Laser hull - where is COG?

jfm

New Member
Hi. New here, though sailed Lasers on/off since a kid

Does anyone know the position (in the fore-aft sense) of the centre of gravity of a Laser classic hull?. Ideally I'd like the dimension in inches/mm from the bow or stern, and for the bare hull with no rig or foils, but if anyone has the data for the hull fully rigged that would be gratefully received too.

I would just go and figure it out by trial and error and a tape measure, but I don't have a Laser to hand right now. New boat doesn't arrive till November. Reason for my question btw is that I'm designing a rig to attach to the Laser to it can be craned on board another boat. Thanks
 
Hi. New here, though sailed Lasers on/off since a kid

Does anyone know the position (in the fore-aft sense) of the centre of gravity of a Laser classic hull?. Ideally I'd like the dimension in inches/mm from the bow or stern, and for the bare hull with no rig or foils, but if anyone has the data for the hull fully rigged that would be gratefully received too.

I would just go and figure it out by trial and error and a tape measure, but I don't have a Laser to hand right now. New boat doesn't arrive till November. Reason for my question btw is that I'm designing a rig to attach to the Laser to it can be craned on board another boat. Thanks

I'm not sure the center of gravity, but...

LOA 4,064 mm (13 ft 4 in)
LWL 3,810 mm (12 ft 6 in)
Beam 1,422 mm (4 ft 8 in)
Hull weight 59 kg (130 lb)
 
Are ya lifting from a single eye hook or something? :)

Figure 6 feet from the stern and you're gonna be pretty close.
 
Hi. New here, though sailed Lasers on/off since a kid

Reason for my question btw is that I'm designing a rig to attach to the Laser to it can be craned on board another boat. Thanks

Cool! Please let us know how that project goes and post photos!
 
It's been a while, but when I moved the hull around by myself, my hands were approx 6-8" behind the front end of the hiking strap attachment and the boat was pretty well balanced
 
Thanks everyone for the replies

As a few people asked what I'm doing I'll briefly explain. This Laser is going to be a tender/toy on a larger (80 foot) boat currently in build and due for delivery Jan 2011. The boat builder is deleting the standard jetski and fitting a Laser and chocks instead. It will be on a flybridge deck and lifted on/off using a typical Besenzoni crane.

My current plan is to attach the crane hook to a 4 point rope harness that will attach to the Laser. Four "legs" of rope, about 4 foot long each. The aft two "legs" of the harness will I think clip onto two stainless steel eyes that I'll through-bolt to the inside of the Laser cockpit, very close to the aft ends of the two Laser grab rails, on the athwartships bulkhead. I'll have to fit a 6 inch plastic inspection hatch to that aft bulkhead to get a hand in to put the nuts on the bolts(and plywood pads to spread the load) but I'm ok with that.

The front two rope legs of the harness need to attach to another two stainless steel eyes, forward. I guess these will be flat on the deck, somewhere forward of the front edge of the dagger board and aft of the mast, and each eye about 10 inches out from the Laser's centreline. I need to get the fore-aft position of these eyes right so that the centre of the harness is very close to the Laser's COG, else it wont hang straight when craned. Hence my question, to plan the fitting of the eyes to the Laser

I'll have to fit another inspection hatch to the deck on the centreline between the mast and daggerboard to get a hand inside to attach the nuts and plywood backing pads for these two eyes, and that's a shame because the inspection hatch will spoil the deck imho. But I can't think of an alternative. Suggestions welcome!

I am in all this kinda spoiling a nice new Laser by bolting these four (small) stainless steel eyes through the GRP but I gotta have a convenient easy-clip-on way to lift the thing and launch it. The Laser will be recreational use only

Happy to post pics when done, but it will be a few months

Incidentally, and changing the subject, the boat that will carry the Laser will be white and the Laser ivory/cream deck will colour clash. So I asked Laser (the UK builder, as I'm in UK) if they would make me a Laser in a custom colour, ie the matching white. They said no problem and charged me £500 inc tax (in the UK Laser is £4000 inc). That was quite good of them. Just telling you this, in case anyone wants a Laser in their custom colours!

