Chine walking?

Ribbie · 16 December 2009, 17:49

OK, go easy on me.

What is it, how does it happen?

Are all ribs affected?

Any to avoid?

Any that escape the curse?

R.

chewy · 16 December 2009, 17:51

Its usually by going to fast and the boat rocks from one chine to another which can lead to you been thrown from the boat.
Either easing back or trimming in can stop it.

See thread below:

http://rib.net/forum/showthread.php?...hlight=ejected

Zubenelgenubi · 16 December 2009, 17:51

http://rib.net/forum/showthread.php?...=chine+walking

GJ0KYZ · 16 December 2009, 18:21

As mentioned above, this involves a rapid oscillation of the stern of the boat that comes on all of a sudden and at high speed. It's sh*t scary when it occurs and if not corrected can be un-nice to say the least. If you start to chine walk, throttle back immediately but not too fast else you'll be catapulted forward. As soon as the front of the boat re-enters the water with reduced speed the effect will stop. To avoid chine walking, try not to have too much trim at WOT, don't over power your boat in the first place (this will back it stern heavy if nothing else), and keep one hand on the throttle if it makes you feel better (I do, always). My boat starts to chine walk at anything above 40kts if trimmed too high and I reckon all RIBs will experience this effect if we're being honest.

raymillard · 16 December 2009, 20:22

Sorry, I'm thick. What do you mean by trimming in?
Thanks.

chewy · 16 December 2009, 20:26

If the engine is trimmed in its as close to the transom as possible, the bow will run closer to the water trimmed in.
Trimmed out the engine will be further away from the transom and the bow will ride higher.

Bigmuz7 · 17 December 2009, 07:54

Quote:

Originally Posted by GJ0KYZ

I reckon all RIBs will experience this effect if we're being honest.

I dont really agree with that

There are certain rig outs more likely to experience it though , commonly being, a maximum powered deep V hull that is also light and a bit stern heavy, in a reasonably calm sea, going flat out ... the trim position will be specific to the boat, but as the driver is usually trimming to get the most speed in these conditions, inevitably most of the hull will be out of the water .. and then bang ! it slaps onto the left side, you correct, then it slaps onto the right, so you need to slow up quick, otherwise the over correction may get someone thrown out , and its a particulary nasty little surprise, just when you think you've got your rig cruising nicely & quickly, both for the skipper, and any crew.

Cookee · 17 December 2009, 08:43

Quote:

Originally Posted by Bigmuz7

I dont really agree with that

It is the case that not all Ribs have sufficient power to go fast enough to chine walk, but given enough power it is my opinion that all hulls, stepped or V will do it eventually.

9D280 · 17 December 2009, 10:24

It's basic phyisics.

I’ll try to keep this simple..... any planing hull is forced up & out the water by the dynamic pressure of the water on the hull as you travel. As it’s a dynamic pressure, (caused by the speed of the water relative to the hull as opposed to actual pressure), the net result is the faster you go, the more lift you get.

So, a quick diversion to describe trim - it's the angle of the engine relative to the back of the boat. Older / smaller engines this is adjusted by moving a pin in a row of holes on the clamp alternatively can be done on the move from the comfort of your seat with a hydraulic ram. As the thrust from a propeller is a vectored force (i.e. it’s directional) by trimming up (or out) , the engine lifts and so the force of the prop pushes downwards a bit more, so the bow lifts. or if you trim in (down) the propeller is facing down, so lifts the stern out the water. If that didn’t make sense, let me know, I'll post a diagram)

So, back to the chine walking- If you have a lightweight / overpowered hull, the resulting speed creates soooo much lift that a V- hull is literally running on the tip of the "V". As you can imagine, not a very stable condition to be in, so it falls to one side, the flat of that side of the V hits the water, and the pressure throws it straight back. It's unstable, so it passes “upright” & keeps going 'till the other side hits..... and so it goes on. If you are balancing on the tip of your V in perfectly flat water, all will seem well until one tiny wave throws the delicate balance.

As a sideline, a chine is a flat area on a hull- dinghies like Mirrors & GP14s are described as “single chine”, as they have one flat surface, likes of Wayffarers & enterprises are called “double chine”.

Throttling back reduces the lift, so drops the hull further into the water – creating stability.
Trimming in is a similar story, as it alters the attack angle of the hull relative to the water surface, so the effective pressure of the water on the rear of the hull will reduce, and again "sink" you a bit further in, while also pushing the bow in slightly will increase drag, and slow you down, again dropping the hull into the water a bit to a point of stability.

Hope this helps.

alystra · 17 December 2009, 17:36

I think that's a very good description 9D280.

Bigmuz7 · 17 December 2009, 19:58

Quote:

Originally Posted by Cookee

given enough power it is my opinion that all hulls, stepped or V will do it eventually.

I dont disagree with that .. but thats not the way I understood GJ0KYZ's point .. but rather than split hairs .. I think its best to highlight the conditions and craft that will do this unexpectedly .. which is what catches out the unwary or inexperienced user in what can rapidly become a violent ejection

PeterM · 17 December 2009, 21:07

Will flatter or deeper V ( at the stern ) be more or less likely to walk ? - All things being equal !

I'm in 2 minds - the flat will get there easier , more 'lift' but less angle to roll ? or the deeper V will flick from side to side more as it has further to roll from one side to another - so may be more violent ?

Bigmuz7 · 17 December 2009, 21:20

Quote:

Originally Posted by Blackroady

Will flatter or deeper V ( at the stern ) be more or less likely to walk ? - All things being equal !

I'm in 2 minds - the flat will get there easier , more 'lift' but less angle to roll ? or the deeper V will flick from side to side more as it has further to roll from one side to another - so may be more violent ?

Exactly .. its much more violent with a deeper V , which also requires more overpowereing to achieve it .. but its amazing how many suffer from it .. and if the owner is surprised because they thought the power was ok, its because they have a decent V but light hull ... , with a 'bow-light' fit out IMO