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Old 03-05-2016, 04:19 PM   #1
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GB 42 - Boom/mast lifting capacity

Looking for a new/used RIB for a GB42/1981 classic, which has the aluminum mast/boom combo. What is the lifting capacity of this combination? I intend to use part of the aft cabin for storage.
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Old 03-05-2016, 04:44 PM   #2
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Originally Posted by BinkleyBoat View Post
Looking for a new/used RIB for a GB42/1981 classic, which has the aluminum mast/boom combo. What is the lifting capacity of this combination? I intend to use the part of the aft cabin for storage.
Thanks
If you want to left anything substantial you need to be sure you have 4 stays.
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Old 03-07-2016, 10:24 PM   #3
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similar questions have been posted on the GB Owners forum. Apparently, the company has not offered a rating for the mast and boom, nor has GB endorsed using the combo as a davit. It is generally thought that 300 lbs is the max; even so, we increased the size of the shrouds on our 91 and installed back-plates on the forward fittings. Our 9' Livingston with a 6 hp 4 stroke weighs about 220 lbs and the rig seems to handle it with no strain.
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Old 03-07-2016, 11:30 PM   #4
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I'll second the 300 pound weight limit. Most dink/outboard combos weight in at 250 pounds or less. You should be good to go. Search the archives and ask your question on Grand Banks Owner's Resources
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Old 03-07-2016, 11:37 PM   #5
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I'll second the 300 pound weight limit. Most dink/outboard combos weight in at 250 pounds or less. You should be good to go. Search the archives and ask your question on Grand Banks Owner's Resources
But Ray, you have an additional/expensive crane to launch/recover your dinghy.



The original is as useful as an appendix (as in one's gut)? Why not use it to fly a steadying sail?

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Old 03-07-2016, 11:52 PM   #6
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Yes, I have a Roskelley Olsson davit on the GB42. It's rated for 600 pounds, I think.

The mast and boom is set up for a steady sail but the five previous owners did not think it was necessary. If I had one, I'd probably hoist it once to take photos and stow it!
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Old 03-07-2016, 11:56 PM   #7
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Regardless, the steadying sail would look lovely.
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Old 03-08-2016, 07:40 AM   #8
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Originally Posted by BinkleyBoat View Post
Looking for a new/used RIB for a GB42/1981 classic, which has the aluminum mast/boom combo. What is the lifting capacity of this combination? I intend to use part of the aft cabin for storage.
Thanks
Hi Bob,
About your question for the weight limit on the mast and boom to lifting a RIB tender :

In 1986 I visited the Grand Banks shipyard (American Marine LTD) in Singapore. On this occasion, I asked many questions to the technicians of the shipyard, one of my questions was the weight limit of the lift capacity with mast/boom.

The answer I got was very clear : the woody 42' GB have mast and boom made with wood, the weight limit of the lift capacity with wood mast/boom was 200 kg maximum (440 pounds). The fiberglass 42' GB have mast and boom made with ALUMINUM, the weight limit of the lift capacity with wood mast/boom was 150 kg MAXIMUM (330 pounds).

With both wood and aluminum mast/boom they told me it is very important to check the wire tension of the shrouds of the mast before operating a lift.

Fair winds,

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Old 03-08-2016, 07:50 AM   #9
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I would bet that GB as well as any other "trawler with mast" companies suggest if at all very low lifting capacities, not because of the mast and boom but the hardware used.

My mast and boom could easily lift 500 pounds or more with a huge safety factor but looking at the cast bronze fitting used (unrated/untested I am sure) I can guess why the load capacity is downrated to a minimum.

The other factor would be knowing the captain and crew would most likely be untrained in rigging and lifting so a super conservative number was chosen.


