Re: Mary Anne Design/Rivets


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Posted by JLabaree on April 27, 2005 at 15:40:56 from 216.220.235.91 user JLabaree.

In Reply to: Re: Mary Anne Design/Rivets posted by Owen roberts on April 27, 2005 at 11:28:51:

(Apologies to all – long treatise and curt opinions follow. Not sure if this is off topic. I refer John, however, to the Woodenboat Forum, where many far more capable boat builders seem to pass much of their day answering questions and making suggestions.)

I understand that this project is a training exercise in a way for your Swallow project. Good idea. But I hope you reconsider a couple of things.

I hope you do not plank Swallow in oak. Perhaps I am way off base and others can set me straight, but I suspect that traditional English dinghies were not planked with oak. As you have discovered, it is a tremendously difficult wood to use as planking. From an engineering perspective, it is over-kill. Planking does not need to be made of such stiff, unyielding material. The boat will be overwhelmingly heavy and be a beast to row and sail, not to mention load and unload from a trailer.

Pine or, preferably, cedar (Atlantic white cedar, if possible) is far superior for planking. These woods are much easier to use, they are perfectly durable (esp. cedar), they will swell nicely, they are light, and they provide plenty of structural strength. Cyprus is also a good choice. All of those ought to be readily available in Texas.

It is very unusual to put epoxy between the laps in a lapstrake boat unless built of plywood. The reason is that as the wood swells, the resulting stresses will tend to split the planks if they are not allowed to move slightly. Epoxy doesn’t allow for that movement. As you are using oak, you may get away with this, but I worry that you will see splitting along those laps in due course, especially if the boat stays in the water for any lengthy periods. Plywood doesn’t move around, so you can put epoxy between the laps.

I agree about staying away from plywood. I have built a lapstrake boat from plywood and it is not as much fun as using the real thing. The big advantage, however, is that you can build a wooden boat that can stay on a trailer and not leak without swelling up (because you can epoxy the laps). So, if this is how you envision using Swallow, you may want to reconsider plywood. An extremely well constructed lapstrake boat, built of pine or cedar, will also not leak even when dry, but that is not an easy ideal to achieve.

I disagree about the screws v. rivets. Properly installed copper rivets are extremely strong (the Vikings discovered that a few years back). As you are planking in oak, you can get away with screws, but if you use softwood when planking Swallow, you will need to use rivets or clench nails to fasten the laps (if you like, by all means, use screws to fasten the planks to the frames, but rivets are acceptable here, too).

As for never having to remove the garboard – John discovered in SD that planks do often need replacing for reasons other than natural decay or flaws in construction. Having worked for some years in a boat shop restoring old wooden boats, I am particularly sensitive to thinking down the road to when the boat will eventually need to be repaired. As you say, since you are epoxying the planks together, using epoxy in the screw holes is the least of your worries if you need to replace any planks. If you’re using the same stuff I use (WEST), you’ll find it doesn’t always bond that well to metal anyway (indeed, it can be a trick to get a good bond to oak as well).

Now, about those drill bits. Another good option is the “Countersink drill pilot bit”. Vermont American makes them – they accept a regular drill bit if (when) you break the drill bit. The nice thing about these bits is that they create the same kind of hole with one pass that you are making with three passes. The shape of the hole ought to be precisely what you need. The only issue with tapered bits is that, since they taper and screws do not, they don’t quite get the hole exactly right. These bits avoid that problem, but they can be a bit of a pain to adjust and they tend to slip.

End of treatise (plenty more curt opinions where those came from, however).



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