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Old 04 November 2002, 09:14   #21
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Tiger

I agree with your comments.
I can also inform the Forum that I will be testing on the new RIB in the next few months 4 and 2 stroke Yamahas and props, until I set it up for the races.
Will post any results on fuel etc.
Will let you know
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Old 04 November 2002, 12:35   #22
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interesting so far.

I have used the larger Yamahas, optimax, and ficht 2 strokes all of which are comparable on fuel consumption 2 a large 4 stroke., i.e. (Honda) from three quarters power to flat out ( I have limited experience with Suzuki) I will say that the price of oil is a big difference between 2 stroke and 4 stroke especially as the new fuel efficient 2 strokes take specific oil depending on the manufacturer.

I prefer 4 strokes for teaching and safety boating, as they are far better a tick over though any one who likes power would go for a 2 stroke they are lighter better at providing power and generally respond better (which is good between waves). The new 2 strokes are so much better than those from a few years ago. At half revs the new 2 strokes are between 10 and 30% less efficient than an equivalent 4 stroke and at tick over are much less. Lets face it who drives their rib at tick over for long you may as well get a diesel launch.
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Old 04 November 2002, 12:41   #23
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Hmmmmmmm. 2s v 4s?

Why aren't there any 2s cars?

Keith (ponder that then) Hart
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Old 04 November 2002, 12:46   #24
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2 stroke v 4 stroke

To solve this problem every one should buy a diesel engine. Much better and the saving is huge on fuel. It does take a few years to get your money back from the cost of the engine but its well worth it and a diesel rib holds its value much better.

Julian
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Old 04 November 2002, 13:03   #25
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Keith,

The Trabant P50 and P60 Cars had a 500cc 2stroke engine in it

I don't normally know these things, but just happened to see it whilst watching the repeats of Coltrane's Planes and Automobiles the other night!!

-Alex
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Old 04 November 2002, 13:03   #26
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Diesel ribs v 2s & 4s

Arrrh, quite so,
But in the case of a safety boat for sailing, the RIB needs to be very manoverable as well as fuel effeicient, so most tend to be around 5m with a 40-50hp. You cant put an inboard in a 5m and you don't want a diesel outboard!

Thus for small - medium Ribs (4.0 - 5.5m) the compact 4s 40-60hp is very good.

I would go so far as to say the Mariner 50hp 4s on a Tornado 4.8 is probably the best combination you can get for a safety boat, agile, reasonably fast, great in big weather (F7+) at sea, good acceleration, lots of grunt. Much better than the Honda 40hp 4s it replaced!

tiger
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Old 04 November 2002, 14:36   #27
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2 stroke v's 4 cost of repair!

ever caught your prop on a rock ,me thinks most of us have at one point in our ribbing life. Thats o.k. on 2 strokes but on four strokes you can lose all your valve gear in the engine this is because of fly wheel momenton. I know of two engine rebuilds because of this. BIG BILLS for small accidents
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Old 04 November 2002, 15:22   #28
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Quote:
Originally posted by Keith Hart
Hmmmmmmm... Why aren't there any 2s cars?
There were some terrific 2-stroke cars, like the Saab 94/95, but anti-pollution regulations eventually finished them all off, like it will to marine 2-stroke engines after 2006.

The orbital technology (aka Optimax) used by Mercury/Mariner was (I believe) developed for car engines...
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Old 04 November 2002, 18:55   #29
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The HPDI engines (leastways according to my Yam dealer) do not need the "fancy" stroke oils that Mercs and Ficht do. They use standard TCW3. I agree the oil is a significant cost and the lack of it a benefit for 4 strokes. Personally though I wouldn't want the additional weight penalty - taking the figures kindly supplied by Manos the Yam 4 stroke equivalent of my HPDI is another 70 kgs!
The new 2 strokes are in a different league to old carb engines.

Of course as Julian says we can all go for diesel, providing of course you want half your boat taken up by your engine, can afford 5k a pop for a new Bravo 3 leg every 150 hrs, have beefed up the engine mounts to cope with the weight, don't mind lifting the engine out to do any major servicing and are sanguine about the inevitable imposition of full duty on marine diesel in the next few years !

Optimax came from the Orbital engine corp of Australia. Their tech has never made it into cars. Probably down to the same conspiracy that says that boffins have developed an engine that runs on water but the oil majors are supressing it
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Old 05 November 2002, 14:19   #30
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Quote:
Originally posted by GED
Ever caught your prop on a rock ,me thinks most of us have at one point in our ribbing life. Thats o.k. on 2 strokes but on four strokes you can lose all your valve gear in the engine this is because of fly wheel momenton
Is this really true?

I can't seem to imagine how this would happen. The flywheel is connected directly to the prop shaft, so if the propellor comes to a complete stop then so will the flywheel. In essence, the momentum of the flywheel will just make the damage to the prop worse. The valves should just follow happily, unless the timing belt pops of or somthing.

After all if you stall a car you don't damage the valves
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