Lifting Harness

[Kevin]

I'm planning to dry sailing out of Montrose Harbor in Chicago this summer. This assumes a few other i550 puzzle pieces fall into place and I have my fingers crossed that they will. They have pretty typical lifts and I would like to buy the parts to make a harness now while things are on sale.

My question is, if I wanted a ring to go onto the hoist's hook, how big would it need to be? That seems like the simplest way to go and pretty fool proof.

I plan to copy the viper and use a 3 line harness. The aft 2 lines will go down to my mainsheet bridle points aft of 169 and the forward line will go to the bow fitting. A forth optional line will go down to the keel. This will allow the whole launch operation to be in one step and I can work with the line lengths so the the lift is centered over the keel as well.

Thanks, Kevin.

[Chad]

Go big on the ring! Also, if going from bow to f169, either you'll have flat angles = much higher loads, or you'll need to lengthen your lines and hoist from way up in the air above the boat. How strong are those mainsheet bridle connections? How does a line get to the bow, with a mast in the way?

How about folding padeyes each side of the companionway at f110, then a single leg aft to the middle of the mainsheet bridle?

[Mist]

Kevin,

I'd use a Colligo softie soft shackle. The large ring, probalbly metal, will knock around and ding up the boat. You can make your own by following the video instructions on thier website. I've made a few and have practiced with line other than the Dux. Their plenty strong and will not come lose unexpectedly. Just a thought.

http://www.colligomarine.com/ http://www.youtube.com/watch?v=jH66tGsW ... r_embedded

[Kevin]

I hoisted my boat from the chainplates with aft lines to the spin block locations several times without rig. Chainplates are just forward of 110 on my boat. In general I found it to be pretty unstable with little load on the aft lines. Maybe my bow is extra heavy? Did it work, yes. But it moved around more than I wanted and the rig would add weight forward of the balance point. I felt at the time that there was a better solution that I hadn't thought of yet. Then last winter I was in CA and went sailing with Tim Carter on his viper 640. That's when I saw his 3 point harness. It was very simple and stable. And he had tuned his lengths so the mast stayed clear of the hoist which is a bonus. Now with the opportunity to sail at Montrose this summer coming up, it's time to consider this issue more fully. I've usually ramp launched in the past.

Rear bridle points are harken medium size forged eye straps mounted to the cockpit sole just inboard of the side panel with 1/4" bolts into 6mm g10 plate with backup fender washers and nuts. I think I'm about a foot behind frame 169 but I haven't measured it exactly. The hull and rig should be 615lb assuming a 185lb keel and a class minimum 800lb all up weight. Add in a little for the cooler and gear... I'd think the aft angles wouldn't be that low. 75" aft of frame 110 and 60" above the cockpit sole put that at 40 degree(ish). The forward line would be 115" forward and probably a 48" rise, being conservative and not factoring in a bow down desired attitude to keep the rig off the hoist. I could go down to the bow eye to lessen that angle, but that creates some other challenges. Deflection around the 3" mast spar should be minimal. I also need room below the lift point for a purchase on the keel so I can drop the keel separately if needed.

Tim K, I've made plenty of those soft shackles myself. They in general rock. I have talked with the colligo guy in the past. He looked unhappy when I said to him that it just looks like a diamond knot to me. He does load set his which adds to their awesome. I'm down to just 3 or 4 metal shackles on the whole boat. I do have a spectra grommet (thanks to Brion Toss) made of 6mm spectra, that should be good for 6-7k pounds our double that if I double it up.

[Chad]

My CG is somewhere around 124, so that's 14" of deflection I need to accomplish with aft lines, maybe a little more if you want to trim bow down to clear the rig. A couple sails in the bow will have an effect though. With the pull aligned near the back of the keel, I'm wondering if that's going to be good for the foil, getting pulled aft like that -if you go for the 4th string, all in one lift and deploy setup. Not sure...

[Kevin]

I confess that I'm confused about what is problematic with the three point harness idea. To keep the boat steady while lifting it seems to make sense to have the lift points further and roughly equal distant from the center of gravity. My plan puts the rears at 30 inches from the transom and the forward line at the bow. While not exact, it seems more balanced than 14 inches in front and 60 inches behind the center of gravity. Also, with the longer leads I should have more adjustability so that the lift point is right over the keel. My experience using a manual purchase and the mainsheet was that it work best riding against the front of the keel box versus the back. Boat should hit the water and level out before the keel is dropped.

