Why does my boat rock? - Page 2

Petrov · 31 March 2005, 20:29

Quote:

Have you tried putting extra weight on bow before you adjust engine height this will help

The console are pretty far front so that should`nt be the problem, ok that twin 4-stroke 115hp has plenty of weight but still boat is not overpowered so it need any ballast in bow compare to the fitting of console and seating (only my opinion of what i se of pics)
Offcourse ballast in bow will help to get the wobbeling away but than the boat will be heavier in bow wich will get more wet surface and and not pleasant to drive as it should be in the ruff seas and it will also make the fuleconsumption higher on flat water.
It`s nice to have heavy boat in bow in ruff seas but it is still important to have the possibility to trim up the bow in ruff seas and this will disapere with to much weight in bow.

Martin · 31 March 2005, 20:32

I think your boat was owned by a chap who did a lot of powerboat race safety. Therefore he would always have divers on board and all the weight that goes with that. It may be that the boat needs a bit more weight.

M

Petrov · 31 March 2005, 20:49

Quote:

Therefore he would always have divers on board and all the weight that goes with that. It may be that the boat needs a bit more weight.

Dont really agree, you can have a light boat that is over powered without any wobbeling, most of the wobbeling depends how boat is balanced compare to the outfitting and engines.
Boat looks little heavy in back but not so heavy that it should start to wobbel at 40 knots.
Another idea is the props, do you know how many revs you have at full throttle, maybe you need some other props to get better grip, it will effect the topspeed a little but a more pleasant ride without compensating the wobbeling all the time.

benc · 31 March 2005, 20:49

I believe the boat is an ex life boat...

Is anyone up for coming out with me at some point to see how it handles ... like I say, im new to ribs... and its a totally different experience for me...

However, I am loving it and will never look back at any other boats again!

Would just be nice for others to tell me what I should be expecting and things.

benc · 31 March 2005, 20:53

not sure how many revs it has - will look at rev counter next time im out...

Also, the steering has slight play in it, I assumed that that might be right so that when you bounce from the water you dont come down with the steering in a different place... should the engines move immediately the wheel is turned?

Its only about 1cm the movement I have..

Petrov · 31 March 2005, 20:53

PS: Benc you say that 75 % is 40 knots, this means that boat can do around 50knots, sounds very fast for that boat, i would guess 45knots, i can be totaly wrong

Petrov · 31 March 2005, 20:56

1cm if you talk in steering wheel is nothing, do you have twin steerings with a bar between or just one steering and a bar that is fitted to one of the engines.

Petrov · 31 March 2005, 21:02

Looked at the other pics and can se that you have single steering with a bar between engine, its ok as long as it`s hydraulic on thoose heavy engines.
I would recomend double steerings but it shouldnt be the problem in your case.

Andy · 31 March 2005, 21:25

As I have said: Ring Laurence Lock @ Barnet marine (www.ribs.co.uk) and ask him. He built it! (almost!). He is a very helpful guy and he has owned many 7.5owm himself ... as well as sold many hundreds of Tornados.

Certainly at 50 mph, my 6.8m Tornado can chine walk if my trim is high, and so a trim is down a little and it stops. It does sound odd you experience this at the speeds you say on a larger boat. I would have expected it to be rock steady.

Just one question ... have you checked your hull cavity is dry?

Hightower · 31 March 2005, 21:28

Any play between wheel and outboard/s might promote chine walking, how much are the engines moving relitive to the wheel and do they move relitive to one another?

Do a search for chine walking and you'll see what problems others have been having and what their solutions were. It could be something as simple as air in the hydrualic system.

Also, and excuse me....But!! I don't see the point of moving the weight up front to increase the wetted area under the hull to get over the problem of chine walking unless you're already fully trimmed in and still get it? I mean, if by increasing the weight up front to effectivley increase the surface area in contact with the water, isn't that going to slow your top speed? Its the same as trimming in isn't it? And by having a lesser weight up front you would have an advantage in a following sea.

Andy

Andy · 31 March 2005, 21:37

This pic:

http://dogscogs.com/gallery/album01/DSCF0759

Suggest you may have counter rotating props ... or are my eyes getting old?

