What's your cruising speed.

[Baker]

markpierce wrote:
Mid-day yesterday in Carquinez Strait, I made 4.9 knots SOG at 2200 RPM going east but 8.7 knots at 1300 RPM going west.* Let's say water currents influence my cruising and engine*speeds.

Now realize I said the same thing on Dec. 21 but with less specificity.



-- Edited by markpierce on Friday 3rd of February 2012 01:54:15 PM

*That is a very good point, Mark. *How many people maintain their cruising RPM when they have a fair tide and revel in the added speed. *Or how many people actually bring the power back to match their "normal" cruising speed and save on the fuel???

 

[twiisted71]

Baker wrote:

*That is a very good point, Mark. *How many people maintain their cruising RPM when they have a fair tide and revel in the added speed. *Or how many people actually bring the power back to match their "normal" cruising speed and save on the fuel???

*I keep my RPMs the same and consider myself getting better MPG due to burning the same amt of fuel but going faster due to the current.

 

[Dougcole]

Baker wrote:FlyWright wrote:
8 Kts at 2300 RPM seems to be where my Perkins 4.236's are happy. I get 2.1 NMPG at that speed. 7 Kts/2100 RPM gives me closer to 2.5 NMPG and is much quieter, but feels too slow. Call me a speed freak.

*Flywright, something doesn't seem to jive here. *I had that same engine in a Prairie 29 with about a 25ft waterline and the engine was happiest about 18-1900 RPMs(6.5kts). *It is a 2600RPM engine. *I think running it at 2300RPMs is a bit much. *Not only that, if I ran mine at *that RPM in that little Prairie it would be doing damn near the same speed as your boat(at least 7.5 and with a lot less waterline). *Are you sure your tachs are correct??? *Are you sure your props are properly pitched? *And what RPM can you attain at WOT?

Personally, I would not feel comfortable using 2300RPM as a "normal" power setting. *Not knowing the power curve of that engine but I would assume it to be well over 80% and quite possibly over 90%. *Old tech diesels aren't very happy in that realm nor will they give you the service life they are known for.

*My 4-236's are happiest at lower RPM than that as well, I usually cruise between 1750 and 1850 RPM.* I wind out about 2200.

Never totally trusted my tachs though, as the feed off of the alternator.

 

[Woodsong]

currents....gotta love them!
When we were bringing our "new" boat up the TN River last week the river was/is at flood stage. Of course I had the luck of going up river.
When I should have been doing 9 knots at about 1,700 rpms, I was doing 4.2 to 4.3! Current was so strong the big channel markers were being pushed all the way under water.

 

[Pineapple Girl]

Baker wrote:markpierce wrote:
Mid-day yesterday in Carquinez Strait, I made 4.9 knots SOG at 2200 RPM going east but 8.7 knots at 1300 RPM going west.* Let's say water currents influence my cruising and engine*speeds.

Now realize I said the same thing on Dec. 21 but with less specificity.



-- Edited by markpierce on Friday 3rd of February 2012 01:54:15 PM

*That is a very good point, Mark. *How many people maintain their cruising RPM when they have a fair tide and revel in the added speed. *Or how many people actually bring the power back to match their "normal" cruising speed and save on the fuel???

as long as we are making forward progress, we cruise around the same RPMs.**

*we try to plan trips to have the current in our favor or at least not too strongly against us.*

 

[Fighterpilot]

Guess I will be the odd man out of this group. 34 Californian LRC with 3208 NA 210HP, rated 2800RPM. Our use is different, some fishing trips and some exploring the local water ways. On the fishing trips intend to cruise 2400 RPM and take what ever cruise we can get. Thus far seems to be 16 to 17 knots, but that is but one short trip. Still working the project boat up to get ready for the summer. Boat is a compromise between family/children friendly and go faster for 50 mile trip to the fishing grounds. First boat was 31 Chris Craft Commander with yanmar 170s--too slow, next was 29 Aquasport with yanmar 240s, Ok at 23 knots but not too family friendly. Next boat was an experiment as just a fishing boat, now and than. 2550 Hydrasport with twin 200 Johnsons. 31 knots, than the oil spill came, and fishing ended, so sold it. Finally decided to compromise and get a family friendly boat that could still go fishing now and than. We looked at numerous boats, from Galveston Tx, across to St. Augustine FL. and on down to Palm Beach Fl., but ended up with the Californian almost in our own back yard. That is where we are now, my son-in-law and me. This process started in 05 so not a long drawn out evolution. Appreciate all the help this forum has been as we work the latest boat. My fifth great grand child was born Saturday so have to get that boat working. Thanks


-- Edited by Fighterpilot on Monday 6th of February 2012 01:49:47 PM

 

[Marin]

Baker wrote:How many people maintain their cruising RPM when they have a fair tide and revel in the added speed.

