Cavitation/ventilation issue

[Assasn2k]

So I'm a long time lurker on the here. Finally registered because I've got the infernal cavitation. I've read and watched almost everything I could. This is my first jet boat, but I have turned a few wrenches in my life lol. Backstory.... The boat has never maxed out RP m's I realised it could be a throttle stop issue even though I've managed to squeeze about 52 miles an hour out of it. So I am fairly happy with its performance. About a week ago my daughter and I went to the Lake and we toed 2 boats almost immediately that were dead in the water. When we told the 2nd boat I realised I lost Almost all propulsion I instantly went to the Clean out port and realised that it was undone. Yeah now this is about 4 miles down the Lake and after telling another pontoon about 2 miles so my only assumption is that it worked its way loose somehow. I have the twist lock style. We went camping last weekend and I realised that the boat was cavitating. If I went ahead and sealed some parts of the tunnel that looked like they may have gaps. He went out last night and although it seemed slightly better it is still definitely cavitating. So today I pulled everything apart received the jet pump even though I know it's not completely necessary check my impeller which has 2 minor cavitation marks. The edges are fine and the wearing looks fine. The concerning part is that my clean out port looks like it has cavitation damage as well. This is not the plug but the actual tunnel itself. Between all the forums of the tunnel filling with water and blow by et cetera I have not ran across anything like this any ideas.... Before I forget to mention it The gasket around the clean out plug does not seem to be seated well on one side.

 

[Assasn2k]

Anyone?

 

[mrcleanr6]

Cavitation can be from a few things. I will list them….

1 impeller damage or wear
2 wear ring damage or wear. Take a set of feeler gauges and make sure the gap between wear ring and edge of impeller are within spec.
3 seams in jet pump not sealed
4 transom plate not sealed to hull. This happens alot because yamaha only used to use silicone to seal it and if you have what i mention in #5 then the sealant blows out. You will usually see water accumulating in the bilge when boat is running at speed.
5 transom plate or clean out port housing mounted so its hanging down into the jet stream. This seems to be a big one. I have seen more boats and skis with this issue than without.

 

[Assasn2k]

Cavitation can be from a few things. I will list them….

1 impeller damage or wear
2 wear ring damage or wear. Take a set of feeler gauges and make sure the gap between wear ring and edge of impeller are within spec.
3 seams in jet pump not sealed
4 transom plate not sealed to hull. This happens alot because yamaha only used to use silicone to seal it and if you have what i mention in #5 then the sealant blows out. You will usually see water accumulating in the bilge when boat is running at speed.
5 transom plate or clean out port housing mounted so its hanging down into the jet stream. This seems to be a big one. I have seen more boats and skis with this issue than without.

When you say the transom plate and clean out housing are hanging in the jet stream, are you referring to the raised edges prior to the wear ring cavity? I've attached a photo of that area on the boat. I've sealed it to smooth out the transition. I'm still massively worried about the clean out port housing having cavitation damage.

 

[mrcleanr6]

The picture is so close up its hard to tell exactly what is going on there but basically any metal parts that hang down and disturb the smooth flow of water

 

[rkluck]

It seems like you may need to look at the gasket that is not sitting tight. The seal should be even and tight. Are you sure the plug is seated all the way down and locked?

 

[Assasn2k]

Tight and locked in 100%. I slathered it with Vaseline and am on the way to the lake to test it. Poured water in the tunnel and it held for 24hr at the mark. I ordered a plug rebuild kit either way. My main concern is the pitting in that housing....doesn't seem like something I can just buff out?

 

[Assasn2k]

So I've sealed the tunnel, rebuilt the clean out port and am heading to the lake tomorrow to test it out....wish me luck

 

[sunbyrned]

Did you check the hose clamps that are around the top and bottom of the clean out tube? You can check them by lifting the transom plate. Just make sure the tubes are seated correctly and the hose clamps are at the very top and the very bottom.

 

[RobbieO]

I'm still very confused on this subject. Sometimes I have one cleanout port that is full, but most of the time both are. I have been told that is normal so I'm just accepting that it is blow by from the tunnel. The seals on the cleanouts are lip seal designed, which means with more pressure they should seal tighter. I'm going to clarify with the dealer next week before I spend $150 on new seals for the clean outs. This is a new boat. Should be covered under wty.

 

[sunbyrned]

I'm still very confused on this subject. Sometimes I have one cleanout port that is full, but most of the time both are. I have been told that is normal so I'm just accepting that it is blow by from the tunnel. The seals on the cleanouts are lip seal designed, which means with more pressure they should seal tighter. I'm going to clarify with the dealer next week before I spend $150 on new seals for the clean outs. This is a new boat. Should be covered under wty.

