Re: [Amel] Re: Maramu prop shaft alternator


David Mackintosh <sv.highland.fling@...>
 

OHHHH a moderator in waiting AND one with a crystal ball to who speaks for
'most of us' on the group

OH MY :-(

David

On 22 July 2011 19:45, thomas.kleman@... <thomas.kleman@...>wrote:

**


All- while I enjoy and learn from most of the threads, of late there has
been quite a bit of dreary pablum and self aggrandizement by people who
must
have missed the "amelyachtowners" part of the URL. Like most people, I
belong to several groups outside of this one for general sailing info. This

group is valuable to me (and dare I speak for most of us) because it is
AMEL
specific. Someone's flying resume would seem to fail the relevance test. As

the site supports direct person to person email for these enthralling
exchanges of credentials, perhaps we can keep the site clear of them in the

future.

Connected by DROID on Verizon Wireless


-----Original message-----
From: David Mackintosh <sv.highland.fling@...>
To: amelyachtowners@...
Sent: Fri, Jul 22, 2011 13:39:13 GMT+00:00
Subject: Re: [Amel] Re: Maramu prop shaft alternator

Well what can i say,

My flying starts with PA28's and included the PA 30 with non contra
rotating
props and the PA 39 with contra rotating props and goes all the way up to
the L1011 B757 and even the LHD Death Cruiser he he.

The P factor will i suspect actually de power the wind generator sadly i
dont have the time or the motivation to actually sit down and calculate
this
- perhaps introducing the P factor into this discussion was not helpful -
it
is as you probably fully understand one of 'the results' which is why i did
include it.

All i know is real time actual results. When i was sailing with many of my
friends in the Caribbean they tied off their W/G's when out sailing in
20+knots of wind as they complained of 'problems' in high winds and big
seas. Now they were all on dedicated W/G poles or Radar Arches. Having the
W/G on the mast well you may not notice 'issues' as the mast is supported
to
handle sail loadings.

But we have all played with a gyroscope i am sure and we know how hard it
is
to move it when it is spinning - put that gyroscope/W/G on the end of a 10
foot pole or even a 30 foot mast and well you are amplifying that effect.
Now put that pole/mast on a sailboat that is moving in a variety of
directions at unpredictibale speeds and rates of change and you are
introducing some serious loads to your W/G mount(s).

I can see a use for wind generators at anchor in anchorages with >10knots
of wind and for sure they work when the sun does not shine - like i
explained i am conflicted as to the CBA vis a vis burning diesel and
purchasing and installing W/G and Solar. I should add i dont have an Amel
nor a generator on board and as we have added more and more electrical
loads
we need to seriously look at some means of generating more electricity
'MOSTLY' when we are sailing as the autopilot and all the new electronics
and new 12V freezer (soon new 12V Fridge) and other loads mean that on
passage (only inter island stuff 8 to 16 hours at most) we need to either
run the engine (do some gentle motor sailing) or selectively switch on and
off various bit of kit as well as hand steer for a while something we enjoy
in the heavy weather but not for 8 or more hours. We have a Raymarine E120
plotter and that is too heavy on power consumption for use all the way
through any inter island passage but we have a Raymarine Raynav 320 which
uses much less power so that gets used for power saving navigation. As they
both talk to each other we can share waypoints etc. Obviously the E120 does
much more for us but ATM its power consumption is unsustainable for inter
island passages. I would love a PSA and i am planning to put one on our
boat
ASAP my preference would be to use a PMA as a PSA but cant see an easy way
of stopping that charging - sounds like a job for a lead screw to adjust
belt tensioning or diverting that output to a 12V element in the hot water
tank IF or once the batteries are fully charged. Obviously the normal
car/boat style alternator has advantages in a PSA application as you can
simply switch it on and off BUT the down side of that is that to power the
coils and excite the alternator you are going to use 1 amp.

To get back to non contra rotating props :-) i am always amazed and it is
fun to watch and to see the difference in reaction and rotation of twin
W/G's on other boats.

regards

David

On 22 July 2011 02:07, Dave_Benjamin <dave_benjamin@...> wrote:

**


David,

In my flying career I spent close to 5000 hours in large turbo-prop
aircraft so gyroscopic effects are well known to me. (Not all twin engine
aircraft have counter-rotating props). In any case, perhaps you can
explain
how "P-factor" would impair a wind generator that is free to swivel. The
force vector is going to simply cause it to rotate one way or the other,
isn't it? Given the movement of the boat, there's not going to be a
steady
force in any one direction.

--- In amelyachtowners@..., David Mackintosh
<sv.highland.fling@...> wrote:

I think you will find a wind generator is not really usable when
sailing
in
decent winds and seas as gyroscopic effects and precession all start to
have
a serious effect.

You are correct of course water being denser than air it is much easier
to
extract power from a water driven propeller. BUT i think you miss the
point
- lets say a PSA producing 10/15 Amp takes 1.5 HP to drive That HP has
to
come from somewhere - the sails :-) To get your say what 22 metric ton
Amel up to hull speed is going to take say 80 HP so the losses assuming
they can be measured in a real live real time situation are going to be
insignificant really

Plus if you have 150/200 HP from your sails you have an excess of power
and
since your Amel cant get up and plane - you have oodles of spare free
HP
to
drive your PSA. Any time you have more power from your sails than that
needed to drive the boat at hull speed..there will be no actual loss of
performance when using the PSA.

Actual real time real life reports on the PAS performance say the
losses
are
insignificant - not really measurable.

Now lets look at the trasmission designed to drive this 22MT boat with
say
70 SHP..............do you really think you can damage that
transmission
in
any way by powering a 1.5 HP PSA with it? I think NOT!!!

IF anyone wants to dump their PSA then please contact me i would love
to
have it :-)

regards

David

On 20 July 2011 00:13, Dave_Benjamin <dave_benjamin@...> wrote:

**


I'm a bit confused about the comparison in losses between the PSA and
a
wind generator. Water is far denser than air. The prop becomes a
speed
brake
of sort. I'm not a physicist but I'd wager that amp for amp the
performance
loss with a wind generator is negligible compared to a PSA.



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