Lifting a Rib - Page 2

jwalker · 31 July 2003, 00:29

You are letting your hearts rule your heads. Hypalon is fabric. It's floppy bendy stuff. It can be folded right back on itself and suffer no damage. Unless it is being severely nipped, just let it squidge into whatever shape it wants. The air pressure distributes the load throughout the whole of the tube.
Now, lifting eyes. Let's see, a boat like JK's is likely the weigh about 2 tons. You are going to apply a load of half a ton to each lifting point. Unless the reinforcing plate is very thick, or reasonably thick and carfully shaped to preload the lifting area, almost all of this load is going to applied to the hull over the area of approximately the washer. If it's a U bolt, the 2 washers. At the transom it's a bit different because the load will put the bolt mainly into shear, but you are still carying a load of 1 ton on the transom.
Now, you work out the surface area of the strops under the boat and compare the loads. I know what I prefer.

DM · 31 July 2003, 12:05

What's this Ovlov engine you've got Jeffrey? Did you buy it in Pwllheli?

DM

jwalker · 31 July 2003, 14:20

Oops, must have spelt in wrongly.

Nah, I bought it in Glasgow. Are you nuts?

I did buy my Suzi 200 in Penrhyndeudraeth. Lleyn Peninsular, north east of Pwllheli. Will that do?

What's this Jeffrey thing? That's a hairdresser's name, isn't it? Can't be me then.

timw · 31 July 2003, 17:11

Oh dear...I had been convinced that fitting lifting eyes was the way I would go.
Now I'm not so sure. I know that my yard won't use a spreader each time so that method's not available to me.
I suppose if I get the manufacturer to fit the lifting eyes and they approve of them for the weight, that should be OK?

John Kennett · 31 July 2003, 17:24

Lifting points bolted through the hull with sensible backing plates are tried and tested and I am not aware of any reported problems.

I have had two RIBs with this arrangement and there has been no indication of any undue localised stress (gell coat cracking etc).

The backing plates were something like 4mm thick stainless steel, and they were positioned on a flat section of the hull. As far as I can tell they spread the load adequately and this remains my lifting method of choice.

Decisions, decisions!

John

Richard B · 31 July 2003, 17:30

Quote:

Originally posted by timw
my yard won't use a spreader each time...

Why not? Do they just use slings up to a hook?

timw · 31 July 2003, 17:35

yes, they just have slings up to a hook.

This works well on small hard sided boats like my old one and all the ribs they lift have lifting eyes.

I believe the spreader is only brought out when lifting a large yacht.

They haven't the time to use a spreader on the small boats as they are being lifted in and out all day, and I would want mine in and out quite frequently.

jwalker · 31 July 2003, 17:51

Lifting points bolted through the hull with sensible backing plates are tried and tested and I am not aware of any reported problems.

JK, I wasn't trying to negate your comments. 'Just indicating the possible loads. I've even seen ribs lifted by a single eye in the wheel-house roof.

John Kennett · 31 July 2003, 19:25

Quote:

Originally posted by jwalker
I've even seen ribs lifted by a single eye in the wheel-house roof.

That would take a bit of thought in the design stage!

A lot of the "fast rescue craft" and duaghter ships have single point lifts don't they? I've never really looked to see how they do it, but I suppose it may be another option.

John

seafariskye · 31 July 2003, 19:33

I had my 8.5 craned out today - simply to clean its bum.........

and after reading all the previous, thought i would check up on what was best as the crane does not have spreader bars - by chance i had lifting eyes put on the boat when i bought it and this is the first time i used them.
The reccomendation from the maker was not to crane out unless lifting eyes are fitted??? from the maker, so that is their view??

We put decent size shackles on the eyes, 2 on transom, 2 forward, and lifted it out no bother, all very level and all that.

Personally i think if i was going to do it often, i would have the lifting eyes fitted, not a hard thing to do??
(as long as you do not mind drilliing 8 M10 holes in your hull)

pete f

Chris Murray · 02 August 2003, 11:12

Hi JW,

Sad as it may seem, I was thinking about this in the early hours of this morning.

