Avon unstable at speed

teamplonker · 01 March 2013, 22:40

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

NSS · 01 March 2013, 22:46

This should be interesting. Someone daring to suggest a Searider might be unstable. My guess is it must be a Chinese copy ;-)

ribsta · 01 March 2013, 23:25

Hi, it is quite surprising you can get this from your 75 four stroke. Normally SR 5.4 won't chine hop until about 37, 38 knots. My guess is you might be trimming the engine up a bit too much and rising the bow high. With the added weight of the 4 stroke might make a difference to trim. If you think you're not, then not sure about this. I have a 85 yamaha 2 stroke on a 5.4 and actually find it hard to chine hop until getting about 37 knots. A possibility is the build of the Deluxe version on the early models seamed to be lighter than rescue version. That might make a difference. Not sure which you have.

Nos4r2 · 01 March 2013, 23:40

The Honda 75 is a heavy lump as well, that might contribute a bit.

teamplonker · 02 March 2013, 00:02

Quote:

Originally Posted by ribsta

Hi, it is quite surprising you can get this from your 75 four stroke. Normally SR 5.4 won't chine hop until about 37, 38 knots. My guess is you might be trimming the engine up a bit too much and rising the bow high. With the added weight of the 4 stroke might make a difference to trim. If you think you're not, then not sure about this. I have a 85 yamaha 2 stroke on a 5.4 and actually find it hard to chine hop until getting about 37 knots. A possibility is the build of the Deluxe version on the early models seamed to be lighter than rescue version. That might make a difference. Not sure which you have.

I am unsure of model
I think it was trimmed correctly, the boat was level on plane but as soon as I nailed it I thought I was going to lose control a feeling i have never had on a boat before.
Do you think fins may give a little more stability.

Nos4r2 · 02 March 2013, 01:19

Quote:

Originally Posted by teamplonker

Do you think fins may give a little more stability.

No.

Changing the weight distribution a bit might.

bkils@mac.com · 02 March 2013, 01:47

I have a SR4 w/ a 50 2stroke Yamaha and put fins on the outboard once, which made it extremely unstable. With no fins she starts chine walking at 35+ if trimmed up too high with only one person in the boat.

HUMBER P4VWL · 02 March 2013, 06:28

We had modern 90 2stroke opti on 5.4

It flew, but only chine walked right at top end.

There's something amiss

teamplonker · 02 March 2013, 06:37

I only had me and my son on the boat ,The boat is set up with a jockey console positioned centrally and a fuel tank directly behind the console . At low speed the boat sits level .
Will the boat feel more stable with more passengers ?
Would the console be better positioned further forward?
Am I trimming the boat wrongly ?
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.

whisper · 02 March 2013, 06:51

Trim it all the way in and then trim it out slowly until it starts to feel wobbly.

Things to look for, trim tab behind prob needs adjusting, the engine should be offset to the starboard on the transome, get some more weight upfront. Also check to make sure that your gear box is a righthand (clockwise) rotating.

It might be when it's right up on the planing pad you are not used to it. Can you get another member to drive it?

We are out today if you are in the south?

treerat · 02 March 2013, 06:57

I've used Joc's boat before and never found her unstable. However she was always loaded.

With 1 person and no kit on board it sounds to me like a center of gravity thing.

Trim as above or make sure you have enough weight in front of the console. to balance the fuel tanks etc that are behind it.

C-NUMB · 02 March 2013, 07:01

Mine is stable until 36-37 knots, chine walking in 30 knots, no way. How about slack in steering system, that might explain the issue?

teamplonker · 02 March 2013, 07:05

Quote:

Originally Posted by whisper

Trim it all the way in and then trim it out slowly until it starts to feel wobbly.

Things to look for, trim tab behind prob needs adjusting, the engine should be offset to the starboard on the transome, get some more weight upfront. Also check to make sure that your gear box is a righthand (clockwise) rotating.

It might be when it's right up on the planing pad you are not used to it. Can you get another member to drive it?

We are out today if you are in the south?

Thanks for the offer I am in the southwest ( Bristol ) and it would be great for someone else to try the boat but unfortunetly I have a lot of work on today.

I think I will try it with a little more weight in the front .
Are you saying the outboard should be sat slightly to the left on the transom?

whisper · 02 March 2013, 07:08

Quote:

Originally Posted by teamplonker

Thanks for the offer I am in the southwest ( Bristol ) and it would be great for someone else to try the boat but unfortunetly I have a lot of work on today.

I think I will try it with a little more weight in the front .
Are you saying the outboard should be sat slightly to the left on the transom?

As you are standing at the back of the boat and looking at the outboard it should be offset to the right. This is the correct way to rig it but many have their outboards in the middle.

I have an sr too that I hope to take out next weekend?

teamplonker · 02 March 2013, 09:31

Quote:

Originally Posted by treerat

I've used Joc's boat before and never found her unstable. However she was always loaded.

With 1 person and no kit on board it sounds to me like a center of gravity thing.

Trim as above or make sure you have enough weight in front of the console. to balance the fuel tanks etc that are behind it.

Thanks
I think the weight maybe the issue

teamplonker · 02 March 2013, 09:35

Quote:

Originally Posted by whisper

As you are standing at the back of the boat and looking at the outboard it should be offset to the right. This is the correct way to rig it but many have their outboards in the middle.

I have an sr too that I hope to take out next weekend?

I have referbished many old boats all with outboards but never refitted the outboard with an offset, Always straight down the middle.

If factory purchased does a boat come with the outboard offset ?
What are the benefits ?

teamplonker · 02 March 2013, 09:43

Quote:

Originally Posted by C-NUMB

Mine is stable until 36-37 knots, chine walking in 30 knots, no way. How about slack in steering system, that might explain the issue?

The steering is fairly new so I don't think its that.
I think it maybe not enough weight up front or could just be me not used to it and this is how it feels.

Alan Priddy · 02 March 2013, 09:45

The Engine is in the wrong place Alan P

alystra · 02 March 2013, 10:25

Quote:

Originally Posted by teamplonker

I have referbished many old boats all with outboards but never refitted the outboard with an offset, Always straight down the middle.

If factory purchased does a boat come with the outboard offset ?
What are the benefits ?

My Humber 5.3 was factory fitted with a Merc 90 4str. offset 2 inches to starboard. I believe the idea is to counteract the propeller torque which, when planing, will tend to make the boat heel to port.

With one or two people aboard it could start to chine walk beyond 35 knots (max 39). In calm water (and I wouldn't want to go that fast in lumpy water) I found harsh, WOT acceleration would initiate a chine walk. With gradual acceleration it remained stable.

The Merc was replaced by a Honda 90, which is around 30 kg lighter. It took me a season to sort out the fore and aft gear stowage and get the weight distribution right so I got the same performance out of the boat. With less weight on the transom, she feels more stable flat out too. Only chine walked once since, again as a result of harsh acceleration at near 40 knots.

Of course, I know it's not a Searider.

C-NUMB · 02 March 2013, 10:36

Can't swear my engine is totally in center(need to check) but have a vague memory that previous owner moved the engine from offset to centre of transom, so not so sure that is the issue, as it works fine on this boat.

At least I would not start with moving the engine sideways at this stage. But would try another propeller and also playing with weights also sideways. My console is offset to starboard.

SR 5.4 dos not have a significant planning pad, but think it would have less high speed chine walk if it would.