Cavitation issues?

[Sink]

I had the boat out on Saturday and the left engine did great! The right engine is running well but when it hit 5000 rpm, it went right to 7000. No resistance between 5000 and 7000 rpm. I checked the wear rings and they appear to be new. I can hardly see clearance between the impellor and the wear ring. I haven't taken the grate off yet to see if anything was in the impellor but from the back end I couldn't see anything. Any ideas on what else it could be? The boat does around 55 once it "grabs" with just me in it.

Also, the boat takes a bit to get on plane. It also doesn't want to go 15 to 25 mph. It wont stay on plane that low. It wants to go more 30+. Even with only me in the boat. I'm not a small guy. Could this be the same problem with the cavitation?

I'm obviously new as you can tell by all my questions. Thanks for your help!!!

 

[Dr Honda]

You have an air leak somewhere. It could be the drive shaft seals... or around the ride shoe.

As far as be'ing on a plane at low speeds... no boat does that. You have to be going fast enough to support the weight of the boat. On a 14.5' seadoo... that's probably around 20~25 mph.

 

[Sink]

So, how do I find an air leak??? There wasn't any water in the boat and I let it sit at the dock for probably an hour while we ate supper. The bilge pump wasn't on... unless it is automatic that is... When I pulled the plugs after taking it out of the water, NOTHING, not even a drop came out. I was totally surprised!

As far as the planing goes, how do you tow a tube? Or pull a skier? Not on plane??? Remember, I'm so new to this boating thing it ain't even funny! I watched the prop boats and they were on plance pulling tubes and skiers. I was able to put the boat on the trailer easily (after playing around the dock for probably 15 minutes, practicing slow speed maneuvers). I'm really anal about stuff like that.

 

[Dr Honda]

An air leak isn't a water leak... so you won't see water coming in.

On your boat, your drive shaft seal is a pack with 2 seals... and a bearing. Chances are... the outer seal is dead... and the inner seal is still OK. Seals are normally only good for one direction... so... the inner seal keeps the water out of the hull... but it will allow the pump to suck air past it.

Unfortunately... most of the time, you don't find a real problem that would make you say... "there's the air leak." When this happens... you normally take the pumps out... reseal the shoe, rebuild the driveshaft seal... and make sure the pump is sealed when it goes back on.


As far as towing... pull them fast !!

Sorry... But once the pumps are sealed up better... you will have more speed control. Even if you are plowing water... you can pull them at whatever speed you want.

 

[Sink]

Is the drive shaft seal where the grease is added with a grease gun? Would adding a little grease be a way to check if this is the problem? Would that possibly solve it temporarily?

 

[korn82787]

here is a picture of the driveshaft and boots.

 

[korn82787]

The grease fitting on the left will not cause cavitation. What we are looking at is the boot on the right and the parts/seals/orings in that section of the driveshaft.

 

[parrothd]

The 95 speedster doesn't have the carbon ring setup, it has the better carrier bearing setup, yes this is where you add the grease. I'd check the pump/wear ring and impeller for damage, add grease to the bearing and a last resort reseal the ride shoe...

 

[Sink]

Reseal the ride shoe?? Huh??

Just got back from the lake... I did some reading and thinking then test drove the boat to see if I knew what I was talking about. With some practice, I can keep it at about any speed I want. At least I got that figured out.

Cavitation is only under full throttle and only from 5000 to 7000 rpm. The left engine seems to rev much easier than the right one but that's not the one that is cavitating. Not sure if I'm believing the tachs. Wish there was someone around here that has a clue about these things. The engines dont react the same to the throttles. Sometimes the throttles are even to hold the same rpms, sometimes not. Do you need to mess with them to keep them equal?

Still floating,
Sink

 

[parrothd]

The speedster is a strange bird, it has 2 different impellers, one for low end and the other for the high end. When I had mine I just kept the throttles together and ignored the tachs. When you punch (WOT) it does it take off or does it sputter?

 

[Sink]

You have no idea how much sense that makes, parrothd! It doesn't sputter at all. The engines are running great just differently. This would be explained by 2 different impellers. That would also explain the difficulty in setting the throttles. It also kinda explains why the boat wants to go left or right under different throttle settings. I was trying to set the engines to "sinc" like on a twin propeller aircraft... to stop the droning... (probably doesn't make sense unless you fly multis) The impellers aren't in too bad a shape... a bit chewed up on the leading edges, but the wear rings have very minimal clearance. The boat takes off pretty well when I punch it. I'm used to hard acceleration having high performance cars and motorcycles so it's not like those are but I do understand that this is a boat. I did see a small spot on the tip of the gel coat where the flow from the single inlet splits to go left or right to the pumps. Not sure if this could be causing a problem or not. Suggestions on how to repair this? Silicone sealant for temporary or should I get gel coat and do it right? I see the fiberglass in this area about the size of a dime.

SO, do I really have a problem or am I just very sensative to the engines and drives???

Always a sensative guy,
Sink

 

[Dr Honda]

Do you have a problem.... it's hard to say from where I'm sitting. If you can hit the throttle, and it comes up on a step in 3 or 4 seconds... you are about right. If the engines rev, and bounce of the rev-limiters... and it takes a while to get up on plane... there is a problem.

Personally... if it was my boat... I would pull both pumps, and check the driveshaft seals anyway. IF, the outer seal is bad... the water could cause the bearing to seize. AND... when that happens... it rips the boot, and you have a 2" hole in the bottom of your boat.

