guesstimate fuel

JSP · 28 March 2009, 12:24

How many Nautical miles would you guesstimate an old 115hp V4 would get out of 50 litres at cruising speed?

chewy · 28 March 2009, 12:58

Roughly 25 miles if your burning 11 gallons an hour which works out at roughly 50 litres per hour.

Poly · 28 March 2009, 13:15

Quote:

Originally Posted by chewy

Roughly 25 miles if your burning 11 gallons an hour which works out at roughly 50 litres per hour.

I would hope more than that... most folk reckon on 1 US gallon (3.8 L) for every 10 HP on an old tech engine at Wide Open Throttle.

So 11.5 US gal per hour at WOT.
= 43.7 L/hr
So 50 L would last about 70 mins

At WOT I am guessing JSP will be doing 35 knots ? - So Would expect around 40 nm.

At cruising speed possibly a bit better.

J S · 28 March 2009, 13:25

Yes id say more like 35-40 miles. So 0.7 - 0.8 miles per litre.

James

Nos4r2 · 28 March 2009, 13:50

I'd say try it and find out. There's too many variables for a safe guesstimate unless you actually own the boat...

chewy · 28 March 2009, 14:10

Didn't realise it was US gallons.

Are you running 2 25 litre tanks? Just see how far you get on one and double it.

JSP · 28 March 2009, 14:28

Yeah 2X25L tanks.
Just trying to work a rough guess.

Downhilldai · 28 March 2009, 15:45

My V4 Soozook DT100 burns around 1 litre/nm at cruising speed (28ish kts) on a similar size boat. Your Yam may be a touch thirstier, but there shouldn't be much in it.

JSP · 28 March 2009, 16:14

Quote:

Originally Posted by Downhilldai

My V4 Soozook DT100 burns around 1 litre/nm at cruising speed (28ish kts) on a similar size boat. Your Yam may be a touch thirstier, but there shouldn't be much in it.

So going off that and Polwarts sums I should take it at about 35nm on the safe side from a 50L tank. I've only pished about in it so far, thinking of taking it from Preston to Fleetwood which is around 25 nm. If I work off that to start with and then I can see what I actually get. And if it seems to be using more I've got a couple of options to get fuel.
Cheers lads

uncle al · 28 March 2009, 19:40

we used to say as a rule of thumb a third of the horse power in litres per hour st wide open throttle WARNING nobody can give you an accurate answer to this question as weather condition , boat , boat load there is a lot of factors to put into the equation

JSP · 28 March 2009, 19:44

Oh yeah I know this is a wide open question as for an example in big swells you can be adjusting the throttle constantly. Just needed a bit of a loose bench mark

Pete7 · 28 March 2009, 20:19

John, used to recon on about 8 gallons an hour. Didn't seem to matter much if that was with a boat full of divers doing 25 knots or opening her up. I think the Yamaha manual gives a max of 60 LPH at flak speed.

Pete

JSP · 28 March 2009, 20:38

Quote:

Originally Posted by Pete7

John, used to recon on about 8 gallons an hour. Didn't seem to matter much if that was with a boat full of divers doing 25 knots or opening her up. I think the Yamaha manual gives a max of 60 LPH at flak speed.

Pete

Ahh the very man! What size tub did you have the 115 on mate?

Pete7 · 29 March 2009, 08:36

Viper 5.25m to start with and then a Viper 5.95m. The 5.25m had a lethal acceleration on it with a 17" prop and would easily pop wheelies

I would be quite happy with one of those engines on my current rib

If you want to go 25 miles I think you are going to need 4 tanks, btw.

Pete

JSP · 29 March 2009, 18:40

Quote:

Originally Posted by Pete7

Viper 5.25m to start with and then a Viper 5.95m. The 5.25m had a lethal acceleration on it with a 17" prop and would easily pop wheelies

I would be quite happy with one of those engines on my current rib

If you want to go 25 miles I think you are going to need 4 tanks, btw.

Pete

So I'll need 100 litres to do 25Nm?

Chris · 29 March 2009, 19:06

Quote:

Originally Posted by JSP

So I'll need 100 litres to do 25Nm?

I hope not that would be nuts.

With that engine on a small rib you are going to be able to cruise at a nice 30Knots without giving it too much grief.

I would bank on 50 litres being ample and you will probably find you only use half.

JSP · 29 March 2009, 19:12

Quote:

Originally Posted by Chris

I hope not that would be nuts.

With that engine on a small rib you are going to be able to cruise at a nice 30Knots without giving it too much grief.

I would bank on 50 litres being ample and you will probably find you only use half.

I was gonna say! Even when hammering around I don't use that amount , that quick. Thought I'd get more on a cruise out. Cheers Chris

PeterR · 29 March 2009, 20:31

I have found that carb engines use loads more than you really hope for.i,m veryy interested in what you actually used as I,m just now decided to get(being fitted this week) a yam 90hp 2 stroke.would have liked a larger one but do want the best range and speed.Like most things theres a comprise some where.I,m going to make a complete guess and say in calm sea 39 litres any less is wishfull thinking.Good luck

and i hope i,m wrong.Matts got a 90hp three cylinder yours is four cylinder so could you guess at using one third more on average as the engines heavier and juiceyer

JSP · 29 March 2009, 20:36

Quote:

Originally Posted by PeterR

I have found that carb engines use loads more than you really hope for.i,m veryy interested in what you actually used as I,m just now decided to get(being fitted this week) a yam 90hp 2 stroke.would have liked a larger one but do want the best range and speed.Like most things theres a comprise some where.I,m going to make a complete guess and say in calm sea 39 litres any less is wishfull thinking.Good luck

and i hope i,m wrong.Matts got a 90hp three cylinder yours is four cylinder so could you guess at using one third more on average as the engines heavier and juiceyer

Didn't manage to get out today as planned but I will be doing the trip in about 2 weeks. I'll let you know. Once had a Alfa 33 with the boxer engine. That had 4 carbs and when it work (which wasn't often) flew like sh!t off a stick but drank like a glaswegian drunk.
There's someone on here called DM who has a bigger engine than me on a 5.4 searider, come out of the shadows and show ya self

What are the twin engines like on fuel Peter?

PeterR · 29 March 2009, 20:44

Quote:

Originally Posted by JSP

Didn't manage to get out today as planned but I will be doing the trip in about 2 weeks. I'll let you know. Once had a Alfa 33 with the boxer engine. That had 4 carbs and when it work (which wasn't often) flew like sh!t off a stick but drank like a glaswegian drunk.
There's someone on here called DM who has a bigger engine than me on a 5.4 searider, come out of the shadows and show ya self

What are the twin engines like on fuel Peter?

Well i have only been out twice first time still had problem .now sorted out and used 30litres in a hour and a half running about but didnt record how far .Easter weekend will be out with new sat nav.Stormforce 650 for £299.00 so can monitor speed and distance with luck