Blue band mercury problems

[Grimacejane]

I have recently purchased a 14ft Brooker aluminium boat with a 20hp mercury outboard. At low to medium revs, all seems ok, but when the acceleration is increased, the engine seems to rev highly with little increase in power or speed. It is like a clutch slipping in a car etc. I thought it may be cavitation around to prop, but it happens when going straight. The cavitation plate is below the bottom of the boat but some water is getting pushed back towards the back of the boat from the motor. I did get it planing the other day, but I had to gradually increase the acceleration. It still appeared to be revving higher than it should be, with that slipping of the clutch type thing happening. When the acceleration is decreased, at about 50 per cent I could here it stop slipping and all seemed to be back to normal (as in revs appropriate for the speed). With 4 people in the boat, once past about 50 per cent revs it just revs up when acceleration is increased for basically no extra power output.

 

[Dunaruna]

Re: Blue band mercury problems

Hi Grimacejane, welcome to iboats!!<br /><br />Sounds like a prop hub slipping. The hub in the centre of the propellor is rubber mounted (like the harmonic balancer on a car). Pull the prop off and take a close look for cracks, if everything looks ok, put a mark on the hub and a corresponding mark on the prop - go for a spin. Recheck the marks to see if they are still aligned.<br /><br />If they are not, you need to get the prop rebushed.<br /><br />Where are you?<br /><br />Aldo

 

[burnboyy]

Re: Blue band mercury problems

Yup, sounds like you spun a hub

 

[Grimacejane]

Re: Blue band mercury problems

I am in Newcastle, Australia. I will give it a go and see what happens. As tomorrow is Australia day, I will give it a try tomorrow. Thanks for the tip, and I will let you know of the result.

 

[Chris Graham]

Re: Blue band mercury problems

Hi All<br /><br /> As Sam Kekovich from the TV Add would say Have a lamb Chop and a "BOAGS" Beer and head out on the Water fo Aus Day. Well Thats what Im doing anyway. <br /><br />Hope you get the Prop Hub Fixed in Time.<br /><br />Regards<br />Javelin <br />Launceton, Tasmania

 

[Dunaruna]

Re: Blue band mercury problems

Hey Javelin, I believe you may be the first tassie to grace these forums. <br /><br />Boags is a great drop, in fact, I might even crack one right now.<br /><br />Cheers.

 

[triman]

Re: Blue band mercury problems

Slowly but surely the Boys from Godzone are taking over the world, starting with this forum thread.<br />Welcome Javelin, although I must admit, for a Victorian, that Cascade Premium Light is possibly the finest light beer I've ever tasted. Even took some to Guam and Ulsan on a delivery.

 

[Rob Isaacs]

Re: Blue band mercury problems

Well looks like there are a few of us here from down under.

 

[Grimacejane]

Re: Blue band mercury problems

Dunaruna (and anyone else),<br /><br />I have done what you said about marking the hub etc etc and I took it for a spin. The same problem still exists and once at home, I checked where I had marked it and it was alligned perfectly. Maybe a cooincidence, but I will check it next time I go out. I did notice that when I was going along there is some water splashing back from the leg towards the boat. It is as if something is out of alignment, but only just. Iy is hard to say whether this is causing some cavitation or not. Some more advice would be good.

 

[Dunaruna]

Re: Blue band mercury problems

If the hub is not broken (spun) then there may be a problem which is causing ventilation. The symptoms for a spun prop hub & ventilating are the same, broken hubs are way more common though.<br /><br />Can you post a pic of the back of the boat, and maybe the prop?

 

[andrewkafp]

Re: Blue band mercury problems

Whats all this ??<br /><br />Aussie invasion <br />Watched that big US Carrier go past my place the other day... Imagine doing the water pump on that thing..