We have now completed Beta phase testing of the unit and will now
accept orders for 2 bladed units under 40 hp.
Below is a detailed review of selected Beta testing over the
yearts with photo's of the various units after being pulled for
analysis.
The initial unity shown in the photo's were milled ex PETP.
All production units have been very competently moulded in
Urethane 75D by Plus Plastics in East Tamaki.
The colour is Shore 75D blue for the moulded components. The
blades are a natural light cream colour.
The blade attachment bolts are in SS 304 to avoid any potential crevice
corrosion issues with SS 316 grade.
PETP is retained for the 1.5 mm washers under the blade retaining bolts.
as
at:
1 May 2009
We have now completed the very complex die sets in
mild steel and manufactured tooling that will allow for all the
components to be poured in
Urethane to Shore 75D grade and subsequently machined to
finished specifications where required.
The SAE 16/32 17 tooth Spline and all threaded components are removed
from the moulds finished with the Veactran pathway cast into the Boss.
All components, tooling and Drawings and Work Orders
are in place for continuing production going forward.
as
at:
20 April 2009
We have now installed a what is best termed a " Stopper " midway on
the Vectran at address any possible asymetry of the
two blades opening during a reverse function.
This could be initiated from any extreme event such as a single spring
failure or fouling of a single blade with say seaweed or a plastic bag.
In Ahead - the forward thrust of the propeller will ensure that each
balkde will open fully.
In Reverse - where the reverse thrust of the blade is acting against
the the rotational torque of the Vectran attempting to open the
blade fully,
it was previously possible to get partial opening on a single blade
leading to severe vibration and reduced reverse thrust in non normal
and unusual situations.
The " Stopper " -
Hollow with an ID of 6 mm and some 20 mm in length x 12 mm OD screws
together over a small " pig " of 6 mm SS 316
inserted internally into the Vectran braid, which tightens the Vectran
to ensure the " Stopper " can no longer slide over the Vectran.
The " Stopper " assembly then resides in a 25 mm long groove in the
nose section of the Boss of the Vectran pathway - so constraining any
possible asymetry
of the blades in reverse to ~ 1 - 2 ° between the blades
which would be barely noticeable at normal reverse rpm.
As soon as the unit is engaged into Ahead - then any asymetry is
eliminated as before.
as
at:
05 April 2008
Escapade Was hauled this weekend for annual maintenance and
scheduled Saildrive Seal & Zinc replacement.
This provided an excellent opportunity to review their SDC unit which
has now had two years of normal and extensive usage.
There have been no problems reported during this period - other than
the inevitable barnacles and fouling issues on the blades etc.
Reports on this initial installation and details of this unit are
covered in: Initial User Comments
The series of photo's below show the status of the unit post removal.
The first shot below shows the unit post normal cleaning and sanding
prior to repainting.
The zinc on the Saildrive ( now 22 years old ) was still in excellent
condition after 2 years where it would have normally lasted just 6
months.
It was to be replaced anyway with the propeller off and the lower seal
now due for replacement.
The next photo shows the zinc as removed below.
Zinc as removed after two years service.
This shows the front cover removed as a first step to removal of the
Boss for examination.
No wear or cracking was evident. This section unscrewed very easily
with no binding once tapped by hand with a screw driver as designed.
The Boss removed exposing the Vectran drive - Note the very high levels
of grease retention at the end of a full season's usage.
This shows the Vectran exposed near the nose of the Boss - A high
stress area - No wear is apparent
This shot holding the blades open against the springs shows the exposed
area of the Vectran with the highest friction area around the corner of
the body.
as
at:
12 July 2008
...
Nearly Home !!
as
at:
30 June 2008
Currently in the Azores. No reported problems.
Leaving shortly for Fastnet landfall
as
at:
20 March 2008
We still have no reports of any failures but one unit in
Nova Scotia is laid up for the winter.
He’s certainly the high time user ( engine hours not days installed )
and is now heading home after hauling in Florida for a break. He’s in
the Caribbean but has just lost his Saildrive clutch so having his
moments – but by all reports happy with the prop which has not let him
down. He’s certainly stacking the hours on but will soon head off
across the Atlantic to the Azores.
We gave him a new one and used the unit that had taken him from Holland
to Florida for the Tear Down Analysis – now on the web site.
Tear Down Analysis
His currently has a couple of minor mods – better spring tail design (
see below ) and V grooves to ensure reverse always opens the
blades evenly under all conditions.
So far these seem to be working well and have had now nearly 3 months
continuous daily use.
I will feel confident of the Beta Test results and subsequent
production when he arrives home in Holland. Some journey !
The 3 Bladed unit is now ready for installation and test.
as
at:
September 2007
Currently
all units from the initial
production run have now been committed to the test program.
We do not now have any units
additional left for further installations.
There
will shortly be a total of 9 units installed and in
use up
to 35 hp.
Test results will be
added to these web pages as feedback is obtained over time.
The
high time ( installed time ) unit is now over 2 full
season's usage and performing to specification.
as
at:
August 2007
SPRING
DESIGN IMPROVEMENTS:
To lower
the point stresses and ensure retention under all conditions the
following modifications are under bench test
for an
improved torsion spring design. The tail that terminates on the
Blade now ends in a 6 mm ID loop to accept
a 6 mm x 20 Alan Key headed cap screw that is
tapped with Loctite into a flat on the pitch stop of the blade.
This
removes the right angle bend with it's high stress points, allows for
movement about the Cap screw as the spring
reduces in diameter under tension and also ensures that the spring tail
is securely retained by the Cap Screw.
Reducing
stress is important to reduce any possibility of stress
corrosion in the SS spring.
The Loctite reduces further the possibility of crevice corrosion which
is not such an issue with SS 304 as with SS 316.
Centrifugal
force could possibly have allowed the spring tail to be removed from
the blade under the previous design.
To test
this a hand wound spring was mounted as shown and over 5000
full movements undertaken over a period.
This would equate to many years of normal service in practise.
Production
of this design will present no manufacturing problems.
The Cap
Screw is still securely mounted and the spring performing at 100 % of
original specification.
It is planned to incorporate this
modification into all future production.
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