*We run the same cruising rpm at all times, with or against the current.* Given the orientation of most of our cruising routes through the islands it is rare to be able to go the whole way with a favorable current.* You get push down one channel but then turn the corner for your next leg and you can be going across or against the current.* We try to take advantage of the current when we can, or on the longest legs of a cruise.* But it doesn't always work out that way.

But at a glacial eight knots we'll take whatever bonus in speed the current might give us.

 

[rwidman]

Pineapple Girl wrote:Baker wrote:markpierce wrote:
Mid-day yesterday in Carquinez Strait, I made 4.9 knots SOG at 2200 RPM going east but 8.7 knots at 1300 RPM going west.* Let's say water currents influence my cruising and engine*speeds.

Now realize I said the same thing on Dec. 21 but with less specificity.



-- Edited by markpierce on Friday 3rd of February 2012 01:54:15 PM

*That is a very good point, Mark. *How many people maintain their cruising RPM when they have a fair tide and revel in the added speed. *Or how many people actually bring the power back to match their "normal" cruising speed and save on the fuel???

as long as we are making forward progress, we cruise around the same RPMs.**

*we try to plan trips to have the current in our favor or at least not too strongly against us.*

I generally cruise at 2K RPM regardless of the current (and we have a lot around here).* I don't usually try to plan around the current because each time I pass an inlet, it changes.

*

 

[Per]

Fighterpilot wrote:
Guess I will be the odd man out of this group. 34 Californian LRC with 3208 NA 210HP, rated 2800RPM. Our use is different, some fishing trips and some exploring the local water ways. On the fishing trips intend to cruise 2400 RPM and take what ever cruise we can get. Thus far seems to be 16 to 17 knots, but that is but one short trip. Still working the project boat up to get ready for the summer. Boat is a compromise between family/children friendly and go faster for 50 mile trip to the fishing grounds. First boat was 31 Chris Craft Commander with yanmar 170s--too slow, next was 29 Aquasport with yanmar 240s, Ok at 23 knots but not too family friendly. Next boat was an experiment as just a fishing boat, now and than. 2550 Hydrasport with twin 200 Johnsons. 31 knots, than the oil spill came, and fishing ended, so sold it. Finally decided to compromise and get a family friendly boat that could still go fishing now and than. We looked at numerous boats, from Galveston Tx, across to St. Augustine FL. and on down to Palm Beach Fl., but ended up with the Californian almost in our own back yard. That is where we are now, my son-in-law and me. This process started in 05 so not a long drawn out evolution. Appreciate all the help this forum has been as we work the latest boat. My fifth great grand child was born Saturday so have to get that boat working. Thanks



-- Edited by Fighterpilot on Monday 6th of February 2012 01:49:47 PM

*congrats with the grand child!

i am with you, prefer to get there faily quick so i typically run it at 2000 rpm which is 13KTS, sometimes at 2400 which gives me 17KTS.

Yes it burns fuel, around 10 gal/hr but if that was a main concern of mine I guess i should have had some sort of sailboat instead.

 

[Codger2]

Fighterpilot wrote:On the fishing trips intend to cruise 2400 RPM and take what ever cruise we can get.
___________________________________________

I had a pair of 3208..375s in a 42' Ocean Alex & the Cat dealer said that 2400 was max cruise for those engines. So that was what I cruised the boat at. Never had a problem and as you said, fuel consumption was not at the top of my list. (Of course, fuel in those days was .67/gal.)

 

[Fighterpilot]

Up to 375HP the 3208 is a pretty solid engine. When I discussed the NA version and cruise rpm it was noted probably could run a few hours at 2500RPM if proped correctly so as not to be overloading the engine.

 

[KapnKarl]

Question to ksanders

In our 4788 Bayliner with 330 cummins...

We get 1.7 NMPG at 7.8 knots

If we slow down to 6.8 knots we get 2.7 nmpg

If we speed up to 15 knots we drop to .68 nmpg

We think thats pretty good for this size boat.

We've been looking at the 4788 with cummins 330's and wondering if those engines can be cruised slow for an extended length of time without carboning up the works. What rpm are you turning at the 7.8 knots you mentioned? Do you know what the gph is at that or other speeds? Tia Karl

 

[Marin]

Just curious what speed you cruise at. As an aside, how slow would you be willing to go if it halved your fuel consumption?

