Wood-Built Half-Gantry Hoist - Woodworking Talk - Woodworkers Forum
 
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post #1 of 19 Old 01-07-2011, 05:12 PM Thread Starter
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Wood-Built Half-Gantry Hoist

Hello everyone.

This is my first post on the site. I come with questions, since I'm not a fantastic wood worker. I tend to split the wood a lot out of stupidity.

Anyway, I am currently building a 45' catamaran out of fiberglass and foam. Yes, I know... a sin.

I need to rig up a pair of wooden hoist that looks like this:




I'm at a point right now where I'm familiar with scarf joints, gussets and the Warren Truss, but I want to do this in an easy manner. Do I use pairs (or triples) of 2x10's? Plywood with a Warren Truss? 4x4's?

I am lifting hulls that weigh 500lbs initially, then 1500lbs max (when they are finished). This weight would be on two of these hoists, evenly balanced using lifting straps (the yellow in the picture). There are two known lifting points for the hull and I'd have one of these at each lift point.

Basically, I'm trying to figure out the following:

1) What is the strongest design for a loaded 90 degree joint?

2) What is the appropriate material for holding the weight of the hull for all three parts? Upright? Legs? Load Beam? What are the scantlings on the wood?

3) How should I attach things? Lags? Many drywall screws? I will certainly glue every single attachment in addition to mechanical fasteners.


Any tips? Tricks?

Thanks in advance.
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post #2 of 19 Old 01-07-2011, 07:44 PM
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WELCOME TO THE FORUM

You have quite a project there, including the catamaran. If it were me, I would overbuild it. You certainly don't want any failure. For the three main frame pieces I would use a minimum of a 4x4. I might even think about a glue up of 3-2x4's (would likely be stronger). For the truss, I would likely use glued up double 2x4's. Besides the plywood gussets, I would join the frames with half laps, and use a minimum of three (triangulated pattern) mechanical fasteners (bolts, washers, and nuts) at each location.










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post #3 of 19 Old 01-07-2011, 08:06 PM
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Why not use 2 of these?

Very reasonable, ($220) foldable, and will lift 4000# bill
http://www.harborfreight.com/2-ton-f...ane-35915.html
You did not state the required height dimension, so a modification/extension may be needed on the vertical. Maybe you won't need the chain fall??
In the event you make your own make certain the lower legs extend way beyond the lifting point, so as not to tip the whole unit over.

There is no charge for the free advice, but you get what you pay for ... just sayin'

Last edited by woodnthings; 01-07-2011 at 08:10 PM.
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post #4 of 19 Old 01-07-2011, 08:20 PM
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Quote:
Originally Posted by woodnthings View Post
You did not state the required height dimension, so a modification/extension may be needed on the vertical. Maybe you won't need the chain fall??

I think I read the dimensions of 12' overall height and 11' to the bottom of the chain hoist.










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post #5 of 19 Old 01-07-2011, 08:54 PM
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Ahhh so....failure to read the fine print

Quote:
Originally Posted by cabinetman View Post
I think I read the dimensions of 12' overall height and 11' to the bottom of the chain hoist.


Well C-man, you know me well enough that I would be a cuttin' and a weldin' to get that extra 3 ft of height.
Welding wouldn't even be necessary if you cut the post below the cylinder mount and a found a square tube to slip over and then just drill holes for cross bolts. But that really ain't woodworking I suppose. bill
It could be made back to original condition that way however for resale if desired.

There is no charge for the free advice, but you get what you pay for ... just sayin'
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post #6 of 19 Old 01-07-2011, 09:05 PM Thread Starter
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Quote:
Originally Posted by woodnthings View Post
Well C-man, you know me well enough that I would be a cuttin' and a weldin' to get that extra 3 ft of height.
Welding wouldn't even be necessary if you cut the post below the cylinder mount and a found a square tube to slip over and then just drill holes for cross bolts. But that really ain't woodworking I suppose. bill
It could be made back to original condition that way however for resale if desired.
I was thinking of doing this, but there is a problem with the engine hoists in general.

Think about what it looks like when it's fully extended and fully in the upright position. It's nearly a vertical bar. My hull coming out of the mold has quite a width to it. From imagining the situation, I think the arm of the engine hoist would hit the edge of the hull and rotate the hull. That would make the hull need to be lifted up even higher.

