is this normal

[cheech]

this boat is a 18 ft. rodgers with a bbc (460) berk. pump. my question is i can put the pedal to the floor (tach to 5200) and the boat plays catch up.
duane HTP todd said you might know. this is his boat.

[MikeF]

Yea,
That is the way it works. A jet drive is independent from the water and works by processing it rather than moving through it.

[LVjetboy]

Cheech, if you want more answers, be more specific describing your view of the problem . Boat "catching up" says some, but doesn't say much.
Catching up to what? Are you saying it's sluggish out of the hole?
If so compared to what previous experience?
What's your top speed and setup? Etc. The more info you provide the more likely you'll get a good answer.
jer

[DansBlown73Nordic]

Im pretty sure what he is saying is.....He is Trying to catch up to the Fast V-Drive guys......:D

[Moomawnster]

HehHeh .... Dan, so far.... everybody who's beaten my jet was playing catch up to do it ! Note .... I said "so far" you trouble maker :D

[Wet Dream]

Originally posted by Dans66Stevens
Im pretty sure what he is saying is.....He is Trying to catch up to the Fast V-Drive guys......:D
Who has a pic of Big Daddy's V-drive being towed in at Raystown?;)

[cheech]

no my problem is i don't have that much time in jet boats (YET). the boat is going about 10 to 15 mph then put it to the wood (fiberglass) the motor goes to 5200 then the boat starts to accelerate (at a good rate) to about 60 mph (owners guess) two people (total 325lbs)
and as far as the v-drive thing if i wanted to have a boat with a trans i would put my V.W. bug in the water?

[DansBlown73Nordic]

Im pretty sure that picture was deleted.....:D

[BrendellaJet]

Originally posted by cheech
and as far as the v-drive thing if i wanted to have a boat with a trans i would put my V.W. bug in the water?
LMAO!!!!!

[Wet Dream]

Originally posted by cheech
and as far as the v-drive thing if i wanted to have a boat with a trans i would put my V.W. bug in the water
Now thats some funny shit. :D
I think what you are describing is normal. Without knowing your pump condition, the pump "cavitates" on a launch which gives you the feeling of a slipping clutch. As the pump becomes loaded it gains effectiveness and moves water. The boat then accelerates and "hooks up".

[GlastronGuy]

Originally posted by Wet Dream
Now thats some funny shit. :D
I think what you are describing is normal. Without knowing your pump condition, the pump "cavitates" on a launch which gives you the feeling of a slipping clutch. As the pump becomes loaded it gains effectiveness and moves water. The boat then accelerates and "hooks up".
It's "normal" for a pump to cavitate on launch? Mine hooks up immediately.

[BrendellaJet]

mine used to hook up right away:D
The boat will tach very high out of the hole. If you aren't on plane real quick(3-5 seconds?) I would say you need to have the pump looked at...

[cheech]

we took the pump out and you can spin the impeller shaft very easy( two fingers,and it free spins) . the edges of impeller are blunt but no chunks out of edge.we have another pump for another i am doing a motor for an his is real tight, some effort to turn. this one is just re-done. can i measure the drag with a inch pound torque wrench. and what should it read.

[Wet Dream]

Originally posted by GlastronGuy
It's "normal" for a pump to cavitate on launch? Mine hooks up immediately.
Ok, normal for a pump that's well worn. I guess I should have stated that its normal for a worn out pump to react that way. ;)
A "tight" pump (we all like them tight :D) can launch the bow of the boat skyward with a blip of the throttle, trim induced.

[Hallett19]

out of the hole with nobody on-board my boat hits max rpm from a dead stop with my foot on it (4700) in a matter of seconds with very little to no "catch up". But when I am loaded down, it will hit 5300 rpms from take off and play "catch up" till it settles back at 4700.

[Oldsquirt]

Originally posted by cheech
we took the pump out and you can spin the impeller shaft very easy( two fingers,and it free spins) ....we have another pump for another i am doing a motor for an his is real tight, some effort to turn. this one is just re-done. can i measure the drag with a inch pound torque wrench. and what should it read.
The most likely difference between these two pumps is the drag from the shaft packing. It's purpose is to keep the water on the outside of the boat, not leaking in past the shaft. You could probably compare it to the difference in drag on a pinion shaft when measured with and without the pinion seal.
The shaft packing is adjustable by way of the two nuts just behind the thrust bearing at the front of the pump. That old pump has probably not been adjusted during it's life. As loose as you say it is, there is a very good chance that air is being sucked past the packing and into the pump, causing a drop in performance. There is no drag measurement that I know of. Generally they are set to allow one drop of water in the space of a minute or so while running. This allows for cooling/lubrication of the shaft/packing interface.
When we refer to a "tight" pump, we are talking about the wear ring-to-impeller clearances. At no time should these items contact each other, so tighter clearances do not increase drag.

[malcolm]

The only time my pump cavitates is when it sucks up a small piece of wood and it gets stuck on my (too sharp) impeller blade. That piece of wood going around sure messes up the flow. My pump only spins to 4600, but it hits 5000 quick when this happens. The last time it did it, I had to beach and pull the inspection cover to get it out.

[cheech]

thankx so normal ware and tear is most likely the issue. he is going to have it gone though, and i will get on with building the motor the way he wan'ts to go. it appears the only way to get on the write track quicker and cheaper is asking you guy's. thankx again