Most efficient fuel consumption

[innervations]

Hi All,

I was sailing back from Rottnest Island off the coast of Perth (Western Australia) a few weeks back and lost all wind. Problem was I was not very careful about filling up with fuel because I thought heck, just sail to the mainland and fire up the donk to motor into the marina. I probably did have lots of fuel but the gauge on the plastic 40 litre tank is next to useless. Anyway, it got me thinking about the most efficient cruising speeds for the MacGregor M. I have a 60Hp Evinrude E-Tec. Anyone ever calculated some speed and fuel efficiency stats?

On the day I figured stick around 6kts as an efficient displacement cruise but this did not feel very efficient use of the hull or motor - seemed to be quite laboring actually. Would it be better to dump the ballast and get up on plane and if so what speed? Obviously flat out is going to burn fuel fast but has anyone run some tests?

Cheers from West Oz
Rob

[kmclemore]

Yes, sort of. Have a look here:

http://www.macgregorsailors.com/forum/v ... 98&start=0

[Catigale]

Great link above

Exec summary

1 Within 10% or better, fuel consumption is constant at given rpm

2 BEst economy (mpg) is at lowest revs, not surprisingly. THe drop in mpg between 2000 rpm and 3000 rpm (Suzuki 70 HP) is 50%!!!

[Gypsy]

Yes, sort of. Have a look here:

http://www.macgregorsailors.com/forum/v ... 98&start=0

Like it said in this thread , there are so many factors that affect gas mileage on a boat.

We recently completed a 160 mile trip from Montgomery Ala to Selma Ala .
We towed two kayaks , the boat was fully loaded for a week , 40 gallons of water in the bow tanks , and 29 gallons of gas .

Putting around locally , we have always gotten a solid 10mpg , this trip averaged out to 6.9mpg
This inculded going upstream for 30 miles agaisnt a generating dam. The water level dropped by 6 feet when they shut off the generators .

I also raised my usual cruising speed on the Honda 50 , usual is 5-6mph @2,000 rpm , we cruised at
3,000 which is 7-8mph

All this conspired to reduce our mileage from the usual 10mpg to 6.9 mpg .

Part of this 6.9mpg also included being under full sail for the last 10 miles of the trip , when the winds and bends of the river agreed (for a change) to give us a nice tailwind and beam wind in the bends.

[John McDonough]

I dont have any instruments or data to measure fuel consumption.

In calm conditions or very light winds, the Mac 26 just seems to stop.
I leave the sails up and turn on the motor at idle speed.
I will pull the sails in to close hauled, and slowly adjust the ropes, l listening for the motor to increase speed slightly as the wind crossing the sails creates a little extra lift.

Its got to help save a little fuel. It would also help if the ballast tank was empty.

[Matt19020]

Rob I posted this a while ago:
http://www.macgregorsailors.com/forum/v ... =7&t=11997

[dennisneal]

First off, I do not claim to be an expert.

We have a 26M with a 60HP Evinrude Etec Outboard engine.

I usually motor, in the open ocean at about 6-7 knots, which, if I recall correctly, is about the hull speed of the boat.

I get about 6 nautical miles to the gallon, with full ballast, plus all of our gear.

Unless shown otherwise, I think this is the most efficient fuel + time speed.

In particularly rough waters, (where we've been occasionally), I would reduce the speed, but the boat must be going forward in order to have control.

[Terry]

First off, I do not claim to be an expert.

We have a 26M with a 60HP Evinrude Etec Outboard engine.

I usually motor, in the open ocean at about 6-7 knots, which, if I recall correctly, is about the hull speed of the boat.
I get about 6 nautical miles to the gallon, with full ballast, plus all of our gear.

Unless shown otherwise, I think this is the most efficient fuel + time speed.

In particularly rough waters, (where we've been occasionally), I would reduce the speed, but the boat must be going forward in order to have control.

Does Hull Speed really apply to these hybrid boats? They are not really keel hulls and you can raise the daggerboard & rudders plus empty the ballast and convert the hull to a semi planing style hull, so how does theoretical hull speed apply to such circumstances? Under engine power there must be a cruising speed that trumps hull speed given the hybrid nature of the hull, wouldn't one think? I am not sure we should subscribe to a theoretical hull speed in the same sense as we would given a true keel hull sailboat.

[Boblee]

I normally run at about 1500 revs and on a flat sea with no wind or tide this would give around 8kpH (5mph) but given different conditions it can be anywhere between 2-20kph (1.2-12.4MPH) with the upper limit using headsail but dropping down to 1000rpm, if I have tide and wind will sometimes run at 2000 rpm.
Consistently over many tanks and hours have worked it out by using the conditions the fuel consumption has worked out to 5kpl or 11.35mpg but if am in a hurry and raise the rpm over 2000 especially with heavy seas and or against wind or tide forget it.
Last year after getting the new powerhead I took off across Darwin harbor with a couple of short bursts and some sustained running around 3000rpm but when I decided to return from over 20k's away I decided to check the tank and it was almost empty.
With no hope of getting fuel I headed off at between 5-800rpm across the tide and wind and on safe arrival checked the fuel and it seemed unchanged.
To answer the question in the original post lower revs is way better especially if you can use the conditions.

[Catigale]

Terry - these boats certainly dont follow the 'standard' hull speed formulae - but you will see a sudden decrease in fuel efficiency as you cross the 'theoretical' hull speed of about 7 statute mph (6 kts roughly) as documented above. Moe had some pretty good documentation in threads some years back on hull, semi--planing, and planing efficiency of power boats too btw.

[bscott]

Boblee--are you using the Power Thruster?

Bob

[c130king]

Probably an issue for a seperate thread but since it has come up I will add on...

I take it that most of you can run your engines at low RPMs. It is difficult for me to motor at low speeds and low RPMs. My 2-Stroke 40 Horse beast just doesn't run well/consistently below 2000 RPMs. If I try to set 1500 RPMs it will normally start sputtering some and the engine will cough to a stop...or the RPMs will surge. Pretty touchy below 2000-2500 RPMs. No issues above that range.

Makes it a little more challenging to approach the ramp/dock at slow speed as I have to really monitor the throttle and occassionally goose the power a little to keep the motor from shutting down.

Just part of the fun that I have when I go out.

Probably need some sort of throttle linkage adjustment or engine tune-up.

Cheers,
Jim

[Catigale]

I think low rev operation is still where 4 strokes are King, Mr Konig....

Remember Leon's trials and tribulations over getting his low rev operation of his ETEC right??

[c130king]

I think low rev operation is still where 4 strokes are King, Mr Konig....

Remember Leon's trials and tribulations over getting his low rev operation of his ETEC right??

I will defer to the knowledge of the PhD.

But other than that one hiccup I had with the overheat horn the engine has worked like a champ...it always cranked right up even after sitting completely unused for 18 months.

[Catigale]

...most of the time the facts differ to the knowledge of the PHD...