Boom lift capacity

[danboy]

DIYers are often creative and are many times trying to do projects the least expensive route.

Depending on exactly where the genset is located, even a forklift/crane may not be able to lift and get it out of the cabin without other equipment, manpower or PFM, even then the boat doesn't necessarily need to be on the hard. It depends on many variables.

As far as the mast reaching the doors, once I got my genset to the door, it went on a modified dolly to roll to the stern. The reverse for the rebuilt one coming aboard

From there the boom was used to get it off the boat.

I forgot, I also got my old refrigerator off and new one on the boat while on the hard all by myself. Not as heavy as a genset, but a lot harder to handle.

So the real question is how heavy are the gensets the OP is dealing with, how big are they to get around side decks, and is he sure he can get them from/to the bilge into a doorway without a reach-in piece of equipment.

A bit of thinking outside the box goes a long way, which the OP sounds like he just did in post #29.

Good luck Danboy, it CAN be done!

Thank you for your comments!
We removed a deep freeze from the bridge with the boom, which was easily under 100lbs.

The genset is basically a 2' cube (Onan 5 kw- 350lbs with sound cover-2000 model with 100 hours). There is no easier removal than the boat it is in, and a yard in Seattle wanted $ 4,500 USD which for this Canuk is crazy. The next step was can we do it ourselves? Canal Marine can lift it off the boat against their seawall with their boom truck. Disconnection should take no more than 2-3 hours. Lifting it over the transom due to the roof over the cockpit similar to HeadedToTexas's boat pictured above, became the hurdle.

The removal of the old one from our boat- much bigger and heavier, requiring it to be broken down into pieces. Thus the feasibility of other ways of removal and reinstalling started to kick in.

I am not very uncomfortable with the removal from someone's else's boat and would love a much lower cost, but Seattle is pricey. With exchange rates, duty etc, it is challenging to be cost-efficient.

And i have been unable to locate one north of the 49th on the west coast.

The part i don't like, it takes a lot of time and brain power, and i don't have enough to spare! Far too much energy into this project.

Thanks again for your thoughts.
A very Happy New year to all!
Dan

 

[Bob Jack]

Hi "Headed To Texas" I have a Highfield DX 340 FCT with a Honda 25 hp 4 stroke that I lift with a Nick Jackson Davit Crain with a 500 lb rating. I have done this for one year . My dealer said it would be fine to do this.

 

[HeadedToTexas]

I bet the DX 340 FCT with that Honda is pushing 500 pounds. My dinghy is a CL 310, a pull start, tiller steer, manual tilt Yamaha 15 and a 3 gallon tank. It comes in at 300 pounds. I'd love to add an FCT or just upgrade to the current CL 310 FCT, but in an effort to save weight and cost, plan to mount a pair of swivel fishing seats on aluminum boxes and stay with the manual outboard. That will keep me under 350 pounds and I am okay with that on my current aluminum armed Dinghy Butler.

 

[douggairns]

My aluminum tube Dinghy Butler is rated at 300 pounds, but the newest stainless tube version is rated at 700 pounds. Both designs have 2" tubes, both use the same hinge plates, both use the same winch and deadman attachment, and both use the same chains to hang the dinghy. If the new stainless Butler is rated for 700 pounds, it must be the aluminum material that limits the weight rating. Does that make sense?

View attachment 160836

My Highfield CL310 and all manual Yamaha 15 add up to about 300 pounds, but I sure would love to add an FCT helm or upgrade to a new 310FCT. Both would push the weight of the dinghy up to about 380 pounds.

Stainless is a lot stronger than Aluminium. You could just buy some Stainless the same size as your alum ones, and just swap them out yourself. Just get the thicker wall SS tube. I believe they call it "schedule" If you need to drill holes in ss, go slow with lots of coolant, or you'll burn out the bit.

 

[HeadedToTexas]

It's a lot more involved than just straight sections of tubing. The elegant Dinghy Butler arm assembly is a roughly H shaped structure made of bent and welded sections of tubing. I have seriously considered talking with the manufacturer about shipping my aluminum arm assembly back to him and having it remade in stainless. That would let me comfortably upgrade to a new 310 FCT.

 

[douggairns]

My aluminum tube Dinghy Butler is rated at 300 pounds, but the newest stainless tube version is rated at 700 pounds. Both designs have 2" tubes, both use the same hinge plates, both use the same winch and deadman attachment, and both use the same chains to hang the dinghy. If the new stainless Butler is rated for 700 pounds, it must be the aluminum material that limits the weight rating. Does that make sense?

View attachment 160836

My Highfield CL310 and all manual Yamaha 15 add up to about 300 pounds, but I sure would love to add an FCT helm or upgrade to a new 310FCT. Both would push the weight of the dinghy up to about 380 pounds.

Oh! Wait, Let me look and see what it looks like. It might not just be a straight piece, I'm gonna check.

 

[douggairns]

Oh! Wait, Let me look and see what it looks like. It might not just be a straight piece, I'm gonna check.

Not quite what i thought it was, but if you took the aluminum one off, and took it to a good SS shop, they could make a copy of it for you in SS.

 

[douggairns]

I was thinking you could use all the mounts from the old one, and use the same hinge brackets on the ss tubing. Undo the 2 pivot bolts and take it to the shop. No shipping charges and it would fit perfectly.

 

[HeadedToTexas]

I will more than likely be looking into that in the coming months.

