What prop size for my narrowboat

What prop size for my narrowboat?

Hull: 70ft long 6ft 10 inches wide.
Weight: 10 tons
Engine: 48 BHP at 2800 (54BHP at 3000)

There is 11 inches between the centre of the shaft and the counter

I currently have a prop with an 18 inch dia and 13 inch pitch. However the
engine never seems to struggle to turn the prop even when slamming in
reverse from full forwards.

Adrian Smith

"Adrian Smith" <x.TakeThisOut@x.spam> wrote in message
news:rzmMg.16034$r61.566@text.news.blueyonder.co.uk...
> What prop size for my narrowboat?
>
> Hull: 70ft long 6ft 10 inches wide.
> Weight: 10 tons
> Engine: 48 BHP at 2800 (54BHP at 3000)
>
> There is 11 inches between the centre of the shaft and the counter
>
> I currently have a prop with an 18 inch dia and 13 inch pitch. However the
> engine never seems to struggle to turn the prop even when slamming in
> reverse from full forwards.
>
> Adrian Smith

You may well find that at 48bhp the boat has been deliberately underpropped
so it still generates a decent currant at canal speeds.

If you want the most accurate estimate then talk to Crowthers of Manchester.
Some of the online prop calculators throw a wobbly when fed with canal boat
data and I suspect take no account of the restricted waters we tend to
operate in.

If the boat stops satisfactorily and accelerates well then I doubt you have
much to worry about.

If you have a revcounter you should find the engine speed stops rising at
about maximum torque which is at a far lower speed than maximum power, but
as I said it may well have been deliberately under propped.


--
Tony Brooks
www.TB-Training.co.uk