Fuel consumption on a 5.5m rib with 115HP?

[Balthazar]

Hi all,

I have a Humber Ocean Pro 5.5m bought recently and as I had already a Honda BF150 so I decided to use this engine, even being very oversized for the rib (rated 115hp max).

I had my first run yesterday, from Grays to O2 upon the Thames and my fuel consumption numbers where.

1.5L per hour idling at 900 rpm.

She planes at about 12-13knts.

Keeping her cruising at 14-15knts at 2500rpm with 8.2-8.7L per hour. Zero torque on the steering wheel, no hydraulic steering fitted.
Running 3000rpm with 18knts speed and fuel rate 10L per hour. Zero torque, I can leave the wheel and she runs straight.
At 3480rpm she runs 21-22knts and consumes 11L per hour. Slight torque but comfortable.

At all these RMP the fuel efficiency was 1.8 nautical mile for 1 litre of fuel, if I kept under 3500rpm. Once above the 3500 she runs 1.3NM per 1L and goes lower with raising the rpm.

At 4000rpm was making 26knts and consuming 16L.

I did not try above speeds as the torque became very worrying.

So the best economical regime for me is 3000-3500 rpm, cruising at 16-20 knots for 10-11L which I find ridiculously low. I spent 3.5hours cruising and spent about 30L in total for making about 35nm.

Anyone can compare with their own numbers on a similar size rib and with 115hp? Cheers.

[Pikey Dave]

Originally Posted by Balthazar

Hi all,



I have a Humber Ocean Pro 5.5m bought recently and as I had already a Honda BF150 so I decided to use this engine, even being very oversized for the rib (rated 115hp max).



I had my first run yesterday, from Grays to O2 upon the Thames and my fuel consumption numbers where.



1.5L per hour idling at 900 rpm.



She planes at about 12-13knts.



Keeping her cruising at 14-15knts at 2500rpm with 8.2-8.7L per hour. Zero torque on the steering wheel, no hydraulic steering fitted.

Running 3000rpm with 18knts speed and fuel rate 10L per hour. Zero torque, I can leave the wheel and she runs straight.

At 3480rpm she runs 21-22knts and consumes 11L per hour. Slight torque but comfortable.



At all these RMP the fuel efficiency was 1.8 nautical mile for 1 litre of fuel, if I kept under 3500rpm. Once above the 3500 she runs 1.3NM per 1L and goes lower with raising the rpm.



At 4000rpm was making 26knts and consuming 16L.



I did not try above speeds as the torque became very worrying.



So the best economical regime for me is 3000-3500 rpm, cruising at 16-20 knots for 10-11L which I find ridiculously low. I spent 3.5hours cruising and spent about 30L in total for making about 35nm.



Anyone can compare with their own numbers on a similar size rib and with 115hp? Cheers.

I’d be getting hydraulic steering fitted to that outfit, pronto.
My heavy RC 545 does around 1.2nm/L @ 25kn cruising speed with a DF140.

[jonp]

Can't complain at those figures, that's great economy. Just bought a little 14ft outfit with an older bf90 2007 and hoping for good economy and range.

[beerbelly]

my 5.5 destroyer has just recently completed 96 miles on just under 80 litres but a lot of it was 4000 rpm - 5000 rpm with occasional short runs at 6000 rpm .mariner 115 ct

[Escapeskiing]

Originally Posted by beerbelly

my 5.5 destroyer has just recently completed 96 miles on just under 80 litres but a lot of it was 4000 rpm - 5000 rpm with occasional short runs at 6000 rpm .mariner 115 ct

What engine do you have?

[davej]

On a recent circumnavigation of Mull we used 120 ltr for about 120nm , that was using a 115 2 S yam, cruising at about 18kts with 5 person onboard. The engine rpm was around 3k to 3,5 k, this impressed us as we thought we might have to take on fuel at Tobermory but didn’t and in fact finished the day with 50 ltr in reserve back at the marina.

Worked hard I know this rig can use a lot more but run easy in good conditions its fairly frugal.

Dave

[HDAV]

Originally Posted by Escapeskiing

What engine do you have?

Wild guess here a mariner 115 ct?

@beerbelly that seems pretty good

[beerbelly]

Originally Posted by HDAV

Wild guess here a mariner 115 ct?

@beerbelly that seems pretty good

yes i was pretty chuffed

[Miss Guided]

https://www.boat-fuel-economy.com/su...umption-liters

Try this. Covers outboards other than suzuki

MG
x

[69cmw]

5.5 Humber Destroyer and a Yam 115HP 4 stroke, 130 miles and used 77 L

[Gobuchul]

At 3480rpm she runs 21-22knts and consumes 11L per hour. Slight torque but comfortable.

