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| Frequently
Asked Questions |
The following are the most common questions asked
about the design of a propeller.
Q:
How is my propeller and estimated performance calculated?
A:
All the data that you provide on our Henleys specification sheet
is entered into either two or four separate propulsion packages.
The resulting size is then designed with CAD to American Bureau of
Shipping standards and pitched to ISO484/2 Class 1 or 2 standard.
Q:
Will these design packages give a defined result in performance
and engine load?
A:
NO! This is not possible as the number of endless
combinations of vessel design; applied BHP and reductions make it
impossible for a design programme to quantify.
Q:
Will tank testing the design help with defining performance?
A:
Yes - this is the best method known to closely define performance
at the DESIGN STAGE! The next problem is that the vessel must be
built exactly to the design specification, as again all
predictions will fall wide of the mark if say the vessel is
overweight or does not achieve correct designed trim when in use.
Q:
Are all propellers the same?
A:
No – different configurations from various suppliers will give
varying performance results – hence in most cases our own designs
have given outstanding results on the majority of applications BUT
there have been instances where other makes / designs have suited
a particular style of craft better. The unfortunate part of this
is that "discovery" is made through trial and error and one cannot
purchase a “custom built” propeller from Henleys on a trial and
buy situation!
Q:
Should I have my vessel weighed while under construction?
A:
Yes – vessel displacement is critical to vessel performance and
engine load. Most engine makes now require that maximum loaded RPM
is set within a 20 to 50 margin on engine RPM which equals a
target of approximately 1.5%, yet a lot of vessels do not achieve
the correct trial weight specified - being as much as 10 to 30%
out!
Note: Engine suppliers can have a 3 to 5% variance on power
supplied including latest electronic motors! This will affect
achieved performance and rpm. This can only be discovered on sea
trial with the engines being fully tested. Please follow this
link to print a sea trial
result form.
Q:
Will I get any form of performance guarantee with the purchase of
my propeller?
A:
No – due to above stated variables it is not possible for us to
guarantee something that we cannot truly define. A vessel's
performance is locked into the vessel's design and final form – A
PROPELLER IS NOT A MAGIC WAND! We use our past experiences to
provide as accurate as possible performance estimates!
Q:
What form of warranty do I get?
A:
Henleys will warrant the products supplied for 12 months from date
of purchase, to be of merchantable quality and that they meet the
international pitching standard of ISO484/2 Class 1 for the
Propeller Range designs except for the "Skip Jack" and "Groper"
– which are pitched to ISO484/2 Class 2 standard.
Q:
What happens if on trial the engine loaded maximum RPM is not to
the manufacturers specifications?
A:
The propellers will need to be adjusted (if possible) – generally
in the order of pitch, cup, diameter or blade area.
Q:
Who pays for this work?
A:
Henleys will pay up to 50% of one re pitch only for a new
propeller based on the current Henleys Propellers and Marine list
price, and must be claimed within eight months from date of
purchase. This offer only applies to New Zealand. In the majority
of cases one re pitch is sufficient, but as the programmes used to
calculate the adjustment are generic only, in some cases the
client may need to repeat the process. ALL relating extra costs
i.e. loss of chargeable hours, haulage, removal, freight and
re-installation are the owners responsibility.
Q:
What causes a vibration?
A:
In most cases it is bent shafts, engine alignment to drive train
when the vessel is in service or the machinery supplied has not
been fitted correctly as per instructions supplied.
Q:
What about vibration in relation to my propeller.
A:
Henleys will guarantee that their propellers achieve a static
balance at time of manufacture. This is a universally accepted
tolerance and is sufficient for 99% of product supplied. However
some vessels are more susceptible to panel vibration. This becomes
apparent after a sea trial and the first best option that we have
found is to have the propeller dynamic balanced which 99% of the
time improves or rectifies the situation. Any costs involved in
dynamic balancing are the owner's responsibility.
Q:
What happens if there is a vibration?
