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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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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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Old 07 May 2013, 06:54   #11
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What is Chine walking?
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Old 07 May 2013, 07:02   #12
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Chine walk is the tendency for your boat to oscillate back and forth between its port and starboard chines.

Some boats do it and some don't, depends on hull, engine installation, speed, load etc.

If in doubt reduce your speed.
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Old 07 May 2013, 07:05   #13
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Quote:
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If in doubt reduce your speed.
Where's the fun in that

Chinewalking in the VM is great fun, but bloody scary wear a helmet too if you're seeking it out on purpose, very easy to smash your teeth on a screen or it's stainless surround
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Old 07 May 2013, 07:16   #14
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Chinewalking in the VM is great fun, but bloody scary wear a helmet too if you're seeking it out on purpose, very easy to smash your teeth on a screen or it's stainless surround
errr precisely

Raygun has already mentioned he's new to ribbing, best to build his AND his families confidence up gradually - not scare the living daylight out of them. What ever the hobby - scare the wife and kids and you might as well give up the sport.
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Old 07 May 2013, 07:52   #15
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Where's the fun in that
Chinewalking in the VM is great fun, but bloody scary wear a helmet too if you're seeking it out on purpose, very easy to smash your teeth on a screen or it's stainless surround
You also go playing chicken on the M1?

The reason a boat chine walks is instability, its not a design feature.
It means in the current config something is not set correctly, drive a boat like this for long enough and bad things WILL happen.
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Old 07 May 2013, 07:59   #16
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Chine Walking is a fault not a feature. Proposing that people try it out but wear a helmet does not really add to the debate. ("Where's the fun in that" is also ill judged at present IMO)

Chine walking generally indicates that there is something wrong with the set up, or design. (Or helm if you are trying to get a boat to chine walk!)

My worst experience was in a 21ft Fletcher that had some stern damage so the owner had cut the last 2ft off and replaced the transom making a 19ft boat. Without the stability of the flattening V at the stern this thing was lethal and would flip violently from side to side . I never went in it again and seriously hope that it was cut in half and destroyed.

Raygun, it is unlikely that you will suffer chine walk in your Cobra (never experienced it in mine or the 7.5 I have used, but if you do, take Landlord's advice and slow down.
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Old 07 May 2013, 08:03   #17
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The reason a boat chine walks is instability, its not a design feature.
It means in the current config something is not set correctly, drive a boat like this for long enough and bad things WILL happen.
The reason a boat chine walks is when the boat is being used in a different way from what it was designed, or is set up for. I have only ever experienced chine walking on our boat at over 52knts, with just me on board and very little fuel.

At this speed and configuration the boat is not happy, because the propeller pitch is chosen for two up and much more weight on board (and it's a rubbish propellor). There are identical boats to ours, outfitted with a smaller engine, and built lighter and set up differently which do not chine walk until over 60knts.

If we set our boat up like that, it would not suit what we use it for at all.

What I am saying is, that in controlled conditions, and having taken all reasonable safety precautions it is very good fun to really push the envelope. Running at WOT normally does not induce chine walk, so it is not easy to find. When doing so (as always) I have a life jacket on, a PLB and a VHF. Wearing a helmet is also advisable to protect your teeth.

On smaller boats, such as SR4s etc chinewalking is a much more regular occurance and much easier to achieve, not necessarily by having to look for it.

I am not advocating that people do this, I am simply writing about my experiences. Going very fast on the water is one of the key reasons people have RIBs after all.

This is clearly not what happened in the incident though: with a family on board only someone with complete disregard for not only their own safety but also that of their passengers would be doing this.
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Old 07 May 2013, 08:11   #18
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I think the words Capsize and flip and crash have been miss used from the pictorial evidence i have seen. The boats shows no sign of being inverted at any point or any structural damage.

I would suggest the boat was caught droping off a of a wave or wake at speed whilst turning hard, this usually causes a sudden lateral movement, which is then "braked" by the hull re-entering the water.

I really don't think one hull or another can be blamed here, My money would be on a less experienced skipper giving a "thrill ride" Hard turns, hard throttle use which went wrong, and then was compounded by lack of use of a Kill cord.

Boats being driven in a "normal" manner on flat water simply don't throw you out, add excess speed, exuberance , waves/wake, or equipment failure, then you get issues.

I would suggest take some advanced training (not necessarily a course with an exam), but maybe some 1:1 on your boat with an advanced instructor, who can show you what you can and cant do with a boat at the extremes and how to cope with them.
There are many such facilities, I would recommend Tim @Griffin marine from personal experience.
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Old 07 May 2013, 08:12   #19
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The reason a boat chine walks is when the boat is being used in a different way from what it was designed.

What i said......
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Old 07 May 2013, 11:09   #20
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I would suggest take some advanced training (not necessarily a course with an exam), but maybe some 1:1 on your boat with an advanced instructor, who can show you what you can and cant do with a boat at the extremes and how to cope with them.
Bear in mind that there's nothing in any of the RYA Powerboat courses that really covers high speed boat handling, and some instructors may have some race experience, but many won't.

It's not always the case that slowing down is the best thing to do when things look scary. Chopping the throttle can be the worst possible thing to do, and can be a major factor in this type of accident as it can provoke a severe hook. The faster you go the more important it is to understand this.

For anyone with a fast RIB who reckons on travelling at 50mph plus, I would recommend spending some time with an instructor like Neil Holmes who really knows about driving a boat quickly.

http://www.powerboatcentre.com/
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