I was just doing the math tonight to figure out the extra load I'd place on an engine hoist by extending the arm a few feet to see if it seemed safe or was within the safe working load the unit was rated for. I got tired and can't do math tonight! Tomorrow for that...
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post #7 of 19 Old 01-07-2011, 09:16 PM Thread Starter
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Quote:
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WELCOME TO THE FORUM

You have quite a project there, including the catamaran. If it were me, I would overbuild it. You certainly don't want any failure. For the three main frame pieces I would use a minimum of a 4x4. I might even think about a glue up of 3-2x4's (would likely be stronger). For the truss, I would likely use glued up double 2x4's. Besides the plywood gussets, I would join the frames with half laps, and use a minimum of three (triangulated pattern) mechanical fasteners (bolts, washers, and nuts) at each location.










.
Yep... it's quite a project alright. About 4000-5000 hours and I'm only just getting started. I'm lucky that I have many years on boats and a lot of experience, but this is my first hull build.

There is some woodworking involved because I'll be making the main strength bulkheads (parts inside the boat that span from one hull to the other hull across the catamaran) out of scarfed 12mm marine ply. These are the main pieces that keep the boat together. Wood is better than composite for this because it is able to flex over many cycles without losing strength the way composite (fiberglass) structures do. It's a little heavier, but not much for all the extra strength you get. Think of how many times a wave comes by and pushes on the boat, trying to flex it... wood is great for that.

All wood will be treated with 3 coats of epoxy.

I'm way off topic. Sorry. I do have epoxy around for the joints of this hoist/lift though. Do you think that's better or the same as Titebond?

And I'm definitely with you... overbuilding is the way to go. If I drop this hull, I'm out a fortune and several hundred hours of work. I need to make these hoists very strong.

When you use glued 2x4's, do you stack them like a double decker sandwich for the top beam, or do you stand them on their ends?

Here is a picture of a guy I know moving his hulls around with just a boat rope and some pulleys for the boat (using non marine terms there). I am building in a fabric building, so there is no overhead to use to move these hulls.
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post #8 of 19 Old 01-07-2011, 09:29 PM
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Originally Posted by theothersully View Post


When you use glued 2x4's, do you stack them like a double decker sandwich for the top beam, or do you stand them on their ends?

They get used on edge.










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post #9 of 19 Old 01-07-2011, 09:51 PM
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For a one time use??

Consider a bucket truck, tow truck or repair truck or forklift or backhoe??? By the hour rental? Just throwin" that out there.
bill

There is no charge for the free advice, but you get what you pay for ... just sayin'
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post #10 of 19 Old 01-08-2011, 11:19 AM Thread Starter
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Consider a bucket truck, tow truck or repair truck or forklift or backhoe??? By the hour rental? Just throwin" that out there.
bill
Everything has been considered. I had a professional marine rigging company that specialized in finding ways to move hulls inside and outside buildings come in and do an analysis.

The answer was that I should rent an electric, oversize engine hoist from them.

They determined the angle is wrong to use a boom and narrowed down every other possible solution but the oversize electric engine hoist.

It's not one time use. There are 4 half-hulls that come out of that female mold. Two of them need to go back in the mold, with two others put on the top of them while in the mold... you have to end up with "whole hulls" at the end. This is a catamaran, so these are just the two hulls. There is a lot more to build still yet after these hulls are put into place and joined.

I've gone through "how can I move these hulls" ad nauseum on the boat forums. Picture 9 or 10 forum pages with people making guesses on how to move them, each guess not working.

I'm on to building something like a mega engine hoist, but don't need the complexity of the arm and hydraulic lift when I look at what's to be done. All I really need is a moveable lift point up high. That's why I'm on here... to try and find out what type of materials to use and how to join the 90 degree part so it's the strongest possible.

I figured a bunch of people on here who know how to work with wood would know what to use.

Last edited by theothersully; 01-08-2011 at 11:21 AM.
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post #11 of 19 Old 01-08-2011, 12:52 PM
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I figured a bunch of people on here who know how to work with wood would know what to use.

I might make another suggestion. This forum is a woodworking forum and there are many knowledgeable members here. Some may be structural engineers, I'm not one of them. All I can do is offer my opinion on your request.

You might pick up some definitive information as to wood species, dimensional necessities, and joinery, by signing up on a few structural engineering forums. I'm sure those guys have their books of charts and graphs, and would be glad to offer their expertise, just like we do here. It can't hurt.

Here's a few to check out:
http://www.eng-tips.com/threadminder.cfm?pid=507
http://sap2000.org/cgi-bin/ut/forum_show.cgi
http://www.egpet.net/vb/forums/33-Ci...ing?order=desc










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post #12 of 19 Old 01-08-2011, 03:51 PM Thread Starter
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Thanks, Cabinetman. That's good advice.

