DD671’s TI’s fuel consumption

[DavidM]

You can extrapolate the curve backwards from 1,400 to 1,000 rpm and come close. Maybe 3 gph and 35 hp per engine. Note that that is about 11 hp per gph which is much lower than the 16 hp per gph of most diesels at the midpoint of the power curve.

But the poorer specific fuel consumption is offset by the much lower hp required and fuel consumption at slow speeds.

For most boats the most efficient speed is a knot or so below hull speed. Theoretical hull speed is 1.34* sqrt (LWL). So a 47’ boat has a LWL of about 45’ so hull speed is about 9 kts so the most efficient speed would be about 8 kts.

David

 

[Speedcat]

You can extrapolate the curve backwards from 1,400 to 1,000 rpm and come close. Maybe 3 gph and 35 hp per engine. Note that that is about 11 hp per gph which is much lower than the 16 hp per gph of most diesels at the midpoint of the power curve.

But the poorer specific fuel consumption is offset by the much lower hp required and fuel consumption at slow speeds.

For most boats the most efficient speed is a knot or so below hull speed. Theoretical hull speed is 1.34* sqrt (LWL). So a 47’ boat has a LWL of about 45’ so hull speed is about 9 kts so the most efficient speed would be about 8 kts.

David

Thanks David, this is more like what can help me, since I don't own the boat. LOL.

So this is a 52 foot trawler, ~15 foot beam, not sure what that means for LWL. I've seen similar boats with 47.57 LWL. Using that, it looks like 9.24 hull speed, so 8.24 efficient speed. I'll take another look at those charts. Mostly, I don't have far to travel, but need to spend the least $$.

Here's what I've found - if my very rough extrapolation is anything close to accurate, 1000 RPMs would mean around 1.5 - 2gph per engine. Attaching a pic - hope this comes through.

 

[mbevins]

My 44 Viking running at about 960-1000 rpm is just a tad under 2gph per engine so you're accurate

 

[Speedcat]

My 44 Viking running at about 960-1000 rpm is just a tad under 2gph per engine so you're accurate

Thanks. Just curious, what speed do you run at that RPM?