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Old 30 May 2015, 08:28   #11
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Twins v Aux.

I know before I post this, that it's going to be dissed, but that never stopped me before...

There's twice as much to go wrong with twins. I missed many days boating when something was "off" on one of a pair BEFORE departing. That said, each of the engines failed at sea too, one in port in Scotland and one near land in Ireland (EMM fryups). I wouldn't have chanced a return to Ireland on the single (small) twin alone and an Aux would have been perfect for the local failure.

Here's the rub - it's all in yer head. When one of your twins dies, your emergency has occurred and you've played your last hand - your happy time is over anyway. You can go home at half speed or displacement speed - but you're going home either way. A 5kt Aux will get most folks in somewhere safe in a reasonable timeframe - probably their homeport on most days. Fair enough, if you're cruising the Western Isles, twins have an appeal.

If my (single) fails I have no aux. But I have still have a hand to play - I can row the SIB a bit, I might catch a handy current or breeze and make a decent landing. I have a great anchor and lots of warp. I have multiple means of calling for help. I will quite happily take a tow (people LOVE towing in broken down boats). I will more than happily let the RNLI boost their PR stats - their stations are hungry for "lives saved"
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Old 30 May 2015, 08:59   #12
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Single/twins?

Depends on what you're doing with the RIB. Local inshore Port hopping, single every time. Offshore, fishing, safety boat then twins have an obvious advantage.

One thing you ought to be aware of is that with a twin set-up you won't have twice the performance of a single of the same hp. With a twin 60hp set-up you'll have the performance of more like a 100hp single outboard because of the extra drag and prop slip.
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Old 30 May 2015, 09:09   #13
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My dive club used to have an old Humber RH600 with twin 60 Yams. Best we ever saw was 34 knots, and no chance of it planing on one engine, second engine up or down.
My money would go on a decent main and suitable aux, but it ain't my money
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Old 30 May 2015, 09:36   #14
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Quote:
Originally Posted by willk View Post
Twins v Aux.



I know before I post this, that it's going to be dissed, but that never stopped me before...



There's twice as much to go wrong with twins. I missed many days boating when something was "off" on one of a pair BEFORE departing. That said, each of the engines failed at sea too, one in port in Scotland and one near land in Ireland (EMM fryups). I wouldn't have chanced a return to Ireland on the single (small) twin alone and an Aux would have been perfect for the local failure.



Here's the rub - it's all in yer head. When one of your twins dies, your emergency has occurred and you've played your last hand - your happy time is over anyway. You can go home at half speed or displacement speed - but you're going home either way. A 5kt Aux will get most folks in somewhere safe in a reasonable timeframe - probably their homeport on most days. Fair enough, if you're cruising the Western Isles, twins have an appeal.



If my (single) fails I have no aux. But I have still have a hand to play - I can row the SIB a bit, I might catch a handy current or breeze and make a decent landing. I have a great anchor and lots of warp. I have multiple means of calling for help. I will quite happily take a tow (people LOVE towing in broken down boats). I will more than happily let the RNLI boost their PR stats - their stations are hungry for "lives saved"

Pretty much my thoughts on the subject in a nutshell, a coconut shell perhaps. 😉
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Old 30 May 2015, 10:08   #15
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Pretty much my thoughts on the subject in a nutshell, a coconut shell perhaps. 😉
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Old 30 May 2015, 12:16   #16
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Destroyer hull is smooth with one fat chine, ocean pro has multi chimes. It will hop up on the plane more quickly, push more spray away from the boat and sit higher out of the water as a result, basic physics. That said, to a professional (not me) it is a bit more twitchy as there is less in the water.

We have an OP and id agree re fit out. Buy a bare hull/tubes and unfitted console, then get a decent specialist to fit the rest. We bought an ex demo from a specialist. It's been mint.

Agree with all, single not twin. Also for a 6.3 you need a bigger block than a 1.5L (90-115hp typically) the 130-175 bracket tend to be a 2.0-2.5L engine. We use a 175ho 2S 2.5L V6 optimal. They're loud, but great fun. I'd be sorely tempted to get a 6.3OP with a 140 or 175 Suzuki 4S

Careful re beam too. I've seen a 6.0 Destroyer next to a 6.3OP out of the water. The OP typically has a bigger beam, and with just 0.3m more length it was just HUGE in comparison.

A narrow beam 6.0m may be Ok with a 115hp.
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Old 30 May 2015, 12:33   #17
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Lots of talk about separate fuel systems ( yet I bet both individual tanks would be filled from the same potentially contaminated fuel supply...............
Yes but the source fuel is not necessarily the only issue (contamination growing in a tank, a failed pickup, a split tank, a sea water leak into a tank, a blocked filter, a disintegrating fuel line are all possible and so it all needs to be separate), and is not necessarily homogeneously contaminated anyway. But you are quite right, even with dual everything you might be up the creek anyway.
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Old 30 May 2015, 19:23   #18
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Thanks for all the comments.I didn't appreciate two 60's would only be the same as a 100 and not 115/120 horse performance. I get the impression it would be difficult to get one sixty ( with normal pitch prop rather than fine) to get it up on the plane. Its looking more like a single 120 and an auxillary to get us home. i's back to the pub! This has shown me how important it is to actually get out on a rib with the configuration that we're thinking of. Nik
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Old 01 June 2015, 06:46   #19
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Nothing wrong with twins on a 650 rib. Here you have twin 90 HP 2 stroke cos of the weight factor. 2 x F60 4 stoke would for sure be underpowered. We had fitted them as well but quickly replaced. The best single for performance is without doubt the Mercury 150 EFI. 630 or 650 no big difference

a quick quiz but no prizes: Can anyone recognize the mountains in the background
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Old 01 June 2015, 11:09   #20
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Can anyone recognize the mountains in the background
Brokeback..?
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