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Default bilge pump as propulsion

ok, Ive heard this idea brought up before and seen it poo poo'd, but can it
work to some extent?

Ive got a 14' cat that i store next to the beach in sydney harbour and i
like to get out for a sail when i can. Unlike most cats this size, it has
heaps of flotation - 3-4 adults and still not sinking anywhere near as much
as a hobie 14 with 2 POB. It has an outboard bracket on the back which was
on it from the factory, but i've destroyed 2 admittedly cheap and nasty
second hand outboards on it so far. I have a new honda 2hp 4 stroke on my
dinghy that i dont want to put on the cat because it would probably suffer a
similar fate.

What happens is that because your moving so fast, the outboard gets
completely drowned, as do the people sailing for that matter ;-) an
outboard might work on a lake or something, but sydney harbour gets choppy.
The thing is, this boat was designed for island hopping the whitsundays and
the manufacturer claims enough flotation for 4 people, plus camping gear, a
stove, and food and water for a week! I cant see how they get the outboard
to survive...

i do ok if i get the outboard started and there are no waves and i just
motor round on it. a 2 or 3 is plenty to move along. its rated for a 5 at
maximum. the trouble is, as soon as you sail if there's a bit of chop, that
motor is getting a drink - then you'll never get it started. I want a bit
of propulsion for getting into some of the finnicky bay areas rather than
spending a couple of hours tacking to death, 5 minutes of propulsion would
get me there. propulsion would also be nice for getting back in if the wind
dies, and finally as a backup just in case something breaks. i like to go
out when the wind is big, and ive already had a couple of incidents with
snapping a gooseneck fitting, and destoying a couple of jib cleats.

so here's what im thinking; a 1250GPH bilge pump in each hull, intake hoses
going into the water, outlets hooked up to hoses facing rear. these draw 5A
each and are cheap to buy. A 40-50AH sealed gel cell would give me a lot
more power than i need. I cant see myself using ot for longer than about 30
minutes to an hour at a time. Is this going to move me at all? at least
more than trying to paddle the boat by myself (which gets me almost
nowhere!) would i get any benefit from using smaller diameter hoses to
create a stronget 'jet', or am i just unnecessarily loading the pump for no
real gain? am i miles off in the GPH stakes.... do i need a lot more
pumping to get any effect?

im not looking for a speed boat here, just *movement* even 1 knot would be
something. benefits to this system are that its fully submersible,
completely unobtrusive, almost silent, would cost me about $100, starts
instantly when i need it.

thanks,
Shaun


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Default bilge pump as propulsion

does anyone have a good approximate way of converting flow to thrust? as an
aside, do you think you would get more meaningful motion by having, for
example 4x 1000GPH pumps, or 1x4000gph pumps?

Thanks,
Shaun


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Default bilge pump as propulsion

On Feb 11, 8:58 am, "Shaun Van Poecke"
wrote:
does anyone have a good approximate way of converting flow to thrust? as an
aside, do you think you would get more meaningful motion by having, for
example 4x 1000GPH pumps, or 1x4000gph pumps?

Thanks,
Shaun


Hmmm.. Let's do a VERY Quick&Dirty approximation. 5 Amps at 12V = 60
Watts times 2 pumps =
120 Watts. 746 Watts per Horsepower. So About 120 / 746 = .16
horsepower. Assuming there are no losses (!) how fast will that move
your boat??

(Major mechanical / hydraulic issues that I can't figure out
remain).....


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Default bilge pump as propulsion


wrote in message
ups.com...
On Feb 11, 8:58 am, "Shaun Van Poecke"
wrote:
does anyone have a good approximate way of converting flow to thrust? as
an
aside, do you think you would get more meaningful motion by having, for
example 4x 1000GPH pumps, or 1x4000gph pumps?

Thanks,
Shaun


Hmmm.. Let's do a VERY Quick&Dirty approximation. 5 Amps at 12V = 60
Watts times 2 pumps =
120 Watts. 746 Watts per Horsepower. So About 120 / 746 = .16
horsepower. Assuming there are no losses (!) how fast will that move
your boat??