Think of the boat as a 7 metre plank of (very strong non-bendy) material with a mass of 1500kg. Put a triangular piece of wood under each end. I agree that the weight would be evenly shared, with a force of 750NM at each end.

If we then add a load of 500kg directly over one of the supports, the force on this support would increase to 1250NM, whereas it would not affect the other end, which would still be subjected to 750NM. Not unlike a boat + outboard?

Of course, most outboards hang off the back of the transom, rather like moving the corresponding support in a bit. What happens now? Answer: the load on the furthest support is offset by the outboard trying to force the other end down. Put another way, the load on the forward support gets lighter! As you will appreciate, the force on lifting points will be upwards in the same way as the lumps of wood, so they both act as pivots.

I would therefore submit that, in your example, the load on the transom is likely to be somewhat greater than 1 ton, unless there is a very substantial amount of fuel, acting as a counter-balance, with significantly less load on the bow lifting point. I do, however, agree with your comments about pressure being force divided by surface area through which it acts.

Sorry if this is a bit "heavy", if you'll pardon the pun.

Regards,

Chris.

jwalker · 02 August 2003, 12:04

Chris, Yeh, I know. I was just being simplistic to illustrate the point about using strops to distribute the load compared to using lifting eyes. And, indicatating the emotion evoked by seeing the apparent distress to the tubes shown by Charles' picture. Where, in reality, they are probably perfectly happy to be squidged a little. In my post I mentioned JK's boat but I've never seen it I was just guesstimating an approximate weight for the purpose of example. It has an inboard diesel so there would not be the cantilevered load as there would be with an OB. But, I agree the load at the transom is likely to be greater than that at the front lifting eyes.

I quite like pedants.

Outnabout · 14 August 2003, 18:35

Tim,

my 7m Humber/ Merc175 is due to have lifting eyes fitted next week by IMPS who are in the Sparkes yard as that is where I plan to keep it also. They are using two eyes left and right side of the anchor locker with re-inforcement, and adding two eyes either side of the transom. The boat/engine combination is not particularly heavy as ribs go and you're welcome to drop by and view the results.

You can reach Nick Parish at IMPS on 02392 637251 and discuss your needs/concerns!

Pauly1 · 14 September 2013, 21:16

Just made these along with backing plates to use on my Avon 620. Tested it to 5,000kg.

colcreate · 15 September 2013, 00:26

Quote:

Originally Posted by Pauly1

Just made these along with backing plates to use on my Avon 620. Tested it to 5,000kg.

Wow a 10 year old thread rival, has it really taken you that long to weld up them brackets?

Richard B · 15 September 2013, 01:25

Very nostalgic to receive a notification for such an old thread!

Life has changed significantly, no RIB any more unfortunately, but we do have two young boys keeping us busy!

Roughrider · 18 September 2013, 15:00

I am taking my rib out with this. Mine is bigger but the top of the straps is 5.7m apart vs. my rib being 3.33 wide, I think in this instance the tubes will just deform slightly but I will have them inflated but at the very soft end prior to lifting as it is essentially already under a huge spreader - unless anyone wants to tell me otherwise!

Dry Run · 18 September 2013, 16:32

We occasionally lift ribs with strops (normally to get them on or off a road trailer) and provided you can spread them wider than the tubes, move the boat gently and don't make a regular habit of lifting that way, I can't see a problem. Certainly in the last 11 years of dry stacking we have never seen any negative effects of lifting that way (extended fork-lift under the hull is still the best way though!!!!).

ncp · 18 September 2013, 17:15

Never had a problem

EDIT: thought I had a better picture of the boat actually lifted and the tubes deformed...can't find it.

Roughrider · 18 September 2013, 18:18

Quote:

Originally Posted by Dry Run

We occasionally lift ribs with strops (normally to get them on or off a road trailer) and provided you can spread them wider than the tubes, move the boat gently and don't make a regular habit of lifting that way, I can't see a problem. Certainly in the last 11 years of dry stacking we have never seen any negative effects of lifting that way (extended fork-lift under the hull is still the best way though!!!!).

thanks

coming from KB it definitely makes reassures me