Sistered rotten ribs

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FatBear

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Hi,
I am considering the purchase of a boat with sistered ribs. The boat is a heavy-duty fishing boat converted to a "yacht". The ribs on either side of the fish hold were rotten and have been sistered. I understand sistering and that in itself does not really worry me, but I am concerned that the original rotten wood is still in there. Isn't it going to contaminate the new sisters and/or the planking or ceiling?
Thanks for any helpful answers!
 
Yes, the existing rotten wood will contaminate anything that it is touching, so it should be removed. Sistering is a 'quick and dirty fix', used to get a working boat back in the water and earning her keep quickly. Don't forget that these boats were considered to be old at twenty years, and due for replacement. The ends of the sisters are points of stress concentration, and after a while the old frames crack again at these ends. It becomes a tail-chasing exercise. Replacement of the original frames is the target to aim for. Are the original frames doubled futtocks or are they steam-bent?
Peter.
 
What Peter said. It is much better to replace the original frames. Much more work, because you need to get at the ends of the frames, so you need to get lumps of deck off (if she has covering boards, this need not be too bad) and the extra work makes it financially unattractive when done by boatyard labour, compared to the few hours needed for sistering. But your time is your own to spend.
 
Didn't help a great deal. This site shows sistered ribs (crap pic) and the work involved to replace them properly.
And this one shows sistered ribs that are badly done Here But you can see how much easier it is to pop them in than rebuild the hull.
 
Thank you for all of the advice so far.

Here is the boat we are considering: Gallant Girl (link)

The whole story is that she was used as a fishing boat until 2004. She was quality built with steamed oak ribs, very heavy douglas fir planking and ceiling, heavy welded aluminum bulwarks (the green area at the top of the hull sides), bronze railings, ladders, fittings, etc. She was built to work in and survive the North Pacific, which is no pond. And she is in very good condition considering over 40 years as a fishing boat in the rainy Pacific Northwest.

The boat originally had two holds forward of the wheelhouse and aft of the fore mast, each the same size and running athwartships. These holds were filled with aerated water and fish were kept alive in them till brought to market. The ribs which rotted are the ones adjacent to these holds. Some of the planking also rotted in that area. The "deck board" (as I learned they were called by a shipwright) along each side of the deck was also rotted.

In 2004 the boat was purchased by a man who wished to convert it for living aboard. He had the boat hauled and the port side worked on. They sistered 18 ribs, replaced some planks and the deck board on that side. The guy did a bunch of other work and then he died. His wife wants to sell the boat. I would have to do the work on the starboard side. (Hire it done.) I was told that they did the port side first because it was in the worst condition and that was confirmed by the shipwrights who did the work.

There are apparently different ways to "sister" a frame. The conventional way is to form (saw or bend) a matching piece and bolt it to the side of the original one. These guys did it a bit differently. Since they had the deck boards off, they had access to the top of the open space between ribs. They took three pieces of oak, dimensioned them, steamed them, and drove them down into the void next to the rotting ribs creating "laminated" ribs. These they held together with glue and screws and then screwed the new planks to them, leaving the old ribs in place. This will be stronger than I'll ever need, so I'm not worried about their method. I'm just worried that the rotting ribs will pass their mycelia into the good wood faster than the good wood would rot on its own, if you get my meaning. After all, it is a wooden boat and all wood will eventually rot. I just don't want to have to do major re-work for quite a few years. There will probably be other rot to keep me busy in the short term!

I don't actually know how rotten these ribs are. I was told that they've still got a lot of good wood in them. Also, the boat has only the very faintest odor of rot, and I can usually smell rot very easily. So I think we've got a pretty good idea of the extent of the problem.

--Brian
 
Still sounds like a bodge to me. Best remove sisters, original timbers and their rot and start again. You could either steam green oak or laminate (and glue) from thin flexible lengths. They say that more than about three laminated timbers in a row creates a hard patch - but I've never bothered to find out. Old Frank
 
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