So for the OP...I might suggest that if you want to know or improve the capacity of your rig...you may be able to with or without professional assistance...sounds like the rated capacity might be a low based on all I have heard and read when this topic has come up before. Last thread someone did the math for what his actual mast and boom could lift based on wood strength and it was easily over a 1000 pounds if I remember correctly.
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Old 03-08-2016, 09:48 PM   #10
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For maximum lifting weights, I wouldn't trust numbers given to you from someone who has a similar boat, as the chances of them having the identical mast and boom are slim. What you need to ask for, is lifting capacity for an aluminum mast, of whatever schedule yours is, of whatever length yours is, including the same particulars for your boom, held by whatever standing rigging yours has, including the positioning of the stays and their diameter and material. The length of the boom is critical in determining what loading is being transferred to the mast and stays.

Then there is the mast step. What material, how is the mast fastened into it, etcetera.

You might try lifting something that weighs whatever your projected maximum might be, with the weights of dinghy, OB, fuel, anchor, lines, PFDs, flares, wetness etc all counted. Try this slowly, noting whether your pieces are showing any signs of strain. If it all works, you are good to go and put it to a real test with a real dinghy.

From personal experience: When I got my boat, it came with a mast and boom. The mast looked good, it was aluminum, stepped in an aluminum tabernacle on the upper deck, with stays, and with an aluminum boom.
I had a Sabot, 8' sailing dinghy. The class rules require a minimum weight of 52 pounds, fully rigged. Mine weighed in within ounces of that minimum ( I rarely lost a race in it), so stripping off all the removable stuff it shouldn't weigh more than 35 pounds. That turned out to be too much for the tabernacle, (the weak link in the system) as it collapsed, as soon as I lifted the bare hull of the Sabot clear of the water.
The tabernacle was immediately replaced. The mast and boom within a few years, extending the boom so that it could reach outboard far enough to lift from the centre of the design load, a Laser sailboat weighing over 150 lb. I also designed the supports so that no stays are needed, as their positioning effectively barred entry to the Flybridge, as I assume yours will do too.
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Old 03-09-2016, 05:39 AM   #11
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Quote:
Originally Posted by koliver View Post
For maximum lifting weights, I wouldn't trust numbers given to you from someone who has a similar boat, as the chances of them having the identical mast and boom are slim. What you need to ask for, is lifting capacity for an aluminum mast, of whatever schedule yours is, of whatever length yours is, including the same particulars for your boom, held by whatever standing rigging yours has, including the positioning of the stays and their diameter and material. The length of the boom is critical in determining what loading is being transferred to the mast and stays.

Then there is the mast step. What material, how is the mast fastened into it, etcetera.

You might try lifting something that weighs whatever your projected maximum might be, with the weights of dinghy, OB, fuel, anchor, lines, PFDs, flares, wetness etc all counted. Try this slowly, noting whether your pieces are showing any signs of strain. If it all works, you are good to go and put it to a real test with a real dinghy.

From personal experience: When I got my boat, it came with a mast and boom. The mast looked good, it was aluminum, stepped in an aluminum tabernacle on the upper deck, with stays, and with an aluminum boom.
I had a Sabot, 8' sailing dinghy. The class rules require a minimum weight of 52 pounds, fully rigged. Mine weighed in within ounces of that minimum ( I rarely lost a race in it), so stripping off all the removable stuff it shouldn't weigh more than 35 pounds. That turned out to be too much for the tabernacle, (the weak link in the system) as it collapsed, as soon as I lifted the bare hull of the Sabot clear of the water.
The tabernacle was immediately replaced. The mast and boom within a few years, extending the boom so that it could reach outboard far enough to lift from the centre of the design load, a Laser sailboat weighing over 150 lb. I also designed the supports so that no stays are needed, as their positioning effectively barred entry to the Flybridge, as I assume yours will do too.
This complicated demonstration ignored the core problem what is to operate from a place which base is a moving and unstable element : Water.

From my humble experience at the anchor - that is where we mostly use a tender - with the waves and wind acting, the constant and irregular movements of a boat, such as swinging, result in higher additional constraints on the lifting equipment / hardware while operating a lift. The "If it all works, you are good to go and put it to a real test...." seems simple enough in theory, but practice is an altogether different story when the boat and the tender are swinging.

I would closely follow-up the recommendations from the shipyard what is easy to contact through email for a confirmation by indicating the hull # .
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