1,000nm at 30 knots cruise? Suggestions please!

[Sundays_Child]

Paul,

I'd imagine a 75% load for 25 hours, so you're very close to the mark.

I've only done the trip by sail in the past, so I may be in nanoo land.

 

[MapisM]

Well, 30 hour of continuous usage at or near the rated engine speed isn't the typical pleasure boat usage for sure.
Even if that'll be occasional, personally I'd swap a few knots for the reliability of a higher duty engine.
Though continuous unrestricted rating wouldn't surely make sense for the boat you're thinking about.
I'd try to find the most acceptable compromise talking with the builder.

 

[MapisM]

[ QUOTE ]
is what you are saying this:-?
'No MoBos apart from commercial should run their engines continously at say 80% load for 35 hours?'

[/ QUOTE ]
Nope - where did I? But almost, actually.
What I'm saying is that engines fitted on pleasure boats are usually "high performance" rated: vessels operating at rated load and rated speed up to 8% of the time (up to 30% load factor).
In fact, this definition applies also to the engines installed on Rebel Yell.
Now, that's a gorgeous boat for sure.
I guess she can cruise at 30 kts, and surely has a huge range.
But I wouldn't even think of pushing her through a thousand miles at 30kts continuously.
Not with those engines - and not if I were the owner, at least! /forums/images/graemlins/grin.gif

 

[billskip]

Many seem to say engins are a problem.

please excuse my ignorance, but could someone please explain why an engine should not run (within its design tolarance)continious for 30-50 or even 100 hours?

 

[lookout]

I suppose because it's not within the design tolerance.... http://www.cat.com/cda/layout?m=37601&x=7

 

[Gludy]

I am not suggesting Rebell Yell as a solution. I was suggesting a Marlow 53c with large engines.
Rebel Yell is 77 foot long and has a range of over 4000 miles and a fuel consumption at 9 knots about 1.7 mpg using 120 hp. She can crusise at about 20 knots with a top speed of only 24/25 knots. Bigger engines drive her at over 30 knots but you pay for that.
I have driven craft for 17 hours at 80% load without a problem from the engines.
I am sure you are correctly quoting the different ratings and their basic use profile correctly - but a lot of boat owners would be amazed - I really do not accept them as valid ..... I think /forums/images/graemlins/smile.gif /forums/images/graemlins/confused.gif

 

[jimg]

Really cannot understand why this concept is so difficult to understand!
I would have thought it makes sense that engines can be designed to run under different conditions.
An extreme example is F1 where until recently the teams designed the engines to last just for the practice, then a new engine for the race. When the rules changed they had to be able to run for both practice sessions and the actual race.

 

[Sundays_Child]

Alf,

Had never heard of Gozzi before. Thanks for that.

The 29 looks like a tough little thing. Surprised they only went for a CE C rating.

 

[MapisM]

"a lot of boat owners would be amazed"
LOL, yeah, you can bet on that.
Out of the many pleasure MoBoers I got to meet, maybe 5% (most likely less) are even aware that engine ratings actually exist.
On the other hand, it is also true that almost all of them use their boats/engines in a way which is perfectly consistent with their intendend usage/rating.

"I really do not accept them as valid"
To tell you the truth, neither do I. Well, not literally at least; I think that the declared ratings are more restrictive than actual engines design would allow for. Surely the producers prefer to stay on the safe side.
...after all, they would obviously prefer to sell bigger rather than smaller engines, for any given application.
Therefore, they also have some interest in badging with higher ratings only very oversized engines, at any rated power.
Now, having said that, there are surely differences depending on applications.
I was happy to live with high performance rated engines when I had a 40+ kts sport cruiser which I never used for more than 4 or 5 hours a day (and very rarely above 30 kts anyway).
But I wouldn't have been equally relaxed, would I have had the same rating engines on my current displacement boat, when in the middle of a 2 days passage....

Re. Marlows:
I understood that R.Y. already has bigger engines (C18) compared what they suggest as standard (C12).
Anyway, I just gave a look at the 53C specs: 1200 gal. fuel capacity. Let's say 1000 available, considering the usual 20% safety. Considering 1000 miles at 30kts, that means 33 hours, which turns out to 30 GPH.
Now, if they managed to buld a boat with a displacement in excess of 30 tons (when loaded), capable of cruising at 30kts with a consumption of 30 GPH (or 1 MPG), then all other builders around should be extreeeemely worried.
Aside from all engine rating considerations, of course.

 

[MapisM]

I didn't notice the post re. Gozzi - and didn't hear of them before, either.
You're right, that 29 thing seems to have some nice features.
I doubt that it could afford the range you're looking for, though - with standard tanks, at least.

 

[Gludy]

Mapism
I think we are about agreed on engine ratings and how we view them.

I plan to use a 300 HP outdrive on the marlow at about 40% load for slow cruising. Then use the CAT C18s for ghigh speed stuff or when in marinas etc.

This prevents the glazing of the C18's being run slowly, it reduces the servicing costs a lot. It provides good economy and very low noice levels. However will a 300 HP have enough to drive the stablisers? That is being looked into now.

The 53C can be supplied with larger fuel tanks and the boats are about 40% more efficient than their competitors - that boat is 62 feet long! So you could get the range.

I think they are now installing a 4000 USA gallon tank in the 72ELR - that would see me hogging the fuel berth for a while as i cleaned out the marina tanks. /forums/images/graemlins/smile.gif

 

[MapisM]

Interesting. I would have never thought that 300HP could have troubles in running the hydraulic pump of the fin stabs (I guess that's the kind of stabs you're talking about, innit?).
As a rough comparison, on my boat the stabs pump is driven by one of the main engines, but the stabs work perfectly even at idle RPM. According to engine curves, that means less than 20hp.
Now, my fins (and their pump) are surely smaller than those required by your boat, but probably not that much, considering that the displacement is 35T, compared to 42T of the Marlow.
Of course it also depends by how many of those 300hp will be absorbed to trawl around at hull speed...
But then again, it takes just 60/65hp x 2 on my boat, hence I guess that 200 or so should be enough for yours, with plenty left for stabs pump and probably a bigger alternator to keep all 24V services running.
I'd surely go for a high duty rating at least for that engine though, that's the one which is likely to be running continuously at rated power for long periods. In which case, going for high power/lower rating on the mains makes more sense.

Re. fuel, you could consider, instead of cleaning out the marina tanks, purchasing directly a truck tank - though that won't be always feasible. It was possibly also mentioned in the booklet which I sent you, wasn't it?

 

[Gludy]

The marlow 72ELR nneds about 120 hp to drive at 8 to 9 knots.
So a lower rated enghine should do the job.

I think most of my fuel will be by tanker in the Channel Islands as each fill does about 4000 miles.