Thanks again for the info
 
Thanks everyone for the replies

As a few people asked what I'm doing I'll briefly explain. This Laser is going to be a tender/toy on a larger (80 foot) boat currently in build and due for delivery Jan 2011. The boat builder is deleting the standard jetski and fitting a Laser and chocks instead. It will be on a flybridge deck and lifted on/off using a typical Besenzoni crane…

Interesting! Would it be feasible to attach two lines longitudinally, one onto the bow eye and one onto the aft end of the hiking strap? The laser wouldn't be secured in two dimensions like in the four-line scenario, but it ought to be secure enough to lift out of the water and then lash to something. Both lines would be on the boat's centerline and you wouldn't have to do all that work modifying the laser.
 
Interesting! Would it be feasible to attach two lines longitudinally, one onto the bow eye and one onto the aft end of the hiking strap? The laser wouldn't be secured in two dimensions like in the four-line scenario, but it ought to be secure enough to lift out of the water and then lash to something. Both lines would be on the boat's centerline and you wouldn't have to do all that work modifying the laser.

No worky, boat will be unstable and roll. It works with keel boats because the keel keeps the boat upright
 
How about the bow eye and the traveller fairleads? A triangle should be stable enough, and no need to cut the boat.
 
No worky, boat will be unstable and roll. It works with keel boats because the keel keeps the boat upright

Sure, but after it's been hoisted up into position would it not be feasible to lash it securely into place? The modifications to the laser you're talking about would be a lot of work, add more potential places for leaks, and the eyes might get in the way while you're sailing.
 
Didn't think you could lift a laser by the fairleads. Cant imagine they were designed to take force in that direction, the fairleads would rip right out wouldn't they?
Couldnt you create a sling rather than cutting holes is a perfectly good laser?

Jack
 
Didn't think you could lift a laser by the fairleads. Cant imagine they were designed to take force in that direction, the fairleads would rip right out wouldn't they?
Couldnt you create a sling rather than cutting holes is a perfectly good laser?

Jack

Or the mainsheet block ? - which must be near the CoG so would be taking the bulk of the load and thus the traveller fairleads would not be under much load ?

Of even some hooks to clip under the gunwale (that clamp in position). Seems a real shame to destroy a Laser when there are decent alternatives

Ian
 
are you gonna lift it fully rigged?

just a rope through the main sheet block seems to be the way, the boat only weighs 130 lbs.
 
I wouldn't be too concerned about the sway while on the crane using less than four attachment points.

The rotor blast from the chopper landing on the poop deck might cause some issues though...:cool:

(I agree that the bow eye, transom fairlead solution would work fine.)
 
Or the mainsheet block ? - which must be near the CoG so would be taking the bulk of the load and thus the traveller fairleads would not be under much load ?

Of even some hooks to clip under the gunwale (that clamp in position). Seems a real shame to destroy a Laser when there are decent alternatives

Ian

I agree with Ian, something that clamps around the gunnel would be best.
It would spread the footprint of your 'four legs' which would make it more stable as well and would put less pressure on the boat. You could probably even do it with a bit of webbing and a few modified hooks.

Adding bolts, pieces of wood and drilling holes is only going to weaken and make your boat heavier and unbalanced.
 
Thanks for all he replies/suggestions. To give you some more context, the pic at this link shows the crane (on the flybridge deck, right aft) on a sistership to the boat I have in build http://newimages.yachtworld.com/2/2/5/2/9/2252984_1.jpg?1282862368000 And this link shows another shot - Laser will be athwartships, right aft on the flybridge deck. http://newimages.yachtworld.com/2/2/3/6/2/2236246_2.jpg?1278716564000

As for the suggestions:
1. I don't want to use the mainsheet traveller fittings. They're held on with self tapper screws only. I want lots of strength in reserve; if this thing falls on a child it'll be my fault and you just cannot take those chances. The laser is 59kg = 130lbs but while it's being craned the mothership can be rolling thus accelerating the Laser. 1g of acceleration and the Laser now "weighs" 260 lbs. The lift system then needs a safety factor of say x3. So I gotta rule out the aft mainsheet traveller

