Canal Boat — February 2018

canalboat.co.uk Canal Boat February 2018 75

Try a larger pump to cure overheating

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WRITE TO Canal Boat Magazine, Archant Specialist, Evolution House, 2-6 Easthampstead Road, Wokingham, RG40 2EG

Checking prop size is your first port of call

My brother in law bought a fairly old Dutch
built steel river cruiser last year and with it a
raft of issues. I’ll give you the details and my
interpretation and would appreciate your opinion.
He’s experienced engine overheating and the engine
boiling. The installation is a bit esoteric and there
appear to have been a lot of modifications to the boat
since building.
The DAF 575 is keel cooled. On leaving the
thermostat housing there’s a tapping for a calorifier
and for the water cooled exhaust manifold. The
cooling flow then goes to a stainless pipe approx.
50mm bore that looks newer than the hull. It travels
aft under the aft cabin then, still at the same bore
exits the hull. I haven’t seen the hull out of the water
but it appears that the external pipe travels forward
before crossing over and returning down the opposite
side of the keel. It then returns through the hull and
travels forward through similar pipework and through
the oil cooler before returning to the block. The
returns from the manifold and calorifier are correctly
connected to the return pipework. I’ve had a really
close look and have been unable to find any leaks.
Filling with coolant is done through a deck filler.
This leads to a header tank immediately under the
side deck. The pressure cap is on the side of the
tank and there’s two large bore pipes going down
from it to join on to the flow and return sides of
the cooling circuit, presumably to try and eliminate
airlocks. There’s also a small overflow leading down
to the bilge. I couldn’t see that the deck filler would
make a pressure tight seal so I’ve fitted an O ring to
it and that seems to have done the trick (previously

expansion water was leaking from the deck filler

rather than through the overflow). There’s an air

bleed on the exhaust manifold but no bleed from

anywhere higher up on the engine although this does

not seem to be a problem as the flow pipe is getting

hot along its length suggesting there’s no airlock.

The overheating has only occurred when the boat

is being used on a canal, not on a river. I checked

the temperatures with an infrared thermometer and

found that the engine warmed normally and the

thermostat opened as shown by a rise in the flow

pipe temperature. However with the engine idling the

return pipe was cold (around the temp of the canal).

I then advanced the throttle with the drive in neutral

and found the return pipe started to warm rapidly.

My guess is that at the low RPM used on the canal

the water pump was producing insufficient flow.

Being originally a truck engine I imagine it will have

been designed to operate with short pipe runs to a

radiator and it’s now being asked to push the water

through a far longer pipe run. Increasing the RPM

overcame the resistance and the water started to

flow. I considered sludge blockage (my sister-in-

law said that a large gobbet of sludge came out of

the filler during one of the incidents) however the

increase in temp on the return pipe suggest that

there’s no blockage.

MICHAEL CROSS

TONY REPLIES: We operated a range of

smaller engines on river cruisers with keel

cooling with complete success. However

they all used the original automotive engine water

pump, not an additional belt driven one. The majority

of narrowboats are also in effect keel cooled but by

tank rather than pipes. If the belt driven pump you

refer to is a brass Jabsco pump (pictured) rather than

the automotive engine pump then it suggests that

the engine was once either direct raw water cooled

or heat exchanger cooled. If it was direct raw water

cooled then the pump is probably too small so a larger

one is required. If you are talking about the engine

water pump then ignore the last bit.

It’s definitely worth taking the hoses off the keel

cooler and reverse flushing it with a hose. That will

give you some indication of any blockage, the flow

rate and also displace any sludge. If you have not seen

it maybe the under-boat pipe has been squashed.

If you are talking about an automotive water pump on

the engine then I doubt you can get a smaller pulley

unless you have one specially made so an additional

electric centrifugal pump would probably be the

easiest way to solve any circulation issue. As long as

its centrifugal it should allow the engine pump to work

on its own at higher RPMs.

My 70ft narrow boat is

fitted with a VOAC Parker

hydraulic transmission to

enable having the engine to one side

in the engine room.

The system works okay but I’ve

been told that my prop speed is

too high as, unlike mechanical

transmissions, there is no 2:1 or 3:1

gearbox reduction. It means that

slow manoeuvring is difficult. I’m

wondering if it’s possible to have a

valve to limit pressure to the hydraulic

motor to reduce prop speed.

The existing valve only allows

Forward, Reverse and Neutral with no

obvious regulation in between.

CONSORT

TONY REPLIES: I have no

experience of that particular

make but considerable

experience of hydraulic small boat

systems on a Thames hire fleet in

the 70s. First of all it is not true to

say there is no 2:1 reduction because

the reduction is set by the relative

displacement of the hydraulic pump

to hydraulic motor. The reduction can

be almost anything you want providing

suitably sized motors and pump are

available. The systems I worked on used

vane, gear, or sine pumps and motors

but modern equipment seem to use

piston pumps and motors.

Hydraulic transmissions are not

particularly efficient at any time and

trying to restrict the flow to the motor

or dumping excess flow back into the

reservoir will make it even less efficient.

Not a very good idea I would suggest.

Restricting the flow could also cause

the oil to overheat. Often hydraulic

transmissions sound as if the boat is

going faster than it really is but as you

say you have problems with slow speed

manoeuvring I can assume there really

is a speed issue. The way to cure it

is to fit the correct sized prop or get

your prop repitched to suit whatever

reduction is built into your system. First

look for plates on the motor and pump

that should indicate their displacement.

That will tell you the built-in reduction

and from that you can go online to any

one of many prop calculators to see

what size prop you need. If the pitch is

reduced the boat will move forward less

per revolution so move more slowly at

idle but it will reduce the stopping effect

of reverse to a degree. I am sure this is

a prop size problem rather than anything

to do with the hydraulic transmission.

It seems that VOAC are the

makers of the pump and motors

but not necessarily the valves in

the system. Interestingly they list

http://www.arsangliandiesels.co.uk/ as

a dealer who are also arguably the

premier supplier of marine hydraulic

transmissions for small boats so I

suspect that you probably have an ARS

transmission system.

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