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Old 08 October 2012, 13:29   #11
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Controversial I know, but I believe they treat the symptoms of a poor set up rather than improve anything in their own right.

I have used them to great effect on a Flatacraft Force 4 that I re-engined with a 55HP Suzuki triple.
The RIB was very fast, but tail heavy, and Chine walked like a Bast**d regardless of trim because too much of the boat was out of the water and it became unstable.

Putting a set of fins on the engine sorted it all out, and it was great fun to drive, but the real problem they treated was my 'stick a big engine on it' attitude and lack of understanding.

Nasher.
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Old 08 October 2012, 13:30   #12
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Country: UK - England
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Boat name: Northern Storm
Make: North Diver?
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Originally Posted by 9D280 View Post
Gramas,

Not sure from your post whether you have them or are thinking about them.

As said, they are Marmite. (other yeast based spreads are available!)

Personally, I've improved the handling, top speed & fuel economy of 2 ribs so far by removing them, but if you are "thinking", have a play with the trim of your engine and weight distribution in the boat before you start drilling the plate that wasn't really designed to be holding the back of the boat up in in the first place.....
not purchased was just researching and getting good advice, hence im posting alot being a newbie haha
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Old 08 October 2012, 14:35   #13
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Country: UK - England
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Engine: 130 I/O Diesel/90Yam
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Can you explain more about the Zodiac Pro ? Was it a 530. How did it work with 90HP. Was it 2 stroke ? Sorry for asking but I am rebuilding one at the moment and have no engine...
Cheers Thomas
The fins were already fitted when the boat was purchased second hand, it is a 2stroke engine and is used mainly for PBII courses as it has seating and we don't end up with people sitting on the tubes, it has a top speed of around 25/28 knts.
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Old 08 October 2012, 14:46   #14
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I had them on my Valiant 450 with a Yam 50 on it, it's true, they kept the bow down and got me on the plane at lower speeds but only because the boat was poorly set up and had far too much weight at the back.

Once your on the plane, which you will be most of the time, unless you're on a river or a harbour with a speed limit, they do nothing to improve things, only cause a huge amount of drag and reduce your top speed whilst halving your MPG.

If they really were the wonder product for outboards then we'd start to see manufacturers making anti-ventilation plates bigger.
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Old 08 October 2012, 17:36   #15
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Surely they are only the simplified equivalent of trim tabs (common on all types of larger powerboats - are these therefore by definition badly setup/balanced to need them??) - yes they can help alleviate badly balanced or set-up boats but they can also help fine tune perfectly well set up boats. There are so many variables that can affect the balance of smallish outboard powered boats..... passenger load, fuel load, sea state, speed, power, engine weight & hull design etc etc... Engine manufacturers could not hope to provide the perfect configuration (cav plate size) for every eventuality all of the time.

It's horses for courses - may suit some set ups but not others. Either way they are are a cheap & easy way of experimenting (especially if you use the 'no-drill' ones).
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Old 09 October 2012, 02:18   #16
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Originally Posted by thomas View Post
I had them on my Valiant 450 with a Yam 50 on it, it's true, they kept the bow down and got me on the plane at lower speeds but only because the boat was poorly set up and had far too much weight at the back.

Once your on the plane, which you will be most of the time, unless you're on a river or a harbour with a speed limit, they do nothing to improve things, only cause a huge amount of drag and reduce your top speed whilst halving your MPG.

If they really were the wonder product for outboards then we'd start to see manufacturers making anti-ventilation plates bigger.
sorry I 100% disagree. as stated by others on here they have there place i.e. a back end heavy boat where it struggles to get up quickly or where they would like a lower cruising speed or where the engine power is borderline for getting on the plane. so a twin engine set up on a rib, a 50hp on shetland 570 etc would be classic examples of when to use them.

Dave
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Old 09 October 2012, 09:12   #17
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I was going on what I experienced first hand and what I was told by a RIB builder who said I'd be much better off putting ballast up front - I guess it like what was said earlier, you either love them or hate them.
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Old 09 October 2012, 09:27   #18
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I have had them on 3 boats SR4, 5.75 Viper & a 6.5m hard boat, I found the them very stern heavy with too many people wanting to sit at the back the 6.5m hada 220hp inboard so plenty of power but you get 10 people all sitting too far back & it would really struggle to get up and go but ones fitted the fins did a great job making low spead estuary work muck better being able to trim in & putting the bow down!
I bought my SR4 with them fitted & it has a 50hp 2st so again not under powered & again I can trim in & keep the bow well down, I did try I with out the other day as it was just me going out & I gained about2 knots & it chime walked terribly without them so I put them straight back on!

The one Rib I do not need them on is my Ribeye!
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