2. The idea of little clamp devices that hook under the gunwhale edge is a nice one. I'll look into that, thanks. I'm thinking two stainless steel tubes say 1 inch diameter like in the sketch at this link (very rough sketch, needs refinement). http://i275.photobucket.com/albums/jj304/jfm2008/UWL/Squadron78/Laserlift.jpg With two under-gunwhale hooks. One hook slides along the tube and is lockable with clamp screw. To deploy, you put the bar on the deck of the Laser, then slide the sliding hook inward so both hooks "lock onto and under" the Laser gunwhale, then tighten the clamp screw. Two firm foam blocks that you have to press down onto with your hand would keep the whole thing firmly in place in waves, and stop it clattering around all loose. The crane ropes would be attached to the s/s tubes close to ends. With two of these tube devices I'd have a 4-point crane lift, removeable in 30 seconds, and no holes in the Laser. When the Laser is launched the two s/s bars would stay attached to the crane and be left hanging there or craned up out of the way. I have no problem finding a fabrication shop to make all this, and I can have them made over size on the length of the athwartships tube, then trim to the shortest feasible length when I try it on the actual Laser, and put a walking stick rubber foot on the end of the tube

3. The whole thing has to be easy to use and quick, so I am not keen on straps taken under the hull because they're messy/fiddly to deploy, though it would be nice if could be made to work

4. I agree all the comments that eyes bolted to hull, and 6inch inspection hatches, kinda spoils the Laser a bit. And as someone said the eyes could be a nuisance or get in the way while sailing.

5. I mainly plan to lift the Laser as a bare hull, but in v light winds I could lift it fully rigged with the thing in my sketch above, which would be nice. The mother ship will be bow to wind when anchored and the Laser will come alongside the starboard side of the mothership, so will also be bow to wind. Hence it can be lifted, then the mast can be unstepped while it is hanging in the crane, if that happens to be convenient

Thanks again for the ideas. It has reshaped my thinking, into NOT cutting/spoiling a perfectly good Laser. Please post any follow up ideas and I'll post pics when done!
 
I wouldn't be too happy about drilling holes as described into my new Laser. Instead I would rig a bridle to a heavy duty bottom cover, custom made if necessary. Then simply lower it into the water and unhook the bridle and remove the bottom cover.

Better yet, simply design a bridle that wraps around the hull. Support the hull with webbing similar to the webbing on a Seitech dolly, maybe one strap aft similar to the dolly and another forward. Remember the boat is not heavy and won't be in the air very long.

...an 80 footer with a Laser on board... That's my kinda living :)
 
...an 80 footer with a Laser on board... That's my kinda living :)

I have a 15 footer with a Laser on board... it's crowded and difficult to tack in strong winds...

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I would certainly try the two fairlead/bow cleat arrangement prior to drilling holes in my Laser. And if it's concerning, a safety line thru the main block would calm the nerves. However, the strain on the fairleads while sailing is much more than the ~45 pounds exerted by lifting there (albeit in a different direction).
 
I hoist my Laser above the car in the garage over winter using a single point hoist. The balance point is about 4" aft of the front of the board slot in the hull; i.e. about mid-point. Once it's up, I support it near the bow and transom with lashings round the hull and the rafters to equalise the loads.

Not sure how you could attach such a support with the boat in the water; you could try an inverted T which you drop through the slot and rotate 90deg, and lift on that, but it would be difficult to control its position.
 
I hoist my Laser above the car in the garage over winter using a single point hoist. The balance point is about 4" aft of the front of the board slot in the hull; i.e. about mid-point. Once it's up, I support it near the bow and transom with lashings round the hull and the rafters to equalise the loads.

Not sure how you could attach such a support with the boat in the water; you could try an inverted T which you drop through the slot and rotate 90deg, and lift on that, but it would be difficult to control its position.

Thanks everyone for the further replies. I posted a follow up a couple of days ago with links to pictures and sketchs but it has gone into some kind of suspense in the ether, I think because it has picture links in it. Mods have to approve before it appears here, it said. I'm not familiar with how this forum works with picures (you can't just use [img#] picture's url [/img#], without the #'s, right?)

Anyway, thanks, you've all convinced me to find a solution which doesn't involve cutting up/spoiling the Laser. Stephen, thanks for the info above. I thought of an inverted T a while back but wasn't sure the COG was within the centre board. Now that you've confirmed it is, I'll think about some detailed designs for a T. It would hold in place if, after inserting it and twisting it 90deg, you placed a simple wooden locator over it that slotted into the c/board slot and also held the metal T device in the right fore-aft position. That would be very quick to deploy.

I just bought a busted Laser hull on Ebay which I'll collect in a few days, to experiment with
 

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