It is typical for water to be in the clean out tubes. That doesn’t mean water is coming through the clean out ports. Water gets in there from various ways.(splashing, swimsuits, dogs, etc.) There is a drain port under the hatch where most of that water goes but it can also settle in the tubes. When I have water collected in my tubes then I feel good about the seal I have.

 

[Assasn2k]

So just to update...

My clamps on the clean out tunnel are tight. I went ahead and installed the clean out rebuild kit for giggles and piece of mind. I made sure to retain my old one just in case I ever need a spare.

As far as the cavitation/ventilation I do believe that I sucked loose some of Yamaha's silicone in the tunnel. I disassembled the pump and removed the grate and put Locktite MarinePL in the joints. My findings were positive. My loss of "traction" was greatly reduced, but after a few outings the problems resurfaced. As I suspected, reaching into the tunnel I felt where the sealant was coming loose. I did not prep the surface properly. I simply wanted to make sure that I could narrow down the cause.

I am currently in the process of removing all of the intake grates, as well as the ride plate and filling voids and sealing properly. I am going to be documenting the process in hopes of helping others in the future.

 

[Diverseg]

We are also having a cavitation/ventilation issue, ours started when we tied up the boat and left it in the water all weekend without using it.
It stormed heavy all weekend and another storm was forming and we wanted to get it out of the water, when we went to start it the battery was dead and the bilge pump was not running so there was lots of water in the bilge. Jump starting it and trying to get across the lake to trailer it it was heavy and did not want to get on plane. When trying to throttle it it would slowly accelerate to 4K rpms then the engines would immediately wind up toward max rpm and I would back off of the throttle.
I tried several times to get on plane. My first thought was rough water and cavitation. I then resorted to running at 4K rpm going rather slow till I finally made it to the dock and on the trailer.
Pulled the plug and lots of water drained.
I also have read lots of these cavitation posts and some of them mention they first notice it when towing another boat or pulling someone off of a sand bar. I am wondering if the heavy drag causes more suction on the intake sucking the sealant/silicone from the seams.
I don't think its cavitation but more ventilation, Like was mentioned above once the seams in jet pump are not sealed especially where the cleanout port meats the hull, I think it can suck air thru this failed seal joint from the bilge area, or if the transom plate seal to hull is leaking. Since this has happened we get a slow water accumulation in the bilge when boat is just sitting not moving.
We inspected the tunnel and noticed many gaps in the sealant. We sealed them and are waiting a few days for it to set up. We will test it this weekend and try and report back.

 

[Assasn2k]

So I just did the very same thing I attempted to get the jet tunnel off but could not get it removed. I spent a full day getting as much old silicone out as I could and sealed it up yesterday it should be cured by this evening I will have to wait. Been storming like crazy today. I think a lot of it revolves around the excess section from heavy loads. I was really wanting to get that tunnel plate off and fill it with foam and flex seal. I started by trying to trace down the problem and quickly sealed the tunnel it made a massive improvement. This time around I also put some RTV silicone between the jet pump tunnel and the ride plate. I could see a few possibilities in the jet pump sucking air between that gap I know wave runners typically have a lip seal that sits there.

 

[Wildmanthirty4]

I am having similar cavatiton issues that just started the other day. Ran perfect Saturday but on Sunday I noticed the rpms jumping. I found some fishing line stuck on a shaft of one of my impellers. I pulled the impeller cleaned it up and put the boat back in and ran it. Still having the same issue. Could it be wear rings?

 

[tdonoughue]

Wear rings usually don't come on all at once like that--more gradual.

If it was fine and suddenly not, that is usually something stuck in the impeller or around the shaft. If you already pulled the pump and found nothing, might want to check underneath to see if there is something in the grate on the bottom or something.

 

[Diverseg]

A little late in the follow up but repairing loose/bad sealant in all of the seams in the jet pump tunnels cured the cavitation/ventilation issue we were having!!!

 

[Wildmanthirty4]

Wear rings usually don't come on all at once like that--more gradual.

If it was fine and suddenly not, that is usually something stuck in the impeller or around the shaft. If you already pulled the pump and found nothing, might want to check underneath to see if there is something in the grate on the bottom or something.

I
This is my first yamaha jet boat but from what I can see everything looks normal.i will check tomorrow to see if the sealant is coming off.