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Old 07 January 2011, 10:22   #1
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Osprey Vipermax 7.00 issues

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.
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Old 07 January 2011, 11:02   #2
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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.
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Old 07 January 2011, 11:05   #3
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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.
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Old 07 January 2011, 11:12   #4
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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.
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Old 07 January 2011, 11:13   #5
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Thanks for the link.

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

Regards.

Jcn.
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Old 07 January 2011, 11:19   #6
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Still, 8cm still sounds too high for the lowest position. How much does the jack move?

Have you spoken to Roy at Osprey UK?
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Old 07 January 2011, 11:23   #7
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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.
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Old 07 January 2011, 11:32   #8
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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.
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Old 07 January 2011, 11:33   #9
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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?
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Old 07 January 2011, 11:34   #10
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BTW can you set any height on the jack or is it either up or down?
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Old 07 January 2011, 12:01   #11
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I'm not an expert on performance boats and certainly won't claim to know half what the guys at BMC do but I'll air my thoughts anyway!

Steering: Assuming the helm pump is correctly matched to the cylinder, which at 2.1cu sounds like it is, then it's fairly safe to assume this is not where your problems lie re heavy steering. The Seastar pro system is suitable for your application and certainly up to the job.

As far as weight distribution is concerned, we don't know how much extra is in the reinforced transom but I doubt it's a significant amount, not enough to ruin the boat anyway.

So what's left to look at?

Engine height: I know performance boats run with motors set higher than the usual 2.5cm above keel but 8cm at the lowest? Assuming your CMC gives 5" (12.5cm) of travel that means your range is from 8cm right up to 20cm (8") Sounds really high to me, has the jack been fitted to allow you to move the engine down on the jack, or lower the jack on the transom? Worth a try I think.

Engine offset: I can't be bothered to work out if BMC moved it off centre in the right direction, I'll assume they have. But 30mm doesn't sound much for a 300 hp motor. Saying that I don't think the effect of going another 10-20mm would make a "massive" difference.

Prop selection: If I had to put money on it, I would say this is where most of your problems lie. I've experienced how heavy steering can get with the wrong prop, you would be suprised. It can also effect how the boat steers, eg start a turn and the prop can try to tighten the corner forcing you to have to forcibly pull the wheel back to centre.
I'm not that familiar with all the props you mention, but some I think are stern lifting props designed for bigger, heavier boats. This could be causing the back of the boat to get skittish, something like a Laser II might be worth a try, it's a fairly predictable, standard issue powerboat prop designed more for giving bow lift. I don't know much about your hull design, if it is very performance oriented then you can expect it to get flighty under certain conditions, specially when you back off the throttle at high speed.

With a set up like yours you need to accept that there's a trade off for all that top end speed and it's going to demand more user input with the controls to get everything right and allow the boat to perform properly.
With the addition of variable engine height as well as trim in/out, it's going to take a long time to get to know the boat and learn to interprete what she's telling you.

Getting your hands on as many props as possible to try out could be one of the keys to success, unfortunately you've shot yourself in the foot buying a counter rotating leg, although if you can find the right ones second hand they tend to be much cheaper. Pairs of props often get split up to use the RH, leaving the LH sat on the shelf gathering dust. The other problem is CR legs tend to wear out much quicker than RH legs, something about direction of the thrust acting on bearings etc.

I'd also suggest getting on to the Scream & Fly forum and repeating yourself there, there's a lot of guys there running the type of set up you have (just without the tubes) and might be able to offer advice.

Hopefully that gives you something to think about
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Old 07 January 2011, 12:03   #12
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Thanks for your precious advices guys.

The problem is that if I lower the engine too much the steering system will block on the transom.
Even with the current height if I trim too much without lifting the engine up first the steering block and there is a big risk of damage the hydraulic cables.

Then I am reaching my top speed at less than half way up on the jack plate. Indeed if I lift more I am loosing speed. The pitch is clearly too small.

The boat is currently in South Bretagne in France.
Sorry for my poor english. But do you mean by "putting it in clean water" Andy ?

Thanks.

Regards.
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Old 07 January 2011, 12:13   #13
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Quote:
Originally Posted by Vipermax View Post
The problem is that if I lower the engine too much the steering system will block on the transom.
The big problem with using jacks. Can you rearrange the hoses or even fit 90 degree elbows etc? Or will the cylinder still hit?

Quote:
Originally Posted by Vipermax View Post
Then I am reaching my top speed at less than half way up on the jack plate. Indeed if I lift more I am loosing speed.
This is telling you your engine is too high. You should only start to lose speed near the top of the jack's travel. The prop obviously needs more "clean water".

Quote:
Originally Posted by Vipermax View Post
.
Another username I thought would have been taken already
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Old 07 January 2011, 12:13   #14
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Yes you are probably right Martini. I should check several props first. It will be certainly the cheapest way to begin. Unfortunately prop such as Fury or Bravo 1 xs do not exist in counter rotation. That is a shame !

Other rib riders in France told me that the pb could comes from the height of the shaft (25). They recommend me to take a 20. But that means that in the lowest position the anti cavitation plate would be at around 12 to 15cm above the hull....

I have also heard about "torque tab" you can put at the end of the gear box in order to reduce torque effect which could be the cause of the "heavy steering" problem.

Thanks.

Regards.

Jean-Charles.
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Old 07 January 2011, 12:19   #15
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I think I can lowered the engine from 1 hole in the jack plate. (I am at the middle position for the moment). But if I do more I think I will damage the steering or/and the overall hydraulic system.

Yes you are certainly right about the height of the engine. But I was thinking, because I was using a 10cm thick jack plate; that I will able to "take" the water further behind the boat and the propeller will evolve in the rear wave of the boat which is higher than the botom of the hull. (I am not sure I have explain correctly just let me know).

Am I wring ?

jean-charles
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Old 07 January 2011, 12:21   #16
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Here there are couple of pictures of the set up.
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Old 07 January 2011, 12:32   #17
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Quote:
Originally Posted by Vipermax View Post
But I was thinking, because I was using a 10cm thick jack plate; that I will able to "take" the water further behind the boat and the propeller will evolve in the rear wave of the boat which is higher than the botom of the hull. (I am not sure I have explain correctly just let me know).
I get you mean, you're right but the water level will only rise an inch or two (2.5-5cm)
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Old 07 January 2011, 12:33   #18
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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 .
This guy has a 800mm longer hull and TWICE the gee gees!!!! YEEEHAAAA!
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Old 07 January 2011, 12:41   #19
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Quote:
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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.
This is what I said you wind up Nobber
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Old 07 January 2011, 12:44   #20
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Quote:
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The boat is currently in South Bretagne in France.
Sorry for my poor english. But do you mean by "putting it in clean water" Andy ?

Thanks.

Regards.
So that the prop is biting into undisturbed water.

Where in Bretagne do you live? Vannes?
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