Xs rib chine walking

RescueRanger · 11 January 2011, 19:27

I have an Xs Ribs 600 with a opti 150. Over 37 kn it all gets a little lively, and damn scarey at 42kn does anyone else get this or could it be the the set up of the boat?

GJ0KYZ · 11 January 2011, 20:10

I'd say that's pretty normal for a 6m rib. Mine used to chine walk at those speeds, especially when trimmed up. I changed my 3-bladed prop for a 4-bladed Cyclone and this helped significantly. I also got better acceleration and slightly better fuel economy.

Hightower · 11 January 2011, 21:30

I don't really agree that it's normal for general 6m RIB to chine walk at any particular high speed. It all depends on set-up, HP and hull design (some being better than others).

Does your XS Chine walk all the time or are there occasions were it is better ie: Heavily loaded/lightly loaded? When you trim in does it improve?

You might be able to make some subtle changes to weight distribution that would see chine walking disappear.

Bigmuz7 · 11 January 2011, 21:41

most likely when sea is flatter perhaps ?

chewy · 11 January 2011, 21:53

Quote:

Originally Posted by Bigmuz7

most likely when sea is flatter perhaps ?

And trimmed out.

GJ0KYZ · 11 January 2011, 22:03

Quote:

Originally Posted by Hightower

I don't really agree that it's normal for general 6m RIB to chine walk at any particular high speed. It all depends on set-up, HP and hull design (some being better than others).

Does your XS Chine walk all the time or are there occasions were it is better ie: Heavily loaded/lightly loaded? When you trim in does it improve?

You might be able to make some subtle changes to weight distribution that would see chine walking disappear.

I meant it's not unusual. I didn't mean to imply it's acceptable.

Jizm · 12 January 2011, 10:30

Had this with a boat I worked on a while ago, it was about an 8.5m boat that had twin 150hp but hopefully the theory should stand.

The boat was fine up to about 40 knots but chine walked above about 42, sometimes quite violently! We were advised by a reputable outboard dealer/installer to try ballast and let him know how we got on. I put about 100kg in the bow, I used lead shot so max weight minimum space, difference was instant, much improved. He then advised us to raise the motors about 2" if possible. It wasn't without transom work so we used the ballast for a month or so then altered the transom and raised the motors to the advised height.
No more need for ballast and no more chine walk...

I'm not a Naval architect but this worked for us. Hope this helps as the ballast thing is very easy and cheap to try.

GordyP · 12 January 2011, 13:14

I get chine walking starting at about 45kts when the boat is light, it is considerably better when the boat is reasonably laden with people and dive kit, also very rarely blast about at this speed so I have never bothered with trying to raise the engines on the transom. I suspect that you would be looking at a combination of raising the engine and putting in some ballast.

Erin · 12 January 2011, 14:39

Suffered it in my old boat, which was poorly balanced and rather stern heavy. The balast idea is a good one and easy to try.

martini · 12 January 2011, 15:31

So this all seems to suggest it's a lack of lift at the stern or too much lift at the bow that causes chine walking. I would have guessed it being the other way round

GordyP · 12 January 2011, 15:54

No, i would suggest its too much lift at the stern hence why extra weight in the boat helps.

martini · 12 January 2011, 16:03

Quote:

Originally Posted by GordyP

No, i would suggest its too much lift at the stern hence why extra weight in the boat helps.

Extra weight in the bow yes, push the bow down and the stern goes up

RescueRanger · 12 January 2011, 17:45

Chaps your all stars! I was thinking of the ballast idea because it does feel light in the bow but what wouldn't with 190 kg optimax on the back lol!. Was thinking of 60kg as a start point. Only because when we were coming back up the hamble a friend moved to the bow and the boat gained 1.5 kn without touching the throttle. I will give it a try and let you know how it goes. Once again thanks for all you suggestions. All the best and happy and safe ribbing

Erin · 12 January 2011, 17:47

I put mine down to the whole boat being too light. Something to do with a lack of matting or two in the lay up

. Helped make my decision to sell it tho and get a proper rib.

gotchiguy · 12 January 2011, 17:51

Quote:

Originally Posted by Erin

Helped make my decision to sell it tho and get a proper rib.

Not just a proper RIB, the best type of RIB

PeterM · 12 January 2011, 17:56

Quote:

Originally Posted by Erin

I put mine down to the whole boat being too light. Something to do with a lack of matting or two in the lay up

. Helped make my decision to sell it tho and get a proper rib.

I'd second this theory......... just not enough holding the boat down in the water. More weight anywhere will help - in the bow will mean more force needed to 'lift' the bow via trim so more 'down/planted' at the stern...

More weight at the stern may have the same effect in calm water but make it 'flighty' into head sea?

So loose 1/2 knot top end or loose the scary wobble? - no contest for me !

Ps - I get this on the avon when lightly loaded at about 28knts - when loaded it vanished and I get to very very close to the same speed.

GordyP · 12 January 2011, 18:37

When I load the boat up with dive kit, most of the weight is spread around the middle of the boat, too much in the bow causes problems in waves, and as someone else has said to much at the rear makes it flighty. At full throttle with the engines trimmed up there's virtually none of the hull in the water hence the chine walking, with a bit of weight on board the planing pad is forced onto the surface of the water, with more of this in contact with the water the boat is more stable. You could get a similar effect by raising the engines on the transom?

PeterM · 12 January 2011, 20:36

Quote:

Originally Posted by GordyP

You could get a similar effect by raising the engines on the transom?

Not sure - Cookee will know more .. my thinking is that you will have less torque to lit the bow, less leg in the water (less drag), but just the same lack of stable boat/hull in the water.

Props will change the effect depending on the trim also due to the up/down forward/back of the prop blades as they spin etc ( ie the 'real' pitch may change as they rotate due to the angle it meets the water etc etc )

chewy · 12 January 2011, 20:46

Quote:

Originally Posted by gotchiguy

Not just a proper RIB, the best type of RIB

You mean a Searider!

gotchiguy · 12 January 2011, 21:53

Quote:

Originally Posted by chewy

You mean a Searider!

No no, we've had a Zodiac before. Terrible built quality, console nearly fell off on ripped out when we crossed from Cherbourg to Alderney and the seat also bent (mostly because of GDs weight

). Wouldn't trust a Zodiac again