Porpoising in smooth water
Peggie Hall
It should be of MAJOR concern to you--Porpoising is a DANGEROUS
condition! As you've commented, it gets worse until the boat is almost
out of control. Should it get out of control it can throw you out of the
boat, turn you into the path of another boat, or even flip the boat.
Your only safe choices are to sell the boat...repower it with the
appropriate engine/outdrive (I can't believe the dealer admitted to
overpowering...if something happens, his liability exposure is
enormous!!)...or install governors or other devices that make it
impossible to run the boat at the speed and trim at which it begins to
porpoise.
You seem to have figured out what do when it starts, and the conditions
in which it does...but when you're skiing or out playing, it's not
likely that anyone else driving the boat will have the same
knowledge. You're playing russian roulette.
The dealer claims the boat "is within specs," yet says he "gave you a
deal" on the boat because it isn't--and the mfr says it isn't. It's an
unsafe boat...the dealer knew it when he sold it to you. Do whatever
it takes to make him fix it.
Peggie Hall/Peal Products
Specializing in marine toilet systems since 1987
Lew wrote:
>
> Last year I bought a Chaparral 1930 with a 4.3 Gen+ engine and a Bravo
> 3 outdrive. I love the boat and would recommend it to anyone. It
> does however have an annoying tendancy to porpoise in smooth water
> with only me in the boat.
>
> When I am cruising on "glass" by myself (not a condition I encounter
> often) with the trim up and make a SLIGHT turn to the right, the boat
> starts to porpoise slightly, with each bounce higher until the boat is
> almost out of control. I can stop it by turning more or straightening
> out or by trimming down. This doesn't happen with more passengers or
> if the water is even slightly choppy. In a year it has happened only
> three times since the conditions have to be perfect, so I haven't
> worried about it. I am, however, curious.
>
> When it first happened, I called Mercruiser, Chaparral, and my
> dealer. Mercruiser said it was probably a defect in the hull and to
> have the manufacturer check it with a straight edge. If that wasn't
> the problem, then have them check the outdrive allignment. Chaparral
> said porpoising was a characteristic of the Bravo 3, which was not
> supposed to be installed on smaller boats. My Chaparral dealer told
> me the Bravo 3 was installed by mistake; it was supposed to be an
> Alpha. That's why they gave me a "deal" on the boat. They checked
> the boat and said it was within specs.
>
> Again, this is of little concern to me as I LOVE the boat, but since I
> have access to all of your collective expertise, I thought I would ask
> and see if anyone had a possible answer.
>
> Thanks in advance.
>
> Lew
George Jefferson
:Your only safe choices are to sell the boat...repower it with the
its not overpowered, all they admitted to is the wrong outdrive.
Quite an odd thing that the bravo 3 would cause porpoising.
I'd be interested in an explintion of that.
if something happens, his liability exposure is
:enormous!!)...or install governors or other devices that make it
:impossible to run the boat at the speed and trim at which it begins to
:porpoise.
You might be overreacting a little (hard to say without driving it)
If the problem is corrected by the obvious remedy (trim down) I
wouldn't loose sleep over it, unless you are inclined to let morons
drive your boat.
--
george jefferson
*note new email, was geo...@mech.seas.upenn.edu
now geo...@sol1.lrsm.upenn.edu
Mark Whatman
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George Jefferson wrote:
> Quite an odd thing that the bravo 3 would cause porpoising.
> I'd be interested in an explintion of that.
>
The Bravo 3 provides more bow lift than the Alpha 1, especially at
extreme positive trim angles. This bow lift, when over trimmed, causes
the boat to porpoise. The effect is normal in most planing hulls. It
is engineered out with "hooks" on rear of the hull to cover up the
effect. A good set of after planes (trim tabs) are used on performance
boats to allow positive trim while controlling the attitude of the boat.
The action of "turning slightly to the right" changed the geometry of
the outdrive in relation to the running surface just enough to start the
porpoising. This is, again, typical. Dropping the trim slightly on the
onset of a turn is a standard practice. this places the outdrive in a
more square relationship to the running surface which allows for greater
control. All of these are normal procedures for operating a performance
boat. Anyone not familiar with the basic action, reaction of a boat and
trim should never be allowed near the drivers seat.
