Rib lose control at 30knots

[Jason calleja]

Hi all i am new here and i don’t know if this is the right place to ask you if you could help me with my problem.
I own a maxxon rib 4.80mtr and powered with a mercury 60hp 4 stroke all bought new this year when i try to reach high speed the rib at 30knots lose control and start swinging from rear and it becomes very danger and will have to slow down. What i have been told to do is to rise the outboard but this didn’t help. some told me it is over power but i don’t think so. Total weight of the rib is approximately 400kg. What do you think ?.Thanks Jason

[jyasaki]

Swinging from the rear? Or rocking violently from side to side?

From the lead-up to the problem, it sounds like a case of chine walking. Do a search on this site, and you'll find a substantial amount of information on what it is.

jky

[Jason calleja]

yes that is the right description. thanks for your help

[Jason calleja]

Hi and thanks for your information as it was very helpful. Last Saturday i went for a ride with the rib and tried to see if the chine walking was less after i raised the motor by 1” and what i noticed that when i was at W.O.T at about 32knots and was steering to starboard the rib was very stable and good running trim all down but as i steering straight it to trim it out it started cine walking violently. Now i have to ask you what is the best way to try eliminating the chine walking i have read a lot of things here that can cause chine walking. What i have noticed on my steering that it has a little clearance from right to left it has about ½” on both sides. Will this affect the chine walking. Do i have gust to add weight or install a jack plate or hydraulic steering. Thanks to you all again and your help will be appreciated. Jason

[Cookee]

Originally Posted by Jason calleja

What i have noticed on my steering that it has a little clearance from right to left it has about ½” on both sides. Will this affect the chine walking. Do i have gust to add weight or install a jack plate or hydraulic steering. Thanks to you all again and your help will be appreciated. Jason

1/2" will make it difficult to stop the chine walking - take out the play and the boat will behave much better. Hydraulic steering can also have play if not maintained properly but is generally considered to be better other than by the purists.

[wavelength]

I see its only a 60hp outboard. Is it power trim or not? Would suggest the trim angle is too high so perhaps try 1 hole "in" if manual or just trim down a bit if power trim.

[two stroke mick]

32 kn is a good speed for a hull of that size. I would say you are trying to squeeze too much out from the hull

[captnjack]

Originally Posted by two stroke mick

32 kn is a good speed for a hull of that size. I would say you are trying to squeeze too much out from the hull

Agree. Trimmed all the way down you are keeping hull in the water, raising the trim is raising the bow. With less wtted surface the chine walking starts. 30knts is about all that hull is going to do with stability.

[Jason calleja]

Yes it is power trim and when it starts chine walk it is trimmed all down and the other thing is i know another person that has same rib with same outboard it is identical with mine and he is doing 40knots with it and had never chine walked and my brother has a 14ft rib that weights 250kg including outboard and it has 50hp tldi on it and never had problems like this i can’t understand what does my rib could have i will try eliminate steering clearance then i will see if it will reduce the chine walking. Thanks all for your help. Jason

[wavelength]

trimmed in? at full speed? Why?
try trimming out gradually as you speed up-you are trying the equivalent of pushing a weathervane the wrong way into the wind and obviously if the pressure one side of the bow is stronger than the other it will try to whip round. Get the bow up.. with the limiting factors being either the prop will draw air and the motor will over rev OR the boat will become unstable again. Our 4m searider was good for well into the thirties with no problems...our 4.3 humber assault was also ok with the proviso it needed a bag of sand in the front for balance-but both still had to be trimmed out.