 

[ronobrien]

Has anyone tested their booms for load capabilities? My boat is a 1982 42' Californian LRC. Im looking at about 400 lbs max. Thought before i do any type of testing, I would check with the more experienced to see if it has already been done. The photos below show the setup i have. The plate is where im thinking of mounting a winch, The stay is not far back from the mast (6") about 2' apart on each side of the mast mounted to the bridge deck as well as the main mast bracket. I would have to change the block and tackle setup with more sleeves and thicker rope.
Thanks for any insights, ideas, and knowledge sharing!

When considering the capacity of the various components, don't forget that there is "righting moment" or leverage associated with the various points at which load is applied.

 

[Bmarler]

I will more than likely be looking into that in the coming months.

Have you posted any pics of your davit? Just wondering if it can be modified instead of replaced.

 

[Nick F]

2. Establish your normal working load and try and lift a certain percentage over that weight by lifting something of known wight. I think there are standards on what percentage weight you should use, probably based on what you are lifting.

I would go with 100% overload for a test - 800lb - this is a "dynamic lift" since the boat will be afloat it could rock while the load is hanging. Do the test at maximum boom reach (boom horizontal) and different boom azimuths (port side straight aft, stbd side). Hold the load for a few seconds and afterwards check for deformation of any part of the rig.

To give you a sense of safety factors, rigging fittings in this load range are normally rated for 5 times to failure (a 100lb shackle should survive 500lb before it fails).

Better to be conservative than drop a generator through your cabin roof (or, worse, injure someone).

 

[HeadedToTexas]

Have you posted any pics of your davit? Just wondering if it can be modified instead of replaced.

Just the one in post 24.

 

[Bmarler]

Just the one in post 24.

I see. Must be two single tube uprights with cross tubes. Like an H frame or similar. It’s likely the weak point is where the tubes are bent near the top. Heavy loads will bend or break it at that radius area.If there’s room to add another tube either on the inside or outside of the radius area (like a truss) it would hold much more weight. From the pictures though, it doesn’t look like there’s room. Nice davit though.

 

[HeadedToTexas]

Reinforcing the bend with a section of tubing that spans the bend would help, but that would completely change the geometry of the boat when stowed. Interesting idea though.

 

[Binford]

D,
Post up the following:
Boom length to mast C/L.
Height to stay connects on mast from deck
Distance from mast C/L to padeye on deck (I think you said 6 inches.)

I'll try to grind out a simple load analysis for ya. Hope padeyes are through bolted.

(Retired mech E, designed a few cranes)

Hey, GF! The OP didn't appear take you up on that load analysis, but I've got measurements for my mast/boom configuration that I'd love to have you grind out! I've got a 34 CHB Europa that I keep the dinghy up top of. Dinghy weighs 90# and the 5hp Mercury is 45# dry. I launch just the dinghy (with the outboard separately) and that <100# load results in the load-side stays going a bit slack, so I'm nervous about launching the whole ~150# package together as I'd really like to. So I'd love to know what my rigging should be capable of handling.

Mast is 3" diameter aluminum tubing of unknown schedule. Boom is 2" diameter aluminum to which I had a stiffener welded to the top of.

The boom is mounted/hinged to the mast 42" above the upper deck. C/L of mast to pulley at the end of the boom is 11'6".

There are 4 stays that connect to the mast 11'0" above the deck. The lower ends are connected to through-bolted padeyes located 5'6" outboard of the mast C/L. The distance between the forward and aft padeyes is 36".

The boom is centered over the dinghy at about 15° portside of straight aft. The boom must then swing farther off the portside to about 75°, roughly in line with the forward starboard stay, and boom is then lowered to horizontal and the dinghy lowered to the water.

Note also that, by design, the mast leans aft by maybe 10° or so. Purely for aesthetics, but there you have it.

Of course assuming my padeyes are solid and properly installed and the cable stays are adequate to the task and all that, are you able to estimate what the safe load capacity would work out to be?

 

[SteveK]

@Binford
If you cannot load it up 150 lbs, then even 90lb is too much.
I had same weight dingy and motor with not a concern on grand banks. The block connection top of mast and end of boom are the weak links. The rest will handle more than 150.
JMO

 

[danboy]

D,
Post up the following:
Boom length to mast C/L.
Height to stay connects on mast from deck
Distance from mast C/L to padeye on deck (I think you said 6 inches.)

I'll try to grind out a simple load analysis for ya. Hope padeyes are through bolted.

(Retired mech E, designed a few cranes)

Hi GF: I'm so sorry, i just came across this post now. I don't know how I missed it. Thank you for your generous offer. If it's still on the table I will get the measurements and send along. Cheers, Dan

 

[Binford]

@Binford
If you cannot load it up 150 lbs, then even 90lb is too much.
I had same weight dingy and motor with not a concern on grand banks. The block connection top of mast and end of boom are the weak links. The rest will handle more than 150.
JMO

It handles the 90lb okay, but it would save me a bunch of time if I could keep the outboard on the RIB and hoist them up and down together. Maybe I just need to tighten the turnbuckles on the starboard side better.

It's an aftermarket mast and boom which replaced the original wooden one these CHBs came with. I'm probably just being dramatically overcautious; I just don't know what a safe maximum load might be for these things.

The block connections should be fine. Being unfamiliar with those things, they looked to me to be pretty light duty, so I researched them and forget what the numbers were, but they were surprisingly rated to handle way more than I'd ever be lifting.