Giles
07-14-2005, 02:27 AM
I have to say that this forum is the most active and useful I know! I did a search (using the GOOGLE method suggested) but didn't get an obvious match.
I have a boat, 24' gaff cutter, 3"x1" mahogany on 1"x1" oak ribs @ approx 6" centres. NUMEROUS ribs have cracked over the years due to various beachings(not in MY time... tho I'm sure it will happen), and one incredibly annoying occasion when I was assured a mooring was wet, when it wasn't. To explain that last bit; Eider Duck has a broad keel (centre plate you see) and, if the sand is hard, she can dry out (low tide I mean) standing up. Then the wind blows... ouch. Ed & I came aboard midnight one Friday MUCH the worse for wear to find the ship with 10" over the cabin sole!
Anyway, back to her ribs.
Each cracked rib has been sistered. The former maintainer sistered alongside each rib, I followed this lead initially, then changed to sistering midway between ribs (after reading 'The Boat Husband'). The rationale for sistering midway is to avoid water traps. Comments?
To build the laminated sisters I generally use three layers of oak to make the sister a smidge under the 1" of the originals. Laminating them in place allows me to fit them without steaming. So far I have seen no evidence of any problems from this method- eg ribs cracking elsewhere etc. Slight hard spots often pull fair as the roves are fit over the nails, which is encouraging.
I'm now looking at the original ribs, and wondering what to do over the cracked section (which will be over a seam). I was thinking I may cut away completely from the cracked section to, say, a strake-and-a-half or so either side of the crack (perhaps 12"), then route to 2/3 rib depth out another strake or so(18"),then route 1/3 rib depth another strake or so (24"). Once done this will give a good basis for a stepped scarph triple laminated epoxy glued copper rivetted repair section in the rib.
There will be areas where I can't step the scarph so generously but I though is I could step then by one fasteneing that would be better than not.
The alternative is to leave well alone.
Replacement of the whole ribs is more than I can realistically undertake. The last couple of surveys done where happy with the sistering... even though there are so many. Whaddya think? (did that description make sense?)
I have a boat, 24' gaff cutter, 3"x1" mahogany on 1"x1" oak ribs @ approx 6" centres. NUMEROUS ribs have cracked over the years due to various beachings(not in MY time... tho I'm sure it will happen), and one incredibly annoying occasion when I was assured a mooring was wet, when it wasn't. To explain that last bit; Eider Duck has a broad keel (centre plate you see) and, if the sand is hard, she can dry out (low tide I mean) standing up. Then the wind blows... ouch. Ed & I came aboard midnight one Friday MUCH the worse for wear to find the ship with 10" over the cabin sole!
Anyway, back to her ribs.
Each cracked rib has been sistered. The former maintainer sistered alongside each rib, I followed this lead initially, then changed to sistering midway between ribs (after reading 'The Boat Husband'). The rationale for sistering midway is to avoid water traps. Comments?
To build the laminated sisters I generally use three layers of oak to make the sister a smidge under the 1" of the originals. Laminating them in place allows me to fit them without steaming. So far I have seen no evidence of any problems from this method- eg ribs cracking elsewhere etc. Slight hard spots often pull fair as the roves are fit over the nails, which is encouraging.
I'm now looking at the original ribs, and wondering what to do over the cracked section (which will be over a seam). I was thinking I may cut away completely from the cracked section to, say, a strake-and-a-half or so either side of the crack (perhaps 12"), then route to 2/3 rib depth out another strake or so(18"),then route 1/3 rib depth another strake or so (24"). Once done this will give a good basis for a stepped scarph triple laminated epoxy glued copper rivetted repair section in the rib.
There will be areas where I can't step the scarph so generously but I though is I could step then by one fasteneing that would be better than not.
The alternative is to leave well alone.
Replacement of the whole ribs is more than I can realistically undertake. The last couple of surveys done where happy with the sistering... even though there are so many. Whaddya think? (did that description make sense?)