How Accurate Is This Fuel Consumption Graph?

[CatBuilder]

It's hard to make it out, but if you look closely, it's readable.

How accurate do you think this graph is?

[hoytedow]

Can you post it differently so we can click on it to view full size?

[gonzo]

It looks like a sales pitch. They make a nonsensical claim that the planing cat and mono and the displacement cat and mono all have the same length and displacement. I would call it meaningless.

[Brian@BNE]

Accuracy - don't know. But its an interesting graph.

What we need to complete the picture is graphs showing consumption for L/displacement (for displacement boats) and effects of propeller diameter.

Of course we already know these effects in principle. Its just that small high-revving outboard props are inefficient and the fuel consumption for the displacement boats in your chart, particularly at the higher speeds, is much higher that would be the case for a good boat design with optimum engine/propeller configuration. A long and skinny displacement monohull with 30-35" prop could be similar to the others at 20 knots....

[CatBuilder]

Originally Posted by gonzo

It looks like a sales pitch. They make a nonsensical claim that the planing cat and mono and the displacement cat and mono all have the same length and displacement. I would call it meaningless.

I was disturbed by the same length cat vs. monohull at the same displacement as well. Seemed far fetched.

Hoyt: I can't get it in any other size. That's the size of the graph on the website where I found it. I used a "hot link" to put it in here, so as not to waste boatdesign.net's bandwidth.

[tom28571]

Originally Posted by Brian@BNE

Accuracy - don't know. But its an interesting graph.

What we need to complete the picture is graphs showing consumption for L/displacement (for displacement boats) and effects of propeller diameter.

Of course we already know these effects in principle. Its just that small high-revving outboard props are inefficient and the fuel consumption for the displacement boats in your chart, particularly at the higher speeds, is much higher that would be the case for a good boat design with optimum engine/propeller configuration. A long and skinny displacement monohull with 30-35" prop could be similar to the others at 20 knots....

I don't see any note that these are outboard powered or that each engine set and props are not optimized for the particular boat. All the same it may not mean much for a lot of reasons, all unknown.

[TeddyDiver]

I'm agree with Gonzo... Look in the graph monohulls below 10kn.. utter nonsense that a planning hull could be those speeds more economical...

[Willallison]

It's been around for quite a few years now that graph - pops up every now and again on a multihull site or magazine.
I could be wrong, but think it originated from an article written by (the late and well respected) Malcom Tennant. The graph is only 1/2 the story, without the accompanying text.