I'll be back late when it comes time for the woodwork. 6 months of fiberglass and moving around hulls coming up first.... thank you.
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post #13 of 19 Old 01-08-2011, 10:25 PM
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Sully here`s something to think about in the drawing you show a lifting frame, that could be described as a C frame.
Why not build a I frame that would look like a H on it`s side.You could then fasten the top and bottom beams together on the left side of the frame,relieving the pressure on the pivot point in the middle.
There are other ways to strengthen the whole thing That I could talk about but only if your interested.
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post #14 of 19 Old 01-09-2011, 06:31 AM
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Interesting problem. I think there are some questions that need to be answered before any good advice can be given.
First - what happens after you have lifted the hull? Will the hoists with the hull hanging in it be moved somewere or will the mold be moved away?
How much space is there above the hull? Would it be possible to build trusses supported on both sides to hang the hull from?
The suggested "lying H" would offer much more strength than the "C" wich have two weak points.
You will also have to consider how to prevent the hoists from falling sidewards.
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post #15 of 19 Old 01-09-2011, 07:21 AM
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My thought exactly

The initial concept sketch left me wondering...all the stresses at the joints rather than in the members. Lateral shifting is definitely an issue. I don't know if this would work but it's stable and lifts vertically like the guys in the photo.....a gantry:
http://www.harborfreight.com/1-ton-t...ane-41188.html Expensive at $1400.00 for a pair? Not if you have hundreds of hours and $$$ invested already. OR take the concept and make it out of wood. I made one similiar out of 2" water pipe...welded on casters and the top pipe slid in a tube for disassembly. bill

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post #16 of 19 Old 01-09-2011, 08:52 AM
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Quote:
Originally Posted by woodnthings View Post
The initial concept sketch left me wondering...all the stresses at the joints rather than in the members. Lateral shifting is definitely an issue. I don't know if this would work but it's stable and lifts vertically like the guys in the photo.....a gantry:
http://www.harborfreight.com/1-ton-t...ane-41188.html Expensive at $1400.00 for a pair? Not if you have hundreds of hours and $$$ invested already. OR take the concept and make it out of wood. I made one similiar out of 2" water pipe...welded on casters and the top pipe slid in a tube for disassembly. bill
I think you're right on it. That thing would be easy to build from wood also, with a laminated beam on top or a box beam made of plywood. Only problem is that it has to be manouvered lengthwise, I don't know if his setup will allow that?
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post #17 of 19 Old 01-10-2011, 06:53 AM
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Would be very tempted to let gravity work and roll the form.....rotiserie style.

General rambling;Looking at your drawing,that would probably be money better spent making it out of steel.Wood needs more.....how you say?....a broader base.Imagine a cardboard box.Take a horiz. slot out of one side would still see the box rgid in certain directions.Taking a flat pc of cardboard(similar to your drawing),make it a "C" and you lose side/lateral strength.The latter is better done in steel....the former "can" be executed in wood.BW
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post #18 of 19 Old 01-10-2011, 07:34 AM
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Just tossing out ideas....

Instead of hoisting by pulling from above you could jack it up by pressing off the floor, just like jacking up a car, or a wall assembly to replace a sill plate. Over here in this corner of the shop you could have some short sections of 2x4 "wall" framing, with a few gussets to keep it from wracking, in small enough parts to easily handle. Assemble them in a box around your mold, lay beams across the top, loosely tie your rope or straps around the hull and beams.

Once the box/beams/ropes are in place, you jack up the box just high enough to clear the mold. You could use your car jack and lots of cribbing or use a multi-point hydraulic system for even force and instant lift, or anything inbetween. There's some sort of air-compressor bag lifts I've seen in some woodworking mags.

Anyway, once your "box" with the hull has cleared the mold, you need to roll it someplace, right? Depending on the distance of the bottom plate or your "wall" to the floor, maybe you could lower the box a smidgeon so the box comes down to rest on some sturdy mobile tables, or if higher on some sturdy mobile storage cabinets. Something that would serve another use when not moving boats.

Have fun, I wish I could get a check ride when she reaches the water!
SteveEl

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post #19 of 19 Old 01-10-2011, 09:36 AM
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If you are going with your basic design, I would extend the vertical post about three feet above the top horizontal and attach a cable or chain from the top out to the end of the beam to take the strain off the joint. On the bottom you need outriggers at right angles to the bottom beam so it's not tippy along the direction of the hull. This will also strengthen the bottom joint.
If it was my project I would set up two long parallel lvl beams atop 6x6's at the proper height to form a track and add two cross beams on casters and attach the chain fall also on a car. That way you would have a range of motion in every direction.
Good luck on your cat. I sailed a Hobie18 for many years.
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