putting a log loader on a barge

[martinf]

I've got a 1944 WWII Sea mule (bunch of questions about it a while ago--thanks for the good info) and I am moving right along in the restoration. Currently sandblasting and painting. I've got a question about the feasability of placing a Prentice knuckle boom hydraulic log loader with a grapple on this boat. The Forest Service wants me to do a bunch of log moving around for them on our local lake.

Now, I'm not asking for freebie Nav Archt. enginnering advice, just a seat of your pants reaction to this idea. I'm sure I'd be fine with the boom out in front of the boat, but the million-dollar question is how stable I'd be picking up a load over on the side of the boat.

Some data: boat is 40' long with a 13' beam, 1/4" steel thru out. The boat is built as 4 seperate water-tight compartments, 2 engines, 2 fuel tanks, displaces 30 ton.
The log loader is about 3,000 lbs, half of which would be in the vertical upright, the other 1500 would be the boom and grapple.

Any ideas, advice, or just plain out "It ain't gonna work!" will be appreciated.

Originally Posted by martinf

Some data: boat is 40' long with a 13' beam, 1/4" steel thru out. The boat is built as 4 seperate water-tight compartments, 2 engines, 2 fuel tanks, displaces 30 ton.
The log loader is about 3,000 lbs, half of which would be in the vertical upright, the other 1500 would be the boom and grapple.

The structure looks to be very high above deck, what is the height actually? Ahh sorry have overlooked the figures!
Is it possible to ballast the hull (besides, or in front of the fuel tanks), opposite to load?
How much you have to lift? weight

[martinf]

Yes, it would be possible to add ballast (though not preferable). The lifting question is difficult to nail down: sometimes a few skinny lodgepole pines, sometimes a heavy waterlogged huge old growth log; sometimes just lifting right next to the hull,sometimes the boom would be extended; and then, sometimes not even lifting at all but just moving logs around while they are still floating.
I can say that the max lift of the boom is about 4 thousand lbs.

[Village_Idiot]

Methinks you should move the cabin further back on the barge; else, you will have less deck space and maybe too much weight on the fore end.

I would also look into a one-track gantry crane configuration. It is less maneuverable, but will be safer/more stable in a boating situation, especially with heavier logs. I have seen smaller ones mounted on the beds of pickup trucks in Texas that work in oil fields, but don't know who makes them - I think they are custom built by local welders since most of the commercial stuff is jib cranes.

If you do stick with the boom crane, I would definitely add spud bars to the corners of the barge to improve your stability.

With all that being said, I am not an engineer, so take it for what it's worth!

[Ad Hoc]

martinif

Looking at your sketches, I've made a few very rough assumptions.

mainly the underwater part is about 30feet in length when loaded. The VCG around dwl, which is about 2ft 10", fully loaded. This is a simple box hull, so nowt difficult really.

So what is your stability like?...now bear in mind many many assumptions here, so this is a very quick guide. rather than posting lots of equations and iterations, here is the graphical answer!

1st curve, the hull no weights lifted.....all looks ok..but your area under the GZ curve is poor. Its ok..but doesn't inspire confidence for lifting

2nd curve is you lift 1 tonne
3rd curve is you lift 2 tonne

Ok, all in metric, since i don't understand feet and inches...but rough guide doesn't make much difference.

Your bilge is about 23 degree, from upright...ie when heeled or listing the bilge will be exposed around 23 degree, which is less than deck-edge. This is the main bit to look for.

However, when lifting 1 tonne, list is about 13 degrees....not good....scary in fact...things will slide about, any disturbance from craft passing by will be serious. The area under the GZ aint good too...no reserve.

When lifting 2 tonne, the bilge has emerged and list is around 26 degrees....in this condition, the area under the graph is shockingly poor and with any slight disturbance, whoosh, over she'll go.

Summary...not good...with the davit/crane arrangement you have. Too high and too much outreach.

PS..nice little boat..good luck!

[daiquiri]

A Free!ship file of your boat attached here.
Since it is based on your pics, it is approximate (but not too much, imho). It is my little favor, if someone else puts an hour of his time to play with stability diagrams, you could have the data you need.
Cheers!

[daiquiri]

Oppps, seems like Ad Hoc has already done his calcs...

[martinf]

Ad hoc and daiquiri, A huge heart-felt thanks to you both for putting some time into researching my question. Unfortunately, as a newbie, it's going to take me some time to digest your answers (other than the quick answer of it's not going to work) I also need to install a newer version of Free!ship as the one I have won't open your file, daiquiri. But, I'll get the newer version and study both sets of files you guys provided. Certainly, I'll have a question or two after that, assuming you don't mind.

For starters, I'm wondering how dramatic the change would be if I lower the vertical tower that the boom attaches to. It came this way off my Mack truck, and it would be possible to lower it quite a bit, say making it only 5' high instead of 10' high. Does this then make a huge change in the stability?
~martin

[Ad Hoc]

Lowering the hieght alwsy helps.

Since the rise in the VCG of the whole boat is simply:

moment/displacement

In other words with all things remaining the same, the 'moment' is now half, so the rise in CoG is pro-rata half.

However, you really need to find out if their are any local stability codes that your vessel must adhere too when lifting/craning. Then compare you boat against it. That is really you goal. Then a proper stability investigation of various size of weights to be lifted and heights that will not compromise the stability of the boat.

Lowering the structure is one step to a solution, but what about trimtanks, again. Daiquiry, Ad Hoc, thoughts?

[Ad Hoc]

apex

the main problem is overall stability. Large flat ostensibly shallow hull forms are not great once a crane with a long and high reach is used. (Think of carrying water in a large flat wide tray say 1cm deep....not easy).Trim tanks need to be active not passive, which complicates matters and adds cost.

If he is serious about such things, then having a retractable boom which is deployed when in heavy lifting mode, to increase the waterplane inertia (hence aids tranverse stability) is one way of doing it. But takes up space, weight cost etc etc....alternatively, spud poles to anchor her down.

[martinf]

Unfortunately in my situation spud poles wont work since the lake I will be operating in has a max depth of 1500 ft! And, even right along the shoreline it gets 100 - 200 quickly. The lake, Lake Chelan in Washingtion state, is basically a glacier melt-fed valley.

I am going to head down to the shop today and see how much height I can knock off the vertical pole of the log loader and report back.

In the meantime, anyone interested in learning more about this unuisualy project, please visit my blog at www.seamule.blogspot.com
thanks.
~Martin

[wardd]

would winching them aboard help?

put angled plates next to the hull side, this may limit you to loading from one side

Originally Posted by Ad Hoc

the main problem is overall stability.
.

Well, of course. My thoughts went towards passive tanks, with the limiting ability to load / deploy to one side and over the bow only.

[Submarine Tom]

My thoughts exactly wardd, would a winch do the trick?

Tom