(Major mechanical / hydraulic issues that I can't figure out
remain).....



thats a good question. here's one in return; how many hp do you think i
generate with a 3 foot paddle considering that i have to move rapidly from
one side of the boat across the tramp to ther other side otherwise i go
round in circles? surprisingly, it does actually give me some progress.
but if there is a wave going against me, i go backwards.

so four pumps might give me roughly 1/4 hp? just roughly....

would there be any benefit from running the pumps in series rather than in
parallel? if might give me enough thrust to put a nozzle of some sort on
the end.... im open to suggestions!

thanks,
shaun


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Default bilge pump as propulsion

I suspect a water jet is not as efficient as a propellor.
Since you are evidently planning on 12v on your cat, why don't you get a
small 12v trolling motor ? That would take dumkings better than a gas motor,
although you would need to rinse it off.

"Shaun Van Poecke" wrote in message
...
ok, Ive heard this idea brought up before and seen it poo poo'd, but can
it work to some extent?

Ive got a 14' cat that i store next to the beach in sydney harbour and i
like to get out for a sail when i can. Unlike most cats this size, it has
heaps of flotation - 3-4 adults and still not sinking anywhere near as
much as a hobie 14 with 2 POB. It has an outboard bracket on the back
which was on it from the factory, but i've destroyed 2 admittedly cheap
and nasty second hand outboards on it so far. I have a new honda 2hp 4
stroke on my dinghy that i dont want to put on the cat because it would
probably suffer a similar fate.

What happens is that because your moving so fast, the outboard gets
completely drowned, as do the people sailing for that matter ;-) an
outboard might work on a lake or something, but sydney harbour gets
choppy. The thing is, this boat was designed for island hopping the
whitsundays and the manufacturer claims enough flotation for 4 people,
plus camping gear, a stove, and food and water for a week! I cant see how
they get the outboard to survive...

i do ok if i get the outboard started and there are no waves and i just
motor round on it. a 2 or 3 is plenty to move along. its rated for a 5
at maximum. the trouble is, as soon as you sail if there's a bit of chop,
that motor is getting a drink - then you'll never get it started. I want
a bit of propulsion for getting into some of the finnicky bay areas rather
than spending a couple of hours tacking to death, 5 minutes of propulsion
would get me there. propulsion would also be nice for getting back in if
the wind dies, and finally as a backup just in case something breaks. i
like to go out when the wind is big, and ive already had a couple of
incidents with snapping a gooseneck fitting, and destoying a couple of jib
cleats.

so here's what im thinking; a 1250GPH bilge pump in each hull, intake
hoses going into the water, outlets hooked up to hoses facing rear. these
draw 5A each and are cheap to buy. A 40-50AH sealed gel cell would give
me a lot more power than i need. I cant see myself using ot for longer
than about 30 minutes to an hour at a time. Is this going to move me at
all? at least more than trying to paddle the boat by myself (which gets
me almost nowhere!) would i get any benefit from using smaller diameter
hoses to create a stronget 'jet', or am i just unnecessarily loading the
pump for no real gain? am i miles off in the GPH stakes.... do i need a
lot more pumping to get any effect?

im not looking for a speed boat here, just *movement* even 1 knot would
be something. benefits to this system are that its fully submersible,
completely unobtrusive, almost silent, would cost me about $100, starts
instantly when i need it.

thanks,
Shaun





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Default bilge pump as propulsion


"Garland Gray II" wrote in message
...
I suspect a water jet is not as efficient as a propellor.
Since you are evidently planning on 12v on your cat, why don't you get a
small 12v trolling motor ? That would take dumkings better than a gas
motor, although you would need to rinse it off.


the voltage issue is pretty redundant for me as the propulsion will be the
only thing powered, and i will be recharging at home, so it could be 12, 24
or 48. the trolling motor was something i originally considered, but i
heard a lot of bad reports about them, and they seem expensive for what they
are; the salt water ones even more so. There are no fresh water supplies
when my boat is, and its stored at the beach, so washing down is pretty
unlikely.

