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Old 22 September 2005, 17:39   #1
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cobra 8.5 with a 225 opti

ok looking to change to a cobra 8.5 with a 225 opti, any of you experts out there know what sort of top end i can expect and what litres or galls per hours at the various revs and what mph or knots at the revs i can expect, ie 1000, 1500, 2000, 2500 etc

the thing is massive but the mrs likes it, will make sure i get nice white ropes for it

chris
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Old 22 September 2005, 17:45   #2
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We can get .7 nm per litre on 7.4 with 440 ltr fuel tank with 225 opti, full chat 87 litres per hour
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Old 22 September 2005, 17:56   #3
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Hang on a minute! Did you actually buy the 7m with the 200 Opti? As for the other, Use it then fuel it. Why worry? As the Rolls Royce salesman always says " Sir, if you need to consider such things, should you be looking at a Rolls Royce?" Put 100 in mine after two days "pottering".
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Old 22 September 2005, 18:07   #4
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Quote:
Originally Posted by Mollulnan
Hang on a minute! Did you actually buy the 7m with the 200 Opti? As for the other, Use it then fuel it. Why worry? As the Rolls Royce salesman always says " Sir, if you need to consider such things, should you be looking at a Rolls Royce?" Put 100 in mine after two days "pottering".
unfortunatley agreed the sale then.....found out it was 4 years older than he had advertised it as, so decided not to go for that one, making a decision on another tomorrow, will advise.

just a panic pants here as i will use it quite a bit and wondering how much fuel i will use. and what is a reasonable cruising speed for fair fuel usage,
also
tried to update the profile to show buying a cobra but it does not have enough space for all that

but my heart is set on one.....unless someone can talk me into buying something similar, cheaper, nicer, faster and more economical with same sort of layout.
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Old 22 September 2005, 18:08   #5
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Hi Chris. As you know I've got an 8.5 Cobra Nautique with a 225 Opti, so maybe my figures will be of interest. I have a 21p Laser II. Clean, 2 up with 125 litres and flat seas - I get 42 knots @ 5100. If I pulled 5750 I would get over 50 knots.

As for consumption, loaded with 9 persons I get, on average a consumption of 2 litres per mile. Today, I blatted over to Yarmouth for lunch. WOT on the way over and 4K on the way back. I used approx 1.66 litres per mile 2 up with 125 litres on-board. If you are fairly conservative and keep revs @ 4K with a light load, I expect you will get 1.5 litres per mile average. Speed @ 4K is around 30 ish knots. Cobra 8.5 is not a particularly light build which is good, 'cos they're strong.

Hope this helps
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Old 22 September 2005, 18:13   #6
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Quote:
Originally Posted by hard1
Hi Chris. As you know I've got an 8.5 Cobra Nautique with a 225 Opti, so maybe my figures will be of interest. I have a 21p Laser II. Clean, 2 up with 125 litres and flat seas - I get 42 knots @ 5100. If I pulled 5750 I would get over 50 knots.

As for consumption, loaded with 9 persons I get, on average a consumption of 2 litres per mile. Today, I blatted over to Yarmouth for lunch. WOT on the way over and 4K on the way back. I used approx 1.8 litres per mile 2 up with 125 litres on-board. If you are fairly conservative and keep revs @ 4K with a light load, I expect you will get 1.75 litres per mile average. Cobra 8.5 is not a particularly light build which is good, 'cos they're strong.

Hope this helps
i was hoping you would see my post, cheers for this.....fecking thirsty and slow in my book, what am i getting myself into here, i dont know, but, you only live once.................
what speed is 2k, 3, 4, and 5, or is it all relative to the 42 at 5100?
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Old 22 September 2005, 18:16   #7
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Quote:
Originally Posted by hard1
I get 42 knots @ 5100. If I pulled 5750 I would get over 50 knots.
Less prop slip at higher revs?
Quote:
Originally Posted by Chris Hartley
slow
What sort of speed are you looking for? Speed costs...
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Old 22 September 2005, 18:19   #8
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Hell! a year out on discription is not uncommon, but four! The guy sounds like a robber. What year is the Ex- SAS 8.5m Cobra? Has the 30mm machine gun been removed? If the boat suits your needs and the missus likes it your half way there. I don't think that you'll hear too many neg comments on here about either the hull or the engine. Do your homework this time eh!
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Old 22 September 2005, 18:24   #9
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Quote:
Originally Posted by Mollulnan
Hell! a year out on discription is not uncommon, but four! The guy sounds like a robber. What year is the Ex- SAS 8.5m Cobra? Has the 30mm machine gun been removed? If the boat suits your needs and the missus likes it your half way there. I don't think that you'll hear too many neg comments on here about either the hull or the engine. Do your homework this time eh!
i did my homework on the thing and checked up on serial numbers with those nice folks at picton, very helpful, trouble is the 7.5 boat was a nice boat with a cracking engine but was not prepared topay the price for such an old hull.

actually it still has the 30 mm on the front and one on the rear and i wondered if you fancied coming out some time for some target practice....er....i mean fun?
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Old 22 September 2005, 18:29   #10
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Sorry 4k = 4,000 rpm. As you said, the 8.5 is a big boat and to be honest, 225 is just about the smallest you'd want to put on it. A 7.5 metre with a 200 is probably better pro rata. Any new 8.5 worth it's salt would have a 250, 275 or even 300 on it, but that's because they're 4 strokes. 42 knots slow? This is a 2 ton leisure RIB not a race boat. Believe me, in the average Solent chop, it's mostly quite enough.

As for "feckin' thirsty" my last 2 stroke was a 200 Suzuki that showed 120 litres per hour consumption at 5K rpm, 45 mph.

Any 2 stroke which produces 1.5 ish litres per mile is in some 4 stroke territory. If you want much better from a high horsepower combo, then consider a diesel inboard. Even if the Govt slash the concession on red diesel, they are generally more economical on fuel. But they come at a premium, say 5-8K on the average equivalent length boat? Let me see, even at 1 per litre for gas that's up to 8,000 litres of gas which equates (even at 2 litres per mile) 4,000 miles of RIBing before a diesel makes more economic sense although the resale will always be better. You could even buy a new 250 Opti for around 8k with a couple of years warranty on it, as against 14K for the average 4 stroke and 18k for a decent diesel. You pays yer money and takes yer choice!

As for speeds at the other rpms, it is not at all relative to my 5100 rpm example. I'm on a charter tomorrow with a full load so that won't be exactly relevant either. The thing really doesn't get going until 4k rpm anyway.
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