hp?
It will have enough battery on board to hold 6mph overnight but should be close to finishing the race in daylight as there is typically a 4mph current to add to speed over water.I am trying to wrap my head around that idea. I guess if the induced drag from the aerodynamic lift is less than the waters drag it would make sense. It certainly makes sense if it is the boats velocity that is generating the velocity, it is the headwind idea that is interesting.
So there will be enough battery capacity for 26kW on board? At 100 Wh/kg or 26o kg? Looks like you will be stuffing that boat full of batteries.Talador
__._,_.___
Posted by: taladorwood@yahoo.com.au
| Reply via web post | • | Reply to sender | • | Reply to group | • | Start a new topic | • | Messages in this topic (77) |
.