That's 2.5 gallon per hour for 22kts.

I would say that's very good.

[lakelandterrier]

On my RC5.3 with a 100HP 4 stroke I averaged 0.78 l/NM or 1.28 NM/l

With the current 585 with a 140HP 4 stroke I've averaged this year to date by coincidence 0.78 l/NM or 1.28 NM/l. That's cruising @c. 25kts 2 adults mainly.

[HDAV]

Originally Posted by lakelandterrier

On my RC5.3 with a 100HP 4 stroke I averaged 0.78 l/NM or 1.28 NM/l

With the current 585 with a 140HP 4 stroke I've averaged this year to date by coincidence 0.78 l/NM or 1.28 NM/l. That's cruising @c. 25kts 2 adults mainly.

how strange

[Balthazar]

Done a test run from Grays to Rochester’s Russian submarine, then back to Grays via Queenborough. GPS track has shown 125nm and surprisingly I used about 45L.

I was alone, only some light bag with oilskins and 80L of fuel. Cruising speed on a moderate chop was 18-20knts and always under 3500rpm, trying to keep about 3300rpm.

This gives me about 2.8nm/L which I find very good. Just wonder if this is because of an 150HP working under very light load? Any thoughts?

Also, next year I plan to replace this Honda BF150 by Honda BF60 as this one is way too heavy, do anyone think the fuel consumption will drastically change? I think I would need to run at some 4500rpm just to maintain that 20knts cruising speed with my Humber Ocean Pro 5.5M? Any idea on what the consumption would be?

[HDAV]

60 would seem to be rather low for a 5.5 unless doing safety/coaching work of a dinghy fleet….. 150 might be overkill but 90/100 ideal?

According to this max is 115hp and 200kg https://www.yampower.co.uk/product/h...5m-2-28m-beam/ so a light 90-100 ideal?

[diver 1]

My Delta 5.5 with a 2013 Merc 100 EFI 4 stroke gave 30.8 miles for 21.2 litres of fuel (1.45Nm / litre) and 23.3 miles for 15.8 litres of fuel (1.47Nm/litre). Both local trips each trip included ploughing in and out of Poole harbour at displacement speed which I find very detrimental to fuel consumption figures also doing some performance trials at or near WOT to check prop suitability. I thought it was very economical.

[Nos4r2]

Originally Posted by HDAV

60 would seem to be rather low for a 5.5 unless doing safety/coaching work of a dinghy fleet….. 150 might be overkill but 90/100 ideal?

According to this max is 115hp and 200kg https://www.yampower.co.uk/product/h...5m-2-28m-beam/ so a light 90-100 ideal?

115 is ideal

Personally if I'm going to repower I'd always go for the max power the boat is rated for, with the lightest motor.
One day it may be a nasty day and you'll thank yourself for the extra power on tap to get the bow up/spin yourself round fast/ get on the plane faster.

It's your hand on the throttle. You don't need to open it full...

[Daibheid]

Originally Posted by Balthazar

Hi all,

I have a Humber Ocean Pro 5.5m bought recently and as I had already a Honda BF150 so I decided to use this engine, even being very oversized for the rib (rated 115hp max).
.......
I did not try above speeds as the torque became very worrying.

Well that's a surprise ☺️

[Balthazar]

Originally Posted by Daibheid

Well that's a surprise ☺️

What is surprising? The torque of a 150hp at 6000rpm without hydraulic? Oh yes, it is, highly recommended surprising experience

[Daibheid]

Originally Posted by Balthazar

What is surprising? The torque of a 150hp at 6000rpm without hydraulic? Oh yes, it is, highly recommended surprising experience

I was referring tongue in cheek to where you asked for advice on fitting a "massively oversized outboard" and the general advice was don't because it would be unstable/unusable/uninsurable. Although your thread refers to a 115, you confirm above you actually fitted the 150 anyway.

https://www.rib.net/forum/f8/anyone-...ard-86468.html

BTW I concur with the advice on this thread that a 60HP would be seriously underpowered on your RIB. But you may want to fit one anyway and see if that's also a surprising combination when it won't get up on the plane in rough conditions or with a few adults on board.
As for hydraulic steering on your current rig, IMHO, you'd just mask the problem possibly leading to achieving a higher chinewalk speed before the boat bites back.
Keep us posted.