Thinking of making some davits, I like this design by batsystem as I need to lift a dinghy up an over a folded wind vane (dinghy on deck when vane is in use and visa versa). I am contemplating integrating some attachment points for a drogue into the mounting brackets. See links
www.boatsystemgroup.com/en/equipment-to-boat/davits-cranes/davit-kit-for-straight-stern-100kg-arm
www.boatsystemgroup.com/en/catalog/product/view/id/4785/s/fitting-rounded-stern-120x200-mm/category/387/
32mm x 1.6mm 316SS Tube and bends are readily available and really pretty cheap
tubebendonline.com/collections/stainless-steel-316/products/32mm-180-degree-mandrel-stainless-steel-bend-316
Questions are
how difficult is stainless welding, do you need a tig or can satisfactory result be achieved with an arc welder
Would the materials I am looking at suffice, ie is a 1.6mm wall thickness sufficient, just thinking atm but interested to hear pros and cons from the brains trust
1.6mm wall is Schedule 5s 316 tube and the most commonly stocked (unless for very high pressure duties) and the thinnest. Schedule 80 is the usual highest wall thickness used at 4.85mm - there are higher wall thicknesses globally available. The Schedule / wall thickness needed depends on your davit structural design geometry including welded joint design (fillet or full pen), end bolted pivots etc including stress concentrations at holes and bolt grades, and the static strength working load limit you want out of it. Both of these are governed by what you are lifting and the reach out needed. If you are going to use it at the WLL more than 1,000 times then design for fatigue comes into it. Need to consider the centre of gravity of the load if it is offset to one davit - eg due to outboard on transom.
I bought one of these stick welders to weld 316 ss tube to 316 ss 3mm thick flatbar to make 6 normal stanchions and 2 transom stanchions which will need fore and aft and lateral 1/2 height bracing - 25ft yacht. Last welded 50yrs ago mild steel and did that ok - maybe well. ss welding these now is a complete nightmare. Can do a tack weld but not a good perimeter 2-3mm fillet weld without a heap of angle grinding and re-welding repeated 20x per stanchion joint. Nothing wrong with the welder or the stick electrodes I got from Bunnings. Have a $650 quote from a young bloke professional welder and will go with him - TIG must be the process used as regards strength and quality achieved.
www.bunnings.com.au/full-boar-arc-140-inverter-welder_p0253797?store=7334&gclid=EAIaIQobChMIpqnD3aaLgAMVOQx7Bx3UCAUIEAQYAiABEgJeX_D_BwE&gclsrc=aw.ds
The installation documents on that site don't indicated the bolt strength grade to be used. Normal 316 strength grade bolts are inferred - so around 4.6 grade strength. 316 grade 8.8 high strength grade Bumax A4-70 or 80 are available - Anzor will have them.
I've been getting reasonable results welding 3-10mm 304 & 316 to its self to each other and to mild steel using weld all rods with an old transformer welder. It can be done. I'm sure a pro will drop in soon
, I weld a lot of stainless and Aluminium , stainless mig , gas or gasless, is quite easy to weld , have to do test welds first , to setup machine,
gasless stainless wire works well, , if you have gas [Argon} then Tig is the way to go, I find this to be the easiest with best results and is good for thin metal, you can pickup a DC tig cheap these days
Have started making a dinghy crane SWL about 50kg with 2m span for small inflatable
Want it to be demountable
no welding involved using 11/2 in SS tube using Bimini fittings and a cheap pipe bender from trade tools
just waiting on a few parts and will post pic when done
L
I do a fair bit of welding with mig and arc. The mig is good for aluminium and thin mild steel but I prefer to weld stainless with arc. 316 and 304 1.5mm is not a problem but you have to use quality electrodes. I use 2.5 rods and don't do continuous runs on this SS. Find the brand you like and stick to it. I like the Gemini stuff in 2.5mm, it's expensive but worth it.
www.ebay.com.au/itm/233463921765?_trkparms=amclksrc%3DITM%26aid%3D1110006%26algo%3DHOMESPLICE.SIM%26ao%3D1%26asc%3D20201210111314%26meid%3D8d25f24c40974b13a17d23cd31c26af9%26pid%3D101195%26rk%3D2%26rkt%3D12%26sd%3D122130517679%26itm%3D233463921765%26pmt%3D1%26noa%3D0%26pg%3D4429486%26algv%3DSimplAMLv11WebTrimmedV3MskuWithLambda85KnnRecallV1V4ItemNrtInQueryAndCassiniVisualRankerAndBertRecall%26brand%3DGemini&_trksid=p4429486.c101195.m1851&amdata=cksum%3A2334639217658d25f24c40974b13a17d23cd31c26af9%7Cenc%3AAQAIAAABYNaJCFP3eaFlNU%252FMPxRY0TCMczVKEUB5MsBytoCwPnd71M08lfrVO4PuTCchnU42KC4W4fZqxBROE%252BM7tSL%252BgZgL1kWiIUBRsEpydVTA61DhOJDUizwNgM7HKYQEqSaBlM9PvOYoOgcM1%252BzxL2OeicTJ6FyJFDz9L2elq5CnJTFTZfTdsEtxKOuxSFHuJJxHYoKr%252BRmE09ADO98YfKN2FFU4MyIz0tkGDLmJ1zBQcVR7pXeFT5uLvso8WxDgm5aSl9ys7WSoib2PfFV7ycoDSmHCRILJrTXH8b%252FjwjlyD1vdZPcN7h9uYrbLqUaA%252BFmdzYMjU1YMGwr1G7eHWX403Hrok18Z6O1u6HyfFw1%252F3nGg23MqLneJxH0%252FhvwHfR5dWBMOuIPzsBUWQ03nC2dPWIsp2yXri8vfln%252BH9ESQeZgrZsUNXFi%252Bktn1BZzAUlwsmzislo3BxbYn6hUkY6NQlyA%253D%7Campid%3APL_CLK%7Cclp%3A4429486&epid=1038349000
Thank you all for the replies, keen to see pics of the crane
I was thinking of a stick welder as well as I have used them a bit in the past, don't mind paying for expensive rods. The Davits I like are about 5K so even buying a new machine and selling s/h when I am done will be huge savings.
Got a friend who is buying a TIG to do the same (that's what got me thinking) I will have a sticky beak when he starts.
