What's your cruising speed. - Page 8

RCook · 04-11-2015, 10:12 AM

Hi Eric,

Our Bounty 257 may not be the most fuel-efficient 26-footer around, but it may be one of the most quality-built, and best-equipped for both cruising and fishing, at least among planing hulls.

Thought many times over the years about switching boats. If we were to decide to spend a bunch to sell our 17-year-old boat (still in very excellent shape) and upgrade, it would be for a much larger cruiser, like maybe a 37 Nordic Tug.

rochepoint · 04-11-2015, 12:56 PM

Quote:

Originally Posted by deepsix

New boat to us last season. single perkins 6354m na 135hp ,It seamed to like about 8kts at 2100rpm. From what I can figure its burning under 2gph . Does this sound right?

Sounds just like ours......

Submarine deckhand · 04-12-2015, 08:39 AM

We did the math with the general formula: hull speed = 1.34 x square root of water line
(not loa) and try to stay just under for least effort.
It turns out for us that's 1250 rpms running ford lehmans.
Apparently it's not good to run at such moderate/low rpms, but it sounds so stable and reassuring. (And she's a smokey wee tart any harder)

saltcod · 04-12-2015, 10:37 PM

Depends how soon we want to get someplace. 10 Kn is comfortable, 15 kn accomplishes the job that much sooner. The advertised top speed of our boat is 18 kn. Have not pushed the throttle levers all the way forward...
I really don't care about fuel consumption, you might burn more fuel going faster, but you will also get there sooner. Depends what your time is worth.

markpierce · 04-12-2015, 11:03 PM

Today, this kayaker rode my boat's mild wake today for about a mile while the Coot was making its normal cruise speed of 6.3 knots.

Britannia · 04-13-2015, 09:30 AM

So far I'm finding that 1600rpm at 7.3kt with 3.7 gph fuel consumption works well for my KK54. That's probably a medium speed cruise. 1800rpm gives me 8.3kt and about 5 gph for a faster cruise. I'm not sure about the lower end yet since my experience has only been with my delivery and I haven't wanted to go that slowly.

Richard

HiDHo · 04-13-2015, 10:12 AM

The Volvo TMD31A (100 HP) @2500 RPM 6 1/2 knots and the 5 KW Generator burns about 1 1/2 GPH total @ 2500 rpm.

PuppyR · 04-13-2015, 01:48 PM

Around 8K at 1550 rpm on my Lehman 120. Burn under 2 gph.

Bendit · 04-15-2015, 12:27 AM

Our slow cruise is at 1100 rpm, 8 kn, burning 11 litres (2.8 gals) per hour. This is for looking for fish and pottering about.
Displacement cruise is at 1300 rpm, 9.2 kn, burning 18 litres (4.7 gals) per hour. We find this a good compromise.
Fast cruise is at 1600 rpm, 11 kn, burning 30 litres (8.5 gals) per hour. This is great when the weather is bad as the chines work to reduce rolling. I previously thought we used 45 litres at this speed but discovered an error in the dipstick markings.
Lately we've been using the fast cruise a lot because diesel is cheap!

The Cat 3406 gets a bit smelly after prolonged slow running - crankcase fumes leaking back from air-cleaner/Racor CCV. A short (10 mins) run at 1600 eliminates fumes. Wouldn't want to travel any slower....

djones44 · 10-30-2015, 05:45 PM

As a recovering speed freak I find that having six people on board is the cure. The boat sits in a deep hole at WOT and creates one in my bank balance. So I affect all manner of aged maturity and set things back to 1500 RPM. Then I take a pee and enjoy the contentment of the engines and the way the wash still pours past the window.

Having the option to boot it makes restraint possible, even for an Irishman like me.

drb1025 · 10-30-2015, 07:13 PM

BoatUS magazine featured a Back Cove 41 this month. The author stated, apparently with a straight face, " throttle back a bit and she'll happily cruise all day at 22 knots burning a respectable 25 gallons per hour." That's respectable for a 41 with a single?

BandB · 10-30-2015, 07:55 PM

Quote:

Originally Posted by drb1025

BoatUS magazine featured a Back Cove 41 this month. The author stated, apparently with a straight face, " throttle back a bit and she'll happily cruise all day at 22 knots burning a respectable 25 gallons per hour." That's respectable for a 41 with a single?

Here are some Back Cove numbers I found.

With a 600 hp Cummins. 18 knots at 19 gph. 22 knots at 25 gph. WOT is 27 knots at 32 gph. 7.2 knots at 1.5 gph.

With a 715 hp Cummins. 21 knots at 23 gph. 24 knots at 27 gph. WOT is 29 knots at 38 gph. 8.5 knots at 4.1 gph.

Oh and at 22 knots, range is around 320 nm so will cruise all day.

MYTraveler · 10-30-2015, 08:50 PM

Typically 1060 rpm, which gives an average of 8.6 knots (maybe 8.7) at about 7 gph. Lately, I have been bumping up to about 1250 rpm which gives 10 knots but at about 11 gph. Rarely slower, although at about 6.5 knots and 800 rpm I burn less than 4 gph.

oscar · 10-31-2015, 09:57 AM

I have read this entire thread and am thoroughly scratching my head. The numbers are all over the place. Some folks may not be measuring/doing the match correctly. Applying the bell curve theory I have arrived at some numbers for chainsaw math.

I do know that when the day comes, I will be installing fuel flow meters and carefully plotting some numbers in still water.

Nomad Willy · 10-31-2015, 10:35 AM

We cruise at 6.15 knots.

What's all this talk about engine rpm? What has it to do w anything.
Fuel consumption is highly related of course.

**Baker** · 10-31-2015, 10:56 AM

I am sure I have replied somewhere in this thread but......17 knots at about a gallon a mile...or 16gph

koliver · 10-31-2015, 11:05 AM

djones:
We Saltspring Islanders should band together.
Where are you on SSI?
I look out on Convoer Cove.

Art · 10-31-2015, 11:23 AM

Quote:

Originally Posted by Baker

I am sure I have replied somewhere in this thread but......17 knots at about a gallon a mile...or 16gph

Yup - that's the ticket! ! Our twin screw gasser Tolly averages same mpg at same speed.

If we want to go slow on twins - i.e. just under calced 7.58 knts hull speed (e.g. 6.5 to 7 knts) we gets near 2 nmpg. Really s-l-o-w (5 +/- knts) on one engine with dead prop left in freewheel (BW trany allows that and no dripless on shaft) we can get upwards of 2.75 nmpg.

Can't beat those "fun" numbers with a stick! - So to say!! LOL

Hey Baker - No Mermaid picts recently - What up??

BandB · 10-31-2015, 11:39 AM

Quote:

Originally Posted by oscar

I have read this entire thread and am thoroughly scratching my head. The numbers are all over the place. Some folks may not be measuring/doing the match correctly. Applying the bell curve theory I have arrived at some numbers for chainsaw math.

I do know that when the day comes, I will be installing fuel flow meters and carefully plotting some numbers in still water.

All the numbers I have quoted are from performance tests. None estimated. Anytime I quote any of our numbers it's metered and then verified by then matching fills to projected fills.

**dimer2** · 10-31-2015, 11:40 AM

8.7 Kts or 10 mph when cruising. About 2.5 mpg running at 1350 rpm