Merry Fisher 855 Cruising speed

[Thomas Lewis]

Hello does anyone know the average displacement cruising speed of a merry Fisher 855 with twin Yamaha 150s. And also the cruising speed where at which it is most economical.

 

[gordmac]

Hull speed will be about 7kn I would think. Most economical will likely be as slow as it will go! It will drink fuel between Hull speed and fully planing. Between fully planing and nearly flat out the mpg probably won't vary a lot but most economical planing speed depends on engine and Hull design.

 

[Hot Property]

Based on your power to weight ratio of around 90bhp per tonne (almost identical to my 7 metre boat with 200 hp). I would expect 20 knots to be the most economical cruising speed. As mentioned, once you are on the plane then fuel consumption is pretty much proportional to speed.

My new years resolution is to cruise at 27 knots rather than 20 - I'll use similar amount of fuel, arrive early and the boat quite likes that speed (as do i)!!!

 

[Thomas Lewis]

Yes on the plane it is happy at about 24 knots but I yes I just wondered what the hull speed average would be. Thankyou

 

[Hot Property]

There isn't an average hull speed, it's a calculated figure.

I can't find the waterline length but estimate it at around 25 ft giving a hull speed of 6.7 knots.

Crunching Numbers: Hull Speed & Boat Length - boats.com

 

[Jamie Dundee]

Economy will also depend on the props being correctly pitched. If the engines are significantly under or over propped both fuel consumption and engine life longevity will be compromised.