Bud
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- Izzy Rose
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- Grand Banks 49
Mast and Boom lifting capacity
- Thread starter Bud
- Start date
The friendliest place on the web for anyone who enjoys boating.
If you have answers, please help by responding to the unanswered posts.
If you have answers, please help by responding to the unanswered posts.
jungpeter
Guru
Hi Bud,
Calculating the loading in your rigging is not particularly difficult for a competent mechanical engineer or sailboat rigging specialist. However, once the loads are calculated, the real issue becomes the reaction of those loads to the boat itself. In particular, the compression load on your mast is substantial. How the boat is designed to absorb the reaction loads of your rig is something a marine structural surveyor might well investigate.
A good starting place for your investigation should be to locate a sailboat rigging specialist that you feel is experienced and competent to answer your basic question-what are the loads in the various components of your rigging? From there, depending on what weight you actually desire to lift with your mast and boom (presumably a dinghy of some sort), and your comfort zone regarding margins of safety, you might further pursue just how well your boat can absorb those loads. I.e., are the chainplates (and chainplate bolts) sound? Is the mast adequately supported at it's base? Are the shrouds still good (broken strands, cracked swadges, suspect rigging pins, etc.)? Is the running rigging intact and sound?
And beware-just because someone else that happens to have a GB49 that routinely lifts a XXX dinghy that weighs YYY pounds doesn't mean YOUR GB49 can safely do the same. Lifting loads to/from the water from a floating structure isn't for sissies, and should be considering the safety-threatening event it truly is. Yes, dinghies are routinely hoisted aboard all the time. And yes, rigging on boat hoists fail all the time.
I'm not suggesting you be paranoid about the subject, but please take care. Marine professionals are your friends here.
Regards,
Pete
Calculating the loading in your rigging is not particularly difficult for a competent mechanical engineer or sailboat rigging specialist. However, once the loads are calculated, the real issue becomes the reaction of those loads to the boat itself. In particular, the compression load on your mast is substantial. How the boat is designed to absorb the reaction loads of your rig is something a marine structural surveyor might well investigate.
A good starting place for your investigation should be to locate a sailboat rigging specialist that you feel is experienced and competent to answer your basic question-what are the loads in the various components of your rigging? From there, depending on what weight you actually desire to lift with your mast and boom (presumably a dinghy of some sort), and your comfort zone regarding margins of safety, you might further pursue just how well your boat can absorb those loads. I.e., are the chainplates (and chainplate bolts) sound? Is the mast adequately supported at it's base? Are the shrouds still good (broken strands, cracked swadges, suspect rigging pins, etc.)? Is the running rigging intact and sound?
And beware-just because someone else that happens to have a GB49 that routinely lifts a XXX dinghy that weighs YYY pounds doesn't mean YOUR GB49 can safely do the same. Lifting loads to/from the water from a floating structure isn't for sissies, and should be considering the safety-threatening event it truly is. Yes, dinghies are routinely hoisted aboard all the time. And yes, rigging on boat hoists fail all the time.
I'm not suggesting you be paranoid about the subject, but please take care. Marine professionals are your friends here.
Regards,
Pete
OP
OP
Bud
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Thanks for you thoughtfull reply. I owned and operated a commercial fishing vessel in the Gulf of Maine for 25 years so my knowlege is just based on experience not really technical. I did ask my brother who is a marine engineer and his first question was "what do other boats that are rigged the same way lifting safely"
I am looking to lift 420 lbs of dingy. The mast is supported adequately for compresion. the base is hinged and bolted and there is a bulkhead directly underneath it all the way to the hull. The rigging is all new and is all rated to >1200lbs working load. In addition to the wire stays are a set of aluminum pipe stays on opossing side. I am wondering about the side load the boom puts on the mast.
Thanks
Bud
I am looking to lift 420 lbs of dingy. The mast is supported adequately for compresion. the base is hinged and bolted and there is a bulkhead directly underneath it all the way to the hull. The rigging is all new and is all rated to >1200lbs working load. In addition to the wire stays are a set of aluminum pipe stays on opossing side. I am wondering about the side load the boom puts on the mast.
Thanks
Bud
Rain Dog
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- Rain Dog
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- Grand Banks 42 Classic
Oxford has done a lot of modifications to the BT masts to allow them to lift that much weight. You might give them a call to discuss:
An uplifting experience | Dickerson Service Log
An uplifting experience | Dickerson Service Log
To paraphrase what was stated in another thread: I charge $400 per hour for my time, but I am not a Mechanical engineer, I am only a lowly lawyer.
Your mast and boom are IMHO totally inadequate to lift a load of 420 lbs safely.
You need to go to a commercial marina where there are boats with masts designed for actual lifting and compare their scantlings to your own. Yours is designed to look nice. Mine was a lot like yours when I used it to lift a Sabot from right beside my boat, onto the boat deck. The base failed on that lift, of somewhat less than 50 lbs. I subsequently redesigned the mast and had it completely rebuilt.
The boom was too short, the mast was too short, the stays were in the way, the amount of mechanical advantage way too little.
My redesigned mast was to lift my Laser, 150 lb empty, but since it had a crushed bow, it was usually half full of water, so maybe 300 lb all in. When lifting that much weight, I found I needed a forward stay, so put a line on the bottom of the Radar platform to the handhold on the fwd flybridge seats opposite the side the lift was occupying.
