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Old 11 May 2003, 17:23   #1
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Country: Cyprus
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Make: novamarine
Length: 7m +
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which engine is ideal on 5.5m RIB?

i have a gemini 5.5m rib with mercury 75hp but the engine is alittle old and i think is time to change it. iam thinking of twin yamaha 70 2strokes , twin 50 honda 4strokes or single yamaha 115 4stroke.

any suggestions or ideas?
hope to hear from you you guys soon
marios
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Old 11 May 2003, 17:29   #2
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Country: UK - England
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Make: Avon Rover 3.4m
Length: 5m +
Engine: Mercury 15hp
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recommend single larger single, optimax preferable, as unless you use it a lot you will not recoup the extra 4 stroke costs....
you can then fit small say 5-10hp auxiliary engine as a get u home...
Keeps servicing costs down and running costs...
Also manoeuvrability....is not gonna be hugely affected by twin engines on a boat that size they are pretty easy to manouevre
Obviously two engines can be more fun turning on the spot etc...but how often do u need to do that???
Alex
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Old 18 May 2003, 10:46   #3
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I have a yamaha f100 on my 5.5 meter rib and it is underpowered when you really need it ie. fully loaded in a big following sea. On a 5.5 m rib go no less then 115 hp
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Old 18 May 2003, 11:54   #4
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Check the maximum engine size on the identification panel on the boat - that'll tell you how much hp you can put into it. You may find at 5.5m, you can only put upto 115hp max on it.

The Gemini website says for the Waverider series that "The 550 can take either a single or twin motor installation with a 115hp being the best option."

-Alex
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Old 18 May 2003, 12:21   #5
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Country: Greece
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Boat name: GATO DI MARE
Make: MAR.CO
Length: 9m +
Engine: Yamaha 200Vmax
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2 vs 4 again??

GEIA KAI XARA MARIE

I use to have a 5 mtr GEMINI with a 75bhp Marine 2stroke and 17" pitch aluminium Quick Silver standard Prop. Very good boat and I am very sorry that I have sold it.
Now back to your question. If you listen to all the prons and cons about 4-stroke engines (and I have done my sums so far) for a 115 Yamaha 4-stroke you will need approximately to run it for 8000 miles in order to achieve a break even point (low consumption vs purchacing costs). Plus the fact that all of them are car engines, complicated mechanisms, with computers on them and VERY EXPENSSIVE repair bills. Also they have not been tested extensively in the sea environment and they are heavier than the 2-stroke equivalent.
On the other hand two stroke outboards are cheaper, lighter, simpler, have been tested extensively at sea and currently they all run (more or less) without any problems.
I do not understand why you want to mount a twin installation. It will make your boat heavier at the back and the behaviour in big seas will change dramatically (so I was told) plus the fact that I do not think you can find left and right screw engines under 100 bhp (correct me if I'm wrong).
In my humble opinion may I suggest that you go for a YAMAHA 2 STROKE rather than the 4-stroke??
Is just a thought and my personal view on the matter. Others of course may argue differently.

KALO KALOKAIRI STHN ELEFTHERH KYPRO!!
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Old 18 May 2003, 13:31   #6
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115 hp two stroke.

I have a Zodiac Pro 550 with a mercury 115 two stroke on the back. It goes like a hot snot ! even with six people on board.
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Old 23 May 2003, 22:41   #7
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Country: USA
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Length: 5.89
Engine: 115 Yamaha 4-stroke
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Hello from th other side of the pond............I have a 5.85 Nautica with a 115 Yamaha 4/stoke. With a load - two people and 6 tanks + gear and cooler w/ 50 gals and s/s prop = 37knots out river torwards jetties to ocean ( Same one as yours by the way) Seas
18 mi out 2-3 & 6ft swells. Ocean speed 26 knots @ 5000 rpm
Fuel consumption 6 us gal/ hr.

It is the size of your prop that makes a big difference -19 x 22
and non-flexing stainless prop that make it go better....
Hasta l'uego muchacho...........happy ribbing
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Old 24 May 2003, 03:33   #8
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engine

sorry about this everyone but didier just got my interest so here goes!!

I lost an engine off the back of my rib at 35 knots as yet it has not been found I know kindof where it is but I didn't notice till I was moored up!! ( don't laugh its a long story!!!)
Anyway you list finding underwater metal as an interest , is it by diving or some other means??

anyone got any ideas I would be grateful, I'm not too sad but as it was only 2 weeks old i would enjoy the challenge of finding it!!

SORRY TO DRAG AWAY FROM THE THREAD.

RE ENGINES , I PUT THE MAX ON MY 6 MTR AND HAVE NEVER REGRETTED IT I OPTED FOR TWO STROKE FOR THE POWER AND WENT FOR THE OPTIMAX FOR ECONOMY. IF THE BUDGET WILL GO TO IT I WOULD ALWAYS RECC THAT YOU GET THE LARGEST UNIT YOU CAN DEPENDING ON THE LIMITS OF BOAT AND THE TYPE OF SEAS YOU WILL USE IT IN, ALL I CAN SAY IS THE EXTRA POWER ON MINE HAS OFTEN BEEN GOOD IN HEAVY SEAS ETC.
135 MERC /MARINERS OPTIs ARE BECOMING AVAILABLE USED SO IT MAY BE WORTH LOOKING BUT IF YOU DO GO OPTIMAX OR ANY OF THE NEWER DIRECT FUEL INJECTIONS DONT BUY USED W/O A SURVEY
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Old 24 May 2003, 04:35   #9
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Country: Greece
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Hi Mike

Sorry to hear for the loss of your aux engine. It can happen to any one. Is just the luck of the draw I recon.
Any way, how to recover it??
First of all you should see how deep it is and if the area it went down is dive...able or not. If yes ask a couple of friends who are divers to have a look around the area.
(HINT: However, if you search for something that you lost in high speeds I was reading that you need to search in a criss-cross patern and in a very wide area. And you should also mark the searched areas on your GPS.)
To assist the divers (if you look in the BSAC DIVE magasine) you can buy these sea metal detectors/sonar things. Now, I have never used one and don't know how much they are but apparently they do the trick.
If is too deep there no solution I don't think unless you employ the expertise of a NITROX or REBREATHER diver/s (the cheaper solution) or the more expenssive a deep sea dive sub. LOLOL just kidding. Good luck!!
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Old 24 May 2003, 04:42   #10
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To all 4-stroke enthusiast please note that is an UNDISPUTABLE FACT that all other things being equal (i.e. props, bhp etc) 4-stroke engines are SLOWER than 2-stroke.
Also if you buy a 4-stroke engine in order to reduce fuel bills you will need on average to make about 8000 miles just to break even .
I recon 2-strokes are tried and tested. Why change??
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