Jet boat cavitation issue

[Bassem]

I own a 2010 Yamaha jet boat (with very low running hours). It was running fine, took it out of the water to apply anti fouling paint. In the process I stripped out the duct and screen intakes, cleaned and painted them, applied some house hold silicone and reinstalled them. After placing the boat in the water and tried to accelerate, cavitation was evident in both engines and acceleration was very slow but eventually reaching top speed of 45 mph. A few days in the water the hull was flooded more than usual and even after pumping out the water the acceleration was even worse and did not move at speeds over 10mph. After reading some similar problems on this website, I suspect it is a silicon sealant issue. Kindly advise what silicon to use and what special steps to follow when applying it. If anyone knows of any other reasons why I’m facing cavitation please advise.

 

[Lunarvrx]

From what I know it appears that the silicone sealing process is key to best performance with zero cavitation. The only reason I suspect this is that with my new SeaDoo 180SE 2009 back in the day, when accelerating from stop to wide open throttle, it would cavitate somewhat until it reached speed then OK. I found from an owners forum that that is not correct and should be fixed under warrantee. After an argument with the dealer mechanic and going over his head to BRP, they told him to fix it. So he did fix it by re-doing the complete silicone sealing. The cost under warrantee was about $900 Canadian. I assume there is a documented process for doing it correctly. Perhaps in a shop manual. I doubt it is the type of silicone issue, maybe more if the edges are not perfectly smooth and create some turbulence as water passes through the intake & jet pump. Getting a shop manual out of these boat manufacturers is usually a no go - there oughta be a law. Suggest you run the problem by an experienced Yamaha mechanic for his/her opinion.

 

[Bassem]

You are 100% correct, a dab of silicon sealant made all the difference. I stripped out the duct and screen intakes again and found out I should have applied silicon on the side walls of the duct intake. After reapplying a liberal amount of fresh silicon on every face and edge of the duct intake that comes in contact with the boat, it was back to preforming as good as new.