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Old 07 May 2013, 04:30   #1
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Deeper V hulls more likely to 'hook-up' & flip you out?

I'm an inexperienced ribster having bought a 5yr old 7.5m Cobra with a 275 Verado outboard in Feb and we (wife and 3 young kids) have used it a dozen or so times since, some in fairly choppy moderate seas. I've been on my PB2 course, VHF, Day Skipper and my wife & boys have done the PB1 too.

Given the weekend's appalling accident, i'm concerned to know what causes a boat to flip violently and are deeper V hulls more susceptible than slightly shallower hulls? I visited the Cobra showroom in Lymington and chatted with the owners Steve & Josh about the 5yr old hull design (mine) being shallower than the more current hull design (the one that crashed). Is a deeper Vee more likely to dig in deep when coming down on a bend and thus more likely to stop the boat sharply flipping the occupants out?
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Old 07 May 2013, 04:48   #2
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a very interesting question
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Old 07 May 2013, 05:27   #3
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What causes a boat to dig in and flip people out?

Usually a combination of unfortunate circumstances, hull design is one of them, wave pattern, angle of attack, speed, steering angle, load, trim, all will have an impact on the result. However experience of those conditions and factors over many years of using a variety of boats large and small and a healthy respect for the power of the sea will help in reducing the risk as far as is possible.

Of all of those I think speed is a major factor, fast boats being driven quickly by inexperienced helms (not saying that this was the case recently) just ups the ante.

Accidents happen and we will all get it wrong from time to time, hopefully none of us will have to deal with the aftermath of events like the one in Padstowe, but it is difficult to escape the fact that simply using the fitted safety devices would have helped to reduce the impact of this tragic accident.
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Old 07 May 2013, 05:31   #4
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I should hasten to add that i'm not intending this to be critical of Cobra ribs. I love ours, an excellent family boat and yesterday i chatted with the ex Head of South Wales Fire Rescue service who operated a 7.5m Cobra Nautique in Cardiff / Bristol Channel in all weathers for many years and rated it highly.

However, much like when a car / motorbike is tuned for speed (or one particular characteristic) compromises have to be made in the design that may make the vehicle more twitchy (or otherwise less forgiving). Similarly, do deeper Vee hulls give a softer ride through the chop but end up being more likely to flip?

One of the ways that ribs can flip, i understand, is if when turning tightly at speed the weight of the boat rests on the inside tube effectively lifting the hull higher in the water giving it less grip and that feeling of slipping. If you then hit a bit of chop with the inside tube can it then bounce & flip the boat right over the opposite way violently launching the occupants out? Is a deeper Vee more susceptible to that?
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Old 07 May 2013, 05:40   #5
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Any boat can hook up, maybe you're turning into a wave and the hull just catches or something. It's not a pleasant experience at all. 99% of times you stay in the boat but there is always a chance you could be sent flying.

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Old 07 May 2013, 06:07   #6
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Quote:
Originally Posted by Oscarguitar View Post

Of all of those I think speed is a major factor, fast boats being driven quickly
+1 especially whilst turning sharply

Raygun where is the boat based ?
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Old 07 May 2013, 06:21   #7
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Based on my drive mainly in Malmesbury, but i'll get it wet in Cornwall, Cardiff (Bay & B Channel), West Wales & Dorset etc. Thanks for the video, the helm starts shouting 'whoa' when the boats begins to slip it seems. Throttle off immediately if you feel slip, is that correct?
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Old 07 May 2013, 06:35   #8
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Reduce speed / power in any situation your not comfortable with. Give yourself time to assess, plan, react. It will eventually become easier with experience.

You've probably seen the Round IOW thread for Macmillan Cancer. Why not bring your RIB down for the weekend, meet likeminded RIbsters and enjoy the day out with people of all skill levels. Great way to build up experience and chat to others who have similar questions

Round Isle of Wight for Macmillan Cancer Support-Sunday 26th May 2013
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Old 07 May 2013, 06:39   #9
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Quote:
Originally Posted by Raygun View Post

However, much like when a car / motorbike is tuned for speed (or one particular characteristic) compromises have to be made in the design that may make the vehicle more twitchy (or otherwise less forgiving). Similarly, do deeper Vee hulls give a softer ride through the chop but end up being more likely to flip?
In absolute terms the older Cobra hull is not really tuned for speed compared to many and is actually quite a "soft" hull with a slightly rounded keel . Unless you strap an enormous amount of power on the back (which you can, the 8.6m next to mine in the marina has twin 250 yams) the hull tops out on the 40-45 knot range. Strap a 275/300 on the back of a similar length Scorpion or Pascoe and you could be looking at 50-60 knots. (Friend has a Scorpion 8m with a V300)

I do agree however that there will always be a degree of compromise between speed, handling, stability, load capacity, maneuverability etc. An aggressive deep V that rides well in difficult conditions might be a factor in encouraging the helm to drive faster than a harder riding hull might do in similar conditions, resulting in the speed factor (as well as the hull design) increasing the inherent risk of a "catch"
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Old 07 May 2013, 06:52   #10
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Basically it's caused by:

Going too fast.

Tight turns at speed if the keel comes out of the water and digs in again.

Chine walking can be another cause.

Going to fast for the conditions or hitting a wave or wake from another boat.

Showing off or not paying attention.

Alcohol !!!!

Put any of the above together with a kill cord that is not working or not worn could mean disaster....
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