New to me ribs trying to kill me

[Smagu]

So I recently “upgraded”
From a 5.2m Humber assault with a 80hp 2 stroke Yamaha

To a 5.6m osprey stealth eagle with a 2005 mercury 4 stroke 115.

First outing today.

Whilest powering up the rib violently tipped to the starboard. I did manage to solve this with adjusting the trim.

Now at full speed 34mph 1pax and full tank of fuel the rib shifts from left to right (resolved by going slower). Is this called chime walking?

This forum has helped me so much with my first rib and would appreciate any advice with this one.


I didn’t have any of these issues on my old rib. Is this normal for some?

Is there something I can do differently?

Does 34mph seem a little slow? I mean my 2 stroke 80 would easily do 38mph. I know it’s 2 stroke but there’s 35hp different there.

The other rib did have hydraulic steering. This one doesn’t and I really feel that any little turn under power and the rib wants to change direction. Again normal for cable steering?

I can take some photos of things tomorrow if there’s anything people would find beneficial.

Any advice greatly appreciated

(Side note anywhere know where I can buy a workshop manual. Even an online one)

[beerbelly]

i had an osprey eagle that was less than predictable .mine would if crossing someone elses wake just flop to one side quite violently and behaved similar in certain confused seas was absolutely fine on flat calm water and would top 40+knotts..i put it down to the fact it had an extra long leg outboard that was also counter rotating.the outboard was set as high as it could be to try and get the cav plate in line with the keel it didnt behave so unpredictably with it lower but produced a massive rooster tail .i gave up in the end decided it needed a different outboard and sold it on

[Nasher]

If you are taking more pictures, it would be helpful to see some images of the engine on the transom, particularly the relationship between the Cav plate and hull.

Also if the engine has been offset to one side when fitted or not.

What prop is fitted and what revs are you achieving at 34mph?

I assume you've checked the basics like play in the steering?

[Smagu]

Thanks for the direction so far.

So as for steering play. I have roughly 30degrees movement (assuming one turn of wheel is 360 degrees). This is only from going full lock right to turning left.

Outboard position looking at the boat from behind the outboard is 43cm from the port side and 42cm from the starboard

Prop is 13x19 (sorry unable to check RPMs currently)

Cavitation plate is 9cm below the transom

Throttle position seems to be in the WOT slot

I have attached some photos


Outboard seems quite low. Would that affect speed this much? Would raising it risk damage to the transom? Would it make handling worse? There is no plate on the boat saying may outboard HP/ weight?

Sorry for all the questions.

[Orwell boy]

Is the hull dry below the floor ? ,sounds like a load of water changing direction?
quite surprised to read beerbelly,s resume of his as i thought they were one of the good british builds ?

[Smagu]

I wonder if I have bought your old boat 😂. Sounds like mine

[Smagu]

This I am unsure of. The deck was flooded last week with rain water. But there’s no bung below the deck level on the transom.

I did see some water draining down the side of the console. (Small stream of bubbles). As this is my first time out on it I’ve nothing to compare it to. I actually bought a bung to install.

What I will say tho is I didn’t notice it any heavier to tow/ push. Hard to hear anything as it’s full of fuel too.

[Pikey Dave]

If I didn't know any different I'd say that engine is too long for the transom. Looks like an XL engine on a L transom. Can you measure from the transom to the keel & get the model number of the engine?
Engine running too low will reduce the top end speed as you have more drag, also a too deep prop will exacerbate prop torque, causing the tilt to STBD.

[Smagu]

From transom to keel is 54cm

Engine numbers are
115f23dy

Then serial 1B202085

[beerbelly]

engine looks too low like mine with a xl leg on a longshaft transom .its not my old one as that went to poland seems to have the same issues though. to be fair though with a little care i could work around most weather conditions and it wasnt too bad just had to be carefull .no such issues with my current humber

[beamishken]

Engines too low jack it up so av plate is 1" above the hull get a tacho & try again without a tach your wasting your time

[Smagu]

Originally Posted by beamishken

Engines too low jack it up so av plate is 1" above the hull get a tacho & try again without a tach your wasting your time

I can get it up 4cm using the existing holes. (This would leave it at the very top of the transom). The cav plate would be 4.5cm below keel (currently is 8.5cm).

Any higher I’d need a jack plate.

[Pikey Dave]

Originally Posted by Smagu

From transom to keel is 54cm

Engine numbers are
115f23dy

Then serial 1B202085

That's a 21" long transom, but I can't make sense of the engine numbers/model. Have you got a photo of the plate?
As Ken says, without any RPM data, we can only make educated guesses.

[Nasher]

As has been said, the Cav plate is far too low, and without being able to measure the revs you won't get anywhere deciding if it has the correct prop.

The transom can be raised with a piece of 15mm Ali plate.

.

[Steve509926]

I've never had a rib, however, is that a Dole Fin attached to the AV plate? Wouldn't have thought that's helping much with the issues you're having.

[Smagu]

Ok so my plan is I’m going to raise the outboard up 4cm (max I can go). See what speed and rpm I am at with this reading.

Remove the whale tail things to see if that makes a difference.

I’ll do this over the next few days and update from there.

Thank you everyone for your advice

[Smagu]

Unfortunately can’t raise mine like this as it hasn’t got a cut out. It’s sitting at the top of the transom

[Nasher]

Originally Posted by Smagu

Unfortunately can’t raise mine like this as it hasn’t got a cut out. It’s sitting at the top of the transom

Why can't the top of the plate be higher than the top of the transom?

I can't think of a reason why it has to be level or below the original transom.
15mm Plate will more than handle the load.

[beamishken]

Originally Posted by Smagu

I can get it up 4cm using the existing holes. (This would leave it at the very top of the transom). The cav plate would be 4.5cm below keel (currently is 8.5cm).

Any higher I’d need a jack plate.

You need a jack plate! Or a longshaft engine instead of xl or a conversion kit depending on engine
Nashers suggestion should work

[Nasher]

Originally Posted by beamishken

Nashers suggestion should work

It's been tested on my Ocean for 18yrs.

I settled on 15mm plate after talking to the boat builder on Hayling at the time manufacturing commercial Aluminium catamarans.
They assured me 10mm would be enough, but me being me went with 15mm, just to be sure.