Towing a Seadoo behind a sailboat
QWeaver
Can I tow my GSX behind my sailboat without special preparation? The book says
not to tow above 15 MPH or flooding may occur...max speed on the sailboat will
be @ 7 Knots. The book suggests clamping the water supply off. Anyone have
experience with this. Seems funny having a 10 HP boat pull a 110 HP "boat".
Quinton
Eugen Jeggle
All I know is that you MUST clamp the water supply of or else you will
force water into the engine (not just the engine compartment) and more than
likely damage it.
I have an 85hp 1996 SPX, love it man! What is the 110hp GSX like?
Regards
Eugen.
QWeaver <qwe...@aol.com> wrote in article
<19971204014...@ladder02.news.aol.com>...
George Jefferson
:All I know is that you MUST clamp the water supply of or else you will
:force water into the engine (not just the engine compartment) and more than
:likely damage it.
at sailboat speed you should be ok though..
--
george jefferson : geo...@sol1.lrsm.upenn.edu
to reply simply press "r"
-- I hate editing addresses more than I hate the spam!
QWeaver
>All I know is that you MUST clamp the water supply of or else you will force
water into the engine (not just the engine compartment) and more than likely
damage it.
I have no point of reference since this is my first PWC and we have only ridden
it four days, but it seems to haul ass. The speedo showed 62 mph down wind and
53 up wind so I would think that 55 mph is a reasonable guess at top speed. We
all (wife,daughter etc) like it a lot!
Quinton
Drew
The 785 Rotax is tried and true, and the hull is race proven durable.
The GSX is probably the best 2-up all around ski on the market.
Great for long distance cruising, towing toys, and all around FUN.
I love mine, and with a few bolt on mods (thanks Bill), my GSX is seldom
left looking at anyone's stern. With exception of that 1050 Polarii (it
was glassy) and the new GSXL (although I took the hole shot, thanks
again Bill).
Great all-purpose ski.
--
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__________ / / /__ ___/_ _ \__ | /| / /
_/_____/_ /_/ / _ / / __/__ |/ |/ /
/_____/ /_/ \___/ ____/|__/
***to reply, remove NOSPAM from my email address**
W.S. O'Neal
Quinton,
That is a real good guess as to the speed of your GSX as 56 is the going
number. What does the wind have to do with your speedo reading ? The pick
up for the seedo is under water on the ride plate.
Bill
--
Bill @ E-MAIL: Water...@worldnet.att.net
QWeaver <qwe...@aol.com> wrote in article
<19971204210...@ladder01.news.aol.com>...
Eugen Jeggle
Boy, I just bet you like it alot! :)
I took mine on the ocean and it was incredible! my 85hp really goes fast,
very fast
so I can imagine 110hp, awesome.
Anyway, enjoy it!
QWeaver <qwe...@aol.com> wrote in article
<19971204210...@ladder01.news.aol.com>...
Drew
QWeaver wrote:
>
> >What does the wind have to do with your speedo reading ? The >pickup for the
> seedo is under water on the ride plate.
> >Bill
>
> will certainly go faster through the water downwind than upwind. We had about
> a 20 knot wind on the day that I quoted the figures and there was nearly a 10
> mph difference in indicated speed.
I'm a bit skeptical about that.... maybe a slight factor, but nothing
noticable.
Current, on the otherhand, will not affect
> the indicated speed but will affect the speed over the bottom.
>
Current WILL affect the indicated speeds. The guys who ride the
whitewater can be going nowhere, yet the speedometer reads 20 mph, due
to the current rushing over the pickup.
>
> Quinton
George Jefferson
:Most of the boat is out of the water and is greatly affected by the wind
:We had about
:a 20 knot wind on the day that I quoted the figures and there was nearly a 10
:mph difference in indicated speed.
20 knots of wind means a good chop as well, which generally
slows you down (Ive heard claim of increased speed, but I think
thats by 'feel' or speedo error).
QWeaver
>20 knots of wind means a good chop as well, which generally
>slows you down (Ive heard claim of increased speed, but I think
>thats by 'feel' or speedo error)
I,m not claiming an increase or decrease of anything, it's obvious that most
of the people that replied to this post"don't have a clue"
Quinton
Drew
Say what?