During a lift of the Laser, empty, so only 150 lbs, the mast would bend, even with a stay fastened, so I would be reluctant to use mine for anything as heavy as you plan.
As long as I have been boating, I have yet to see anyone with a decorative mast and boom like yours, lift anything as heavy as my Laser, let alone a 420 lb dinghy.
Friends who have converted work boats have dinghies weighing 700 to 1000 lbs, for which the rigging includes 1/2" cable for each of boom up/down, load up/down, Port sway and Stb sway. Mast height and diameter are dramatically more than yours, as are boom length and diameter.
So rather than polling us here at TF, I would like to know that before you use your present lifting boom and mast for that weight, you would get a proper engineering opinion of its capacity.
Despite my first line, this is just my free opinion, please take it only for what it is costing you.
psneeld
Guru
I lift my 200 pound dingy and motor and contents regularly with my stock (teak) Albin mast.
Last summer I had it hanging during a torential downpour where I believe it accumulated enough watef to weigh 400 pounds easily. It had the boat healing about 5 degrees.
Not all trawler masts and booms are rated to lift much, But I will bet many can handle 400 pounds if not more. Now that may be above the "safe eorking load" but from a materials point of view, I think all if them exceed the 400 pound loading.
If you dont feel comfortable lifting an increasing amount of wright to see how the rig handles it....hiring an engjneer is expensive but one of the few choices you have.
Last summer I had it hanging during a torential downpour where I believe it accumulated enough watef to weigh 400 pounds easily. It had the boat healing about 5 degrees.
Not all trawler masts and booms are rated to lift much, But I will bet many can handle 400 pounds if not more. Now that may be above the "safe eorking load" but from a materials point of view, I think all if them exceed the 400 pound loading.
If you dont feel comfortable lifting an increasing amount of wright to see how the rig handles it....hiring an engjneer is expensive but one of the few choices you have.
Monk38
Member
I removed the pole davit from Monk 38 as the 15 horsepower Yamaha outboard on a 10 foot dingy was spooky when lifting onto the boat deck. Plans are to add an extended transom and carry the tender on the tail. Benefits are a huge deck area, weight moved lower and shifted aft, larger real estate on the swim platform and faster rescue boat launching.
Trawler Sandpiper
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Monk38
Member
Nicely done! May I ask how much the fabrication and install set you back?
healhustler
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I’ve seen few mast/boom setups that I would trust with more than 300 lb. I asked Krogen for the rated capacity of the setup on my Manatee and got 600 lb. in response. Well, OK, maybe brand new and in perfect condition, but I was there when a Krogen Rep. had the boom to mast hinge point come apart with no more than 200 lbs. on it.
Rigging needs to be up to the capacity as does mounting brackets, but if you’ve got old style rivited collars and hinge points, try not to forget that a failure could leave you with a huge lever out of control and a good bit of weght at the other end.
Rigging needs to be up to the capacity as does mounting brackets, but if you’ve got old style rivited collars and hinge points, try not to forget that a failure could leave you with a huge lever out of control and a good bit of weght at the other end.
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psneeld
Guru
That's why I progressively test any lifting setup I use...whether the tranny from the bilge, a freezer to the flybridge or the dingy where ever.
If the rig can lift it one inch, it doesn't matter one inch or 100 feet.
You just have to inspect and trust it not to fail during your lifts.
For many of our rigs, I would bet 300 is a safe bet....much more if you do the math and inspections.
Safety is great, and one should know how to stay out of harm's way when backyard engineering....and executing.
But one shouldn't be too fearful of simple things either.
If the rig can lift it one inch, it doesn't matter one inch or 100 feet.
You just have to inspect and trust it not to fail during your lifts.
For many of our rigs, I would bet 300 is a safe bet....much more if you do the math and inspections.
Safety is great, and one should know how to stay out of harm's way when backyard engineering....and executing.
But one shouldn't be too fearful of simple things either.
Last edited:
Trawler Sandpiper
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Hey Monk,
Fabrication was about $2000 (1999), did the install myself.
Fabrication was about $2000 (1999), did the install myself.
Wxx3
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Hey Bud,
If you lived in NY, you would be right at home. But I digress.
Your boom looks sort of like mine on my KK42. I've been told it's rated at 500 lbs, which I think is about right. The PO was lifting a dingy that all in probably weighed 450 lbs.
Now most of that weight is supported by the two forward stays. I have seen some KK42's with only one stay. I couldn't tell from your picture if you have one or two.
If you lived in NY, you would be right at home. But I digress.
Your boom looks sort of like mine on my KK42. I've been told it's rated at 500 lbs, which I think is about right. The PO was lifting a dingy that all in probably weighed 450 lbs.
Now most of that weight is supported by the two forward stays. I have seen some KK42's with only one stay. I couldn't tell from your picture if you have one or two.
jrhodes777
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Mast lifting capacity
I have a 1988 GB 46. Having looked into this in the past the GB published capacity is 300 pounds. However looking into it further the limiting link on my boat is the two forward shroud connections to the fly bridge rail. I am in the process of fabricating new shroud connections that will be tied onto the outside of the cabin. Overall I would suggest you look at your shroud line connections.
I have a 1988 GB 46. Having looked into this in the past the GB published capacity is 300 pounds. However looking into it further the limiting link on my boat is the two forward shroud connections to the fly bridge rail. I am in the process of fabricating new shroud connections that will be tied onto the outside of the cabin. Overall I would suggest you look at your shroud line connections.
