TWL: Re: Balto power
In a message dated 3/4/04 12:08:48 AM,
trawler-world-list-request@lists.samurai.com writes:
<< The 200 hp is a little under powered for 52', but it will drive the boat
to
hull speed.
The amount of hp is a bit low for 60 tons of displacement, but it is pretty
optimal for
fuel burn. Since there is little that more power can do to make the boat go
faster,
the 200 hp being more than enough to force the hull to maximum hull speed. The
only major weakness is lack of extra power to force the hull against wind
or wave pressure. >>
Keith's formula, as given in Skene, shows that it should require 184 hp to
move Balto at hull speed in calm water. I, personally, would like to see about
250 hp in a boat of that size and displacement to deal with waves and wind but
Balto is not "seriously underpowered" by any means.
At first approximation, with a 3:1 reduction gear, Balto should use a 32x19"
prop with the engine running 2800 rpm. Static thrust will be 3852 lbs. and the
efficiency will be 49%.
Ain't computers wonderful?
Larry Z
Larry Z. wrote:
Keith's formula, as given in Skene, shows that it should require 184 hp to
move Balto at hull speed in calm water.
Which he doesn't have if you use Skene's (and Keith's) 85% rule. 85% of 195HP is
~166HP, so he's low on installed HP even by Keith's (arguably) liberal estimate.
I, personally, would like to
see about 250 hp in a boat of that size and displacement to deal with
waves and wind but Balto is not "seriously underpowered" by any means.
My exact statement was "you are seriously under-powered for the areas you're
considering cruising", which I stand by.
Unless, of course, the vessel will only be used during calm winds and seas,
something we both know is ludicrous.
I'm sorry that this appears to be such a contentious issue on the list, and I'm
particlarly sorry to be the lightning rod for the matter as a newbie, but I gave
voice to truly felt concern.
Regards,
James
[snip]
I, personally, would like to
see about 250 hp in a boat of that size and displacement to deal with
waves and wind but Balto is not "seriously underpowered" by any means.
My exact statement was "you are seriously under-powered for the areas
you're
considering cruising", which I stand by.
Unless, of course, the vessel will only be used during calm winds and
seas,
something we both know is ludicrous.
[snip]
Well,
some builders and desingers seem to think that bigger boats will survive and
also make it to next harbour with smaller engines.
Vripack yacht designers is saying 5 hp/ ton will move boat to hull speed,
for Balto that would mean 5 * 50 is 250 hp. Now this is hull speed, and if
you try to make max range, hp rating will drop of course. At low end you can
do about 3.5 hp for ton, for Balto this would be 175 hp and range would be
greatly inproved.
Please dont tell me that 175 hp would not be enough for Balto to go anywhere
her owner would like to go, I am not surveyor or yacht desinger but I would
be very intrested to find out that Vripack could not design bigger boats and
properly size their motors.
Turmoil by Palmer Johnson, 330 tons and 151 feet has twin 800 hp Cats, 15.3
knot tops and 12 knots range 10000 miles. 4.8 hp per ton.
Another 121 footer 215 ton vessel has twin 480 hp and it makes hull speed of
14 knots, her sister has twin 400hp and she makes 13.6 knots, this is 3.7 hp
for ton. Now these boats are designed to go anywhere, loooong range.
I think they can get insurance too.
Also diesels love to work, they should have over 50 % load for best economy
and life.
See http://www.vripack.com/main.htm
J.T.Tuomela
Jupiter, FL
their motors.
Turmoil by Palmer Johnson, 330 tons and 151 feet has twin 800 hp Cats,
15.3
knot tops and 12 knots range 10000 miles. 4.8 hp per ton.
Another 121 footer 215 ton vessel has twin 480 hp and it makes hull speed
of
14 knots, her sister has twin 400hp and she makes 13.6 knots, this is 3.7
hp
for ton. Now these boats are designed to go anywhere, loooong range.
I think they can get insurance too.
1.5 hp/ton moves MOJO along quite nicely, even in rough seas and wind. 4.5
hp/ton moves her at hull speed.
Ray B.