Scott Yellig wrote:

Any thoughts or experience using LN-2000 for screw-and-glue joints below the waterline?

Scott.

He also said he has built a dinghy from what we in New Zealand would call a waterproof PVA glue, and apparently with good results. We discussed our Gorilla Glue and decided that would be very good for a large number of boat building applications but maybe not for the exterior. We also talked about the older Resourcinal glues which were a powder mixed with a liquid and were usually quite red in colour. There have been a lot of boats built with these glues and which after 50 years or more are still sound.

So there are alternatives to Epoxy. Of course the thing of I love the most about Epoxy is it's gap filling characteristics.

Scott Yellig wrote:

Any thoughts or experience using LN-2000 for screw-and-glue joints below the waterline?

Scott.

We have an adhesive here in New Zealand called Gorilla Glue, which I imagine is available in other countries. I know that is used a lot in boatbuilding and seems to have properties which allows it to expand into the wood fibers for an effective bond. It also involves no mixing of different parts the way epoxy does. However I do not know if anyone has used it in hull construction such as gluing on the exterior hull planking. 

David Tyler wrote:

Nicholas Head wrote:
Is it possible to weld stainless to mild steel and achieve a decent result?

It's commonly done on steel boats, to add components subject to wear - fairleads, rubbing strips etc. I suggest it here if the inside of the tube is inaccessible for painting, but if the tube is short enough that you can paint, use mild steel. There are some technicalities to take care of, the main ones being to use 316 tube, with 309 filler rod, and to overlap the repaint of the mild steel an inch over the stainless steel. But your welder should know this if he works on boats.

Nicholas Head wrote:I see. Yes, thank you Darren and David for those ideas. Obvious now you say it but not to a numpty like me. I will use those hints for sure. I can see the attraction of a welded pipe drain solution. Something like this below?  And then just need to find a competant welder in Cardiff somewhere in the Bristol channel to attach them. I am so glad I asked for help on this. I have learned a lot and can proceed with some confidence of a good result. Thank you again.

I think your boat is on the hard?  If so, I'd ask around the yard if there is a welder around or works near.  Having him take a quick look at it is a good first step, like David said he may have some suitable material on hand.

If you need to buy material, then it is again worth poking around the boatyard to see what can be found, many have a bin of metal somewhere.  A piece of 3" dia 316 stainless pipe could work.  If you can't find it in the yard, then a scrap yard is a good place to look.  No idea if you can do this where you are, but here there are still some yards that sell the better bits they have on hand.  Around here stainless is about $2 per pound bought this way.   If you go, bring one of those strong rare earth magnets you got for grabbing the swarf while drilling.  A very strong magnet won't stick to piece of 316 stainless (except very weakly on an end where it has been sheared or cold worked) which is the best marine grade. If the magnet sticks weakly all over the piece, this is grade 304 and not as corrosion resistant as 316.  If the magnet sticks with any tenacity at all, you are going to have to epoxy/paint the material to keep it from rusting.

From the hull pics, it looks like you already have some experience dealing with rusty steel bits :-)  if your pipe is short enough that you can get into it to clean it from either end, then you could use mild steel (cheap and common) and protect it the same way you do the rest of the hull.

Buying directly from a bulk metal supplier yourself isn't really practical for a small project like this.  You usually have to buy full lengths (20') which often isn't economical.  Again, going through the welder here might be more practical.

I'd say to first find your welder/fabricator. You only need a couple of short ends, which he may have in his scrap bin, or know where to find them.

Subject to better advice from the welders among us, I'd use stainless steel for this, as it would be difficult to paint mild steel well, inside the tube, and galvanising has to be stripped back clear of the weld area. Then you'd just have to touch up the paint in the immediate vicinity.