In the same way that you wouldn't want your $150,000 porsche driven by a
student driver you shouldn't allow a performance boat (one capable of
speeds over 50 mph) to be driven by a novice. Education and experience,
not governors is the answer.
My 2 cents.
Mark Whatman
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Chuck Jackson
<snip>
> I continue to think of this as a minor problem. The conditions have
> to be perfect and as I said before almost any driver input will stop
> it, and there IS a performance gain over an identical boat with an
> Alpha 1. Everything considered, I am happy with my boat. However,
> anyone considering a boat under 23' should be aware of this possible
> problem when choosing an outdrive.
>
<snip>
The Bravo 3 is a great outdrive for larger Deeper V's as you have
stated.
However, the performance in your boat/engine configuration would most
likely be increased with an Alpha 1 drive. The Alpha is more
hydrodynamic (less drag in the water) and has fewer moving parts....the
increase would be minimal in your speed range (probably around 45-50mph)
but the Alpha 1 is considerably less expensive (maybe not in your case
since you got a great "deal" as you have stated.)
Harry T. Stone
I have a 93 Chaparral 205 SL, I have an AlHPA outdrive and I porpoise in
smooth water. I just drop the bow a touch or add a little throttle. When
I bought the boat I asked the local dealer and he said it was an
inherent action because of the deep V hull design Chaparral uses. I
installed a Hydrfoil and it stopped altogether.
Harry T.
--
Suffering in silence, they've all been betrayed.
They hurt them and they beat them, in a terrible way,
Praying for survival at the end of the day.
There is no compassion for those who stay.
Harry Krause
Harry T. Stone wrote:
> I have a 93 Chaparral 205 SL, I have an AlHPA outdrive and I porpoise
> in
> smooth water. I just drop the bow a touch or add a little throttle.
> When
> I bought the boat I asked the local dealer and he said it was an
> inherent action because of the deep V hull design Chaparral uses. I
> installed a Hydrfoil and it stopped altogether.
>
> Harry T.
> --
Sheesh. Lots of planing boats will porpoise at certain speeds and trim
levels. That's why you can trim in the engine or use the tabs. Of
course, you could have a boat bottom problem such as a hook or rocker,
but most likely, if you are porpoising, you are overtrimmed and using
too many rpm's.
Harry Krause
Post Office Box 7575 Jacksonville, Florida 32238
- - - - - - - - - -
You have only a very small head and must live within it.
Peter W. Meek
On Mon, 28 Jul 1997 18:05:08 GMT, ham...@mindspring.com (Lew)
wrote:
>When I am cruising on "glass" by myself (not a condition I encounter
>often) with the trim up and make a SLIGHT turn to the right, the boat
>starts to porpoise slightly, with each bounce higher until the boat is
>almost out of control. I can stop it by turning more or straightening
>out or by trimming down. This doesn't happen with more passengers or
>if the water is even slightly choppy. In a year it has happened only
>three times since the conditions have to be perfect, so I haven't
>worried about it. I am, however, curious.
>
Frankly, this doesn't sound too much like a porpoising
PROBLEM, inasmuch as you have to TRY to set up the
exact conditions to make it happen. Almost any boat
will exhibit poor handling of some sort or another
if turned while the motor/drive is trimmed way out.
Mine skids, hops, and ultimately ventilates the prop.
Under just the wrong conditions, I expect that the
outside chine could hook a wave and flip the boat.
Solution: I trim in a little as I begin a high speed
turn. Watch the pros on ESPN some time -- you'll notice
they do the exact same thing (or the equivalent on
non-outboard/IO drives).
If you have a boat that is powered up near the
limits of the boat, you have a "high-performance"
boat. You owe it to yourself and the rest of
the boaters out here to learn to drive it
properly, and *especially* not to turn the
helm over to someone who hasn't been trained
to drive it properly. It sounds as though
you are training yourself by investigating
rare handling problems; just make sure you
pass those discoveries on to anyone that
you allow at the helm.
