Avon unstable at speed - Page 2

Al Baker · 02 March 2013, 17:43

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

In my experience sea riders tend to chine dance if you put a four stroke on them. In general four strokes are heavier than 2 strokes they also tend to sit higher up. Seariders don't like having a high centre of gravity due to their deep V hull which was designed before 4 stroke outboards became popular. There's a lot of them around now with 4 strokes on. Quite often with their self ballasting holes blocked up so they don't sink at displacement speed.

teamplonker · 02 March 2013, 19:47

Thanks for all the advise, after listening to you all and watching some videos of avon seariders out on the water I am starting to think that it may be me expecting a little to much from the boat as it is.
My little caribe at 35mph feels very stable and I was expecting to get around 40+mph from the avon with the same stable feeling.
If i get the chance tomorrow I am going to take the boat out again but with some empty 25 ltr drums and fill them for ballast and see if there is a difference.

I am going to change the console position forward soon any way to get more seating for passengers, if the barrels make a difference then it will be a judge of how it will perform once the console if moved

If there is no improvement then I will look at moving the outboard

Would be nice to get someone who has a similar boat to take mine out and let me know what they think

ribsta · 02 March 2013, 19:50

Hi, It might be worth putting a few photos of the boat in here so we can get a feel for the layout and console position. Take a picture of the stern looking forward as well.

Nos4r2 · 02 March 2013, 21:18

Quote:

Originally Posted by ribsta

Hi, It might be worth putting a few photos of the boat in here so we can get a feel for the layout and console position. Take a picture of the stern looking forward as well.

Agreed. The standard offset console on the 5.4 should negate the need for offsetting the engine, but if you have a centrally mounted console it may be a different story.

treerat · 02 March 2013, 21:36

She was used for mark laying and team boat for the last few years so would have been set up for the anchors, weights, chains etc that she usually carried.

RIB-Teccie · 02 March 2013, 22:16

I ran a 5.4 SR (offshore oil type) with an 85 yam for years with no chine hop. However on a 6m SR with twin 75hp yams she run with the port sponson lower in the water i.e, she heeled to port and didn't feel level. The steering was also stiff. This was cured by raising the engines by one hole so the cav plate was an inch above the hull. The 5.4 also was better with the set up. My guess is if you do this it will improve. Also put two 25l fuel tanks forward of the console. Remember the 90 hp rating is for a two stroke. You must remember the 4 stroke is governed by the weight rating not the hp rating and 90hp 2 strokes were around 120kg. How heavy is the 75 honda?? Finally my next project may be to fit twin 55yams to a 5.4 so watch this space.. I have been out in huge seas in the 5.4 and have never felt as if it was out of its depth. For what they were back in the day, they were safe and guaranteed to put a smile on your face.

teamplonker · 02 March 2013, 22:44

Quote:

Originally Posted by RIB-Teccie

I ran a 5.4 SR (offshore oil type) with an 85 yam for years with no chine hop. However on a 6m SR with twin 75hp yams she run with the port sponson lower in the water i.e, she heeled to port and didn't feel level. The steering was also stiff. This was cured by raising the engines by one hole so the cav plate was an inch above the hull. The 5.4 also was better with the set up. My guess is if you do this it will improve. Also put two 25l fuel tanks forward of the console. Remember the 90 hp rating is for a two stroke. You must remember the 4 stroke is governed by the weight rating not the hp rating and 90hp 2 strokes were around 120kg. How heavy is the 75 honda?? Finally my next project may be to fit twin 55yams to a 5.4 so watch this space.. I have been out in huge seas in the 5.4 and have never felt as if it was out of its depth. For what they were back in the day, they were safe and guaranteed to put a smile on your face.

So it maybe completely the wrong type of engine for the boat if i want to go at top speed from A to B.
Its funny as it was the outboard that attracted me to the package being as it was Big, Honda and 4 stroke, The rib and trailer just came with it and they looked tired and tatty .

teamplonker · 02 March 2013, 22:45

Quote:

Originally Posted by treerat

She was used for mark laying and team boat for the last few years so would have been set up for the anchors, weights, chains etc that she usually carried.

