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Old 30 July 2010, 11:45   #1
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Dont want to start full debate

Dont want to start full debate again twin 90s or single 225 , twins giving about 40 knots single 46knots but then will have to look at a aux i really can not make my mind up on this
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Old 30 July 2010, 11:52   #2
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i would think the speed difference would be more than that.
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Old 30 July 2010, 11:56   #3
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You lose about 30% power I think running twins.
I have a single outboard on my RIB but will be fitting twin outboards to the Tremlett.
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Old 30 July 2010, 11:58   #4
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i would think the speed difference would be more than that.

thanks the figures are from ribcraft
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Old 30 July 2010, 12:53   #5
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thanks the figures are from ribcraft
Its not just the speed its the cost of fuel. If you are going with twins then you will also need twin tanks, twin electrical systems to actually have the full benefit.

IMHO a well serviced and looked after single engine and a decent sized aux is a better bet, unless the boat is going to be doing commercial or lots of offshire work where you need the added security.

Where are you going to be using the boat and what sort of use do you plan.
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Old 30 July 2010, 15:06   #6
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Single for me too

Apart from the VERY good points Chris makes, the extra weight,and corresponding handling,AND loss of performance on a MID SIZE RIB [not to mention the considerable extra exspence] coupled with the loss of economy twins represent... would sway me to a GOOD Large Single every time!They are pretty reliable these days!!
Also, and it may be the last thing your thinking about at the moment!! but I think the used market would more often than not, favour a good performing,well balanced, single set up!
Either way I wish you all the best with the new boat!
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Old 30 July 2010, 16:11   #7
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Also, and it may be the last thing your thinking about at the moment!! but I think the used market would more often than not, favour a good performing,well balanced, single set up!
I'm not so sure. I keep an eye on this, and they seem to sell well, some of them very well. Obviously the market is limited, but then so is the product, so much of a muchness. They certainly seem to command a small premium over a similar "single". I wouldn't let that aspect influence a purchase.
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Old 30 July 2010, 16:34   #8
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One aspect of having twins that people tend not to think about is reliability.

Yes, if one breaks down when you're out the other will get you home.

But having twins means you WILL have twice as many breakdowns and obviously you're not going to take the boat out anywhere if they're not both running right. Result= boat spends twice as long sat on the trailer waiting for outboard tech, parts etc.
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Old 30 July 2010, 17:51   #9
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But having twins means you WILL have twice as many breakdowns and obviously you're not going to take the boat out anywhere if they're not both running right. Result= boat spends twice as long sat on the trailer waiting for outboard tech, parts etc.
So what you are saying is that they are better for getting home but sh&t for getting out there in the first place

Never thought about it like that, but good point
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Old 31 July 2010, 02:39   #10
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thanks the figures are from ribcraft
The twin rig has 45hp less than the 225 single but only goes 6 knots slower? I would ask them if this is from actual experience or calculations personally
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Old 31 July 2010, 02:40   #11
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One aspect of having twins that people tend not to think about is reliability.

Yes, if one breaks down when you're out the other will get you home.

But having twins means you WILL have twice as many breakdowns and obviously you're not going to take the boat out anywhere if they're not both running right. Result= boat spends twice as long sat on the trailer waiting for outboard tech, parts etc.
So what's happened to yours then did you have one breakdown on the way back from the Alderney trip?
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Old 31 July 2010, 02:43   #12
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The twin rig has 45hp less than the 225 single but only goes 6 knots slower? I would ask them if this is from actual experience or calculations personally
plus all that extra drag
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Old 31 July 2010, 03:27   #13
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So what's happened to yours then did you have one breakdown on the way back from the Alderney trip?
Yes in Diellete, came back to the boat after lunch and one was cranking and not firing
Wasn't looking forward to 40 nm home on one motor but then she changed her mind and ran fine. Then typical woman changed her mind again with 5 miles to go!

That's todays main job, diagnose a fault that currently doesn't exist
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Old 31 July 2010, 07:29   #14
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Whats the point in having twins
unless you are doing cross channel off shore stuff.
I think in a lot of cases its the fuel to blame and having twins will not help
two lots of engine service charges etc etc, your into desiel / out drive costs.
with out the savings on fuel.
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Old 31 July 2010, 08:52   #15
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I think in a lot of cases its the fuel to blame and having twins will not help
but that is the point of having twin everything twin tanks separate electrics twin batteries etc so you have two completely independent systems
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Old 31 July 2010, 10:22   #16
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The whole fuel thing is overplayed, IMO. Unless you rupture a tank, I can't see the point of two tanks. After all, are you going to fill them from different sources? In the event of an engine failure, suddenly half of your fuel reserve is difficult to access if you have twin tanks. I think one tank and good fuel handling/filtering is sufficient for non-commercial use.

I'm not a fan of bowl filters where you can't see the fuel/water
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Old 31 July 2010, 12:16   #17
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suddenly half of your fuel reserve is difficult to access if you have twin tanks.
Good point usually overlooked on twin rigs. Mine has 2 take offs from each tank with quick release hydraulic fittings. This allows me to use any combination of tank and engine, takes seconds to change. I also often use this to ballast the boat, eg if I'm on a long trip in a following sea I'll connect both motors to the fwd tank to get the bow up a bit.
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Old 31 July 2010, 12:24   #18
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That's todays main job, diagnose a fault that currently doesn't exist
1x crank position sensor required
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Old 31 July 2010, 12:37   #19
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Glad you found the problem. Must have been a tricky one to diagnose.
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Old 31 July 2010, 12:43   #20
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Glad you found the problem. Must have been a tricky one to diagnose.
On the plus side having two engines you can swap parts till you find whats at fault.
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