Avon unstable at speed - Page 3

Nos4r2 · 03 March 2013, 01:30

Have a look at these for a comparison-both were taken from a 5.4 Searider at full throttle with a handheld camera-of 2 Seariders at full throttle. It was flat calm in one-which is me solo, and a bit bumpy in the 2nd, which is Doggypadddle from here solo.

Finally-my own boat on video! - YouTube

Searider gathering 6 20/09/2008 - YouTube

edge0895 · 03 March 2013, 03:18

Quote:

Originally Posted by teamplonker

Hi All
I need a little help with my new acquisition a 5.4m Avon Searider with the flooding hull sealed and a Honda BF75 hung on the back.
I took the boat out today for the first time and was pleasantly surprised with how quick it got to plane but it was very twitchy at 30+ .
It felt like it was perched on a peak and was just waiting to fall off

, A couple of times I had to pull the throttle back sharply or it felt like I was going to flip over sideways.
Is this normal with deep v hulled ribs, I have never had this with my little caribe rib and I am often flying around at 35+ with no problems.

All help welcome

Hi there,
a friend of mine had the same problem with his phantom powerboat (not rib) he retro fitted the Hydro planes that you can buy relativley inexpensive to the cavitation plate on the leg and this sorted out the problem straight away.if youve had planing hulls before i imagine that you will know about over trimming the boat and its effects.
Hope this helps.

treerat · 03 March 2013, 07:28

Quote:

Originally Posted by teamplonker

How do you know the boat so well

I've do a fair bit of work at the center where Joc used to lease her (and his other boats) out to.

When carrying the weights and anchors up front she never used to be a problem. Move the fuel forward, trim with engine height, add some extra chain, carry a 24l spare.

Doesn't really matter, the key thing is you need to balance the boat against teh weight caused by having the operator further back and a big lump. It's not teh boat, just the way she is now being used.

Moving the console forward would also work, but I'd be trying balance weights first as it's easier and less effort.

teamplonker · 03 March 2013, 12:56

How its looks now

teamplonker · 03 March 2013, 12:57

How it looks now.

ribsta · 03 March 2013, 14:24

I would agree that looking at your last picture of engine and transom, it might be one hole too low.

RIB-Teccie · 03 March 2013, 16:04

Console looks a bit far aft if the footprint was the original console, engine could do with being raised. The big one is the closure of the flooding hull, this could be full or half full of water. Still a hole to see and fit a bung. You could have too much weight aft. Engine weight may not be terrible as people fit twin 40 two strokes to these which would be around 160kg.

whisper · 03 March 2013, 16:39

Quote:

Originally Posted by RIB-Teccie

Console looks a bit far aft if the footprint was the original console, engine could do with being raised.

Yep

Quote:

Originally Posted by RIB-Teccie

The big one is the closure of the flooding hull, this could be full or half full of water. Still a hole to see and fit a bung. You could have too much weight aft. Engine weight may not be terrible as people fit twin 40 two strokes to these which would be around 160kg.

Yep, good advice too

Also if those are holes in the transome, they need to be dried and filled.

I'm about this week near J16 of the M4 if you need any help, I also have the correct gelcoat pigment for your rib

I should be out on the water later in the week if you can make it down to the solent, maybe friday?

teamplonker · 03 March 2013, 17:56

Quote:

Originally Posted by RIB-Teccie

Console looks a bit far aft if the footprint was the original console, engine could do with being raised. The big one is the closure of the flooding hull, this could be full or half full of water. Still a hole to see and fit a bung. You could have too much weight aft. Engine weight may not be terrible as people fit twin 40 two strokes to these which would be around 160kg.

Jock did say it had twins on before.
I plan to move the steering console forward to where it was before then I can fit the rear seating console as well.

I want to get the outboard off and clean up the transom ( it has more holes than a culander ) whilst off I will fill all holes and put a drain in, could do with a new elephant trunk just don't know where to get one.

paul tilley · 03 March 2013, 18:02

engine looks very low , console too far back , i have elephant trunks

teamplonker · 03 March 2013, 19:08

Quote:

Originally Posted by whisper

Yep

Yep, good advice too

Also if those are holes in the transome, they need to be dried and filled.

I'm about this week near J16 of the M4 if you need any help, I also have the correct gelcoat pigment for your rib

I should be out on the water later in the week if you can make it down to the solent, maybe friday?