You said:
"Most of the boat is out of the water and is greatly affected by the
wind,
It
will certainly go faster through the water downwind than upwind. We had
about
a 20 knot wind on the day that I quoted the figures and there was nearly
a
10
mph difference in indicated speed. Current, on the otherhand, will not
affect
the indicated speed but will affect the speed over the bottom."
And several of us said it wasn't true, because it isn't.
Chop will be a factor, but the wind will *hardly* affect such a small
boat. What are *you* talking about? A sailboat or a PWC?
And where is your speedo paddle wheel located? On the handle bars?
I think you are the only one without a *clue*, as you put it.
QWeaver
>And several of us said it wasn't true, because it isn't.
>Chop will be a factor, but the wind will *hardly* affect such a small
>boat. What are *you* talking about?
I'm not going to waste time trying to convince anyone about anything if they
will not listen. I live on a very protected Bayou with a fairly long straight
run. I'm not basing what I said on conjecture or what I "think" will happen
but real, observable, repeatable evidence. The force or resistance created by
air is equal to the square of the speed. The frontal/cross sectional area of
the ski is significant and WILL be a factor. I didn't pull these figures out
of a hat!!! I saw them on repeated runs up and down the bayou just last
weekend.
I,m a skydiver and at 110 MPH my body no longer accelerates because the drag of
the air is sufficient to support my 220lbs. I raced formula cars for many
years( with cross sectional areas not much larger than a PWC) that would go 10
to 15 MPH faster downwind than up. We often had to change the gearing to avoid
over revving if the wind switched If you don't think that the same set of
rules apply to boats then I am wasting both your and my time in this debate.
The easy solution for those of you who doubt is to go try it. But be fair and
unbiased in your test, select an area where the wind is dead ahead and
protected from large chop. ( Like in front of my house)
Quinton
George Jefferson
:And several of us said it wasn't true, because it isn't.
:Chop will be a factor, but the wind will *hardly* affect such a small
:boat.
20mph wind adding or subtracting 5mph sounds very plausable to me.
I'd be interested if anyone has done radar runs in high wind..
W.S. O'Neal
George,
Yes, I have run some radar runs in wind and it does have an effect on
speeds achieved, But it wasn't alot of wind or alot of speed loss.
As any wind over 10 mph will cause a chop on the water, and thus cause a
speed loss, it is useless to test for maximum speed in those conditions. A
light breeze can help speeds though, because it will ripple the water just
enough to lessen hull drag. A very slight headwind can give a hull a little
more lift too, again creating less hull drag.
Where I do see a 2.5 MPH difference is in the River. With a 6-8mph current,
there is a variance of about 2 1/2 MPH difference in the speed depending
upon the direction of travel. Also, I noted a tachometer difference of over
150 RPM drop going upstream against the current. This is due to better pump
loading, and the more aggressive the scoop grate, the bigger the losses in
rpm's.
When any testing is done, a quality radar gun must be used. When I'm just
riding a ski for fun, it always feels faster when I'm going into the wind
than when I'm going away from the wind, just like any car or bike without a
windshield.
Bill O'Neal
WCM
George Jefferson <geo...@sol1.lrsm.upenn.edu> wrote in article
<66brc6$jt7$1...@netnews.upenn.edu>...
Drew
QWeaver wrote:
>
> Many times I have actually stood still or even gone backwards while sailing at
> FULL hull speed(7 knots) against the tide between the Galveston >jetties.
Here lies the confusion.
If you were standing still or going backwards, you were *NOT* going at 7
knots. Your *speedometer* stated you were travelling at that speed, but
you were not. Hence the reference I made earlier to the whitewater rider
whose speedometer says 20, when he's standing still.
Get it?
> I agree that testing for maximum would be useless but testing for the
> difference between upwind and downwind would be absolutely valid. A radar gun
> is not a good choice for this because any current would influence the speed
> relative to the "fixed" radar gun.
Huh?
Wrong. The radar gun would give you true MPH, without the influence of
the current! True MPH in terms of actual forward motion, not motion
through the water. Obviously a current ar wind in your face would slow
you down a bit.
