Cruising RPM

Biggles · 10 November 2007, 01:37

Whats a good engine REV speed to cruise at. I keep my engine around the 4500 RPM mark for cruising but sometimes it seems a little slow. Is 5000 RPM a fair enough speed for cruising.

I ask because 5000 RPM on a car would be harsh.

Nos4r2 · 10 November 2007, 01:41

Quote:

Originally Posted by Biggles

Whats a good engine REV speed to cruise at. I keep my engine around the 4500 RPM mark for cruising but sometimes it seems a little slow. Is 5000 RPM a fair enough speed for cruising.

I ask because 5000 RPM on a car would be harsh.

Depends on your redline really. Mine's recommended 4.5-5.5k max at WOT so cruising at 5k is caning it.

I cruise at around 2/3 to 3/4 max rpm.

Biggles · 10 November 2007, 01:47

My engine maxes at 6200 therefore Your saying between 4650 and 4687 RPM. So 4500 isn't too far out. I'll maybe run just a little above that on my analogue gauge.

I ran at 5000 on 10 June when we went to the Dancing Ledge and I surprisingly got a good fuel consumption and didn't seem to be caning it.

Nos4r2 · 10 November 2007, 01:57

Quote:

Originally Posted by Biggles

between 4650 and 4687 RPM.

Ah. Didn't realise it was actually such a narrow band-I actually cruise around 3.5-4.2k rpm but it looks like 2/3 to 3/4 rpm when I'm glancing at the revcounter.

Realistically it equates to about 22-28 knots with WOT being 36-39 knots depending on load.

Poly · 10 November 2007, 08:48

Quote:

Originally Posted by Nos4r2

Didn't realise it was actually such a narrow band

I don't think it is! Biggles is needing to get his calculator serviced.

2/3 x 6200 = 4133 rpm
3/4 x 6200 = 4650 rpm

Andy Moore · 10 November 2007, 09:44

We tend to cruise at around 5000 RPM. By the sound of it the outboard is getting a good workout at those Revs. However, bearing in mind that one is only running like that for 10-15mins at a time, I reckon its okay.

Max Revs is c. 600RPM.

Biggles · 10 November 2007, 12:29

Quote:

Originally Posted by Andy Moore

However, bearing in mind that one is only running like that for 10-15mins at a time, I reckon its okay.

I wouldn't call that cruising though. I would say about 30 minutes at least constant running would be cruising ! Maybe even more.

Biggles · 10 November 2007, 12:30

Quote:

Originally Posted by Polwart

I don't think it is! Biggles is needing to get his calculator serviced.

2/3 x 6200 = 4133 rpm
3/4 x 6200 = 4650 rpm

Maths never was my strong point.

Downhilldai · 10 November 2007, 14:02

Quote:

Originally Posted by Biggles

Whats a good engine REV speed to cruise at. I keep my engine around the 4500 RPM mark for cruising but sometimes it seems a little slow. Is 5000 RPM a fair enough speed for cruising.

I ask because 5000 RPM on a car would be harsh.

I was told you Solent boys cruise at 40kts

Mollers · 10 November 2007, 14:17

Quote:

Originally Posted by Downhilldai

I was told you Solent boys cruise at 40kts

Yep, I've heard that aswell.

Hightower · 11 November 2007, 00:31

Only down Hill and with the wind behind

Nos4r2 · 11 November 2007, 01:14

Quote:

Originally Posted by Biggles

I wouldn't call that cruising though. I would say about 30 minutes at least constant running would be cruising ! Maybe even more.

Nah. It's just a throttle range that's quick enough but not thirsty(in perspective!). You can do that for 5 minutes.

As for cruising at 40 knots, some of them do (coming along the Solent with Bedajim, the Jackeens and Leeway was bloody expensive trying to keep up!)

Hightower · 11 November 2007, 01:25

Quote:

Originally Posted by Nos4r2

Nah. It's just a throttle range that's quick enough but not thirsty(in perspective!). You can do that for 5 minutes.

As for cruising at 40 knots, some of them do (coming along the Solent with Bedajim, the Jackeens and Leeway was bloody expensive trying to keep up!)

Trouble is, 40 knotts is cruising speed for the Jackeens and Leeway

Nos4r2 · 11 November 2007, 02:19

Quote:

Originally Posted by Hightower

Trouble is, 40 knotts is cruising speed for the Jackeens and Leeway

I get the impression that 40 knots is Lee's stall speed....that's when his hull finally drops back into the water

Mollers · 11 November 2007, 10:03

Let's define what 'cruising' speed is, as I tried
to with the member that informed me that he and other Solenteers 'cruised' at 40 knts. Cruising, in my view is passage making over a distance where a reasonable ratio between speed and economy is to be acheived. This is not a flat-out blast for 4 or 5 miles with a bunch of mates or even a dash around the island showing off one's greater HP.
We 'cruise' to the Scillies, from Falmouth this is a 200Nm round trip. Fuel on the islands is £1.45/ltr so we carry enough not to have to buy more over there. Blasting out from Falmouth at 40knts would be crazy, it would get us there a bit sooner and double the fuel bill.Our optimum cruise speed is around 25knts which relates to 4100-4200 rpm on my boat.

bedajim · 11 November 2007, 10:45

With the added weight aux+fuel on the back I seem to get the best fuel figures at 28 29 knots but don't normally look at the revs more interested in water pressure etc
Go more for comfort in the conditions and staying in a group if out with others, I would think 3500 to 4500 rpm but don't tend to let it sit at constant revs

40kts ruins the wife hair so that's a no no

Mollers · 11 November 2007, 10:49

Quote:

Originally Posted by bedajim

With the added weight aux+fuel on the back I seem to get the best fuel figures at 28 29 knots but don't normally look at the revs more interested in water pressure etc
Go more for comfort in the conditions and staying in a group if out with others, I would think 3500 to 4500 rpm but don't tend to let it sit at constant revs

40kts ruins the wife hair so that's a no no

My figures relate only to flat water.

Hugh Jardon · 12 November 2007, 13:09

Quote:

Originally Posted by Biggles

I ran at 5000 on 10 June when we went to the Dancing Ledge and I surprisingly got a good fuel consumption and didn't seem to be caning it.

that was a fun trip wasnt it

if a bit of a long day for the little kids being over 90 miles.

if we knew you were only at 5k revs we could have picked up the pace a bit......just kidding

Paul Beaurain · 12 November 2007, 18:11

Mollers
with common sense like that - I am surprised we have not yet cruised in copmany.
For us (like you) it is making big distances safely without using excessive fuel.

Most RIBs, I guess, are only run for for short periods - but when you are doing 100to 150Nm per day it makes a big difference.

Also comfort wise - why speed and be uncomfortable.
The exception to this (there is always a get out clause) is when you know the weather is deteriating fast and time then is more critical than absolute consumption.
PB

Mollers · 12 November 2007, 20:29

Quote:

Originally Posted by Hugh Jardon

that was a fun trip wasnt it

if a bit of a long day for the little kids being over 90 miles.

if we knew you were only at 5k revs we could have picked up the pace a bit......just kidding

Biggles-Jardon, Jardon-Biggles, Jiggles- Bardon, Jargles-Biggon. Anyone ever seen them both at the same time?