BTW, don't trim in too far in high-speed
turns or you may discover high-speed
bow-steering. I saw a boat swap ends at
high speed once, and stop in a couple of
boatlengths. This almost always throws
people violently around inside (beaking
limbs) or throws people out of the boat.
If the transom is driven under, it may
swamp the boat almost instantly. Your
boat may not have a deep enough forefoot
to make this a problem, but some boats
do.
BTW, my own understanding of the Bravo3 is
that it was intended to allow some of the
advantages of I/O drives to be applied to
heavy boats. It isn't so much that it isn't
safe on smaller boats; just not what it
was designed to be most efficient on.
It seems to me that one of the mags did
an A/B comparison of Bravo3 vs one of
the other versions on several different
boats and came to the conclusion that
it was a waste of money on light boats,
but very useful on heavy ones.
--Pete
pwm...@mail.msen.com (Peter W. Meek)
http://www.msen.com/~pwmeek/
pa
This sort of dynamic instability can often be traced to a CG problem (CG too
far forward). Since you state that it only happens when the boat is running
light (no passengers etc.). Try moving whatever weight is in the boat as far
aft as possible. It may help.
Also check the bottom of the boat for a hook at the transom on one side. This
can happen if the gelcoat pulls off the mold before it is skinned. A hooked
bottom can act as a trim tab and put the bow down when you need it least.
As everyone else has said, be careful. This sort of thing can get out of hand
quite easily.
Regards,
Phil
George Jefferson
:This sort of dynamic instability can often be traced to a CG problem (CG too
:far forward).
I'd have thought the opposite.
Sealegs940
all small boats will porpoise with the drive trimed up to far when you
trim up do it slowly untill it just starts to porpoise and just touch the
down trim and youll find it will stop and you should be at about the best
running plain at that point ,see the trim will change with load thats why
you have a a proublem with just yourself or a light load on board the
drive over trimsbefore it hits its limit if you have more wieght on board
you need that extra trim so I guess im trying to say dont trim all the way
up play with it and get to know were the ideal position is after a while
it will be automatic so no mater what the load trim up till the bow feels
overly light then tap the trim down a touch I hope this makes sense
GOOD LUCK KEN
Start Your Engines Inc.
In article <33DCE6...@worldnet.att.net>,
Peggie Hall <peg...@worldnet.att.net> wrote:
>It should be of MAJOR concern to you--Porpoising is a DANGEROUS
almost
the
>boat, turn you into the path of another boat, or even flip the boat.
>
>appropriate engine/outdrive (I can't believe the dealer admitted to
>impossible to run the boat at the speed and trim at which it begins
to
>porpoise.
>
conditions
>in which it does...but when you're skiing or out playing, it's not
>likely that anyone else driving the boat will have the same
>knowledge. You're playing russian roulette.
>
>The dealer claims the boat "is within specs," yet says he "gave you
a
>deal" on the boat because it isn't--and the mfr says it isn't. It's
an
>unsafe boat...the dealer knew it when he sold it to you. Do whatever
>it takes to make him fix it.
>
>Peggie Hall/Peal Products
>Specializing in marine toilet systems since 1987
>
>Lew wrote:
>>
>> Last year I bought a Chaparral 1930 with a 4.3 Gen+ engine and a
Bravo
>> 3 outdrive. I love the boat and would recommend it to anyone. It
>> does however have an annoying tendancy to porpoise in smooth water
>> with only me in the boat.
>>
encounter
>> often) with the trim up and make a SLIGHT turn to the right, the
boat
>> starts to porpoise slightly, with each bounce higher until the
boat is
>> almost out of control. I can stop it by turning more or
straightening
>> out or by trimming down. This doesn't happen with more passengers
or
>> if the water is even slightly choppy. In a year it has happened
only
>> three times since the conditions have to be perfect, so I haven't
>> worried about it. I am, however, curious.
