cavitation

[jgm7739]

I have a '86 115 yamaha on the rear of a 19 bow rider. At WOT I'm in the range of 5300-5500 RPM. I'm also runnung a stainless 19pt prop. I know this is nearly maxed out. But should I expect added performance when trimming. I am able to trim very little before the prop begins to cavitate.

 

[cinder1995]

Re: cavitation

Look at buying a hydrofoil fin for your motor. I believe it helps with cavitation.

 

[Spidybot]

Re: cavitation

There are several factors involved. The motor height on the transom, the hull/transom design and the trim.<br /><br />And more than anything: The prop. Props have different 'grip', are designed for different uses (surfacing) and varying bow lift.<br /><br />If your 19 performs OK and you're within recommended range at WOT, a prop that allows proper trim will lift the boat, reduce displacement and give you more rpm. So looking for better grip might include a higher pitch.<br /><br />How high is your motor mount on the transom?

 

[Jack Shellac]

Re: cavitation

jgm, welcome to the site. Your motor may be mounted too high on the transom. The cavitation plate should be level or very close to level with the bottom of the boat. The usual procedure is to raise it a notch at the time until it starts to cavitate in turns and then drop it one notch for it's permanent position. Yours may already be too high.

 

[sharkcat]

Re: cavitation

I have just changed props on my boat from mercs to hustlers.I have found the WOT to be the same, the max speed to be slightly higher,the holeshot much quicker but most importantly I can now trim out much further without the props letting go really helps keep the bow up in a following sea.The main difference in the props seems to be the amount of cupping at the rear of the blades.A good prop shop should be able to help you try:www.BoatpropRus Good luck

 

[jgm7739]

Re: cavitation

Well, I have noticed that there is about a 1" gap or so between the top edge of the transome and the motor mount. Also, I do not think the cavitation plate is in line with the keel of the boat. Would it be recommended to drop the engine that 1" to gain better performance from the motor.

 

[Dhadley]

Re: cavitation

Be careful dropping the motor. You will certianly lose rpm's and you are at the low end now. <br /><br />You didnt mention what brand prop you are running but the cup at the tip and around to the leading edge of the blade is very important. If yours is worn or was never there, we need to deal with that. <br /><br />As mentioned, a fin will help. The bigger the fin the more it will help. <br /><br />Motor height (X dimension) depends largely on prop technology in relation to hull design.<br /><br />Good luck!

 

[jgm7739]

Re: cavitation

Taking a closer look (while at lunch). I did notice the cavitation plate was level with the lowest point of the keel.<br /><br />As far as brand prop....not sure. It came with the boat when I bought it. It is stainless however. But does not resemble a stainless prop most would tend to visualize. It is painted and has that plump shape of an alum. prop. I did not know it was stainless until I first removed it and noted its weight. The only markings I found on it were "19K"

 

[Dhadley]

Re: cavitation

Sounds like the cup is worn down as well as the blades (probably). You could have that prop rebuilt if you havent lost too much of the diameter. <br /><br />Or you could opt for a new prop. Again, how much you spend on technology will determine the X dimension.<br /><br />Once you get the cup and diameter back you may be able o raise the motor and gain performance.<br /><br />Good luck!