>The boats speedo would be the best
> indicator since what we a seeking is the speed difference through the >water. We
> don't care that the calibration of the speedo is correct all we are >seeking is
> relative speed at full throttle.
> Quinton
Look Quinton, forget the stinking speedometer. It isn't accurate anyway.
You want a speed that can be used as a *BENCHMARK* against other
machines??? Use radar. Period.
Wind and currents are just contributions to real speed readings.
W.S. O'Neal
--
Bill @ E-MAIL: Water...@worldnet.att.net
QWeaver <qwe...@aol.com> wrote in article
<19971206223...@ladder01.news.aol.com>...
> >As any wind over 10 mph will cause a chop on the water, and thus >cause
a
> speed loss, it is useless to test for maximum speed in those >conditions.
> > Also, I noted a tachometer difference of over
> >150 RPM drop going upstream against the current.
> I am reluctant to continue this discussion, but... The area of fluid
dynamics
> is well known and developed. A boat or a plane or any other object
driven
> through any fluid behaves exactly the same way no matter which direction
it is
> driven through the moving fluid.
Quinton,
You are correct, as far as the hull is concerned. But the prop and scoop
grate will put more load on the engine going upstream. I have tested this
many times on the river and it does make a difference in both speed and rpm
( which is a reflection of load on the motor). Are we both on the same page
here? I'm concerned with the groundspeed of a PWC, relative to my radar
gun, which is fixed on shore.
In aircraft it is commonly described by
> imagining the plane to be in moving ocean of air(or in the case of a
boat,
> water) The only relative motion between the fluid and the object is that
> created by the engines.
> i.e, the boat or plane does not "feel" the movement of the air unless
the
> moving air changes velocity rapidly(turbulence/wind sheer) What does
happen is
> that the relative speed between the driven object and fixed objects (the
> ground/bottom of the river) is different as the craft changes directions
in the
> flowing liquid.
> Many times I have actually stood still or even gone backwards while
sailing at
> FULL hull speed(7 knots) against the tide between the Galveston jetties.
Last
> weekend we had 58 knot winds at 14000' and were bearly making headway
over the
> GROUND when the pilot slowed the plane to door speed for us to exit. But
I
> guarantee that the plane was still flying at the same speed through the
air
> and did continue to fly at the same speed as we turned downwind... it was
just
> hauling ass over the ground now.
Isn't that why we have *ground* speed and *airspeed* calculations to
make when figuring out our ETA's , while flying ?
How about when we are cracking open our throttles when facing an
upstream current to keep our relative position from changing ?. Our ground
speed is still zero. Isn't ground speed what we are discussing here? If you
want to test for speed, relative to a fixed object, what is wrong with
using our radar guns ?
>
> >As any wind over 10 mph will cause a chop on the water, and thus >cause
a
> speed loss, it is useless to test for maximum speed in those >conditions.
>
> I agree that testing for maximum would be useless but testing for the
> difference between upwind and downwind would be absolutely valid. A
radar gun
> is not a good choice for this because any current would influence the
speed
> relative to the "fixed" radar gun.
Why Not? If the boat is travelling 65mph away from the radar gun, and
only 60mph toward the gun, Didn't the boat lose 5 mph relitive to the fixed
position of the radar gun ?
T he boats speedo would be the best
> indicator since what we a seeking is the speed difference through the
water. We
> don't care that the calibration of the speedo is correct all we are
seeking is
> relative speed at full throttle.
If you have a speedometer that is reliable, then this would be true.
This would be an indicator of *waterspeed* not ground speed.
When we speak of a boats speed here in this NG, aren't we speaking of
ground speed ?
> This has peaked my interest enough that I will make a more "controlled
" test
> the next time the wind gets up. I have the perfect test area as my house
is
> located on a bayou where the wind can blow like hell without making a big
chop.
> I also agree that the chop would affect the speed as the shape of the
wave is
> different from upwind to downwind.
The effects of choppy waters to our Jet driven boats are that the water
gets aerated , producing less thrust, and that our boats get airborne,
producing alot less thrust (and drag upon re-entry), thus slowing them
down. There is alot more of an effect on our speeds because of this, than
you will ever experence because of wind drag on the hull. These things are
not sailboats.
