54 motor yacht

[Pascal]

Bull... oney. 20 inches of beam means nothing. Ever see a hull speed calculation take beam into account?

Hull speed isn’t about the amount of power therefore fuel it takes to push a hull. Plus the basic calculations we all use is an approximation anyway which doesn’t take into account a number of factors incl hull shape.

If you don’t believe beam affect fuel burn or energy required to push a hull thru the water, look at row boats and performance sailboats. Minimum beam.

I remember that 54 ED I delivered and measuring fuel carefully. It burned more at the same hull speed as a 53 and it had nothing to do with larger displacement of the V8s

[Freeebird]

Hull speed isn’t about the amount of power therefore fuel it takes to push a hull. Plus the basic calculations we all use is an approximation anyway which doesn’t take into account a number of factors incl hull shape.

If you don’t believe beam affect fuel burn or energy required to push a hull thru the water, look at row boats and performance sailboats. Minimum beam.

I remember that 54 ED I delivered and measuring fuel carefully. It burned more at the same hull speed as a 53 and it had nothing to do with larger displacement of the V8s

Larger engines don’t burn more fuel?

If that’s the case, why didn’t you drop a REAL pair in yours?

[Pascal]

They only burn more fuel if producing more HP. It s pretty simple. It takes X gallons of fuel to produce Y HP. That s basic engineering. Yes significantly larger engines, like a V12 vs a 6, will burn a little more fuel due to parasite loads but not that much much more. In the context of this thread the difference in fuel between an 8V71 and an 8V92 producing the SAME HORSEPOWER is non existent. Look at fuel curves for both.

The difference is the beam and the slightly higher weight of the wider beam boat. Not the engines.

As to my repower decision it had nothing to do with fuel burn but cost. $80k on the engines and gear was enough and the next step was significantly taller

[Freeebird]

This just keeps getting better! LOL

[krush]

They only burn more fuel if producing more HP. It s pretty simple. It takes X gallons of fuel to produce Y HP. That s basic engineering. Yes significantly larger engines, like a V12 vs a 6, will burn a little more fuel due to parasite loads but not that much much more. ..........

Since we are all about semantics, I request you be more precise and use "frictional losses" instead of the more broad "parasitic loads". Now carry on, lol.

[Pascal]

You guys look up fuel curves and data. I m done.

[Boatsb]

Ok.

So just to be correct. A parasitic load is where additional work is needed to be produced to drive accessory shafts or take offs. The work required to drive the apparatus could be described as a parasitic load.

Frictional losses occur when things run. Larger surface areas may increase the frictional loss. Add more cylinders increasing frictional loss. Dont use oil, increase friction loss until it siezed up.

A shape traveling through a liquid at a certain speed may have additional frictional loads when its width is increased or its shape is changed but the hull speed where running is most efficient is just where the length of the waterline is equal to the wavelength ( bow wake to stern wake). Width (beam) is not a huge factor in the equation. When running racing shells where the hull length is shorter than the wave length associated with a speed the narrower profile allows easier pushing through the bow wave.

I'm pretty sure a 53 hatt MY is not working in a similar manner as a rowing shell.

[Captain Ralph]

Bull... oney. 20 inches of beam means nothing. Ever see a hull speed calculation take beam into account?

It is nice for some folks to show them selves off well.
For better or even to embarrass them self,, well.
It is obvious that you have embarrassed your self with this comment.

Yes, hull speed calculations are based on beam dimensions and further, where the widest part of the beam is is relation to the wet LOA or water line lenght.
Every inch of beam makes a difference in hull drag.
Every bit of hull drag makes a difference in propeller load, horsepower required to move the hull at a stated speed. and the amount of fuel required to produce required horsepower at the same stated speed.

Every inch of wet surface matters including the density of the water against the surface. More drag at 4 feet vs at 1 foot for similar square inches.

FI

[oscarvan]

. .

[Westfield 11]

Bull... oney. 20 inches of beam means nothing. Ever see a hull speed calculation take beam into account?

Maybe that’s why hull speed calculations are never accurate when checked with accurate fuel flow meters? They are just a rough approximation due to factors like beam, draft and wetted surface area among others.