Catapillers ?

theguvnor

theguvnor

Well-Known Member
Joined
9 Jun 2003
Messages
1,786
Location
Holland
Visit site
I am considering buying a 41` boat with 2 x 375hp 8cyl diesels. I have been on the Thames with a 27` Sunfury diesel (MD30A) with ridiculously low fuel consumption, but now want to venture seaward. My Sunfury is great on rivers but complains if at 3000 rpm making 5 knots - not ideal for tidal waters!

I presume I would have a nasty shock with the Cats but any ideas what to expect consumption wise? (derogation included)
 
Depending on how heavily the engines are loaded ie do you cruise at 70% of Max or 50 or 80 etc. MY engines are 370 hp and cruising including idling in harbours, 85 % of my time is at cruising speed. I burn between 80 and 110 litres per hour for both engines .
 
Assuming 75% load @ 22 knots, taking out approx 570HP, you'd be looking at approx 120 - 140 L/hr.

Calculate with 200 grammes per HP/hr and diesel weight of 0.86Kg per litre and you'll get those figues above...
 
If max is 24 knots I would beg to suggest that 22 kts is not an economical cruising speed. I would have thought between 18 and 20 kts would be more sensible.
If your figures are manufacturers speeds, knock off another couple of knots for the weight of your cruising gear and a bit of undergrowth on the bottom.
 
The difference is

1/ How heavily loaded is your engine a planing boat at full speed on the plane may be as low as 50 to 60% of full power once on the plane where as a semidisplacement boat trying to go over the hump may be at 90%

2/ Are you talking average fuel burn with port movements included or purely what you burn while cruising .

3/ My 2 x 370 hp 36ft boat 11 tonnes is 80 to 110kg average including minimal port movement.

4/ I agree with the Gramms per kw hr incidentaly and from that you can work back to how hard your engine is working.
 
I assume thay are CAT 3208s. My 47ft, 14 tonne (dry) planing boat with 435hp CAT 3208DITAs averaged about 5 litres/nm over many thousands of miles of all sorts of use including long distance cruising.
 
Thanks one and all for you help. I`m always amazed at the wealth of experience on this forum.

Now I have a good grasp of the fuel costs I must go and check my overdraft facillity
 
Cat 3208's are v good engines and the 375hp version even more long lived than the 425hp version but these are not yer modern electronically controlled engines and they're 10.4 litre cubic capacity each so don't exactly expect frugal economy
In a planing hull you could get 0.8mpg at cruise but in a semi displacement hull it could be as low as 0.6 - 0.7 mpg overall
What boat is it? Hatteras? Taiwanese make?
 
You must log in or register to reply here.

Share this page

Top