Re-Powering Weypago - Part 1 of 3
A week or so before Easter we were sailing
Weypago around Lyttelton Harbour when we chanced to see, beating up the harbour,
a very smart looking H28. We were running goose winged at the time but after a
hurried conference we decided to pursue this fine looking ship and find out
more. It took a minute or two to get set up and then we set off in pursuit.
We don’t get too many opportunities to
sail with H28s down here and it soon became apparent we were going to have
trouble catching this one. My crewman, Roger, is always full of ideas of how to
improve sailing performance and we began to experiment, first with sail trim and
then propeller drag and noted that speed and pointing ability did improve with
the prop allowed to free wheel. (I normally keep it locked). Now, I am not
advocating free wheeling your prop as this can cause problems with the gear box,
but the exercise did highlight the effect of propeller drag.
Even with this little bit of extra speed ,
it wasn’t until the mystery boat eased off a little that we were able to catch
up and exchange greetings. She was the “Molly Malone” and though she looked
like a new boat in expert hands, her skipper said he was having their first sail
after a long re-fit. Boy, Molly Malone certainly looked beautiful and her owners
can be very proud of the job they have done.
Getting back to the original story, this
chance meeting and the propeller experiments set of a chain of events which has
lead me to consider repowering Weypago.
When I got home that night I dived into
Boating Mag looking for an advert for a feathering propeller. It sounded pretty
good so I sent off an E-mail enquiry to the manufacturer about suitability of
their product for H28s. They replied that the H28, in standard form, did not
have room to swing one of these propellers. They went on to say that
modification of the propeller aperture was necessary to create the room, and
that running a left hand prop (which meant the shaft would have to run in
reverse) would give a more suitable gear ratio. This is because the engine is a
2GM20 Yanmar (18hp max @ 3600, 16 hp MCR @ 3400) fitted with a gearbox that
gives 2.2:1 ahead and 3.0:1 astern. A mechanic friend of mine who has a lot of
experience with this engine tells me it would not be a great idea to run it
astern like this so for now, I have given up on the feathering prop.
However, all this talk of aperture size,
prop size and reduction ratios prompted me to review the whole propulsion
package currently installed.
One of the things about being Lyttelton
based is that trips up to the Marlborough Sounds often involve a lot of
motoring, so you want a good set-up in terms of performance, weight, and fuel
load, and you certainly don’t want to have the fillings shaken out of your
teeth or risk damaging your hearing with exposure to high noise levels for long
periods. The purist will say “wait for the wind” but unfortunately in this
modern age, we are compelled to live to a schedule and, barring inclement
weather, we have to push on at best speed by all means available on this coastal
passage.
Now, I am not entirely without experience
in this area, having previously been involved in engines and marine equipment
mainly to do with larger vessels, and, having completed two successful re-powers
on my own boats, one yacht and one launch, I propose to consider the current
installation and its draw backs, and then look at what might be done to improve
the situation.
The Propeller
Len Gilbert, well known expert on high
speed diesel propulsion systems, often stresses the importance of the propeller
in any assessment of power requirements. When I first purchased Weypago her
performance under power was very poor. This was because she was severely
over-propped (14x10) 2.2:1 reduction which allowed the engine to develop only
2200 rpm maximum. This meant that the engine could produce only about 10 hp
according to its performance curves and explains why the vessel could not
maintain more than two or three knots with a decent head wind.
This problem is easily fixed, and I had the
propeller re-pitched to 14x8 inches which then allowed the engine to develop its
full potential power at 3600 rpm, improved the boat’s performance in all
conditions and reduced fuel consumption.
However the very high shaft speed does
create noise and vibration, and it is well known that small, high speed
propellers are less efficient than slower larger propellers. So I wonder, while
the engine can now develop full power at the flywheel, how much power is lost
through the inefficiency of the high speed shaft set up?
Bearing in mind that the original design of
the Compass H28 was around a 10 hp motor with suitable propeller, I strongly
suspect that the current set-up does not make good use of the available engine
power at all. It would seem that a smaller engine with a bigger reduction ratio
and appropriate propeller might well produce similar performance.
Weight
As we know the H28 has very fine lines aft
and does not carry weight well in this area. With my wish to locate gas bottles
and one or two other items on the pushpit, it would seem desirable to reduce
weight in this area if possible. A lower powered installation might result in a
weight saving.
Space
A lower powered engine may well be smaller
physically and create a little more cabin space.
Technology
The engine I have, whilst very popular in
New Zealand, is quite a dated design. I have watched other manufacturers
introduce new “improved” models on a regular basis and no one can doubt
there have been significant advances in engine technologies of all types over
the last 20 years. Just take electronic engines and emission controls on diesel
engines for example.
Cost
Well this is a sticky point. Some folks I
know would take the accountant’s view that one should be careful not to over
capitalise one’s boat. To others, myself included, messing about with and in
boats is a main hobby and a source of much pleasure and enjoyment.
However, this exercise, when complete, may
well be of interest to those H28 owners who are considering upgrading from 10 hp
engines. At the very least you would expect that a lower powered engine (less
than 18 hp) would cost less and if similar performance can be achieved that will
be all to the good.
In the next edition I will cover the choice
of engine, its features, and how they compare with the existing engine.
Mike Holibar – “Weypago”
