Fifty Feet of Grey (steel)

[Divemaster1]

.....engines are cummins 6.7l 480 ratings. the torque figures were really good for over the hump improvements on the 5.9l ....

Nice engines Rob, and made me go out and have a look as I do like the Cummins range, but came across a strange thing here between the 5.9L, 6.7L and the 8.3 in respect to fuel consumption and thought you should know and hoping that someone would come along to explain...

Now let's say you are to run at high cruise and draw out about 400 HP +...., From the Cummins Website, I then get:

5.9 L @ 480 rating - 13.7 GPH @ 448 Hp propellor load
6.7 L @ 480 rating - 20.8 GPH @ 400 Hp propellor load
8.3 L @ 500 rating - 12.2 GPH @ 474 Hp propeller load

If I read these figures are right, the 6.7L is not the most economic engine around ....

https://marine.cummins.com/MarineEC...ts/Commercial_Propulsion/QSB6_7/QSB6_7_SS.pdf

Happy to be wrong, but thought it prudent to highlight this from the website for you to question Cummins.....

 

[Robg71]

thanks very much Alf, I will bring that up in the morning.
I had a good chat with Cummins at SIBS, the 8.3L was ruled out on weight...
I would imagine a typo, i certainly hope so....

 

[Divemaster1]

thanks very much Alf, I will bring that up in the morning.
I had a good chat with Cummins at SIBS, the 8.3L was ruled out on weight...
I would imagine a typo, i certainly hope so....

Cheers.... and LOL .... The Cummins 8.3's would save me some serious weight ... our DD's weigh in at nearly 1500 Kg each... against the 8.3's @ 900 Kg +gearbox....

 

[Robg71]

then she might bob about like a cork.... or you could load up on cases of beer

 

[Divemaster1]

More fuel ... or a combination of fuel & booze .... but she would fly irrespective...

 

[Robg71]

I see what you mean though Alf
the 6.7 drops 73 hp from 3300 to 3100
the 5.9 drops 6 bhp from 3400 to 3200 and another 10 down to 3000.
something odd there, makes the 6.7 look peaky....

the 6.7 makes max torque at 2000 rpm, same as 5.9
increase from 1278 to 1580 Nm

 

[MapisM]

Just gained four feet of accommodation space.
V drives are go.

Don't want to teach the designer/builder to suck eggs of course, but did they consider the effects on weight distribution?
That's a substantial change, if the hull was originally designed for straight shafts, with the consequent engines position.

 

[Robg71]

yes
they were originally placed there for shaft angle etc...
Its all a compromise somewhere.

Don't want to teach the designer/builder to suck eggs of course, but did they consider the effects on weight distribution?
That's a substantial change, if the hull was originally designed for straight shafts, with the consequent engines position.

 

[MapisM]

Mmm... moving the engines astern as much as required by V-drives vs. straight shafts is a bit more than a compromise, in my books.
I'd rather call it a radical change, possibly requiring other structural adaptations, even in the hull design, to keep the boat properly balanced.
Even more so considering that you mentioned a 4 feet gain in living area, which leads me to think that also the tanks are being moved astern?
Just a thought, anyway. As I said, not meant as an egg sucking lesson...

 

[Robg71]

The engines were very much a long way forward, this was to get the shallow shaft angle. It has been a moot point for me for a while. They are now closer to a third than before. We actually think weight distribution has improved.

 

[Robg71]

Had a trip to the boatyard on sunday/monday.
Beautiful part of Wales.
Lots of planing progress, the lads are keen to get stuck in now. Just waiting for 14tons of steel to turn up.
Unfortunately I will probably be blowing bubbles when it does... (No comments about Michael Jacksons monkey... thank you very much

 

[Robg71]

today we have started cutting.... again....
The first sections of plate are going through the laser.....
shame i wont be here for long...

 

[rustybarge]

today we have started cutting.... again....
The first sections of plate are going through the laser.....
shame i wont be here for long...

Are they cutting the thin plate under water?

 

[rbcoomer]

today we have started cutting.... again....
The first sections of plate are going through the laser.....
shame i wont be here for long...

Could they not drop a few sections into the Briney off the NE coast of Scotland so you can do some in your bored moments...

 

[Robg71]

yes, all plate is cut underwater.... not by me though.... my tools of the trade may be a bit.... rough....

 

[RobWales]

Hi Rob,
Out of interest,what sort of prep will the yard be using on the welds for the main hull structure? (not the ribs & internals)...
Full pen partial pen or butt maybe?
Cheers, Rob.
PS Visiting a customer of mine tomo at Westhill to discuss a couple of proposed Sat systems on the drawing board, wild up here in Aberdeen this eve!

 

[Robg71]

Bevelled plates. 2mm gap.
tack weld completely first. Then run in the main welds.
stitched intermittent on stringers and longitudinal's. Hull waterline and below welded both sides.

Aberdeens always bleak.... actually... try peterhead....

 

[RobWales]

Looking forward to seeing photo's when manufacture commences...

PS returned your pm...very small world hey!

 

[RobWales]

Bevelled plates. 2mm gap.
tack weld completely first. Then run in the main welds.
stitched intermittent on stringers and longitudinal's. Hull waterline and below welded both sides.

Aberdeens always bleak.... actually... try peterhead....

Rob,

If the main hull structure is (if i'm correct) 6mm plate don't you think you are creating a lot of extra welding hours in "doing both sides"?
IMHO A full pen prep one side (in or out) would more than suffice! OK very different if we were talking 10mm plate but 6mm will allow this with excellent results..

 

[Robg71]

You are absolutely right. Unfortunately the weld schedule stipulates this, for below the waterline. Bearing in mind the external welds will be ground flush. The hull is a mixture of 4,5,6 mm depending on where in the hull it is.