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Old 18 March 2016, 10:46   #11
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As a guide I've always used the Tohatsu chart.

Tohatsu Outboards - Fuel Consumption

If you look at the 15hp 2-stroke their 7.3lit/hr at WOT or thereabouts equates to around 2.3Nm/lit at say 17Kts so they expect a little better than your figures Max. My tanks per 20Nm day out figure is very approximate but give or take 10%-15% equates to the Tohatsu figure.

My only experience of larger craft is displacement diesels of my Father's and I think like Wilk's comments they used less than a fairly modest outboard on a dayboat.

But if you compare a bit more like for like that Tohatsu chart shows an old tech 115hp 2-stroke would be burning 50lit/hr compared to the 7.3lit/hr of the 15hp. Of course it would be faster so going further but relating consumption to hours is legitimate for a pleasure craft.
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Old 18 March 2016, 15:48   #12
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I think it's all relative surely. If I can spend all day boating for 20 of fuel in a SIB, distance is irrelevant, it's a full days boating for the price of a round in the pub and hugely pleasurable.

On the other hand I could take out a chunky 150hp RIB and spend all day blasting around, I'm guessing I'd not have change from a Ton for fuel...

Can you really compare the two?

If it's purely miles per gallon or ltr/hr then knock yourself out on comparison but in my own little world SIBing is a more economical option and ain't no one going to tell me different ;-)
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Old 18 March 2016, 16:39   #13
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SPG Smiles Per Gallon??
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Old 18 March 2016, 16:54   #14
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2014-en Greece:


HONWAVE T38IE2 + HONDA BF20.
5 persons. Me and wife 150 kg, 3 kids total 100 kg, 24l tank + 12l spare, some equipment - about 300 kg in total.
Average consumption was 4-5 liters (per hr - more realistic 5l), average speed was below 20 km/h so we can say that per 100 km it was 5*5=25 liters.
We did max trips 20 km one way if I remember.

2015 Greece again (5,4RIB 115 HP engine):


Again the same family but all kids had 170 cm height and kids weight in total was more than 150 kg, me and wife again 150 kg, equipment (snorkell equipment for 5 people include neoprene short suits, fishing equipment for 5 people, some food, spare shoes, many things - I think in total 450 kg include petrol (100l + 20l spare)

Average speed was between 40 km/h and 50 km/h (mostly near 50 km/h)
Usual trips 60-80 km one way
Average consumption 2km per 1liter so about 50 liters per 100 km

So:

- on the same distance consumption was 2 times greater use RIB
- speed average was 2 times more than SIB
- average range was more than 3 times

I used to love my SIB but:

- I do prefer jockey seats or stand when drive -> 0 problems with my back (I had such problems uses SIB)
- Kids are much bigger every year (now boys have 175 cm)
--- I doubt if be able to handle family on HONWAVE 3,8 again + equipment
- We do like very much to explore coats, islands by boat so minimum range one way is 50 km usually max 100 km so use RIB is out of question now

>>>>>>

OK, to be honest boat total cost almost 3-4 times more ...
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Old 18 March 2016, 20:56   #15
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I don't measure too precisely (20 HP 2 str) as I passage plan based on 1 US Gal / 10 HP / HR basis and know that is conservative (especially when applying the 1/3rd extra safety net). BUT, from the rough calculations I have done - lightly loaded in flat conditions I can get close to 2 NM/L, but in normal conditions and loading its more like 1.5 NM/L.

Max is quite right, over the course of a week with lots of boating that is certainly not an insignificant cost, however I probably spend more on Tea and Cakes in cafes than I do on fuel! If ever I start to think I'm using a lot of fuel I recall a friend with a jetski and teenage sons... I can get a weekend long trip out of what they burned in 35 minutes.
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Old 19 March 2016, 06:27   #16
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You're all correct chaps - relatively speaking it is not much money for the occasional use most of us have a SIB for. When the old man had his Ski-boat in Majorca he worked out each ski session (1-2 hours for all of us) was about 100 or so a time each morning (all running costs considered) and that was 20 years ago.
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Old 19 March 2016, 06:45   #17
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>>>relatively speaking it is not much money for the occasional use most of us have a SIB for.

Yep and another bit of my man maths... there is a fast ferry ride to Jura from the village where we'll holiday this year. For 4 of us to have a day out there the trip each way is 160 just for the ferry. The Mrs has just been away to an event where the modest level entrance ticket cost is 360 for 4 folks for 5hrs entertainment.

So 10 in fuel for 4 to enjoy a beach day out in the SIB is peanuts.
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Old 19 March 2016, 16:31   #18
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I haven't worked it out specifically for distance etc. But Aerotec 380 with Tohatsu 9.8, and I used about 7l of fuel on a January day out exploring Poole harbour, out to Old Harry and back, much of which was spent at WOT.
Bargain boating in my book!
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Old 19 March 2016, 17:07   #19
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Edit re my post #17...

Don't want to mislead... the Jura ferry is 160 for the four of us as a to/fro trip day out.... not 160 one way.
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