understanding a seadoo functionality - newbiew guide

[cykrus]

Hello team,

I am kind of new in the "business" i own a challenger 1996 modified with an engine 2004 rotax 1503 4tec and a RXT dashboard (pictures on another thread). Now, i have beed a few times on the water i kind of learned how to use it but, as an engineer and because i LOVE it and how it drives i would like to find out a bit about functionality, especially the engine in order to take good care of it. And here goes my first set of questions:

1. The RTX dashboard .. does it have a back-light ? mine does not ... is there a wire I am missing (one of the picn should power the backlight? or no backlight at all ?

2. How does it know the cardinal point that is being displayed on the LCD ? ... the sensor is inside the dashboard or it is an external sensor ?

3. this is the tough one .... How does a jet engine work ? ... i understand that is has a 4 stroke engine ... that connects through an ax to the propeller that is inside the channel between the bottom intake and the jet nozzle at the back of the boat. That is in big terms how i see it. But how does it cool the exhaust ? where does it take water from and how does it throw it out ?

4. I understood I have 2 cooling systems, one closed circuit for the engine itself (cooling the piston housing) and the second one with water lake cooling the exhaust .. right ? How often do i need to replace the cooling liquid ? How to take the old one out ?

5. For the engine oil I saw a video on youtube about how to remove the old oil (with a suction pump) through the "oil level indicator". How much oil this engine has ? What kind of oil should I replace it with ? How often to do this ?

6. Is there any other type of oil or lubrication I should do on a regular basis ? like bearings etc ?

7. I have 3 levers on starboard side. 1st is forward-n-reverse, the second on is the acceleration and the third one i have been explained it is the VTS (variable trimming system). I realized that this one lifts or lowers the water jet. Now when the boat is not running i can put it in either position. When in speed (30 mph) i can only have it in the forward position and then the bow is a little bit raised or at the middle and then i get full speed but i get a VERY hard resistance (and i am afraid to pull more not to brake something) to set it in the "back" position .. why is that ? What is the "back" position for ?

8. I have opened the dashboard and on the RPM meter on the back there is a sort of small tube (it reminds me of old vacuum controller gauges). Nothing is connected there ... what is that one used for ?

9. I have successfully installed a hummingbird 153 fish finder and it works great. I have installed the transducer on the stern, and run the cable through the "old" water in hose. (while modifying the engine a new "tap water in" has been added and the old one was filled with silicone. 99% of the time it words great but sometimes, when driving in forward, not high speed i get for 2-3 seconds random reading of 80 - 100 m depth while in 3-04 meter water. Does anyone know what could be a reason ? Is this something that usually happens ?

10. Under the jet part (i am going to name it "jet exit" the part that throws the water - maybe someone tells me exactly the name) the guy who modified the boat added 2 plates of metal. The guy i bought the boat from is not the one doing the whole modification but he explained me that the "jet exit" is kind of long and in order for it not to be slammed by waves while a jump the metal place part has been added. Now i see that that metal part looks like a chamber (double wall) and in fact there are 2 hoses going inside it at each end (left and right). Was this indented to be some kind of radiator for the coolant liquid ?

11. yesterday I was at a boat ramp where there was a lot of grass. I guess it sucked grass into the intake because when i tried to accelerate there was a strong vibration and no power. Then i put it in reverse and accelerate a few times until it blew the grass away (i think) and then it was all back to normal. Is there another way to solve this problem ? And speaking of which what happens if i go in a shallow water and mud or sand gets sucked into the intake. Will that damage the propeller inside the turbine ?

I know i have asked a LOT of questions ... I am just curious (being an engineer) to find out as much as I can about this boat and be able to maintain it. I need to tell you that i have watched LOTS of videos on youtube and read articles but did not find the answers questions posted above.

Thank you !

 

[red2blue]

No back light on the older dash's. Illegal to operate in the dark.

Simple 4stroke motor turns a shaft with a prop on it. The prop is at the end of the tunnel....water is exited faster than it comes in and focused through a nozzle. Cooling water is drawn in through the pump and sent though lines to the exhaust and ic if it's got one. It leaves with the exhaust.

Motor hold about 4.5 US quarts. Only replace what you've removed....keeping the level correct.

The older reverse drops the bucket....do not operate that at high speed. It has been known to be blown across the lake when used at high speed.

Pics of mods please.

Do not operate the ski in shallow water.

