Plank /Frame ratios

[mobi]

I am replacing the frames in a 30' displacement power cruiser. The planks are 20mm (3/4') thick. I believe a ratio exists for frame thickness and spacing relative to plank thickness. I would like to replace every second frame, using the same rivet holes if possible. The frame spacing is 8'' at present. Can any one help? John

[Thorne]

More info, please. Are the current ones rotted, broken, or ? Any photos?

[Nicholas Carey]

I am replacing the frames in a 30' displacement power cruiser. The planks are 20mm (3/4') thick. I believe a ratio exists for frame thickness and spacing relative to plank thickness. I would like to replace every second frame, using the same rivet holes if possible. The frame spacing is 8'' at present. Can any one help? JohnIf you get a copy of Skene's Elements of Yacht Design (preferably an older edition), it contains 2 sets of scantling rules: those used by the Nevins yard, and those used by Herreshoff Mfg. Co.

But if you're reframing an existing boat, you probably want to just replace like with like, unless the existing frames are obviously undersized. I'd probably replace sawn frames with frames bent in place.

[edited to add...]

The "usual" frame replacement schedule is remove/replace every third frame, repeat and repeat once more. This ensures that 2/3 of the structure is still in place to support the hull.

[mobi]

Not adept at posting photos yet. The boat had sat in Sydney Harbour (the best in the World!) for ten years, covered with a tarp. The boat was built in 1936, by A C Williams,designer and builder of launches. The nameplate was still attached. Also, found under the king post was an Australian 1915 one shilling piece, polished smooth but with King George v's head and the date still discernable. Apparently to "paye the devil".

When the tarp was removed, the cabin etc collapsed into the hull. The hull is in surprisingly good condition except for the frames at the turn of the bilge aft of the foredeck. The planks have been preserved both sides with red lead which has been banned in Australia for many years. The frames are 3/4" x 17/8" spotted gum, a hardwood, at about 71/2" centres.

[Thorne]

Are the frames cracked or rotted? If the former you *may* want to replace them with something a bit thicker/stronger. If the latter you can probably go with an exact match size-wise.

Do a search on red lead primer here, there are several recipes you can make from fireworks supplies...