This question was first asked in 2011. Still eight knots in the PNW but 30 knots on the other side of the Atlantic. Thirty knots is way better...

As to the second part of the original post, eight knots is bad enough. No way we're going to slow down no matter how much it reduces our fuel consumption. As to the other boat, well, once you've cruised at 30 knots you realize how little you care about fuel consumption.

 

[Crusty Chief]

Fighterpilot,
Did you serve on the Connie around 73? Tail markings look familiar, but that was a long time ago.

 

[ksanders]

We've been looking at the 4788 with cummins 330's and wondering if those engines can be cruised slow for an extended length of time without carboning up the works. What rpm are you turning at the 7.8 knots you mentioned? Do you know what the gph is at that or other speeds? Tia Karl

1300 rpm

I have NEVER seen a documented case of shortened engine life in a Cummins 6b engine due to low rpm use in a boat.

I'd check with Tony Athens as well. H's a cummins expert and I don't think he's seen one either.

 

[BandB]

Depending on boat either 20 knots or 35 knots. Not interested in going half of 20 knots.

 

[timjet]

We mostly cruise our Cummins 6BTs 330 Hp at 1400 rpm or 7.5 knts. Last summer at that speed 95% of the time from Key West to Annapolis. Will plane at 16 kts to outrun wx or make bridge openings, but not often. Reason: engine longivity and fuel savings.

 

[Vashon_Trawler]

We cruise at 5 to 6 knots and 2600-2700 RPM or so (max WOT is 3600 RPM). I probably burn around 1/2 gallon per hour--maybe a little more.

 

[O C Diver]

Just curious what speed you cruise at. As an aside, how slow would you be willing to go if it halved your fuel consumption?

When I asked this 3 years ago I didn't have my trawler. My 35' dive boat is a very light cored Downeast hull that originally had a Cummins 6BT 210. They aren't true planning hulls and definitely not displacement hulls. Before repowering the boat cruise 15 knots at 2 MPG, 10 knots at 4 MPG, and 7 knots at 5 MPG. It liked to run on top with the 6BT and didn't suffer a great penalty for increased speed.

Fast forward to my 45' trawler with the slow planing hull. With the Cummins 6CTA 450 the fuel burn looks something like this: 7 knots at 1.7 MPG (4 GPH), 8 knots at 1.3 MPG (6 GPH), 9 knots at .86 MPG (10.5 GPH), and supposedly 14 knots at .66 MPG (21 GPH). With the repower, I expect the fuel consumption with the smaller more efficient for slower cruising speed John Deere to be between 3 and 4 MPG. If the boat was for day or weekend cruising, I would have kept the original motor. As I plan to do mostly long distance cruising, I needed a fuel burn that didn't meaningfully impact my cruising budget with the wild fluctuations of fuel prices. The difference between 1.8 - 2.3 GPH and 21 GPH for only twice the speed was an easy choice.

Ted

 

[dimer2]

8 Kts at 1300 RPM burning 4 GPH (DD 8V71)

 

[RT Firefly]

Greetings,
Aprox. 2gph/engine (2 Lehman 120HP) @ ~1750RPM. Boat weight-25tons displacement hull. Aprox. speed-8knots.

 

[slowandsteady]

7.5 knots at 1500 RPM around 2 GPH

 

[MT Nest]

7.5 knts at 1800 rpm. Why would you want to go any faster? I enjoy the trip more than the destination sometimes.

 

[Nomad Willy]

6.15 Knots at 2300rpm w a Mitsubishi S4L2. 107 cu in and 37hp.
Willard 30 hull 8 tons disp.

 

[BlueYonder]

When I'm just stooging around with not much distance to cover, 8 KTS at 2.5 GPH. When I'm trying to get somewhere quicker, 18KTS at 14 GPH. Flat out is 27 KTS at 30 GPH

 

[Codger2]

..... well, once you've cruised at 30 knots you realize how little you care about fuel consumption.

 

[O C Diver]

7.5 knts at 1800 rpm. Why would you want to go any faster? I enjoy the trip more than the destination sometimes.

I go faster across the featureless ocean when it's all about the destination (my work). Prefer a leisurely pace when cruising as the scenery is much more interesting inland and near coastal.

Ted

 

[Moonstruck]

25 to 27 knots. .9 to 1.0 mpg. We run 25 knots at 2400 rpm. That's 650 off the top.

 

[Francois]

At 1450 rpm, boat does about 8.5 kts which is fine with us. If on beam seas, I'll bring her up to 10.5 kts which stabilizes the boat (more comfortable).
I twin have DD6V92...

 

[Brooksie]

6.5 k, .9 gph, 7.25 nmpg