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Old 11 September 2005, 04:48   #1
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cobra 7.5, opti 200 would engine or doel fins help in any way with planing or perf

this might be a silly question but wanted to get some input

i am buying a 7.5 cobra with merc opti 200, i recently put doelfins on my shetland 4 + 2 with honda F90 and what a difference, wish i had done it years ago as it planes easier, earlier and lower speed. No i know the cobra is a different kettle of fish but wondered if anyone has any experience of with or without fins on a boat/engine combination like this

i have been looking at ribs on the chichester harbour area for the last year now and notice some do have them some dont, so any experience out there would be good.

cheers

chris
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Old 11 September 2005, 06:40   #2
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Forget it! That Shetland had a 30+ year old hull design and was heavy for it's length. You also had the heaviest engine possible on the back.If correctly propped the Cobra will hop onto the plane instantly. You'll be well impressed. Those Doelphin things are for boats that are under-powered and need help. 200 ponies behind a 7.5m rib is spot on.
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Old 11 September 2005, 07:50   #3
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Quote:
Originally Posted by Mollulnan
Forget it!. 200 ponies behind a 7.5m rib is spot on.
i am hoping most people will give this view but i have a nagging suspicion that lifting the bum of a boat to run thru the water has to be good in slow speed activities like making the 500 mile (seems like it) journey from ichenor to the entrance of chichester harbour.

if there is no need for them but no harm in fitting them and they would help with slow speed 8 knt cruising i might give it a try.

i was so impressed with the difference they made to the over weight, over heavy engined, underpowered sheltie i might fit them to my car as well! just kidding. any advise and opinions are good in my book

just ordered a set for my father for his new boat as it is slower on the plane than is other one......nothing exciting except a fishing boat!

i have a quicksilver 3.4 and even considered a pair for that one the 15 yam but, when they are fitted they would take up too much room in the back of the disco as the boat and engine and all bits fit just perfectly in the back of a landy TD5

cheers

chris
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Old 11 September 2005, 08:39   #4
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Personally, I've not seen fins fitted to anything bigger than a 75hp. But, as you seem such a fan, stick em on. I'm sure someone on here will tell you that there is some highly technical reason not to ie. drag, trim or cornering characteristics etc. You're not an agent for Doelfin and Shetland boats are you?! One other thing, why do you cruise at 8knts?
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Old 11 September 2005, 09:40   #5
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Quote:
Originally Posted by Mollulnan
Personally, I've not seen fins fitted to anything bigger than a 75hp. But, as you seem such a fan, stick em on. I'm sure someone on here will tell you that there is some highly technical reason not to ie. drag, trim or cornering characteristics etc. You're not an agent for Doelfin and Shetland boats are you?! One other thing, why do you cruise at 8knts?
chris here with new name as per another thread
is the speed limit in the harbour i am afraid and it is quite a long drag. no not a sales man for doelfin or shetland except it has been a fab boat for the river and the family as i can still trailer it and get loads in and we have a great time.

will see what others say and if most say dont bother then i will take the collective advice.

mrs at the beauty show in earls court today so stuck at home with little ones when i could be on the sea
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Old 11 September 2005, 10:13   #6
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Quote:
Originally Posted by Hugh Jardon
chris here with new name as per another thread
is the speed limit in the harbour i am afraid and it is quite a long drag. no not a sales man for doelfin or shetland except it has been a fab boat for the river and the family as i can still trailer it and get loads in and we have a great time.

will see what others say and if most say dont bother then i will take the collective advice.

mrs at the beauty show in earls court today so stuck at home with little ones when i could be on the sea
So is she visiting the beauty show or featuring in it? If the latter, when are you next in Meva? We ought to pair up for a bit of cruisin'
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Old 11 September 2005, 13:03   #7
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haha love it

she is attending the show as she has her own beauty salon, but i personally think she is good enough to be in the show!!
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Old 11 September 2005, 14:52   #8
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Nah!

Haow many spray rails does the hull have!!
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Old 11 September 2005, 14:58   #9
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I had a 7.5 Cobra with a 200 Opti and it was a great marriage. No cavitation, quick out of the hole. Couldn't fault it.
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Old 11 September 2005, 15:44   #10
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Sold my Cobra in Aug we had a 225 yamaha four stroke and it trimed up a treat went out in some big seas very stable. i would not see the point of the fins.
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