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Author Topic: 2stroke or 4stroke  (Read 6461 times)
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claudevella
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« on: July 28, 2008, 14:50:07 CET »

I go trolling and have a 4.3lt inboard 190hp 4 stroke and a 8hp outboard aux. 2 stroke. I am confused which would be the most fuel efficient whilst trolling the big engine or the 2 stroke engine?
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fishfinder
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Kaptan Leisure with Suzuki DF115 4 stroke


« Reply #1 on: July 28, 2008, 15:07:07 CET »

It depends how big is your boat. when you use the out board what speed can you reach with 1/2-2/3 gas?
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Kaptan Leisure with Suzuki DF115 4 stroke
blueskip
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On the plane!


« Reply #2 on: July 28, 2008, 16:45:02 CET »

If you can achieve 3Kn SOG with a pair of oars, then use them, 3Kn SOG is about all you really need I reckon, unless you are fishing a string of teasers for marlin or billfish, but having never done it, only seen it Cool
I dont know how big your boat is, but if your 8HP is a true "auxillary", it should have the power to push you along fast enough to troll, at a fraction of the cost of the other engines.
blueskip
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Blueskip
claudevella
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« Reply #3 on: July 28, 2008, 16:48:56 CET »

its a 21ft boat goes to some 4knots at 3/4 throttle
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skip
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« Reply #4 on: July 28, 2008, 18:25:30 CET »

You really need to check the rpm's you are hitting on the aux with your current prop. It could be that the prop is too aggressive for the weight of the boat and the engine is bogging down. This is what's happening to me, whether I'm at 2/3 throttle of full there's hardly any change. Basically the prop is preventing my engine from getting to its ideal WOT wide open throttle range, so I need to decrease the pitch to compenstate and should push me faster as well.
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claudevella
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« Reply #5 on: July 28, 2008, 20:02:04 CET »

yes thats true. The motors come with a standard prop which is a compromise btw a good push and top speed for a smaller boat. hence on a bigger boat you get a lot of slippage. in fact the water is very bubbly around the prop. So a smaller pitch should do the job.   Unfortunately the manual tells you to consult the dealer (i guess the japs do not know how friendly and at times dumb maltese dealers are!) with regards to getting a suitable prop without ruining the gear case. I am trying to get a second hand one over from ebay... will see
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skip
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« Reply #6 on: July 29, 2008, 04:47:05 CET »

What prop do you have on at the moment? Can you read off the markings?
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claudevella
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« Reply #7 on: July 29, 2008, 16:28:56 CET »

will get u the markings during the weekend....
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claudevella
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« Reply #8 on: July 30, 2008, 12:42:19 CET »

Prop markings 9x7-C or (9x7-G - not clear).
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skip
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« Reply #9 on: July 30, 2008, 12:56:21 CET »

Claude, first marking is the diameter in inches and the second is the pitch. You might want to try a 6P if you aren't noticing much difference between 2/3 and full throttle. Listen to see how much the engine pitch changes and the speed as well. If both changes are minimal then chances are the engine is not revving up and then a lower pitch prop will definately help.
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claudevella
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« Reply #10 on: July 30, 2008, 18:03:19 CET »

you know where i could get a good price one... maybe ebay. if you are interested we can share postage
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skip
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« Reply #11 on: July 30, 2008, 20:12:56 CET »

I need to get one for my 9.8hp as have too much pitch on that as well. Was looking at www.steeldevelopments.com

See if they have a prop for you and let me know, would be a good idea re: postage
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skip
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« Reply #12 on: August 01, 2008, 17:02:26 CET »

Btw what engine do you have that prop on at the moment. Basically you're either over-pitched or under-pitched.

Prop I have on my Tohatsu 9.8hp 4 stroke is a 8.9 x 8.3P, whereas for heavier boats they recommend an 8.9 x 7 or 8.5 x 6.5

Any ideas how many splines you have on your prop? Could be that you need more pitch maybe in which case you could try my prop and maybe I could try yours as I definately need less pitch.
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claudevella
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« Reply #13 on: August 04, 2008, 15:53:35 CET »

8hp 2 stroke engine.....yamaha enduro...prop...9x7C or 9x7G (not very clear) ...  what do you think?
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skip
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« Reply #14 on: August 04, 2008, 16:03:08 CET »

I would be inclined to say you need a 8.7 x 5P 4 bladed high thrust prop but it seems that at least Solas dont make a 8 spline prop that you need for your Yamaha.
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