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  Lifting sling for 15' SuperSport Limited

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Author Topic:   Lifting sling for 15' SuperSport Limited
mudpuppy posted 03-28-2002 09:50 AM ET (US)   Profile for mudpuppy   Send Email to mudpuppy  
Looking for any info on setting up a lifting sling for a 15' SuperSport Limited powered by a 2 stroke 60 hp Merc. Length of lines, comments on balance, etc, would be helpful.
Thanks.
Tim
where2 posted 03-28-2002 03:52 PM ET (US)     Profile for where2  Send Email to where2     
If you don't already have the lift, and want plans to build one like this, let me know.
http://tfn.net/~wendtm/dock1.jpg
http://tfn.net/~wendtm/dock2.jpg
http://tfn.net/~wendtm/dock3.jpg

The rear floats are hollow, allowing air to be used to displace water making it float level, or released to ease launch and retrieval. The middle and front floats are foam filled for full time floatation. The boat is a 15' Sport with a 70Hp 2-stroke on the rear. The air pump is a Shop-vac.

mudpuppy posted 03-28-2002 04:46 PM ET (US)     Profile for mudpuppy  Send Email to mudpuppy     
Thanks for the cool pics of a great setup, but we're looking for a sling or harness used to lift the boat off the trailer with a crane and place it in the water where there is no ramp available.
Flipper posted 03-29-2002 02:45 AM ET (US)     Profile for Flipper  Send Email to Flipper     
Using three cables, with safety hooks, to clip on to your lifting eyes (on the inside of the boat)would be the fastest system. I'm setting up this system for our boat house this summer, but I haven't looked for the boat's balance point yet.My 15 is more ass-heavy than normal though, with a 90hp.
Ron Brassord posted 03-29-2002 08:08 AM ET (US)     Profile for Ron Brassord  Send Email to Ron Brassord     
I am also looking for the besr way to pick up my 15 using a single davit on my dock. I have been using a wire cable harness on my old 13 that clipped into the three lifting eyes and each of the three cables conected to a two foot length of 3/8ths chain in the middle. This allowed moving a shackle along the chain to get the best balance for the pickup. Worked slick.
But now I am told that with a 15 I should have a beam in the lift harness to spread the load of the lift, instead of the chain. I guess the theory makes sense, but I only want to lift the boat to place it, not leave it hang on the lift.I would not like to stress the boat, but would like to keep the process as simple as possible.
Ideas greatly appreciated. Ron B
Jerry Townsend posted 03-29-2002 10:24 AM ET (US)     Profile for Jerry Townsend  Send Email to Jerry Townsend     
The purpose of the spreader bars in a lift rig is to lift the boat using vertical forces. As such, there are no lateral loads. Theoretically, an infinitely long sling will do the same thing - but cranes are always a bit shorter. However, if the sling cables are at an angle of - say at least 60 degrees - the lateral load will be about 29% of the vertical load - so that with 3 sling cables on a 1000 lb boat, the lateral load on each cable would be less than 100 lbs - not bad.

Looking at the thing in a different light - if the sling cables are at least 10% longer than the length of the boat - you should be fine. ------------ Jerry/Idaho

mudpuppy posted 03-30-2002 12:08 AM ET (US)     Profile for mudpuppy  Send Email to mudpuppy     
Jerry:

All good info, but I'm still struggling to find out abou the lengths of the bow rope versus the stern one when using a single lifting point. It's all a balancing act, I guess.

Jerry Townsend posted 03-30-2002 01:30 AM ET (US)     Profile for Jerry Townsend  Send Email to Jerry Townsend     
The length of each of the three sling cables will be the same length - each one between a lift ring (1 on the bow and 2 on the transom) and a common point on the crane lift cable. The load will balance itself automatically. I believe that this is what you questioning. ---- Jerry/Idaho
mudpuppy posted 03-30-2002 09:56 AM ET (US)     Profile for mudpuppy  Send Email to mudpuppy     
Jerry:
That's exactly what I was looking for. Intuitively , I thought the three lengths ought to be the same, but then someone else suggested that the bow, being lighter, might tip up during lifting (as the heavier stern might pull it up.) I guess they installed an anti-gravity device in their bow, as I don't see any other way you could get the bow to rise when it's suspended by a lifting cable!

Thanks. I'm gonna try it with all three cables the same length and go slow.

Any other info you come across would be welcome. Should I put a control line--a length of rope--on each end of the boat to hold onto during the lifting process to keep the boat from spinning (rotating) around the single lift point?

Tim

mudpuppy posted 03-30-2002 10:03 AM ET (US)     Profile for mudpuppy  Send Email to mudpuppy     
Jerry:
That's exactly what I was looking for. Intuitively , I thought the three lengths ought to be the same, but then someone else suggested that the bow, being lighter, might tip up during lifting (as the heavier stern might pull it up.) I guess they installed an anti-gravity device in their bow, as I don't see any other way you could get the bow to rise when it's suspended by a lifting cable!

Thanks. I'm gonna try it with all three cables the same length and go slow.

Any other info you come across would be welcome. Should I put a control line--a length of rope--on each end of the boat to hold onto during the lifting process to keep the boat from spinning (rotating) around the single lift point?

Tim

Jerry Townsend posted 03-30-2002 11:29 AM ET (US)     Profile for Jerry Townsend  Send Email to Jerry Townsend     
Tim - good point - a control line from at least one end is desirable. You would note on large construction project that many times, a "control line" is attached to one end of the load. You would also note that on many large construction projects the cranes often use swivel hooks - which, in part, is intended to eliminate the tendancy of the load to rotate.

Also, make sure your lift rig is of good cables, using good, tight clamps and terminated at the boat lift rings with a good quality hook or clevis. Those rings on the boat (1 on the bow and 2 on the transom) were designed to lift the boat as you are doing.

And remember - there is no problem with longer cables - only shorter. That is 20% or 30% longer than the boat doesn't hurt a thing. ------- Jerry/Idaho

mudpuppy posted 03-30-2002 02:42 PM ET (US)     Profile for mudpuppy  Send Email to mudpuppy     
Jerry:

Appreciate the advice. I was thinking of using a retired rock-climbing rope rather than cables, and some rescue carabiners to clip onto the lifting eyes. There will be some stretch of the rope (it's designed to elongate elastically under loads), but with the lengths involved, it'll be minimal. Can you think of any downsides?

Jerry Townsend posted 03-30-2002 04:19 PM ET (US)     Profile for Jerry Townsend  Send Email to Jerry Townsend     
I would not use rope! If it were me, I would not want any stretch - which would only make the situation worse - that is, say you use rope and one of the transom rope stretches more than the other - which will raise the unloaded lift point and put more load on the loaded lift point - making that rope stretch more. One quarter or 5/16" cable will do the job nicely - you should not be talking of more than 1000 or 1200 lbs. Regarding the carabiners - I don't know what their ratings are, but for the loads that you are talking about, I suspect that they should be fine. That is, the carabiners are designed to hold a man (200 lbs?) and they should be designed with a hefty safety factor. Just my thoughts. ------- Jerry/Idaho
mudpuppy posted 03-30-2002 11:27 PM ET (US)     Profile for mudpuppy  Send Email to mudpuppy     
sound thoughts, jerry.
The 'biners are rated at about 2500 kg (5500 lbs) static load, so no problem there. I've broken logging chains attached to the truck by a carabiner!

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