 

[cykrus]

thank you for your answer, this brings a little more light in my mind ... but what do you mean i cannot operate in the dark ? Why do i have the green,red light at bow and the white light at stern ? and i have the lights switch near the steering wheel. Or should i understand that the dashboard that I have comes from a jet ski and not from a boat and that is why it does not have back light ?

pics of the mods are on this thread http://www.seadooforum.com/showthre...2004-questions&p=426319&viewfull=1#post426319

 

[red2blue]

Ah....okay...you got a boat...with an rxt dash?

Can't operate a pwc in the dark.

 

[cykrus]

this is my dash ... it's an image from ebay i have found. On this image the lcd seems to be back light in red ... is that standard or a mod ?

 

[red2blue]

Beware all those hull mods...trim tabs are supposed to move...as for the plate extension under the pump......I'd be talkin with the boat guys about that.

 

[red2blue]

this is my dash ... it's an image from ebay i have found. On this image the lcd seems to be back lightView attachment 27630 in red ... is that standard or a mod ?

It don't look like mine...if it's a different year...maybe....would think all pwc's would have no back light.

 

[Coastiejoe]

As Noted above; the RXT is illegal to operate at night. As such, no need for a back light. You can operate your boat at night, thus the port/stbd lights. If you can't come into the dash from the back of the dash, then mount a tiny LED on top so you can see the gauge.

 

[Chakane]

Let me see if I can't answer some of these questions for you, although I'm fairly new to the seadoo boating scene also:

1. The RTX dashboard .. does it have a back-light ? mine does not ... is there a wire I am missing (one of the picn should power the backlight? or no backlight at all ?

As already discussed, the holder RTZ dashboard doesn't have any internal lighting in them. Depending on your local laws, this may mean you will not be able to operate at night.


3. this is the tough one .... How does a jet engine work ? ... i understand that is has a 4 stroke engine ... that connects through an ax to the propeller that is inside the channel between the bottom intake and the jet nozzle at the back of the boat. That is in big terms how i see it. But how does it cool the exhaust ? where does it take water from and how does it throw it out ?

The engine turns the impeller, via the drive shaft. The impeller, given it is sitting inside the thrust tube, draws water through the inlet and ejects it at a high velocity through the venturi port. This port is a slightly reducing cone. This reducing cone, through the workings of some amazing physics, accelerates the water even higher (a reducing aperture requires the same amount of water to travel faster). Physics then plays a further part with every force having an equal and opposite force, thereby pushing the vessel forward. Now from what I understand, the water to cool the exhaust manifold is drawn from the main thrust tube for when the vessel is in the water and travelling otherwise you need to have the hose connected to it. As it is drawn in by the pressure of the water being pushed through by the impeller, this is why, when the vessel is under tow, you need to ensure that the hose feeding this water to the exhaust manifold is pinched off because water flowing through into the exhaust manifold won't have any exhaust gases to push it back out and it will then flow through into the cylinders making for a very messy (and potentially expensive) thing to deal with.

4. I understood I have 2 cooling systems, one closed circuit for the engine itself (cooling the piston housing) and the second one with water lake cooling the exhaust .. right ? How often do i need to replace the cooling liquid ? How to take the old one out ?

The closed system cooling runs similar to the radiator in your motor vehicle except the 'radiator' is two heat transfer panels on the bottom of your vessel. Hot cooling fluid from the motor is pumped through these heat transfer panels where heat is transferred (hence the name) to the surrounding water. On these panels you should see a couple of plugs. Removing these plugs empties the fluid from the loop. How often you change the fluid depends a lot on how often you use your vessel. As a general rule of thumb, once every two hundred hours or two years is good.

5. For the engine oil I saw a video on youtube about how to remove the old oil (with a suction pump) through the "oil level indicator". How much oil this engine has ? What kind of oil should I replace it with ? How often to do this ?

Fourtec engines contain approximately 3 litres of oil in them but you won't get all of it out when you change the oil so you only replace what you get out with what you put back in, otherwise you will overfill the sump. A good four stroke 10W40 non synthetic oil is what you need. The non synthetic is important, especially if you have a supercharger. The timing of oil changes is again dependent on how much you use it but a general rule is every 100 hours or 12 months.

6. Is there any other type of oil or lubrication I should do on a regular basis ? like bearings etc ?

If you download he service manual for your vessel, this will give you the indicators for regular servicing and lube points. A significant game changer here is if you run in salt water or fresh water with salt water obviously needing much more attention post the run to remove any salt from the exhaust and generally everywhere.

