Osprey Vipermax 7.00 issues

[Vipermax]

Hi everyone,

I am new on the forum and I am looking for any help in order to fix couple of issues I am encountering with my boat.
As I said I have recently bought a brand new Osprey Vipermax 7.00 with Kris Deraedt from Brugge Marine Center (BMC) and Marc Dano from Atlantic Ribs (France).

I wanted a High performance boat so in agreement with BMC and Marc Dano we fitted a Mercury 300xs with an CMC hydraulic lift at the back.
As you certainly know the 7.00 Vipermax is rated for a maximum of 250hp. Therefore to match with the CEE rules the structure and the transom have been totally reinforced. The transom has been switched to 58MM but the boat keep exactly the same dimension as the classic one. Only the weight slightly changes. The boat is a bit heavier.

The engine is a 2008 Mercury Optimax 300xs with a 25 shaft counter rotation fleetmaster shaft with gear ration of 1.75.1. (The last available on the French market that is why it is in counter rotation).

As I said I encounter some issues with my boat and I wonder if you will be able to help me in order to get further into the performance.

Here is the boat specification:

The boat has been fitted with a big fuel tank (220 liters) which in the middle. It is not a classic inox steel fuel tank but a "gel coat" tank moulded within the overall boat structure.
It has got four Solent RIB jockey seats with backrests and infill and the console is the sea-rider model without steel surround. (the one with two seats at the front).
The boat also got a raised bow with two lockers at the front.

The setting:

The steering is a 2.1 helm with a sea star pro direction for 300hp.
The engine has been shifted from 3cm to the left in order to avoid torque effect. The pilot seats is also on the left as well as the battery which is in the console.
When the lift is at the lowest position the anti cavitation plate of the engine is at 8cm above the lowest point of the hull.

The performance:

The current performance is 58 knots with a tempest plus 23 at 5950rpm. The engine over reps certainly because the pitch is too small.

Propeller tests:

With a maximus 26 the top speed is 58,7 knots with two people aboard and half fuel tank at 5800rpm. But the boat is impossible to drive. Indeed the steering is like a truck and even with two hands you can't turn the boat.
With a bravo 1 28 the max rpm is 5300rpm with the lift at the highest position and the speed is 53 knots with two people and 150liters of gas. And the steering is really heavy and very difficult to turn.
With a Bravo 1 26 the direction is better but still heavy and the top speed is around 55knots.

Conclusion:

According to my tests and Kris advices, which has been racing a 7.00 vipermax during the offshore belgian challenge, the most suitable prop is the tempest plus for the boat. He was doing +60knots with a 225 etec evinrude HO with hydraulic lift, interceptor console and a tempest plus 27 lab finished.

But the thing is that with my tempest 23 sometimes the boat has got some bad side effects. Indeed when I am at WOT and I am trying to reduce speed from 55+ to 45knots the boat seems to drift on his planning pad and go side to side which is very dangerous. The phenomena increase when the boat is lighter.
Then during hard curves under 25 knots the boat is strange. Indeed when I turn on the left the boat does not take many heel (almost nothing) and when I turn to the right the heel becomes nearly dangerous.

My general feelings is that the boat stick to the sea indeed when the sea is flat the boat seems to cruise, even at wot, on a bigger surface than just its planning pad. And I am disapointed about the top speed. Indeed when I bought the boat I was hoping more than 60knots.

As you will certainly notice and the transom picture there is a slightly difference of symmetry between the two latest "virure" from each side f the planning pad. Could it explain the problem on its own ?

If you need any information just let me know.

Best regards.

Jean-Charles Nocera.

ps: If you need more pictures just let me know.

[Hightower]

Offset is to the correct side. I have a CCW engine on my 6.2 Vipermax and it sits 1.25" (3cm) over to the port side. My engine is a 150 though so a bigger outboard might need to sit further over.

I would say that 8cm is on the high side for the outboard and would always recommend starting at a neutral position with the Cav plate level to the bottom of the transom.

This would explain why you are having handling problems in turns and are chine walking on deceleration. There's not enough prop and leg in the water to give bite to the prop. I thought the Idea of Jacks are to have great handling and stability in rougher weather and not to compromise on the top speed.

So drop your Cav plate to level with the hull with your jack plate in it's lowest position and start your set-up from there.

[Downhilldai]

Welcome to Rib.net & to Team Viper

Has the steering system been bled to remove all air bubbles?

You may wish to post this thread on www.boatmad.com There's a lot of guys on there running big Mercs.

[Vipermax]

Thanks Andy for your advices.

The yard which has done the set up has followed a simple rule which is "1cm of shifting for each hundred of horsepower".
I do not know if its good but on the solent and hydrosport ribs they have set up with 300merc xs it was brilliant.

Jean-Charles.

[Vipermax]

Thanks for the link.

Yes the steering system is clean and there is no air bubble in it.

Regards.

Jcn.

[Hightower]

Still, 8cm still sounds too high for the lowest position. How much does the jack move?

Have you spoken to Roy at Osprey UK?

[Vipermax]

The jack move to 12cm.

Yeah I have speak to Roy but he told me to see that with Kris from BMC who is the owner of Osprey.

Regards.

[Erin]

I am no expert on performance matters, but Andy's advice about reducing the height of the engine does make sense. The higher it is, the less bite the propellor has in the water, and therefore the more chance of different effects between turning left and right. I would try it set a little lower if possible and see if it makes a difference.

[Hightower]

I'm going to hazard a guess that the 23" prop is ventilating too much at WOT. You've got the speed with too many revs. Putting it in clean water might reduce the slip and lower the Revs which will give you better performance.

Where is the RIB now?

[Hightower]

BTW can you set any height on the jack or is it either up or down?