Bill O'Neal
> Quinton
>
Drew
QWeaver wrote:
> I came to this NG to get info and have fun and I certainly
> like a good logical debate as long as it does not get ugly. Maybe I'm reading
> something into this that is not there and I apologize if that's the case.
>
>
> Quinton
I enjoy a logical debate as well.
I guess I am accustomed to measuring a PWC's speed in terms of land
speed, as Bill described it. That is where I find a few of your
statements erroneous. Another thing you will learn to understand (as you
become more familiar with the pros/cons of PWC) is that speedometers are
essentially worthless.
If you want to argue that wind and current has an affect on PWC top
speed, I will agree. But one cannot use the PWC speedometer as a guage
of that varience. It is not accurate. You must rely on "land speed" as a
benchmark, with either radar or possibly an extended GPS run.
My only argument with you is your insistence that you may be running 7
knots, while going nowhere. That is completely possible, in terms of
water passing across your hull (and speedometer pickup), but in common
PWC practice (oh boy), you are going 0 mph.
And you can't possibly use one PWC's speedometer to compare to
another. That is why we refer to speedometers on PWC's as
"dream-o-meters!" Too inconsistent, and too many variables- like
current, and air time.
That's all.
That's all.
Drew
QWeaver wrote:
>
> > How about when we are cracking open our throttles when facing an
> >upstream current to keep our relative position from changing ?. Our ground
> speed is still zero. Isn't ground speed what we are discussing here? If you
> want to test for speed, relative to a fixed object, what is wrong with using
> our radar guns ?
>
> valid measurement of the true speed produced by the propulsion system if there
> was no wind or current to factor in.
>
> I have shown these posts to two friends, both engineers.One's degree is in
> marine engineering and the other(Fred Jiran, Composite Design and Consulting )
> mechanical. Fred builds and repairs high performance glider and is an expert
> on this stuff They are not desk jockies, they do the work and they can explain
> it much more elequently than I can. Maybe I am just not communicating it well.
> I'll try to get them to post something.
> Quinton
I'm not debating that point....
You don't need a marine engineer to come to the conclusion that 30 MPH
(land speed), plus 10 MPH current (travelling AT you) equals 40 mph
water speed at the hull (or speedometer paddle.)
That's common sense.
What was the point again?
:)
QWeaver
>Here lies the confusion.
>If you were standing still or going backwards, you were *NOT* going >at 7
knots. Your *speedometer* stated you were travelling at that >speed, but you
were not.
by running with or against the wind. In that context the speed through the
water is the only thing that can be measured that will accurately determine
what effect the wind will have. You all are trying to compare apples to
oranges.
But believe what you want...it's your right to do that. But I have a very
good friend that has a marine engineering degree from Texas A&M that has
advised me to bet you as much money as I'd like that my statements are
true...and he'll take a little too.
Patronizing statements like "Get It" do little to convince me that your
argument is valid. I came to this NG to get info and have fun and I certainly
QWeaver
Drew
QWeaver wrote:
>
> Drew writes
> >I guess I am accustomed to measuring a PWC's speed in terms of land
> >speed, as Bill described it. That is where I find a few of your
> >statements erroneous.
>
>
> So if I go stand on my dock today and the current is running out at 8 mph and I
> ride up current while measuring the speed of my GSX with a radar gun and then
> three hours later when the tide is slack I measure it again. Then according to
> your statements, those two readings are an accurate guage of the true speed of
> my PWC???? I don't think so!
Reading number one: 50 MPH (for example)
Reading number two: 42 MPH.
What's the problem?
> I think the difference between the two readings are a pretty good measurement
> of the speed of the current at the time of the first reading
Ummm.. of course.
> I'll wager that the speedo on the ski is a much better indicator in this case.
Probably, if you used the landspeed as a benchmark, subtracted the two
readings, you would have an idea of how the current was flowing.
Alot of variables though... you're using the PWC as a current measuring
tool?
>
> >And you can't possibly use one PWC's speedometer to compare to
> >another.
> I never said you could!
>
> The laws of physics don't change just because we happen to be setting on a PWC
> (:-]
>
> Quinton
What was your point again?