Welding - internal aft access?

Hi,
This is my first post so please be easy on me.

I have just purchased a sail boat - a 41' Van De Stadt with pockets of rust.

The following photos show an area of concern.
Q. How would I gain access to this aft corner where there's extensive rust for fire spotting internally ?

I've included images of the rudder shaft as I was thinking I'd probably access here but it looks that this area under the steering will not provide enough access to the rear stbd corner.

 

You'll probably get some helpful answer here on this forum but i'd also not hesitate to contact vd Stadt with your question. They sell plans to homebuilders and are know for their support.

https://www.stadtdesign.com/pages/van_de_stadt_design

 

This kind of job requires removing a lot of equipment. Also, do as much welding from outside as possible. The paint will burn, so there will have to be a fireman on watch when the welder is working.

 

Firewatch is the least of your concerns, that can be done with a wet rag on a stick. The real problem is getting in there with grinder and brush to properly prep and paint after welding. Your only real option is to cut a big hole in the deck or transom in an area that is more accessible from the inside.

Looking at the pictures I would say that anything that is under the trim is suspect, remove all exterior wood and repair as needed. After repairs, replace wood with stainless steel.

Is the boat insulated, and if yes how?

You got a big refit coming your way, I hope the boat was really cheap.

 

Banksy can you post some more photos showing what the rest of the boat looks like please?
The transom corner shown in your first photo looks rather ominous - however what we can see of the bilge in the last 2 photos does not look too bad really.
What are the rest of the bilges like?
Did you have a survey carried out on the boat before you purchased her, or perhaps do some ultrasound hull thickness testing in any suspect areas?
If so, what were the results?
Do you know what the original hull plate thickness is?
If you did not have a survey done, then as Rumars says, I hope that the boat was very cheap.
Even if it was very cheap, you should now do a thorough assessment of all the work that needs doing before you start throwing money at the re-fit.

 

The ultrasound results only showed below the water line. 3.9- 4mm
No survey - I already know there's a load of rust to take care of. It's mainly in the bow.
Picked her up for $20K (AU) It's this area around the transom that worries me in terms of gaining internal access.

 

If you have to remove the paint from the inside of the hull an option is to use a dry ice blast. Basically a machine grinds up frozen C02 and air blasts it. The advantage is that there is no abrasive to deal with, ie sand, walnut shells etc.
The only thing that you have left is the rust and paint. It can be used outside as well and in some marinas where they do not allow sandblasting, they often allow the dry ice method
There is a company called Cold Jet in Sydney, and probably others, mobile unit.

 

Wow, dry ice blasting is a very intersting method of removing paint. I'll contact them for a quote.

 

I'm thinking at this stage of cutting out the area around the rust with an angle grinder & then reach inside to remove excess paint and place a wet cloth internally at the same time. Cover the hole & weld her up.
The issue still arises in terms of priming the internal area after welding.
Perhaps once I cut out the rust affected area I could then look inside to establish an access area I could also cut out but that area would also require access internally once I weld it closed.
note: I might have to cut several access points initially coming in through the cockpit seating area or the transom step & then backing out with internal welds as I seal each area up. Sure is a massive work around but might be the most economical for me.
Tools I have available include

• MIG / TIG welder
• Plasma Cutter
• Mag Drill
• portable metal bandsaw ( not much use here)
• Sand blaster.
• Grinding wheels + Tercoo wheels.
• Needle gun + compressor.
• Paint Spray gun

 

Remove the hydraulic powered monstrosity from the stern, recycle the steel and wood. Remove pulpit and rework into something useful for sailing. Remove rudder, sandblast, etc. Cut out the entire transom step. Now you have access to repair the corners and close the slots in the bottom. Consult original plans (may have to buy them from van de Stadt) to see how the transom and cockpit end was designed and restore (that big cutout does not make much sense in the absence of a gate, and this is not a racer to need fast cockpit draining).
I know it's a lot of work, but it's faster then cutting small holes and fiddling around. You have a lot of work in that area, just cut the big hole.
The big concern is what is under the teak deck and the toerails, those need to come off and the entire deck sandblasted.

Ice blasting is very useful for paint removal, but it does not prep the steel for paint like sandblasting does, you still have to grind.

 

Hi Rumars - You mention "cutting out the entire Transom step " note: I've attached an image where I have marked the area in red I feel you might be referring too ..yes ? If I do cut out the step... I'd have to weld it back in again and then I might not have access interanlly to weld the step area. Note: not sure why I'd have to remove the rudder as it's much further fwd. But having said this it def. does need some grinding and repainting. That hydraulic davit sure does look like a beast.. might consider ditching it.

 

Would it be plausible to cut out this area (as per image below ) The red denotes a square access cover I could make & the pink denotes bolt holes. Only issue I see here is with the stern tie - might loose some strength. This area is slightly raised 2" looks like a square step with the tie located center of it.
note: In one image you can see a spot of rust at the base of the tie step. SO might be best I cut it out

 

Yeah I plan to remove the teak decking as well. The fwd hatches on deck have rust aound them so they will be cut out. Several staunchons also have rust around them.

 

The rudder needs to come out for several reasons, first it needs to be inspected (shaft, bearings), then it needs to be blasted and painted (much easier out of the boat), plus you have the skeg wich needs the same and can't be done properly with the rudder in place, and lastly now you can crawl to the transom to grind and paint without twisting into a brezel.

"Might consider ditching it"? I am sure whoever did that was very proud of it and his other extensive stainless work, but you must realize it's a significant weight in a place the designer envisioned thin air.
The sugar scoop transom with cutout and fixed beam was popular at the time on cruiser-racer boats. It's only useful if you don't have a big high pulpit, the ideea is you step over the big beam that keeps you safely in the boat, while the cutout is for fast draining. If you google pictures and videos of van de Stadt Caribbean (wich I believe yours is, with a shorter cabin trunk, but you will have to confirm that) you will find several stern types, flat transom, sugar scoop with and without cutout, and walk through.

For repairs I would cut out the entire step area, including the sides and inner transom (I drew it on the picture). Why, because from what I can see you have more work to do than just the corner, and the flat area around the step is simplest to reach from the inside for painting after rewelding. Depending on how you plan to use the boat you can reshape the stern to your liking. The sugar scoop is useful, so I would cut the beam and replace it something removable (chain, gate, bar depending on how structural it is).

If you can reach that corner from inside for painting you can cut the deck only in that area. The mooring clamp probably has to come out and be rewelded anyway, you don't know how far the rust goes under the paint.

Do you know how the wood is fixed to the steel (screws, glue only) and how the boat is insulated?

 

https://www.gullco.com/ceramic-weld...MIiI_45frD9AIV_wytBh08_AJGEAAYASAAEgKsc_D_BwE

I have include a single website that may provide an option to produce a complete weld from one side.
So the concept is to attach a ceramic backer bar that enables a high heat root pass from one side only and the ceramic will "hold the shape of the weld bead and permit a weld pool/bead that is homogeneous. Most people in the industry are aware of
the straight ceramic backing bars but at Fabtech maybe 10 years ago there was a company that used smaller squares, say 1 inch by 1/2 squares affixed to a sticky tape so that the squares could follow a curve.
So with proper cleaning, sticking the ceramic tape/backer to the hull from the open hole, then inserting the preformed patch, you would be able to get sound welds from one side only.

Video to show the process
So you would need only a few smaller holes cut in the deck to affix the backing, remove it and paint the finished weld