Engine noise

[Warpa]

Something i noticed while out this evening that i didnt feel last time out was a type of vibration. While up on the plain i thought i would max it out for a few seconds to see what it can do, the rev note went up but the speed didnt change and to be honest i cant really describe what i felt or heard. The leg was fully trimmed down, half a tank of fuel and me and one other adult in the boat.

it felt a little like my old inflatable with a 4.5hp merc outboard, if i trimmed it up it would over rev and create air pockets? around the prop and lose drive. This is on a 17' bowrider with 3L mercruiser IB. We were also traveling with the incoming tide along the Solent.

 

[sarabande]

cavitation probably. Is the prop nice and polished ? Any dings, especially on the trailing edge and suction side ?

 

[Seahope]

Something i noticed while out this evening that i didnt feel last time out was a type of vibration. While up on the plain i thought i would max it out for a few seconds to see what it can do, the rev note went up but the speed didnt change and to be honest i cant really describe what i felt or heard. The leg was fully trimmed down, half a tank of fuel and me and one other adult in the boat.

it felt a little like my old inflatable with a 4.5hp merc outboard, if i trimmed it up it would over rev and create air pockets? around the prop and lose drive. This is on a 17' bowrider with 3L mercruiser IB. We were also traveling with the incoming tide along the Solent.

Do you have a prop diffuser and is it still attached?

 

[Warpa]

Do you have a prop diffuser and is it still attached?

prop is in perfect condition, nice polished stainless steel. i have know idea what the diffuser looks like? I have a spare prop on board (the original) but that has a different fitting arrangement my engineer was telling me (the stainless is one piece) the spare one i have to make sure the inside bits dont fall out when fitting and removing.

 

[Warpa]

Not sure of your set up, but mine looks like this...

That is the same as my spare prop, on my stainless one just the nut is removable...looks like another job for the engineer From my google search the symptoms of a cracked diffuser do sound like the prop spin i had

 

[carlton]

Oops - posted the wrong image. Here's what mine actually looks like...

(By 'diffuser' do you mean Part C in the diagram?)

 

[Seahope]

Oops - posted the wrong image. Here's what mine actually looks like...

(By 'diffuser' do you mean Part C in the diagram?)

No the diffuser is the cylindrical rig which attaches to the end of the propeller, shown on your diagram as part of the propeller. He is a picture of mine with it missing and the other one with it still attached.

 

[Warpa]

Well thats not the issue with mine then, i took some pics as it was out of the water for so i could wash the hull. On another note i took a pic of a bung that is missing, would this be the problem and how can i find a part number and where to order?

miissing bung

 

[carlton]

If you're referring to the hole at the aft bit of the drive (enabling access to the trim-tab anode bolt head) I wouldn't worry - both of mine have been missing for at least 6 years with no noticeable difference.

 

[sarabande]

a couple of points. I don't know very much about high speed props, but the trailing edge of at least one blade seems to be square cut, rather than a fine edge.

And bit of rust in corners ? That might be another sign of cavitation at speed; the low pressure gas bubble can do exciting things to the underlying metal.

http://www.wildcatprops.com/articles-corrosion.asp