I'm planning on oversizing these lines quite a bit. Looking at 3/8" line with 6k breaking strength for the forward line and using some "first try" 5/16" jib sheets which didn't work out for the aft legs. That's plan a anyway.

[Chad]

I just saw the big bridle approach as more hassle and more loads. I have no nonskid forward, so I'm reluctant to choose a solution that involves shimmy-ing to the bow. It'll definitely work. It's just my nature to analyze and optimize whatever I see around boats...


Here's a pdf of what I think the geometry and loads you've described looks like...

i550_bridle.pdf.zip

[Kevin]

My issue with using something at frame 110 is that it seems like it is risky if you have too much weight forward. Be it is a motor you forgot to move or water that you didn't bail out before you hoist the boat. Stuff happens. Understand not wanting to walk forward on glossy paint too. I'm marginally more safe with kiwi grip up there.

So your plan would be to use the chainplates or pad eye's on frame 110 and the mainsheet bridle or other hard point aft of frame 169. How do we add a factor of safety to keep it from going to the zoo. A fourth line around the mast to the lifting ring might do the trick. Also, you have the lifting point directly over the CG. With either setup, if that's the best way to set up the harness, then the keel needs to be on a separate purchase or allowed to hang from the boat while hosted and use the trailer to push it back up.

[Chad]

Yeah, bilge water is the biggie. Too much, and things get real heavy and the CG is guaranteed to move in the wrong direction. Basically, looking at the PDF above, if the CG (of the whole shebang, boat plus contents) is outside the area within the bridle angle, the boat goes fully end-up, not good. With your big bridle, almost the whole boat is inside the bridle angle, so it's tough to stuff up. With the f110 bridle I have now, it takes moving the 800# CG about 16" fwd to mess me up. So a change in moment of 600 ft-lbs, or 60 pounds (1 cu ft, 7-ish gallons) sloshing from mid-boat to the bow (10').

The crane line will be vertical, and its hook must be over the CG, with the boat trim separately determined by the bridle lengths. In other words, you can't have the bridle over the middle of the keel, and the boat trimmed bow down, unless you also move the CG forward to match the desired hoist location.

In the pic, to avoid keel edge rubbing you'd need to do a sort of 2-stage hoist, propping a support stick/bracket under the raised keel before lifting the boat with the bridle.

[noemar]

Chad
I was trying to locate some pictures of the boat lift/gantry i thought you had sent in recently.do you still have them?
Noel

[Chad]

Page 7 of the "build status" thread...
viewtopic.php?f=3&t=149&start=150#p2713

Pic, and a drawing a few posts after.

[noemar]

Thank you

[Kevin]

OK. I'm catching up here mentally.

Center of gravity for the boat will find equilibrium when it's directly below the lift point since there is only one. While I know Chad has located his CG for his hull, mine will be different due to all the differences in our builds. But in general it shouldn't be too far from frame 124. So if that is where CG is without the keel and we hoist the keel from the top of the mast on the mainsheet halyard (or use another line at from the hounds, doesn't that mass move the CG forward? And if the keel is resting in the keel box then that would be a different CG as well.

I guess what I'm struggling with is how do a figure this out other than trial and error. I'm, of course, more worried about the error part.

If only I had some warm weather to go out and experiment.

[Chad]

The CG of the boat is determined by the location of its parts, not how they are connected to each other. So hoisting the keel only changes things if the keel doesn't rise vertically with respect to the frame of reference (with the bow down as in my pic, the keel shifts forward maybe an inch or two, changing the overall CG by about 1/4 of that). It doesn't matter if you use a line to the mast or a cockpit-mounted keel crane.

I'd make the bridles about as drawn, but leave the splice for the bow long and with its end un-buried (I think you did this with your mainsheet bridles, no?), so you can adjust it a little during your first hoist and get the trim angle just right.

[Kevin]

I did make my original mainsheet tails adjustable by leaving the tails out and un-tapered. That's a good idea to allow fine tuning of the bridle. And the 5:1 purchase to lift the keel will still be needed which worked fine in the past.

updates to follow when I have the harness made and it warms up a ton. Thanks.