Cruising RPM - Page 2

Hugh Jardon · 12 November 2007, 21:30

Quote:

Originally Posted by Mollers

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

?

Bigmuz7 · 12 November 2007, 23:01

Quote:

Originally Posted by Mollers

Jargles-Biggon. rolleyes:

He was in a two Ronnies sketch I think

Jon Brooks · 13 November 2007, 10:24

Agree will Mollers.

Cruising is about covering lots of ground in a day at a good speed but for the best comfort and fuel ecco.

For a long trip 3-4k would be my choice, 3k will gives us about 20-25 knots depending on sea state and good fuel ecco too.

Of course if we want to raz it up a bit then 5.5-6k then we are looking at about 55knots!!!

9D280 · 13 November 2007, 10:30

Quote:

Originally Posted by Biggles

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

But no worse for your car engine that your outboard!

Your car engine will hack that, but the big difference is that your car's powertrain is inextricably linked with the road by the tyres, you therefore need gears to get the ton or so of car moving, which in turn means you can gear it to run at a more economic RPM. If you could fit a variable pitch prop to your outboard / sterndrive, you'd be running a far higher pitch once you were on the plane than you'd need to get out the hole.......

Also can you imagine anyone wanting to sit in a car that is screaming it's bits off all day? (granted, it may be music to some) Most cars are designed to run quietly - the noise of an outboard could be a selling point, but how many of you are sayijg how nice & quiet your 4- strokes are? There are also lots of nice EEC rules to a) keep them quiet and b) not drink / emit too much.

How many outboards are based on "car" lumps?

Remember on a lot of motorbikes 6K rpm is not far off tickover!

Nick Hearne · 13 November 2007, 10:40

I think we have some boy racers around!
Cruising at anything near WOT is not cruising in my books, for me 2 to 2.5 RPM is a nice 20 to 25 knots fuel consumption around 7 to 10 GPH & you can have a chat with out shouting!

May be you should ask this question on boat mad!

Carl · 13 November 2007, 10:57

3500 revs = 55 mph,lovely cruise speed if the conditions are ok. as for outboard engines that have derived from a car engine,that would be the honda 225

Biggles · 14 November 2007, 00:37

Quote:

Originally Posted by Nick Hearne

I think we have some boy racers around!
Cruising at anything near WOT is not cruising in my books, for me 2 to 2.5 RPM is a nice 20 to 25 knots fuel consumption around 7 to 10 GPH & you can have a chat with out shouting!

May be you should ask this question on boat mad!

Thats the answer I was looking for.

Maybe its because we don't get out on our boats that much that when we do we want to really enjoy them. Thats when the red mist comes down and cruising is done at such a breakneck speed.

My ideal cruising speed seems to be between 26 - 28knots.

Hightower · 14 November 2007, 01:23

What defines cuising speed? Everybody's Ideas are different! Who really cares! If you where that concerned about fuel figures, get a Yacht or something.

My defintion of a cruising speed is an RPM where the engine can run quite happily all day long. 3000-4000rpm sems like a good range to be in. Quite frankly, if I where worried about my fuel costs, I wouldn't choose a RIB to race around in.

Biggles · 14 November 2007, 01:55

If you didn't worry about the fuel cost I think you'd bin the RIB and get a Motorcruiser. All that plush space and somewhere to kip in whichever port you decide to stop.

Most people worry about fuel costs. Unless that is you only use it once in a blue moon ! Or only T Shirt days for our Devon boys. My they are hard.

At 5 pound a gallon and most boats using a gallon in 10 minutes or less then its certainly a consideration.

Especially if your out every week.

Their again you could always spend all day looking at your boat on dry land and appreciating its finer points. Then Engine size and sound might mean more than how much your paying for fuel. If fuel is that frivolous to you then the next time I meet you Andy mines a quadrouple whiskey with ice. And your a good buddy.

I also say this about my car. Its a thirsty beast. Not as bad as Jonos Range Rover but bad enough for me.

Quite frankly, if I where worried about my fuel costs, I wouldn't choose a RIB to race around in.

But many people run a thirsty boat and then try and save a few pennies on towing it with the smallest car they can get away with. Much as I love my boat the car comes first. Big boat needs big car. Yet more money. Obviously the vending business is thriving. Good job I don't have a vending card for my works machines.

BogMonster · 15 November 2007, 15:45

The maximum I like for any short distance run for me is 4000rpm/30kt approx, much over that and the engine sounds a bit thrashy, ok for short distances but I don't really believe in thrashing engines near the redline even if outboards are "designed for it" - mine isn't getting any younger!

For a more relaxed or sustained trip I would generally use 3200-3500rpm which falls between 20 and 25 knots and would be happy that the engine would run at that speed with no worries for any length of time. I used to think that the fuel consumption increased dramatically over 20kt but I am not so sure now, because you are covering the ground that much quicker! Really need a fuel flow meter but too tight to buy one and not sure how/where to fit it...