Overhead Boat House Lift Structure Design Help - Point Load?

[ED26]

Hello;

I am in process of designing an overhead steel structure that will be fabricated inside my boathouse. I will source the steel locally & have an iron worker come fab & do the welding.

My question comes in regards to making sure the proper 'uprights' (one at each corner) with appropriate gussets for raking, etc, and the side to side upper I-beams are sized correctly. The local marine contractors are not structural engineers, nor am I, so another set of eyes would be great, looking online my setup would consists of a dual point load on the upper beams?

For uprights, I would like to be able to fit these within the 2x4 stud cavity walls (3.5" actual) if possible, so I can finish the walls. Should the uprights be pipe or square tube?

Attached are some pictures for reference, Max weight would be a 25K boat (most of weight in rear due to engine(s) and fuel..

Any help would be greatly appreciated.

Thanks

 

[denis4x4]

There are several things to consider here. Are you going to lift the boat using the eyes on the boat or a cradle. I would contact the boat manufacturer and ask them how they store and move finished boats. Another good idea is to visit boat yards and look at the travel lifts. I made my own davits for my house boat to lift a 12' dinghy and powder coated them. Ended up having them galvonized as the PC didn't last.

 

[kd3pc]

25K and towards the rear, would lead me to a cradle for sure..no way are lifting eyes going to/through the boats composite going to hold that. Either an adjustable cradle or a custom one for this boat, only?? Boats that large are designed to be in the water, I would make sure that your supports are where the maker of the boat has structure, else the hull may oilcan or worse.

that is also 12 tons of boat. If you are not going to run this by an engineer, I would check out some 13-15 ton travel lifts and see their structure. They are not lightweight nor will the steel fit in a 2x4 cavity.

there is actually quite a bit to the lifting mechanism, but that is another question?

 

[ED26]

Sorry for leaving this info out

The boat I am lifting is 8k lbs and is supported by a steel cradle assembled from w6 I beam (to match manufacturers trailer specs). The reason I said 25k is a over kill factor. I would rather over build than under build; so minimum would prefer the beams to support 20k

The current overhead structure is designed from wood (6x6 up rights) and 6x8 timber for overhead front-rear & side-side beams.

 

[jcbarry]

I would look at some boat lifts and see what materials they use for ibeams and cradles to give you an idea of what you would need. They are usually mounted on pilings, so that part would be different if your using steel uprights.

 

[ED26]

The cradle is already fabricated.

My design question is regarding the beams up in the air (side to side and front to rear).

The boathouse has a steel channel foundation that the uprights will be welded to (or simple connection..)

 

[kbs2244]

Your steel supplier will have an engineer on staff that can do the numbers and recommendations.

 

[Nor'Easter]

Your steel supplier will have an engineer on staff that can do the numbers and recommendations.

Highly unlikely. You're probably thinking of a co that manufactures whole buildings. The most math I've seen a structural steel supply house do is calculate the tax owed on a sale.

He needs an engineer that can stamp plans. I could do the calcs but you wouldn't find me sharing it online, that's a huge liability.

 

[tinmanwpk]

I agree that with what you are asking only a structural engineer can answer. Everything else is a guess.

 

[matt_i]

Something to consider but can the boathouse itself handle that kind of load...I see above there's a steel frame but is it ready to handle the additional load of picking up a craft...

Best imo would be to find a lift similar to the one pictured in the first image above, that's working for your size of craft. Crawl all over it taking pictures and measurements of everything until you have a complete detailed drawing (or enough info to create that).

I would approach this as a single 25k load in the center of your beam, there's roughly a safety factor of 4 built in there which is good. That's a conservative way to see if the split loads will be Ok out at the sides. You are going to need some hefty men and some cribbing to rig this all into assembly inside a structure. Due care to not burn it down while welding...

As always, attaching to the beams is critical, don't notch or drill the flanges...

 

[ED26]

sent you a message matt

 

[bpjr]

Dock builders may not be structural engineers but should know what is commonly used for applications like yours. They will also know what is required for permitting..stamped plans, sketches or special requirements. You need more than load calculations to make a proven design. My advice would be to talk to local dock companies before calling a 'structural' engineer or steel worker.
Some info:
Here in Florida 25k lifts are everywhere but they are typically on (6) 8" min dia pilings with an aluminum or galv load bearing beam sitting on top of the piling...with (2) 3/4hp or 1hp motors and (2) 2" galv pipe for the wire to wrap around. 2X safety factor on the structure is normal here, even where people leave their boats on the lift during hurricanes.

I have a 6k lift on (4) 8" pilings with (1) 3/4hp motor and (1) 2" dia galv pipe (mounted centerline overhead) and kept a 4k boat on it for 15 yrs on unsheltered open saltwater...direct pull without reductions and no problems. I overkilled the stainless wire size due to it work hardening over time. Lift has had boats hanging from it since 1992 and been though several hurricanes. Rebuilt hard parts 2 yrs ago but still running on the same motor and pilings.

Good luck with your project. If that is a pic of your boathouse it is waaaay cool.

 

[ED26]

Anyone know of a PE that could draw up a design/stamp if I give dimensions etc. ? I understand the liability involved but I am pretty sure marine contractors are not PE, I want to over-engineer this.