More metals compatibility

[jwilson]

I was talking to the local wholesale supplier of aluminium extrusions about buying some to make up a framework to take an all-over winter cover for when we haul out at the end of next month. I'm trying to design something dis-assemblable and re-usable each year, that will give me room to work under it and allow a bit of airflow, whilst keeping all the leaves, bird *#@* etc off the deck and cockpit. (It'lll be under trees).

He said to NOT to use stainless bolts to join sections, that it would cause bad corrosion. I know that S/S and alloy are dissimilar, and to isolate with Duralac or similar if riveting fittings on to masts, etc., but I was very surprised by his suggestion to use brass. He said this was the best choice. I always though brass/alloy was an absolute no-no.

Anyone really know - I'm no chemist? This is clearly a non-critical application, but I may as well do it right if I can at sensible cost.

 

[Evadne]

I think it sounds a bit odd as well. Aluminium reacts with nearly everything, I find. I find the article on the Classic Marine website very useful and understandable ( here . Looking at the table you'll see the closest to aly is mild steel or galvanised steel. IIRC the latter is what scaffold clamps are made of, and you used to be able to get aluminium scaffold poles. Have you considered using conventional scaffolding?

 

[2Tizwoz]

Perhaps a polytunnel would do your job?
Northern Polytunnels
Secondary use through the summer.

 

[smeaks]

to keep it light weight and avoid all issues re metals action why not use plastic/nylon nuts and bolts. I use them in an industrial application that incorporates a shot peening process and they prove very resilliant!

 

[rogerthebodger]

Brass and aluminium is worse than S/S use ali or nylon bolts.

I made up a sun cover (it gets very very hot in summer 30 C + with very high UV in JHB) out of 50mm plastic waste pipe. Pipe can be bent with hot air gun and glued or bolted using standard elbows, tees on connectors.

 

[jwilson]

Thanks to those confirming what I thought - that brass was wrong. I'll probably use galvanised or plated steel, if I can't find nylon bolts.. I think I'll have to use metal tubing as the whole assembly is going to bre fairly big: all the plastic pipes I've looked at are pretty flexible.

 

[Superflid]

Aluminium greenhouses use aluminium bolts, can pick them up in Focus/B&Q etc. Might be too small, but worth a look.

 

[roger]

Alternative suggestion

In Scandinavia the winters are long and hard. I've seen many systems in use. One good one is just to make up a plank frame house shaped with a door and clad the whole thing in tarpaulin suitable nailed down with battens. You could make it demountable in sections so at least it could be stored as a stack.
There are a number of Swedish web sites advertising components to make the job easier.
www.noa.se supply aly tubes and fittings.
www.press-son.se supply frames; some sit on the deck, others go down to the ground.
There's a third one (can't find it) who supplies odd shaped joints which fit standard timber sections that make building a house shaped frame very easy.
My information comes from the Swedish Cruising clubs magazine Pa Kryss though I doubt if you will want to get it.

 

[halcyon]

We allways used the mast, when stored it was removed and sat on a frame at bow and stern. This gave a ridge to put a cover over, and allowed for mast / rigging inspection each year.
You can set the height to suit you, a couple of local props will allow working on deck while under cover. When ready to launch, fold up cover and put up mast.

Brian

 

[VicS]

Like wise I always use the mast to support a plastic cover. A friend uses lengths of galvanized pipe screwed together supported on various wooden frames for canvas tarpaulins.

However if you really want something fancy Compass Watersports do a frame in aluminium in several sizes from £350 for 8m boats to £450 for 11m boats

 

[rogerthebodger]

PBO's Sketch book No.4 shows a simular idea on the "Lay-up Tips" page.

I had a flat awning with plastic pipes going over the boom as others said. I found these sagged in our heat so in put some ali tube inside to support the span.

Problem solved.

Zinc plated bolts will rust quickly in the sea air.

 

[James_Calvert]

I made up a winter cover framework with plastic household sink wastepipe tubing, and stiffened the ridgepole sections by stuffing them inside with bamboo (pea sticks) from our garden centre. Worked a treat, provided the ridgepole sections were glued together. Each year I'd have to cut off the joints to dismantle it all, but I'd made it well overlength so no problem to reassemble with new joints the following winter.