The only jet boats ive been in are the ones in new zealand, aluminum hulled
driven by either a single or a twin v8 engine and they sure do seem to suck
the gas down, but they have performance to match. I thought at the time
that they were very fuel inneficient, but compared to a similar powered
sterndrive, maybe not.

the 12v trolling motors have come down a lot in price, but they still seem
expensive to me (in australia at least) for what they are.

Shaun


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Default bilge pump as propulsion

Shaun Van Poecke wrote:
"Garland Gray II" wrote in message
...
I suspect a water jet is not as efficient as a propellor.
Since you are evidently planning on 12v on your cat, why don't you get a
small 12v trolling motor ? That would take dumkings better than a gas
motor, although you would need to rinse it off.


the voltage issue is pretty redundant for me as the propulsion will be the
only thing powered, and i will be recharging at home, so it could be 12, 24
or 48. the trolling motor was something i originally considered, but i
heard a lot of bad reports about them, and they seem expensive for what they
are; the salt water ones even more so. There are no fresh water supplies
when my boat is, and its stored at the beach, so washing down is pretty
unlikely.

The only jet boats ive been in are the ones in new zealand, aluminum hulled
driven by either a single or a twin v8 engine and they sure do seem to suck
the gas down, but they have performance to match. I thought at the time
that they were very fuel inneficient, but compared to a similar powered
sterndrive, maybe not.

the 12v trolling motors have come down a lot in price, but they still seem
expensive to me (in australia at least) for what they are.

Shaun


The Minnkota series electric trolling motors can be used successfully in
salt water. I do it with both a 30 lb and 50 lb model. Paint the lower
unit with resin to prevent the paint flaking off. The only thing in the
upper unit is a switch. If you are worried about the switch getting
soaked, simply remove it and connect directly to the battery, or else
move the switch elsewhere.

BS
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Default bilge pump as propulsion

Shaun Van Poecke wrote:
"Garland Gray II" wrote in message
...
I suspect a water jet is not as efficient as a propellor.
Since you are evidently planning on 12v on your cat, why don't you get a
small 12v trolling motor ? That would take dumkings better than a gas
motor, although you would need to rinse it off.


the voltage issue is pretty redundant for me as the propulsion will be the
only thing powered, and i will be recharging at home, so it could be 12, 24
or 48. the trolling motor was something i originally considered, but i
heard a lot of bad reports about them, and they seem expensive for what they
are; the salt water ones even more so. There are no fresh water supplies
when my boat is, and its stored at the beach, so washing down is pretty
unlikely.

The only jet boats ive been in are the ones in new zealand, aluminum hulled
driven by either a single or a twin v8 engine and they sure do seem to suck
the gas down, but they have performance to match. I thought at the time
that they were very fuel inneficient, but compared to a similar powered
sterndrive, maybe not.

the 12v trolling motors have come down a lot in price, but they still seem
expensive to me (in australia at least) for what they are.

Shaun


Should also have mentioned that my 30 lb Endura pushes a 14' Hobie at
about 3.5 mph in still water.

BS
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Default bilge pump as propulsion

Per Shaun Van Poecke:
that i have to move rapidly from
one side of the boat across the tramp to ther other side otherwise i go
round in circles?


Could rudder control be an issue?

I've had Hobie 14's and 16's and as long as I kept steering (with a foot or by
sitting on the tiller bar) paddling continuously on one side worked OK.
--
PeteCresswell
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Default bilge pump as propulsion

Jet boats are not particularly efficient and are used in shallow water
because outdrives tend to come apart when they hit a rock. They are good on
rivers but not on open water.

your trolling motor will probably be less than a battery bank to run a bilge
pump and remember that it is not just volume that comes through but also you
want velocitiy at the outlet of the jet.

Brian


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