hi, don't know if I'm in the right place or not but does anyone remember a couple of months back a news item about a couple of kiwi guys who have invented a new 'device' to get more power or use less fuel, had something to do with the prop or the area around it. I think one of the local boatbuilding companies bought in to it, but haven't heard anything more. Thanks in advance.
donz01,
Mar 12, 9:46am
Was it a new type of jet unit! It appeared to have 2 impellors that ran opposite directions to each other inside the same housing which the company claimed gave more thrust. The company had a trial unit in a large yellow boat ( May have been a coastgaurd boat) I watched the article on TV one night then a few weeks later it pulled into a service station in Balclutha behind a truck apparently on its way to Auckland. I think it was built south of Balclutha.
johnf_456,
Mar 12, 10:10am
I vaguely recall it, I will do a bit of a search now for it.
meathead_timaru,
Mar 12, 12:19pm
Contrapel. It's a hybrid propeller/jet. There are stern legs that have contra rotating blades.
martin11,
Mar 14, 6:34am
Contra rotating props reduce the torque effect not fuel consumption
sr2,
Mar 14, 8:00am
Yes Volvo have been making stern legs with counter rotating props for decades; they are very efficient, they work well but boy are they a nightmare to pull apart!
jenny188,
Mar 14, 10:31am
If it was magic everyone would be making or installing them. Certain circumstances may give them an advantage butnot every instance. Or else every car produced would be turbo diesel. Get the drift!
tazcsv,
Mar 14, 10:25pm
Think it was 2 guys from down here in the deep south in Tuatapere, some sort of modded jet unit that will give more thrust with less power. Think ill just stick with the 383 and 212.
meathead_timaru,
Mar 14, 10:54pm
Stern legs in general are an overly complicated solution to a fairly simple problem. I wouldn't have a boat with one. Outboards or inboard with shaft for me.
sr2,
Mar 15, 12:35am
There is nothing worse than having an old, badly maintained stern leg hanging of the back of your transom, but if you have a large trailer boat (particularly one with a planning hull) and you want it to be diesel powered a stern leg is really your only viable option. A shaft drive in a trailer boat makes launching or beaching a major pain and having a motor in the middle of the cabin takes up a huge amount of space. The American military has implemented a diesel only battlefield policy and are pushing the manufactures to make diesel outboards; apparently Yanmar and Yamaha have models available, it sounds like the ideal solution to me. Till then I??
meathead_timaru,
Mar 15, 12:53am
Yes, that's true.
mm12345,
Mar 15, 5:15am
The "Sea Shuttle" cats in Tasman Bay have an interesting setup.They used to use jets, but now have a system with a prop on a shaft held in a bridle, which rotates in an arc to the side.Belt driven from a pulley on the gearbox, they can even rotate the props right out of the water. They beach these cats to load/unload - some are quite big, 50-60'.Using Scania CR turbo-diesels.There has to be a way to adapt something like this to a monohull. I don't know the HP of the engines in these boats, but if they push a 50' cat at ~ 30 knots, it's quite a bit, I guess 500hp or more.Not bad for belt drive. It's a bit ugly, but the beauty of the system is that you can get to everything that's going to need maintenance very easily, bearings just run under water, no seals on a leg to worry about, no universals.There has to be a way.Hmmmm.
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