Hightower · 31 March 2005, 21:42

Just another suggestion! Are the twins setup correctly, toe in/out if you know what I mean? Not so sure how this would affect chine walk though.

Kernow Buoy · 31 March 2005, 21:43

Quote:

Why does my boat rock?

Hey Dude, all Ribs Rock!!

(sorry, son's in rock band the speak is rubbing off on me

)
Kernow

Andy · 31 March 2005, 22:00

Quote:

Originally Posted by Hightower

Also, and excuse me....But!! I don't see the point of moving the weight up front to increase the wetted area under the hull to get over the problem of chine walking unless you're already fully trimmed in and still get it? I mean, if by increasing the weight up front to effectivley increase the surface area in contact with the water, isn't that going to slow your top speed? Its the same as trimming in isn't it? And by having a lesser weight up front you would have an advantage in a following sea.

Andy

We need more weight in our bow as our Yam 200HP will not trim far enough down, and it needs a little more (not by much). This is because the angle of the transom is not enough for our Yam 200. The boat was designed for a Merc which trim down more than a Yam. However triming it down makes head on solent chop more easy to deal with which is why we have a 50lbs weight in our bow. Another option is to install a wedge to help force the nose down or trim tabs. We dont think we need go that far and the boat works well now.

However that weight does not effect our chinewalking. As I said in an earlier post we get walking when we are trimmed up too high trying to get the fastest from the boat. We get to the point where there is very little hull touching the water and then walking starts. I can minimise it by not reacting to it when it occurs and trying not to swing on the wheel ... I keep it very steady and balanced.

If it walks, trimming down a little solves it and we loose a few mph. However we certainly are not trimmed down as far as the engine will go ..... and so I dont think having weight to hold the nose down is helping much, as there is plenty of trim still available to force the nose down without the weight.

I would be happy to take a look at your boat. We are out Sunday travelling from Portsmouth to Swanage for some diving. Happy to meet you on the way for a quick look, but we will be passing southampton water early! Like 8:30am

benc · 31 March 2005, 22:28

Hi Andy,

Probably going to be a little early, but will let you know either way on here if you are around on saturday.

Rogue Wave · 01 April 2005, 05:06

Andy's thread above pretty much sums up how to get around the wobbly boat syndrome

If it's chine walking then I think you should be able to drive through it with practice and knowledge of the boat.

I used to have an Avon 4.7 with a Yammie 70 (I loved that Boat!) and she used to really rock about 6 knots before terminal velocity, so I took her down to the test estuary for a couple of days. As soon as I got used to the steering I was able to understand the lack of compensation I needed to apply to get through the chine walking.

have you done any powerboat training, if not consider getting some own boat tuition.

I'd be happy to come out with you and burn some of your fuel and tell you if it's an issue or not! Has your boat got footstraps?

benc · 01 April 2005, 07:34

Hi,

No straps, I am getting my RYA done soon... in my own boat, so maybe I can get some tips then.

When are you out next rougue?

benc · 01 April 2005, 09:06

Andy,

I was meant to ask - how do I check if the cavity is dry?

benc · 01 April 2005, 10:19

Laurence Lock was busy, but spoke to a guy called Barry who has pretty much told me the same as you guys - so as soon as I get the battery charged for the port engine, I will try playing with the trim... if that doesnt work I will get the boat taken out of the water and check the cavity also.

Thanks again Guys.

swginn · 01 April 2005, 10:21

Quote:

Originally Posted by benc

Andy,

I was meant to ask - how do I check if the cavity is dry?

At the very bottom of the transom there is a plug that you screw out to let any water in the hull void (obviously the rib will have to be out of the water!!

).

My rib used to chinewalk before from just below 50kts. I thought the boat was overpowered initially but I found that there was water in the hull void caused by the plug not being screwed in tight enough. Emptying the void solved the problem.

Again as Andy said, I suggest you contact Laurence Lock at Barnet Marine who will be more than obliging to help sort it. He knows everything there is to know about your RIB.

edit: just seen you've contacted them already, good luck with getting it sorted. She's a cracking RIB by the way!!