Practical Boat Owner - February 2016

Ask the experts

Q

I am considering replacing
the engine of our Westerly
Konsort, and when I mentioned
this to the boatyard engineer
the subject of prop size
cropped up.
I recollect reading somewhere
that the clearance between the
prop and the bottom of the hull
needs to be a certain amount –
not merely of a size to just
miss contact with the hull. The
engineer was talking about a
slightly bigger prop if I chose,
for instance, a 28hp Nanni to
replace the faithful 30-year-old,
20hp Bukh DV20. The Konsort,

New motor and prop for a Konsort

as you’re probably aware, has a

fairly flat hull bottom around the

region in question, and there is

not a lot of clearance between

prop and skeg.

Also, do you have a view on

which replacement engine

might be most suitable?

Keith Carter

Watton, Norfolk

PAT MANLEY REPLIES: Ideally,

the prop tip clearance should be

15% of the prop diameter, but 10%

is acceptable. Beta are a possible

alternative to the Nanni mentioned

by your engineer – both use

marinised versions of Kubota

engines in this size range. The

Beta 28 seems to have been

discontinued, but there are options

of 20hp, 25hp and 30hp versions.

A 20hp engine should be able to

propel your Konsort at about 7.1

knots in calm conditions, 25hp at

7.4 knots and 30hp at about 7.7

knots, all with a ‘best size’ prop

(about 17in for the Beta 20, 17.9in

for the 25 and 18.5in for the 30).

The actual diameter can be

jiggled by changing the gearbox

ratio or increasing the pitch to give

a smaller diameter. The diameters

mentioned are for a 2:1 ratio and

an ideal pitch. Your chosen engine

manufacturer should do the actual

prop calculations for you.

The Konsort needs more power

than a yacht with finer lines,

especially as the going gets

rougher. If you were completely

happy with her performance with

the old Bukh then 20hp should

be fine, but if you’d like a bit more

speed in heavier conditions then

maybe 25hp would be a good

choice – there’s not a lot

of difference in size and weight

between the two. Check out the

Westerly owners forum – many

Konsorts will have been re-

engined by now, and real-life

experience of engine variations

may help you make a choice.

GAS FITTINGS
Peter Spreadborough,
of Southampton
Calor Gas Centre,
has 20 years in
the industry

PAINT AND

ANTIFOULING

Richard Jerram is

former UK technical

manager of

International Paint

TRAILER-

SAILING

Colin Haines is a

design engineer

who has trailer-

sailed for 25 years

ELECTRONICS

Chris Ellery of

Greenham-Regis

Electronics is a

former Merchant

Navy officer

TOILETS AND

PLUMBING

Gary Sutcliffe of Lee

Sanitation knows

about holding tanks,

toilets and plumbing

YACHT DESIGN

Andrew Blyth is a

naval architect with

interest in stability

and buoyancy

WOOD

Richard Hare is a

wood technologist

and long-time

wooden-boat owner

50 of the most frequently asked boating questions are answered by our experts on the PBO website. Visit http://www.pbo.co.uk

BOATBUILDING

Tony Davies has

been building and

repairing wooden,

GRP and steel boats

for 40 years

➜

ENGINES

BOATBUILDING

Q

I have been using the
information in an article
by Tony Davies (‘The art of
veneering’, PBO February 2012)
to veneer some of the internal
woodwork in my motor-sailer
Cecilia. My first job was the
saloon table: I bought several
leaves of cherry veneer, using
Timebond contact adhesive as
suggested by Tony. The process
went pleasingly, complete with
some hardwood edging pieces,
and all seemed to be well.
However, as soon as I applied
varnish there seems to have
been some reaction between the
varnish and either the veneer
itself or the underlying adhesive.
The veneer buckled, resulting in
many lumps throughout.
At this stage I stripped the
varnish using a water-based
stripper and applied a water-
based varnish, which rescued
the situation to some extent
although some lumps remain. I
am now veneering the forward

Well, buckle my veneer...

This veneer buckled badly 24 hours after a second coat of varnish

bulkhead, including a door that I

brought home from the boat. I

bought new tins of Timebond

and International Original varnish.

Again, the veneer was applied

successfully, as was the initial

coat of thinned varnish, that

caused no buckling. However,

the second coat, shown in my

photo after 24 hours, was badly

buckled. Can Tony please advise

what measures he takes to

ensure that this does not

happen? Any other tips would

be most welcome. Thanks.

Vyv Cox

By email

TONY DAVIES REPLIES: I’m

sorry to hear of the problem with

your veneering project, Vyv. I have

not encountered this problem

before, so I’ll need to guess as

to the cause. I know you are an

expert in many areas from reading

your contributions to the YBW

forums, so I must apologise if

some of my ideas are of the ‘egg

sucking’ variety! Did you use the

appropriate comb applicator when

applying the adhesive, as too

much adhesive may cause this

problem? Did you allow the

adhesive at least 24 hours to cure

before applying the varnish? Was

the varnish applied very thickly,

causing the veneer to lift? (Although

this should not happen if the

adhesive has properly cured.) Was

the work area damp at the time?

I must admit that I probably

didn’t mention any of these points

in my article. I expect you have

tried rolling the bumps out: this

can sometimes work as the

adhesive carries on curing. The

problem occurs due to expansion

of the veneer, which has not

properly adhered to the underlying

surface. You may be able to

improve this by carefully slicing

along the bumps and then

flattening them. This may cause

the edges to overlap, but these

can then be rubbed down flush.