A:
Henleys do not accept any responsibility for vibration levels on
sea trial as the resulting combinations of machinery and vessel
make it impossible to pre-define a level of tolerance unless an
in-depth design study and TVA is undertaken by the client before
any equipment is fitted to the vessel.
Q:
Can galvanic reaction affect my propeller and stern gear?
A:
YES - all propellers (including Stainless Steel) and stern gear
are susceptible. It is the owner's total responsibility to ensure
his bonding system is adequate for total protection at all times.
Henleys certificate, supplied with every new propeller, includes a
full material specification and batch number. There are well known
EXPERTS in this field - please ask for their contact details if
you are not sure. To view some photos of metal galvanic reactions
please click this link.
Q:
How important is the installation of the stern gear?
A:
The correct installation of your drive train equipment is CRITICAL
to the final result. Henleys experience is that over 98% of
problems realised on sea trial are the direct result of
incorrectly installed engines, gearboxes, drive shafts, stern
gear, and propellers. Henleys have taken this area very seriously
and provide full installation instructions with every new
propeller purchased. We also supply full installation instructions
of drive train equipment, available on request to suit each
individual situation.
Q:
How can we ensure the propeller will fit the shaft and key?
A:
If Henleys supply the propeller and shaft, then in approximately
90% of cases the two are fitted (lapped and blued) in our workshop
to ensure an 85% to 100% fit is achieved. For approximately 10% of
our work the shaft is not in our shop at time of propeller
completion - it the becomes the responsibility of the vessel's
engineer to lap and blue on site (at owners cost). Please see
propeller fitting instructions. If the shaft is machined by
another company Henleys do not accept any responsibility for fit
based on given dimensions or a drawing. However, Henleys will
ensure an 85% to 100% fit is achieved to a supplied and tapered
mandrel that is an exact copy of the finished shaft taper. The
above also applies to the forward end of the shaft taper and
coupling.
Q: Why is an anti – singing
edge required on some propellers?
A: In our experience a
“singing” prop occurs approx 4 in every 100 propellers. It can
affect any craft from small cruisers to
large ships in new or recently refurbished existing propellers or
drive train equipment. In twin installations it can be one or both
of a matched pair.
Ever run your
finger around the edge of a wine glass? Depending on the amount of
fluid in the glass and on your finger one can get varying degrees
of harmonics. The same can apply with a propeller and drive train
when rotating at any RPM through the
range. In most cases the rpm bands are only small say 50 rpm but
they can go as far as 400 before it is outside a certain frequency
that we can hear.
The same propeller,
which meets all industry design parameters, can be placed on
another vessel without the same problem occurring.
Q: Why can’t anti singing
edges be applied to all propellers from new?
A: They can but it would not
prevent harmonic’s occurring as a propeller manufacturer has no
way of defining if there will be a problem or at what rpm band it
may become audible – the anti singing edge is only applied after a
sea trial uncovers the problem - in an effort to change the
frequency. In most cases the problem is sorted out first time but
in some vessels the anti singing edge simply moves the band up or
down – shorter or wider.
Q: Who pays for this work?
A: This is a matter of trial and
error to custom match the prop (easiest item to alter in the drive
train) to a particular vessel – there is no other way of defining
a result so the costs fall on the owner.
Q: Will the noise experienced
damage my propeller?
A: NO – it is just annoying if
one cannot drive through the band
quickly.
Please follow this link to learn
some basic technical terms
associated with marine propellers.
Please follow this link to read
the Henleys Terms and
Conditions of Sale.
To find out what is the best
propeller that will suit your vessel, email us at
Henleys Propellers and Marine for a copy of the Propeller
Calculation Sheet to be sent to you or you can
click here to fill out a form online.
As above, to view a drive train
specification sheet please click here
or
email us for a copy that will suit your requirement.
You can click this
link to view a complete drive
train assembly installed in a vessel.
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©
Henleys Propellers and Marine Ltd - 110 Sunnybrae Road, Glenfield, Auckland, New Zealand
Phone: +64 9 443 5886 Fax: +64 9 443 5892 |
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