No props. A set of Kamewah water jets.

Rick

Rick wrote:
No props. A set of Kamewah water jets.

If you want to quibble, the water jets substitute impellers for
propellers. In some cases they are harder to access too, but in general
they're less troublesome IMHO... just like a big pump... in fact that's
what it is.

The trade-off is that they're less efficient at low speed because the
intake velocity gives the impeller/nozzle a boost just like apparent
wind for a sailboat. I don't know from my own experience, but I've heard
it said that they don't give as much kick for maneuvering at low speed,
but don't have prop walk so that's good.

One of the interesting water jets I saw was on a 21' light trailerable
sailboat. The water jet came out the back through an extended nozzle
about 4" above the water line.

Fresh Breezes- Doug King

DSK wrote:

If you want to quibble, the water jets substitute impellers for
propellers. In some cases they are harder to access too, but in general
they're less troublesome IMHO... just like a big pump... in fact that's
what it is.

The trade-off is that they're less efficient at low speed because the
intake velocity gives the impeller/nozzle a boost just like apparent
wind for a sailboat. I don't know from my own experience, but I've heard
it said that they don't give as much kick for maneuvering at low speed,
but don't have prop walk so that's good.

No need to quibble, much less troublesome. Lots of "kick" at low speeds
since they accelerate a huge weight of water in a very short time and
put it anywhere you want it. Twin jets and a bow thruster are lovely.

The OP specified a 150' boat, rapid reversing capability, and precise
speed control ... all the attributes of jets in a boat that size.
Efficiency is not the highest rung on the ladder in that installation.

Rick

Rick wrote:
.... Lots of "kick" at low speeds
since they accelerate a huge weight of water in a very short time and
put it anywhere you want it. Twin jets and a bow thruster are lovely.

That does make sense but I've head a couple of people say that jets will
not give as definite a push when gunned at low speeds as will a
conventional prop.

If you look at it as a problem in differential pressure, it seems to me
a pump & jet nozzle could generate higher delta-P much quicker though. I
guess to make sure I'll have to try it for myself some day.

I have driven a couple of small jets, the biggest one a 25-ish foot
center console... heavy boat, flat bottomed, badly prone to side slip
but a lot of fun in the shallow water it was designed for. It had a
fixed jet nozzle & conventional rudder.



The OP specified a 150' boat, rapid reversing capability, and precise
speed control ... all the attributes of jets in a boat that size.
Efficiency is not the highest rung on the ladder in that installation.

Yep. People that are mega-rich have different priorities!

Fresh Breezes- Doug King

Rick wrote:
No props. A set of Kamewah water jets.

Rick


Also, not a bad way to go. Since money no object, use computer controls
and a "joystick" for handling options .....just watch out for "nasties"
sucked into impellers.

otnmbrd wrote:

Also, not a bad way to go. Since money no object, use computer controls
and a "joystick" for handling options .....just watch out for "nasties"
sucked into impellers.

Real nice, just took over a 104 foot aluminum boat (private yacht) with
two 3000 hp units, joy sticks that combine to run off one stick when in
cruise mode, separate for maneuvering. Bow thruster for docking. Can
reverse gearboxes to flush out debris that isn't minced.

Money is an object for the owners but at the level they operate it seems
like it doesn't matter much.

Rick