Refreshing the driveshaft seals gives peace of mind, and will reduce any cavitation you are feeling. Also... when you put the pumps back on... you will seal them up.


Oh.... and who needs a tach for a twin?? just listen to the props, and give the throttle a tweek. (I fly too)

 

[parrothd]

Wait till winter and do all that stuff and rebuild you carbs and replace the fuel lines, and have the props repaired and new wear rings.....

 

[Sink]

Do you have a problem.... it's hard to say from where I'm sitting. If you can hit the throttle, and it comes up on a step in 3 or 4 seconds... you are about right. If the engines rev, and bounce of the rev-limiters... and it takes a while to get up on plane... there is a problem.

Personally... if it was my boat... I would pull both pumps, and check the driveshaft seals anyway. IF, the outer seal is bad... the water could cause the bearing to seize. AND... when that happens... it rips the boot, and you have a 2" hole in the bottom of your boat.

Refreshing the driveshaft seals gives peace of mind, and will reduce any cavitation you are feeling. Also... when you put the pumps back on... you will seal them up.


Oh.... and who needs a tach for a twin?? just listen to the props, and give the throttle a tweek. (I fly too)

Sounds like a plan, Doc. I have the service manual so it shouldn't be that hard to do. How about the small area that I can see the fiberglass? Is silicone a fix or not? The area will never be seen...

The impellers are not the same? The more I think about this the more sense it makes in the way the boat is feeling. It does get on to plane in about 3 to 4 seconds so things aren't that bad.

Sea doo or aftermarket parts??? Suggestions on where to get the parts? I will get wear rings too so I can do those when they are needed.... My plans on this boat are to fix it up and get it looking good then sell it next spring and find a newer one to work on... until I get the one I want. This boat is too small for us but it is a blast for sure!

I really don't need the tachs... but they are good for a noob trying to figure this stuff out.

What do you fly, Doc? I have my A&P but never got my pilots license... but have flown quite a bit. Many different airplanes.

 

[Dr Honda]

I recommend Seadoo parts almost all the time. You can use the aftermarket stuff... but things like the wear rings can be Hit-or-miss. For a few extra $$$ it's not worth my time to find out that the aftermarket ring doesn't fit right. BUT... if your clearance is less than 0.040"... then they really don't need to be replaced. The seals in the driveshaft aren't as big of a deal... You can take the numbers off of them, and get them local.

I'm not multy cert... but I have a bunch of time in a 310. My buddies dad owned one... and I put about 20 hours on it over the years. I also built a KR2. (fun project) Originally it was a VW powered aircraft... but I ran a Subaru engine, with a RossAero gear drive. It was a good time. I could cruse close to Vne. (at around 190 mph. Vne was 200) BUT... I know the Ken Rand was flying his at well above 200. (he had a 1830cc Turbo VW engine when he stuffed it. RIP)


Anyway... the above work should be easy for an A&P.

 

[Sink]

I will go with Sea doo parts no the wear rings when needed. I hate not having the right parts/tools!

I have time in a 310 also. One of my worst nights... Was up with a fellow mechanic and a friend... test flight. I was left seat... went to put the gear down... only 1 green... The floor in the rear seat bulged up... with a bent pushrod. CRAP! It was dark... Full fuel. I had my pocket small screw driver and we had a pair of needle nose pliers.... and a piece of wood. Ended up flying around for a couple of hours... tore the floor out and bent the rod straight with the piece of wood against the spar and cranked her down... No radio in the plane.... Kinda scary on touchdown but we were fine. I really hate those tip tanks hanging on the ends of the wings when you are worried the gear wont hold... Boating is safer maybe... ?

 

[Dr Honda]

Yep. As long as you aren't boating with sharks... you don't have to worry about a water landing. :thumbsup:


My one scary story was right when I was solo'ed. I probably had a total of 15 hr's under my belt, and I was going out to do a little night flying. I took off just before a NOTAM was released... so I didn't hear it while getting my info. I took off in an old 150, and it was a little bumpy. I thought to myself... "I need to learn how to fly in bumpy conditions"... so I just kept flying. Well I was about 30 mi from the airport (CNO) over my practice area... and I started to get bounced BAD !!!! Out of nowhere... I lost 1000 ft... then gained it back. I dam near pissed my self. After I got calmed down... I turned back... and when I did... I was completely flipped!! I rolled the roll, and basically did a split-S. When I got level... I pushed it to full throttle to help stabilize the aircraft. It helped a little.... but not much. From that point, I called the tower, and requested a straight in approach. Well... the guys in the tower know the rental's... and they knew I was just on my solo endorsement... and they actually held all other traffic until I landed safe, because they knew that the weather was turning bad.

Other than that... it's always been fun.

 

[Sink]

WOW! Sounds exciting! We all started in high school with our flying. CAP and friends and family flying type stuff. A buddy of mine had flown quite a bit before he started his training so it was no surprise when he had the honor of being the lowest time solo at the airport! On his next flight, he had the honor of being the lowest time solo to CRASH an airplane! He was coming in on the sod strip and was a little low to clear the power lines... We all know that pulling up doesn't always make the plane go up if you aren't going fast enough. Needless to say, he HIT the lines... The airplane had about 15 hours on it! Totaled! He is now the director of a larger airport in Texas! Same guy built a scale model of his uncles Bonanza... Beautiful model! First flight landed into the HOUSE! So many little pieces to pick up! OMG! What a mess!

Many stories but not about boating.. Hope my new boating stories are all good ones!

Sink (not crash)