>>
>> dealer. Mercruiser said it was probably a defect in the hull and
to
>> have the manufacturer check it with a straight edge. If that
wasn't
>> the problem, then have them check the outdrive allignment.
Chaparral
>> said porpoising was a characteristic of the Bravo 3, which was not
>> supposed to be installed on smaller boats. My Chaparral dealer
told
>> me the Bravo 3 was installed by mistake; it was supposed to be an
>> Alpha. That's why they gave me a "deal" on the boat. They
checked
>> the boat and said it was within specs.
I wouldn't be overly concerned about it. You say it has only happened
a few times since you owned it, and you already know how to get it
back under control, or to avoid it in the first place. Porpoising is
indeed a dangerous condition, but as in most things dangerous, a
little knowledge goes a long way. You may find that even after
changing the drive etc., that it may still do it, but under slightly
different conditions.
I forget the fellows name, but a few days ago there was a fellow who
gave a full and proper description of what is happening. It is a form
of amplified resonance. When conditions are perfect and everything is
in the required balance (power, trim, weight distribution etc.) for
the particular hull in question the hull can begin to bounce in a way
that amplifies the bounce each time. Anything you can do to upset
that balance will have an effect on the porpoising. In your case, it
seems that adding weight up forward will prevent it, as is evidenced
by the fact that it does not occur with more than one person on
board, (I am assuming that the second person usually rides up front
as is usually the case). However, if it were possible to control the
boat from the stern, you may find that shifting weight to the stern
can also prevent the porpoising. In most cases though, the porpoising
is a result of a bow that is a little too light for the way the boat
is trimmed and powered. In your case, you say it is easily controlled
by trimming the leg in, so it is not even necessary to alter weight
distribution, unless you have a particular reason for running with
the leg trimmed out.
Although porpoising is a potentially dangerous situation, so is
swimming. In the case of swimming, you can avoid harm by staying away
from the water, or you can learn how to swim and minimize the risk.
It sounds to me like you are learning all you can about the
porpoising on your particular boat, and therefore you should be able
to minimize any potential hazards. I would enjoy the boat.
Jamie Bracht
pa
In article <5roaf9$cpe$1...@netnews.upenn.edu>, geo...@sol1.lrsm.upenn.edu says...
George,
There is a good article on planing hull dynamic instability in Professional
Boatbuilder No31, Oct-Nov 94 by Lou Codega.
Regards,
Phil Arnold
Matthew Toly
Mark Whatman wrote:
>
> George Jefferson wrote:
>
> > Quite an odd thing that the bravo 3 would cause porpoising.
> > I'd be interested in an explintion of that.
> >
>
> The Bravo 3 provides more bow lift than the Alpha 1, especially at
> extreme positive trim angles. This bow lift, when over trimmed, causes
> the boat to porpoise. The effect is normal in most planing hulls. It
> is engineered out with "hooks" on rear of the hull to cover up the
> effect. A good set of after planes (trim tabs) are used on performance
> boats to allow positive trim while controlling the attitude of the boat.
>
> The action of "turning slightly to the right" changed the geometry of
> the outdrive in relation to the running surface just enough to start the
> porpoising. This is, again, typical. Dropping the trim slightly on the
> onset of a turn is a standard practice. this places the outdrive in a
> more square relationship to the running surface which allows for greater
> control. All of these are normal procedures for operating a performance
> boat. Anyone not familiar with the basic action, reaction of a boat and
> trim should never be allowed near the drivers seat.
>
> In the same way that you wouldn't want your $150,000 porsche driven by a
> student driver you shouldn't allow a performance boat (one capable of
> speeds over 50 mph) to be driven by a novice. Education and experience,
> not governors is the answer.
>
> My 2 cents.
>
> Mark Whatman
>
the positive trim of the Alpha I or the Bravo I. It consequently cannot
be mounted as high as the I drives and in the smaller application has
trim in limitations as standard rigging. Most manufacturers that have
tested the Bravo III on small boats, (Smaller than 4000lb @23-24')
usually don't reccommend the package. THis does not mean all, but most
generally.
Over....