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Old 25-08-2014, 04:21 PM   #1
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Loosing steering

Hi has anyone tried lengthening there outboard Skeg to regain steering and did it work??

I have found as I raise my 300xs on it's lifter I am loosing steering and the arse of the boat feels loose and slides if you attempt any steering.

I have tried flat out runs with the engine at its lowest setting on its lifter ( it's already high) and it feels a bit loose. As I raise it gets worse, but speed is still increasing slightly.

I have only done flat out runs with 1" of lift, I have tried driving the boat with the full 5" and it just slides all over the place if you try adjusting the steering.

Any ideas on how to fix this anyone??
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Old 25-08-2014, 07:56 PM   #2
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What speed is this problem at and how high is the centre of torpedo in relation to the read pad?
Could be that its bow steering a bit and needs more load on the aft step? Can you move the CG aft?
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Old 25-08-2014, 08:52 PM   #3
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Had a similar problem then changed to a 4 blade prop and problem solved,what prop you using ?
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Old 26-08-2014, 12:12 AM   #4
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Hi Guys

I'm using bravo 1 props at the moment. This particular test was with a 24 that has been thinned down two steps back from collapse.

The problem became worse after I fitted one of my lightened and balanced flywheels.

It seems after some research that mercury racing sell the bravo 1 prop with different length exhaust tubes. The longest stock length tube gives more stern lift and mercury racing are now selling a bravo 1 with a shorter exhaust tube claiming more bow lift, less stern lift and higher top speeds.

Also the angle of rake is 20degrees on the bravo 1 props.

I'm going to try a mercury revolution4 prop which has between 22/23 degrees of rake giving better bow lift, but that is separate testing.

So getting back to the issue in hand, I'm going to start trimming the exhaust tube in 5mm increments to start with until I find negative gains.

My theory is after the lighten flywheel was fitted the engine released more exhaust gases when the pedal hit the metal and gave more stern lift through the long exhaust tube.

Also the engine has higher rpm since the lightened flywheel, with the same prop. So again more gases are being released through the long tube.

Any thoughts, ideas?? Has anyone experimented shortening exhaust tube lengths???

Thanks Dave
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Old 26-08-2014, 12:27 AM   #5
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Dave, your motor is too high thats all.
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Old 26-08-2014, 01:12 AM   #6
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Paul have a read of this.

http://www.mercuryracing.com/propellers/bravoixs.php

My first response after I fitted the lightened flywheel was the handling had changed and the arse felt loose.

The speed was still increasing as I raised the engine, but the handling was getting worse.

So do I, lengthen the Skeg or shorten the exhaust tube??
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Old 26-08-2014, 01:16 PM   #7
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We have only ever used 3 blade props on that hull, you should be lowering the engine for corners and it should have enough steering to keep you in a straight line of you have blow out from the 4 blade prop.
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Old 26-08-2014, 04:26 PM   #8
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Hi Cookee

I had an interesting chat with one of Mercury Racings prop guys and he thinks that the rev4 prop would be better. It has 22/23 degrees of rake, the bravo 1 is only 20.

He thinks that would give us better bow lift and he confirmed that by shortening my exhaust tube it will change from stern to bow lift. However he said that really we need to test it small increments.

If during one of our flat out runs I raise the lifter to high and bearing in mind the arse of the boat is slidey, now pretty much from the lowest setting. But certainly with 1" of lift, we have 5 and 1/2 max, What is likely to happen?

Cheers Dave
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Old 26-08-2014, 05:12 PM   #9
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Cutting the barrel down definitely works... A Raker with the barrel cut completely off had way more bowlift than one with full length on my boat. We've just cut the flair off on a laser but haven't tested it yet, I'm hoping to get halfway between a stock laser and a stock Raker.

If you're feeling the boat get loose to the point it's scaring you then I'd say you're running the motor too high. The Bravo 1 XS you linked to is a different prop to your bravo 1s. We ran a Rev 4 on my Bernico when it had the 200HO. A Bravo 1 handled better but was noticeably slower. The Rev 4 gave more all round lift compared to a Trophy which was a definite bow lifter!
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Old 30-08-2014, 07:31 PM   #10
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Interesting Thanks. I have picked up another cheap Bravo 1 prop. But it says mercruiser down the side. It's still on flo torq hub, so will fit my 300xs fat shaft.

What's the difference?? I just assumed it would be a bit beefier and would need thinning down more.

Also when you say the bravo 1 I linked to is a totally different prop, aren't the blades the same?? I thought the difference was in the exhaust tube length and the finish that you get from mercury I.e how thin the blades are?

I have spoken with a guy at mercury racing and he has given me some measurements to work with, but made clear that there only a guide line and length will need fine tuning. The rev4 prop I have has a huge exhaust tube it's like 60mm long.
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