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Old 02 August 2003, 06:12   #31
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but you are still carying a load of 1 ton on the transom. (JW)

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.
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Old 02 August 2003, 07:04   #32
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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.
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Old 14 August 2003, 13:35   #33
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Sparkes/Lifting Eyes

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!
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Old 14 September 2013, 16:16   #34
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Just made these along with backing plates to use on my Avon 620. Tested it to 5,000kg.
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Old 14 September 2013, 19:26   #35
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Quote:
Originally Posted by Pauly1 View Post
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?
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Old 14 September 2013, 20:25   #36
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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!
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Old 18 September 2013, 10:00   #37
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a case where you may let your tubes down a bit

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!
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Old 18 September 2013, 11:32   #38
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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!!!!).
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Old 18 September 2013, 12:15   #39
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lift

Never had a problem

EDIT: thought I had a better picture of the boat actually lifted and the tubes deformed...can't find it.
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Old 18 September 2013, 13:18   #40
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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
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