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Old 17 August 2009, 03:31   #61
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I am tilting more towards petrol outboards at the moment. I won't go into why because that would take uo another thread and tons of space and discussion. In any case, the meritds of diesels and petrol have been discussed many times, albeit there's always something new around the corner.
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Old 17 August 2009, 03:34   #62
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I am tilting more towards petrol outboards at the moment. I won't go into why because that would take uo another thread and tons of space and discussion. In any case, the meritds of diesels and petrol have been discussed many times, albeit there's always something new around the corner.
So to sumarise, a cabin RIB of 7.5 or more powered by a single outboard, probably a 225HP?
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Old 17 August 2009, 03:58   #63
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Nice name yours = makes me think of Malted Milk (Clapton).

To recap:
7.5/8.0 rib, canopy (not cabin), 250/300 HP outboard (preferably not electronic, but this is not a big issue). Aux. engine (which is what we are discussing here).
Comfort or suspension seats. Probably not more than 4 in the cabin area.
Usual electronic aids: depth sound, VHF, GPS, radar would be useful (have been out in fog around Guernsey before...), safety features, etc.
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Old 17 August 2009, 04:02   #64
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Nice name yours = makes me think of Malted Milk (Clapton).
It seems some beggar on eBay agrees, they have signed up using "Malthouse Motors and Marine". Why I outa.

Sorry, back on thread.... I would rate a RADAR as more important than an auxiliary motor, as you know 30kn fog is scary stuff! (And far more common than engine failure.)
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Old 17 August 2009, 04:06   #65
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Malthouse,

I agree totally. Radar is damned useful in those conditions.

Re. the second engine, it's not such a problem from Gsy to Sark, but rather the Dielette - Gsy/Sark route which concerns me if I have engine failure.
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Old 17 August 2009, 06:18   #66
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Cyp, apologies for jumping on yours rather than any other posts, but it was a useful list to make a comparison with.

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Extra weight.
Tohatsu 2-Strokes. 60Hp - 115 Kg. 30Hp - 52Kg. 2x 52Kg = 104Kg, and that's before you add 20 odd Kg of aux......... That will alternate between bifg single & twins al lthe way up the horsepower range of any manufacturer.

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loss of HP of around 25%,
errrr (Hp/2)*2 = Hp.

I assume you mean the effective horsepoewer drop, which is essentially down to HP lost by pushing more leg through the water, but I covered that already. (see my post above)

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double servicing costs,
Can't argue with that!

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extra drag,
See previous post - but it's all down to your speed & the frontal area of your engine leg. If you cruise at 20 odd knots it'll make a lot less divfference to your fuel consumption than if you cruise at 40. My Merc 60 has the same sized leg & prop as my Suz 25..... Two of them would be a lot les drag than 2 modern 60Hps that will share their leg with most engines up to 90Hp & are therfore Overkill for the smaller HPs

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initial cost
Googled "Yamaha price list" - I'll go Big Hp 4-stroke this time to show it's not just a "small engine" phenomenon:
F100 - 8699; F200 15,799; F9.9 (aux) 2699

2xF100 = 17398
F200 + F9.9 = 18,948



Mollers points out his performance on 1 engine is naff. Of course it is - you're only running on one! We're talking get out of jail here - not the optimal perofrmance between two boats one with half the hosepower. 20 knots on the "Aux"? I'm lucky if I can pull 2 Knots on mine! On a similar theme I have used a 5.4 Searider / Twin 30s that ran happily if sluggish 5 up with one engine dead.


What I'm trying to point out is that the usual "knee jerk" reactions to twin engines are not always true.

Rupert, if you have time, take your time, do the research, base your decision on data. You'd be surprised what you might find.........
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Old 17 August 2009, 07:00   #67
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Thx. 9D.

(d wrote: "Rupert, if you have time, take your time, do the research, base your decision on data. You'd be surprised what you might find........."

I'm doing my best. I have the time, but I am not sure that I have the brains!"
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Old 17 August 2009, 07:26   #68
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My Redbay will plane at about 20kts on one motor at WOT (with the dead stick in the water). It IS overpropped for single engine use (19 pitch) and has to be coaxed out of the water and she isn't making her normal revs either. I wouldn't fancy trying to maintain plane in short lumpy water.



Surely that blows away one of the main planks of the twin argument?

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Mollers points out his performance on 1 engine is naff. Of course it is - you're only running on one!
I think his problem might be that Redbay of his...
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Old 17 August 2009, 07:32   #69
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Mollers points out his performance on 1 engine is naff. Of course it is - you're only running on one! We're talking get out of jail here - not the optimal perofrmance between two boats one with half the hosepower. 20 knots on the "Aux"? I'm lucky if I can pull 2 Knots on mine!

Of Course!! Try buying a decent auxillary not a w**ked out Moulinex.
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Old 17 August 2009, 08:26   #70
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Of Course!! Try buying a decent auxillary not a w**ked out Moulinex.
Can't argue with that!

Still doesn't alter the fact that with my theoretical max displacement hull speed even if I bought a nice shiny new fuel injected 6 horse 4 - stroke I'd still be able to walk faster.........

Difference is your one engine can get you on the plane.
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