steering problems 4.80 mtr. rib

[Gert-Jan Bosch]

I have a Greek 4,8 mtr RIB (see www.mostro.gr, type offshore 4.81) with a Honda 75 hp 4-stroke outboard. When I reach the speed of 28 mph or higher the boat starts to "dance" from left to right, making it impossible to keep it in control if I don't lower speed. The outboard, although it is the recommended amount of hp. is rather heavy for this boat (+/- 60 kgm heavier than 2-stroke same size), and I don't have extra weight in the front of the boat.
I cruise in the Gulf of Corinth (Greece), and it also happens if there are hardly or no waves at all.
Does anyboby recognize this problem, and what to do about it?

[Pete7]

Yep, it's called shine walking and caused by a number of things. Too much power and weight for the hull length. The hull its self can also cause problems. Short deep v hulls suffer more than med v hulls. Osprey used to make a 5m merlin which suffered from this. The boat would always run nose up. I changed from a 75 hp down to a 60 hp which was better however the best soluction came when I changed the boat for the 5.2m. Although both hulls came from similar moulds the extra 20 cm was all that was required to stop shine walking problems. They stopped selling 5m Merlins because of this problem.

You could try altering the weight distribution in the boat with fuel and people up the front. Fit a dolphin plate to the engine, or see if you can borrow a smaller engine, say a 60 hp 2 stroke to try out. John Kennet is pretty knowledgible and might have other suggestions.

[Scubakid]

Hi

the speed you are getting chine walking seems low to me so have a look at the trim on the engine and see if you can trim it in a little, some engines have a stop bar/bolt to stop the engine from beeing trimmed it too far so try moving this in one hole.

Hope this helps

John

[Charles]

Chine Walking: One of the biggest complaints of high performance boats - particularly V-bottoms - is that of the boat "chine walking". Chine walking occurs when the boat is running at high speed - usually at 65mph or higher - and because of the size of the boat trying to run on very little hull, it will fall off to one side, then flop back to the other, etc. etc. There are many myths to chine walking, i.e. "A four blade prop will cure your chine walk". Unfortunately, that is not true. True, a properly set up boat will be easier to drive and may chine walk less than a poorly set up hull, but chine walking occurs due to the laws of physics.
The true way to reduce or eliminate chine walking? Learn to drive the boat. A tip to help eliminate your chine walking is this: Always keep the boat guessing. By just holding the steering wheel, you're going to allow the boat to get into a rhythm which will lead to chine walking. Start out by "tapping" the steering wheel to the left - against the torque. Then as the boat begins to fall to the left, release the steering wheel from the torque and turn the wheel slightly to the right. As the boat begins to lean to the right, return the wheel to the left against the torque. Remember this - KEEP THE STEERING WHEEL MOVEMENTS SMALL. By oversteering, you could do more harm than good. Try to imagine standing on a 2X4 with a ball underneath it. As the board leans to the left, you have to shift your weight to the right in order to keep the board from hitting the floor. Some tips to sort out the problem:
1 A low central point of gravity, i.e. endeavoring to locate such things as fuel tanks below deck, to further aid lateral stability.
2 The positioning of helm console approximately just aft of amidships so that crew weight and seating are not pushed too far aft back to the wettest part of the boat!
3 Ensuring that engine weight is considered properly when power units are fitted or installed. Just because an engine manufac*turer may state a maximum horsepower for your boat model, it doesn't always follow that the largest motor would be best suited to your layout/configuration. Horse power ratings relate to hull design only. (Remember also that 4 stroke engines are considerably heavier than that of their 2 stroke counterparts.)
4 When buying a RIB, ensure that stern bench seating or additional pods situated aft are really capable of being able to accommodate the weight of the passengers they are intended for.
5 If a water ballast tank is to be fitted it should be of more than adequate size. Many tanks fitted are too small. Ensure also that its dumping capability is rapid enough.
6 The weight of any items such as self-righting equipment should be very carefully considered before installation. If retro‑fitted, then consider that the addition of such may severely affect the performance and handling characteristics of the craft, unless proper thought is given to the matter of counter balance etc.
7 To assist lateral stability and help ensure a level ride, endeavour to fit heavy items such as your batterv etc. on the starboard side.
Offsetting the engine is also necessary to counteract the torque of the engine.

[Gert-Jan Bosch]

Thank you for your replies, and by the way, nice boat John! We seem to have the same outboard, but yours a bit bigger...!
About this chine walking: except for steering tricks and balancing the weight, do also trim tabs solve this problem???
As you see, I'm a beginner and I have to learn a lot still.
And Charles, since my steering console is very aft and right side, is it wise to move it a bit forward and to the middle? Why placing heavy stuff to the right side?
For your info, my "deep V" is 21 degrees at transom height,
my clearancebetween low end of transom and "anti-cavitation" plate is approx. 20-25 mm.
Can the chine walking be solved, or do I have to buy another rib if I want to keep my Honda outboard?

[Keith Hart]

Chine walking occurs when the boat is running at high speed - usually at 65mph or higher -

Keith (not a problem I'm likely to have then) Hart