Tubing capacity with sportster le

[Bonmotwang]

I am repairing my seadoo 3 seat tube for tomorrow right now.
It is heavy!
It is a 3 seater with a "bag" outside of the inner tube. Very well made seadoo product.

But I just started thinking if it is too heavy for my boat? It is 7 feet diameter.
Normally I put two adults on the tube , and two adults on the boat (including myself).
The boat performs well with the tube and speed is around 30mph.

Last year I lost a pump, probably mostly from my oil change, but I bet the extra force on the pump thrust bearing accelerated the failure.

Does it make sense and should I get a 2 person tube?

 

[Dr Honda]

A smaller tube will be more fun for the riders. You can go a little faster, and whip it around... But towing that weight doesn't change the pressure inside the pump. Full throttle nozzle pressure really doesn't change. And actually... it will go UP as you build speed, if you have a top loader type intake grate.


So... unless you just want a smaller tube... it's not an issue. Just don't get caught towing 3 people on it, since most states say capacity can't exceed the boat.


Because of the "Fun" issue... I personally have 3 tubes. A single, double... and a big a$$ "Supper Brawler" to safely tow my kids on. (they are only 4 and 9)

 

[Bonmotwang]

Thanks for your opinion Dr.
I will get a single tube and try it out this week.

But I thought more weight or resistance in the water will add more load to the jet pump?


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[Dr Honda]

......................

But I thought more weight or resistance in the water will add more load to the jet pump?


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Full throttle, is full throttle. Remember... these are pump boats, and not your truck. With your truck... when you put more in the back... or the trailer on the hitch... then it has to work harder to pull it. With a pump... you are taking in water, and forcing though a nozzle that is smaller than the impeller. (the resistance is constant, since your nozzle size doesn't change) So, regardless of how much weight is in the boat... or how much drag is back on the tube... the nozzle pressure doesn't change at full power.

Jet boats are also very different from a prop boat. With a prop boat... the prop stays under the water... and as you pick up speed... the engine will "Unload". With a jet boat... (I'm not sure you are aware of this) but the nozzle is actually, completely out of the water. So, the pump isn't pushing on the water in the lake... it's simply a case of "For every action, there is an opposite and equal reaction."


The only real exception to that is with speed.

The PWC guys who are pushing skis up past 80 mph are having serious problems with pump pressure. Basically... the faster they go, the more water is fed into the pump. Eventually, the intake pressure is higher than the fiberglass, or pump mounts can handle... and something breaks. The real speed freaks have a pressure release system in the pump, so some of the intake water can be diverted.

 

[Bonmotwang]

Thanks. I didn't know any of those "things" especially the "complete out of water part". Very interesting.

We went out with ski and boat today. Bought a single tube for the kids. So easier to carry than the big 3 seater!
Had a great time everyone loved the "speed" and "bumps"!


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