Thanks for the offer of help, not sure just how much I can do to the rib this week as I have a little project in the garage that I have not touched all week and I want it finished within 8 weeks.
Oh and I suppose I had better go to work as well.

teamplonker · 03 March 2013, 19:11

Quote:

Originally Posted by paul tilley

engine looks very low , console too far back , i have elephant trunks

Thanks Paul

I'll add the the trunk to the things I need when I come down.

teamplonker · 03 March 2013, 19:13

If I lift the engine up the transom as some of you have suggested will i have to raise the transom so the outboard has some thing to hang on

whisper · 03 March 2013, 19:33

Quote:

Originally Posted by teamplonker

If I lift the engine up the transom as some of you have suggested will i have to raise the transom so the outboard has some thing to hang on

No, i don't think so, some are lifted slightly.

If you think it had twins on before then the top of the transome used to be straight so that cut out would have been done by hand.

I'll measure tomorrow how deep the transome cut out is on mine and that should give you an idea

teamplonker · 03 March 2013, 20:06

Quote:

Originally Posted by whisper

No, i don't think so, some are lifted slightly.

If you think it had twins on before then the top of the transome used to be straight so that cut out would have been done by hand.

I'll measure tomorrow how deep the transome cut out is on mine and that should give you an idea

No it was'nt straight jock showed me it had a crude cover plate, so basically thin air behind a thin plate.

It would be good to no if there is any difference though

Chris · 03 March 2013, 20:28

Quote:

Originally Posted by teamplonker

Am I trimming the boat wrongly ?

Sounds like it is trimmed to far in so the bow is carving.

Quote:

Originally Posted by teamplonker

I was taught to trim the boat by getting up to speed throttle back to bring the bow
down and get the top of the outboard level, you should now be at optimum speed.

No Ideally you trim out until either the engine starts to ventilate. Or if you start to feel chine walk (rib starts oscillating from side to side and the hops from side to side)

TomKat · 03 March 2013, 20:28

I had a similar problem on my 4.8m boat with a 75hp 2 stroke (biggest engine hte hull can take) and moving the console forward 400mm pretty much sorted it out, it went from being frankly terrifying to very fast and fun. I read a lot of conflicting opinions about lifting the engine and personally concluded that it could only make it worse as would have the same effect as trimming it up. But as I say opinions differ widely on this!
So a few drums of water in bow would be an excellent starting point.

pic of how much I moved it forward

and the final configuration

teamplonker · 03 March 2013, 20:39

Quote:

Originally Posted by TomKat

I had a similar problem on my 4.8m boat with a 75hp 2 stroke (biggest engine hte hull can take) and moving the console forward 400mm pretty much sorted it out, it went from being frankly terrifying to very fast and fun. I read a lot of conflicting opinions about lifting the engine and personally concluded that it could only make it worse as would have the same effect as trimming it up. But as I say opinions differ widely on this!
So a few drums of water in bow would be an excellent starting point.

pic of how much I moved it forward

I have been thinking that raising the outboard would lower the center of gravity making it feel more unstable

C-NUMB · 03 March 2013, 21:39

Quote:

Originally Posted by teamplonker

I have been thinking that raising the outboard would lower the center of gravity making it feel more unstable

That's true, but i don't think lifting the engine an inch would do much on CG. A SR has a very low center of gravity....tried to turn mine around, its not easy. I guess standing or sitting down on the bench have a bigger impact than that on CG?

Not two boats are the same, sometimes lifting engine helps, sometimes not. Try to borrow another prop along with swapping weights in different positions, that might sort it out.

Nos4r2 · 03 March 2013, 21:40

Quote:

Originally Posted by teamplonker

I have been thinking that raising the outboard would lower the center of gravity making it feel more unstable

No, it'll be fine.

Having read how you were taught to trim,that could partly be at fault as well. SR5.4's respond really positively to using the trim correctly.

Basically, here's what you do.

In flat water, trim out as far as is comfortable without hearing ventilation or getting chinewalk. Be aware if you're doing that, you'll ventilate in sharp turns so you need to trim in and reduce throttle then bring it back on and start trimming out again if you're going for a flat out run again..

If it's rough.
If you're heading into the waves, trim in to keep the bow down so you don't feel the bow 'flying'.
Let the V of the hull cut through the oncoming waves. If you take off a lot, and you feel a double slam all the time as you land you're trimmed out way too far. A 5.4 will chinewalk if you're trimmed out too far heading into the waves.

If the waves are behind you and you're catching them up, trim out as far as you can-you want to keep the bow up or you'll bury it in the next wave. Work tghe throttle to keep the bow up as well.