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Old 03 April 2019, 04:46   #1
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Country: Australia
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Gemini 550 info with twin engines

Due to my zodiac 550 pro not being in comercial survey, I'm looking into buying a used ex maritime 550 Gemini, for comercial work.

The Gemini has twin Yamaha f70's, an engine I've already owned a couple of and feel extremely confident in. Testing a boat normally means doing so when the owner allows, which aren't normally the kind of conditions I would like to test a boat in. Also buying from maritime it's more a case of view and buy ( so no testing ). I may have to buy at auction, but currently trying to work around that.

Not sure on the fuel tank size yet but range is always priority for me, so keeping the engines between 4200-4500 should give best results. I'm fully aware twin engines create more drag and increase weight and also don't handle offshore as well as big singles, so I'm not expecting the same quick response of my single zodiac. Carrying 4-5 20lt extra fuel cans as well as the underfloor fuel will certainly make it heavy on my remote trips but the second engine will give a little xtra piece of mind.

I do drive a 7.5 Gemini with twin f150's which I wouldn't assume to have any comparisons at all, but the big Gemini is extremely wet, wondered is the smaller ones are the same.

So any info on likes or dislikes of these in twin config would be much appreciated, as well as general handling etc.

Cheers Jon
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Old 03 April 2019, 05:08   #2
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Country: New Zealand
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Hi Jon
I can't really comment. I have single engine and only go out on nice days... Plus due to work and holidays away have only been out once this summer!

Looking at some of the South African fishing sites they all seem to have twin engines. May be worth looking to see what people say?
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Old 03 April 2019, 09:38   #3
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Quote:
Originally Posted by RichardinNZ View Post
Hi Jon
I can't really comment. I have single engine and only go out on nice days... Plus due to work and holidays away have only been out once this summer!

Looking at some of the South African fishing sites they all seem to have twin engines. May be worth looking to see what people say?
Thanks for that, I did have a look but only found 7m+ ribs. I will have another search.
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Old 03 April 2019, 17:31   #4
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I have just converted my Revenger from single 135 to twin 90s. The benefits of twin engines depend on how they are rigged. I set mine up with independent fuel supplies, independent electrical power, and independent wiring. The only link between the two is the steering. This makes the probability of both failing very low - which is very reassuring. If the engines share fuel and electrics most of this benefit is lost, and the only gain is against mechanical failure. The twin engines altered the balance of the boat so I compensated by moving the fuel tanks forward. I am pleased with the outcome.
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Old 04 April 2019, 19:11   #5
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Originally Posted by gareth9702 View Post
I have just converted my Revenger from single 135 to twin 90s. The benefits of twin engines depend on how they are rigged. I set mine up with independent fuel supplies, independent electrical power, and independent wiring. The only link between the two is the steering. This makes the probability of both failing very low - which is very reassuring. If the engines share fuel and electrics most of this benefit is lost, and the only gain is against mechanical failure. The twin engines altered the balance of the boat so I compensated by moving the fuel tanks forward. I am pleased with the outcome.
Thanks for that. When you mention moving the tanks, are you talking about underfloor storage or above floor. If above haven't you lost valuable storage space, or if bellow did you have to re-fibreglass.

I must admit I drive several twin engine boats comercialy but always prefer getting back onto my own single. I'm sure given a couple of months of owning a twin setup I would feel far happier with one. The issues I have in the bigger twin rigs is keeping the rpm equal and trim settings ( in rough conditions ). I find I take my eyes off the sea tweaking trim and rpm trying to equal both engines and then get caught by a 2m wave soaking the passengers ( divers so it doesn't really matter!!).

The idea of everything seperate certainly makes sense, I plan on carrying a smaller pitch prop to swap to which ever engine is running in case of a breakdown, to still enable planing even with heavy loads. Ive had steering failure in both twin setup and single, where in both cases a second crew member have meant getting home without assistance. With the single it was a simple case of one person sitting close to the engine manually turning it while the other worked the throttle. In the case of twin engines, we gaffer taped both so that manually turning one forced the second to turn the same ( this was harder work ). I also use a prop lock rather than the traditional nut and split pin setup, this allows for quick easy prop changes even at sea ( I do carry a spare nut and pin in case).
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