[PCW] fuel per horsepower

[Malcolm Tennant]

Brian Knesal.

I am not an expert on diesel engines, I rely on the advice of those who
know. However I will try to anwer your questions.

Generally you would choose an engine with just a little, say 10% more
horsepower than you need for whatever is your top speed. This makes
allowance for wind and waves but of course you usually slow down in the
rougher conditions anyway. There really is no point in chosing an engine
that has 3 times as much horsepower as you need.

It is not uncommon for people to get a much larger horsepower engine than 
they
need and then run it a very reduced revs in the belief that they are 
prolonging the life of the engine. This is not a smart move. it may
invalidate your engine warranty and probably damage your engine. If you are
doing long hours, long distances etc get a commercially rated engine. All
this means is that the engine will then be governed and injected to develop
its maximum horsepower at lower rpms with the result that the maintenance
intervals will be longer.

Aside from the "hand grenade" engines of dragsters, reciprocating engines
cannot be run at full throtle for ever.

The engines in the Escape are the size they are because it does 25 knots top 
speed in full load displacement. The HP, gearbox, reduction, propeller 
parameters etc are generally all based on top speed in full load. 10
knots is probably the worst speed you could possibly chose for the Escape.
It is right on FN.4 for the hull ie: the point of maximum hull resistance.
You would use less fuel at 15 knots. The Escapes ideal cruising speed 
appears
to be 19 knots at which speed I believe it is using a total of 2.2 litres
per nautical mile.

The Escape is a more recent design than the RagTime and as such has a more 
refined hull form[ie more efficient] and has our contemporay wing deck 
structure and shape.
Any differences are largely attributable to the Ragtime having 4 tonnes more 
full load displacement. They probably have different speed/length and 
displacement/length ratios.

I hope this helps but you will need to consult a diesel engine expert for 
more detailed [accurate] information.

Regards,

Malcolm Tennant.


MALCOLM TENNANT MULTIHULL DESIGN LTD
PO Box 60513, Titirangi.
Waitakere 0642
NEW ZEALAND
Ph: +64 9 817 1988
e-mail: malcolm at tennantdesign.co.nz
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