scarfing planks

[anubis]

I'm still struggling with my Tideway! She has cracks in five planks, each about two feet, a long the copper rivet line, which secures the planks to each other. This leaves the planks floating in this area. Is it possible to scarf repair this, if so has anyone had a go at this? And, how do you do this?
Many thanks.

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[Dirk]

Its not good practise to have a lot of plank joins in the same place. It amounts to having a zipper down one side of the boat. That said, you could get away with it on a small boat.

Lloyds rules for plank joints are as follows:

Joint 1. anywhere on the boat.
Joint 2. (next plank down) 1.2m from the last joint
Joint 3. 1.2m from the last joint and 2.4m from the first
Joint 4. 1.2m from the last joint, 2.4 from koint 2. and 3.6m from joint 1.
Joint 5. back to the first position under joint 1.

It would be wise to obey these rules on an ocean going Yacht but on smaller boats one can uses ones comon sense. You could adjust the above rule to rib spacings. For example lets say 4 to 6 rib spacings instead of 1.2m.

Making a butt joint is quite aceptable provided a pad is riveted on the inside. This pad would have to overlap the upper and lower plank by apromimately 1/3.

If you wanted to scarph the planks it would look neater but is not necessarrily stronger.

Scarph lengths should be at least 6 times the thickness of the plank.

A lipped scarph would work well. Lipped on the outside and feathered on the inside. The feather edge would rest against the rib ( in order to be hidden) and you would rivet the rib as normal plus a couple more rivets at the lipped end of the scarph.

The lip should be aproxomately 1/3 the thickness of the plank. The idea of the lip being that you dont have a feather edge on the outside of the boat that is at risk of damage. It also means that when sanding/fairing the hull the scarph does not get any shorter.

Take your time marking out and cutting these scarphs. the better they fit, the better they will do their job! Bedding the scarphs with mastic is perfectly sound but a little glue never hurt anyone either. (epoxy or resorcinol would be fine)

Good luck

Dirk

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[tillergirl]

The simple answer is yes. I've done it with tilergirl on both a plank and the beam shelf. The most difficult thing was cutting the scarf on the plank left in the boat - awkward rather difficult and required sharp tools. Depending where you cut the scarf ie where there is a curve you will find the cut closing on you as you release the plank end from one of its fastenings. How long are the damaged planks - there is a time cost equation of replacing the complete plank rather than the more time consuming part of cutting accurate scarfs.

One thing to be careful of is short planks, with the repair scarfs all in one area. That would be a potential point of weakness - bit like a brick bond on a wall, the joints need to be staggered over as wide an area as you can arrange.

On a positive note: a successful well cut scarf is intensively satisfying. I would use an 8 to 1 ratio as a minimum.

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[Peterduck]

This is not a terribly unusual problem with clinker planking. I would be removing the rivets over the length of the crack, and routing out the section of plank to just above the line of the split, so that you have a nice straight line of clean wood. Epoxy into place a graving piece to replace the wood that you have removed. Drill new fastening holes using the ones still in the mating plank, and rivet back up. This retains most of the original plank. and is a much easier way to repair it.
Peter.

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