7. I have 3 levers on starboard side. 1st is forward-n-reverse, the second on is the acceleration and the third one i have been explained it is the VTS (variable trimming system). I realized that this one lifts or lowers the water jet. Now when the boat is not running i can put it in either position. When in speed (30 mph) i can only have it in the forward position and then the bow is a little bit raised or at the middle and then i get full speed but i get a VERY hard resistance (and i am afraid to pull more not to brake something) to set it in the "back" position .. why is that ? What is the "back" position for ?

My vessel doesn't have the VTS system but from looking at others I would suggest the backmost position is used for when you are docking or moving around slowly. This moves the thrust into a more downward direction giving you greater steering control than what jet drive vessels are renowned for at slow speeds. I would strongly suggest that if you ever do manage to get it into the backmost position at high speeds, you will be up for some serious repair work as trying to redirect the thrust from the jets at that speed will surely do some serious damage.


9. I have successfully installed a hummingbird 153 fish finder and it works great. I have installed the transducer on the stern, and run the cable through the "old" water in hose. (while modifying the engine a new "tap water in" has been added and the old one was filled with silicone. 99% of the time it words great but sometimes, when driving in forward, not high speed i get for 2-3 seconds random reading of 80 - 100 m depth while in 3-04 meter water. Does anyone know what could be a reason ? Is this something that usually happens ?

Depending on the location of it, it may be some of the thrust water is interfering with the radar waves it uses to get a sounding. The speed of the impellers is so quick it will draw air would the water. This air and the movement of the water, will deflect, refract, and generally play havoc with the radar waves emitted by the transducer. That's my best guess.

10. Under the jet part (i am going to name it "jet exit" the part that throws the water - maybe someone tells me exactly the name) the guy who modified the boat added 2 plates of metal. The guy i bought the boat from is not the one doing the whole modification but he explained me that the "jet exit" is kind of long and in order for it not to be slammed by waves while a jump the metal place part has been added. Now i see that that metal part looks like a chamber (double wall) and in fact there are 2 hoses going inside it at each end (left and right). Was this indented to be some kind of radiator for the coolant liquid ?

I'm not entirely sure what you are exactly talking about here. A very common modification is the addition of trim tabs/plates. Jets drive vessels have limited trim capability on them so you generally can't trim the vessel out while you are underway. Trim plates allow you to trim the vessel out so it sits flatter on the water when underway instead of with the nose in the air. Again, I'm not sure exactly what you are talking about but some pics may help here.

11. yesterday I was at a boat ramp where there was a lot of grass. I guess it sucked grass into the intake because when i tried to accelerate there was a strong vibration and no power. Then i put it in reverse and accelerate a few times until it blew the grass away (i think) and then it was all back to normal. Is there another way to solve this problem ? And speaking of which what happens if i go in a shallow water and mud or sand gets sucked into the intake. Will that damage the propeller inside the turbine ?

This is one of the things you need to be mindful of with jet drive vessels. While these vessels can generally travel in shallower water than out inboard/outboard kin, they can and will suck things up from the bottom, especially if you are giving it some throttle, because of the need for propulsion purposes, to draw water in from underneath. I doubt very much if, by you putting it in reverse, that this cleared anything because the impeller is still rotating in the same direction it was in forward. All a jet boat does when going into reverse is drop a 'reversing bucket' over the thrust exhaust, thereby reversing the thrust back towards the front of the vessel and making it go backwards. Mechanically, everything else is still operating as through this are moving forward, you are just redirecting the thrust. I would suggest that the impeller managed, if it was weed to chop it up or if it was anything else, clear it out. The think you need to be careful of here is that if it was something harder, it can cause damage to the impeller, wear rings and stator fins, causing a lose of performance and again leading to repairs being necessary. Generally, don't run the motor, or not too hard, in shallow water as it will suck anything beneath it up.

 

[cykrus]

Chakane: thank you for your answer ! It really helps understanding things better. I have posted pictures (there is a link in this tread)

 

[Chakane]

If I am looking at the correct photograph, the extra piece of metal is an extension of the trim tabs. The role of the extension is to add extra downward pressure to the bow of the vessel. I would say that the previous owner found the porpoising a little too much for the standard trim tabs with the extensions giving greater adjustability. The negative of this is if there is too much downward push on the bow, it can increase the amount of the hull in contact with the water when it is on the plane, increasing fuel usage and reducing top end speed. It's a delicate balance to get a ride that suits and it's too rough and top speed.

As for the hoses, I am note sure what they are. Where do they lead to inside the motor bay? Is there anything underneath the hose where it connects to the trim tabs? It could be a water pickup but I don't see why or where this would lead to.