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Message board > Engines > Pilot with 75 bhp Honda, fuel economy?

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Message 1 of 9
Posted by member Willem on Friday 26 May 2017

Hi,


First time poster.

Just wondering if any owners have or have had a pilot wth older Honda 75bf fitted?
Wondering what speed or rpm give you the best fuel economy?

Kind regards

Donnie

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Message 2 of 9
Posted by member keith lathwell on Saturday 3 June 2017

Donnie,
I run a Bosun with a 1998 Honda 75HP and hope the following is of interest. Of course engine condition, prop pitch boat trim, hull cleanliness all have great influence. Best fuel consumption will be at minimum engine speed. As revs increase fuel consumption will increase till you reach max displacement speed. If you then get up on the plane speed will obviously dramatically increase. Best consumption planing will be when you throttle back to a just planing condition. For example consumption at say 4000rpm planing would be similar to say 2000rpm non planing however speed could be 3x as great. Best advice for best consumption is to use advantageous tidal flows.
Regards Keith

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Message 3 of 9
Posted by member Willem on Monday 5 June 2017

Thanks Keith

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Message 4 of 9
Posted by member Clive ffitch on Monday 5 June 2017

Hi Willem,

We have an older 4cyl 2003 Mariner 75 which may have similar fuel consumption to your Honda 75bf, with full throttle range 4500 to 5500rpm. Over a measured one hour trip last year from mooring to mooring, including some displacement 5-6kn motoring and a 17kn thrash about in a reasonably choppy sea below max revs, I measured fuel tank usage by graduated dipstick at 5 litres - ie 5 litres/hour fuel consumption in perhaps "general" usage at varying revs.

Always interested in what others achieve,
Clive

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Message 5 of 9
Posted by member Edward Cartner on Tuesday 6 June 2017

This thread has been of great interest to me as I am still on a 'steep learning curve' when handling small motor boats. My 2003 Bosun carries a Yamaha 80 of the same vintage. Her bottom is always very clean as we berth her 'drystack' between trips. Although I have yet to measure consumption accurately, for most trips we have settled down to an easy 6-8kts at around 2000rpm in conditions at sea appropriate to the boat without too much alarm in fuel gauge terms. Around 4000rpm (the engine is 'rated' to 6000) will bring her onto the plane - two up - when, as Keith suggests, I can throttle back and maintain planning progress at about 15kts, depending on surface conditions. On the advice of a local 'expert' I no longer trim 'in' or 'out' - the boat simply does not seem to need it. Certainly, when I did try trim, it did not seem to make any difference to stability or time taken to achieve planing speed. All feedback welcome.

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Message 6 of 9
Posted by member Keith Lathwell on Tuesday 6 June 2017

Edward,
operating as you describe at 2000rpm I get a consumption of around 1.1 mile/ltr at 6k. I use a 17" pitch 13 1/4" dia prop. Keith

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Message 7 of 9
Posted by member Edward Cartner on Saturday 10 June 2017

Thank you for your note, Keith; it all adds to the sum of knowledge. So saying, I must get around to a proper measurement of my prop.

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Message 8 of 9
Posted by member Clive ffitch on Sunday 11 June 2017

Hi Edward,

With our 75HP Mariner we use a 13-3/4" diameter prop with 13" pitch (ie a 3 x 13.75 x 13 prop). You can find the measurements for the prop that you are using, stamped on your propeller between the blades - the "code" is: 3 (no. of blades) x 13.75 (dia. in inches) x 13 (pitch in inches).

The best size for a Hardy FP / 75HP is 3 x 13.75 (or 14) x 13, which is as far as I know the size originally recommended/supplied by Hardy themselves. We had a 3 x 14" x 19" pitch fitted when we bought Adele but this gave us too high revs and would not get to planing speed. The longer pitch is better suited to much lighter planing boats - not a heavier semi-displacement boat like a Hardy Pilot. The 13" pitch prop that we now have has more punch to get more powerfully up out of displacement to planing mode, and we now get to planing at around 12-13kn with revs well under control.

We also have trim tabs that we fitted that some would almost say are necessary on a Family Pilot to make full use of 50-75HP engines. Simon Kidd will be able to advise far more on this, and once you get into engine performance/prop size/trim tabs, there are also some other very good posts on this forum to help you ponder further.

Another fuel figure for chewing over... at low rev displacement, at 5-6kn, we have found consumption to be around 2.5 litres/hr.

Clive

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Message 9 of 9
Posted by member robert sneddon on Friday 16 June 2017

Hi Willem and Edward

Just to add to the other members comments.
I push my 1986 Family Pilot, the model with the deeper keel with a 2004 Suzuki DF70.
Fuel economy runs at approx 1ltr per mile at 5-6 knots
WOT is now the recommended 5500 rpm and I'm fitted with a 3 blade prop, 13.75 X 13. trim tabs fitted.
When I purchased the engine it was fitted with a larger diameter prop and the engine would only reach 4400rpm.
Push on further and depending on the sea conditions this obviously drops.
I must admit I spend most of the time in the 5-7 knot range but it's good to know you have the extra speed and grunt available.

Kind regards
Robert.

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