How do you know the boat so well

teamplonker · 02 March 2013, 22:49

Quote:

Originally Posted by Nos4r2

Agreed. The standard offset console on the 5.4 should negate the need for offsetting the engine, but if you have a centrally mounted console it may be a different story.

pics from ad when i bought it last week, I will take some better ones from all angles this week.

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willk · 02 March 2013, 22:58

Quote:

Originally Posted by teamplonker

How do you know the boat so well

The same way I knew this boat without having to ask. The RIB world is MUCH MUCH smaller than you might think. Everywhere I go, I meet people and boats that I've heard of/seen previously.

Nos4r2 · 02 March 2013, 23:15

Quote:

Originally Posted by teamplonker

pics from ad when i bought it last week, I will take some better ones from all angles this week.

Thats one of Leeways consoles. Centrally mounted and the boat looks like an old Deluxe-a leisure model.It might be lighter than the offshores.

The motor should really have a little offset, and it also looks from the pics like the console is a bit further back than standard but that could be an illusion caused by the camera.

RIB-Teccie · 02 March 2013, 23:16

The console is no longer offset on that RIB. Also is it further aft than the standard console, I can't tell. However I would still try to get weight forward and raise the engine by a hole. You could try re propping to achieve max permissible RPM as a smaller pitch prop helps stop the heeling over to port.

falcon0310 · 02 March 2013, 23:23

I think the Honda is same as 90 Honda and would guess that 97/ 98 engine weight is169 kk, if that helps

teamplonker · 03 March 2013, 00:11

Quote:

Originally Posted by RIB-Teccie

The console is no longer offset on that RIB. Also is it further aft than the standard console, I can't tell. However I would still try to get weight forward and raise the engine by a hole. You could try re propping to achieve max permissible RPM as a smaller pitch prop helps stop the heeling over to port.

The console was further forward the previous owner removed rear seat console and moved steering console further back.
pic shows how it was

teamplonker · 03 March 2013, 00:13

Quote:

Originally Posted by falcon0310

I think the Honda is same as 90 Honda and would guess that 97/ 98 engine weight is169 kk, if that helps

Its a 98, Bit disappointed with the age as joc said it was a 2004

Nos4r2 · 03 March 2013, 00:19

I wouldnt put the console quite as far forward as it is in your pic above if you do move it forward-it won't be comfortable. I'd go with raising the engine a hole as well just to try it before you do anything else though. My Yam is about 1 hole up.

That's a HEAVY motor.

teamplonker · 03 March 2013, 00:23

Quote:

Originally Posted by Nos4r2

I wouldnt put the console quite as far forward as it is in your pic above if you do move it forward-it won't be comfortable. I'd go with raising the engine a hole as well just to try it before you do anything else though. My Yam is about 1 hole up.

That's a HEAVY motor.

In what way uncomfortable ?

Nos4r2 · 03 March 2013, 00:26

The further forward it goes, the more your body goes up and down-a bit like a reverse wheelbarrow.

teamplonker · 03 March 2013, 00:54

So in conclusion.

More forward weight, But not people weight.
Engine higher on transom, and poss offset to the right.
No harsh/sharp acceleration at high speed, smooth and even.

I think I may keep a look out for a different make of rib that is more stable to put my engine on. A little more research maybe needed there.

Thanks to you all for the help and advise

Nos4r2 · 03 March 2013, 01:20

Quote:

Originally Posted by teamplonker

So in conclusion.

More forward weight, But not people weight.
Engine higher on transom, and poss offset to the right.
No harsh/sharp acceleration at high speed, smooth and even.

I think I may keep a look out for a different make of rib that is more stable to put my engine on. A little more research maybe needed there.

Thanks to you all for the help and advise

You're not going to find one. There's very little more stable than a well set up Searider. Yours just isnt very well set up for what you want to use it for.

I can do pretty much anything I want with mine-it's not even particularly bothered by a F8 (though I can be!), but it's set up properly and the 85hp on there weighs 50kg less than your 75.

You can move people weight forwards, just not loads. Being right in the bow of anything when it drops into a trough is painful. It's the same on any boat, and the advice you've had is the same as you'd get for any boat that isn't set up right.

You MIGHT find an oilrig spec or ex military one like mine is a bit less 'flighty' as they are a bit heavier.