Sheer Plank question (Penobscot)

[Miami Mike]

Hello all,

I am slowly building, through trial and error, a Penobscot 14. I have reached the point of planking where all I have left is the sheer planks. The rest of the planks are all 1/4" ocume plywood. If possible I would like the sheer to be made from one piece of solid mahogany that I would finish bright.

Is it okay to use solid mahogany (1/4" or 3/8") in what is otherwise a plywood boat (expansion/contraction issues)?

If so, are silicon bronze screws and epoxy okay or should I attempt copper rivets with some sort of a bedding compound?

I'm happy to have gotten to this point in the builing process. I like the look of a bright sheer plank but don't want to run the risk of ruining the boat when I'm this far along.

Thanks for the help!

[dmede]

Mike, will you have a cap or guard that covers the sheer plank top?

If so you could easily get away with using the ocume ply for the sheer and leave it bright. Few people would ever know. The underside of the sheer plank would still be visable but not very noticable since it faces down. But to cover that up you could run another guard strip along the lower sheer edge as an accent that also conceals the ply edge.

Ocume can look very nice once varnished. Even the exposed edge looks good once epoxy sealed and varnished.

dave

[ 01-09-2006, 03:50 PM: Message edited by: dmede ]

[Thorne]

Why not ask Arch Davis -- he's very responsive.

I researched building a PB14, and several of the builders left the sheerstrake (or parts thereof) bright in nice ply -- looks great!

http://www.duckworksmagazine.com/05/...elass/free.cfm


I'd be very concerned about using solid wood that thin, seems to be asking for warping and other issues.

[ 01-09-2006, 05:29 PM: Message edited by: Thorne ]

[Miami Mike]

Thorne and Dave,

Yes there is a cap and a trim piece that would cover the ply. I guess this is the way to go. I'm somewhat hesitant because my woodworking skills are pretty poor and all though at this point my scarfs are looking better, they are still pretty sketchy.

I have access to a couple pieces of mahogany that I could have milled to 1/4" or 3/8" that are 16' long and could avoid the scarf. However if they were to crack or split it would be an expensive lesson.

Thanks for the help!
Mike

[JimD]

If so, are silicon bronze screws and epoxy okay or should I attempt copper rivets with some sort of a bedding compound?

I'm not familiar with the construction method. Are there battens to support the the plank lands so there is enough wood to hold a screw? Keep in mind okoume doesn't have great rot resistance so whatever you decide do your very best to seal the screws or rivets to keep the h20 out.

[dmede]

Keep in mind that at that thickness and length the ply is relatively cheap so you can take a couple stabs at getting the scarph just right. Using a scarph jig of some kind could be a big help (if your not already using one). Below are a few pics of one I made up recently.

Un-thickened or very slightly thickened epoxy will almost disappear under a layer of varnish and again only a trained eye will be able to easily detect the glue line (especially at any distance over 3 feet, where most admirers stand ).

As for Ocume’s rot resistance… For any boat not living in the water and decently taken care of it should not be a problem. Seal up the edges well with epoxy and keep a good finish on it.

[JimConlin]

If the boat is intended for plywood construction, i'd be concerned that there was sufficient cross-grain bracing behind solid sheerstrakes. There are presentable mahogany and sapele plywoods, but you might not want to buy a whole sheet just for your sheerstrakes. A third possibility is to apply a mahogany veneer to one or both sides of your okoume sheet and then get your sheerstrakes out. Borrow a vacuum pump for this. This will yield strakes with the designed-for cross-grain strength and an attractive appearance. This is only a moderate pain and works well.

[almeyer]

Whether you go ply or real wood for the shear strake, you're probably looking at scarfing the planks either way. I painted my shear strake, but left the badges, rails, and the rub rail at the lower end of the shear bright. Your idea of leaving the entire shear bright would look very nice. The mahog I used for the interior was somewhat darker than the meranti ply I used for planking; you might want to try staining a scrap piece of ply then sealing with epoxy to see how the color comes out before hanging the plank. If you're careful on screw placement, the rail on the lower edge of the shear plank can cover up the screw holes and of course the outwale will cover the screw holes on the upper edge of the shear.
Al

[Miami Mike]

Okay here's where I stand:

After reading all your advice and taking a cue from Mr. Thorne and speaking to Arch Davis I will be taking virtually everyone's advice and continue with the plywood planking.

I suppose I'm somewhat relieved that I don't have to worry about splitting a $150.00 piece of mahogany. Dave's jig for scarfing looks do-able even for a novice like me. So I'll give it a go and try and make the scarf as clean as possible....worse case scenario, I'll paint it.

Thanks for everyone’s input. Thanks Al for the tip on lining the screws up to be covered by the cap rail. I've admired your Penobscot from your past posts.

Thanks,
Mike

[dmede]

The jig pics should be self explanitory but shoot me an email if you got any questions.

It is based around the use of a long jointer plane for cutting the scarph (as see in the pic). 18" seems to be ok but longer would be better and would not require the center cross peice between the ramps.

[Miami Mike]

Dave,

It looks as though the closer ramp has a reveal in the bottom to allow for the swing of the plank, is that correct?

Thanks for the help!
Mike

[dmede]

Originally posted by Miami Mike:
Dave,

It looks as though the closer ramp has a reveal in the bottom to allow for the swing of the plank, is that correct?

Thanks for the help!
Mike

Yup, buttom ramp has a short notch cut out to allow me to angle the plank for dog-leg scarphing. That was done to allow me to use boards of lesser width than needed for a straight scarph. But those planks were unusually wide with a lot of shape to them, yours will probably not need a dog-leg.

The ramps are just 1"x.2" poplar hand planed to a 12:1 ratio. The board across the back is a simple clamp to help lock the board in place.

You mark your planking stock for the correct scarph angle (12:1 in this case) and slide the plank forward until the line marking the back of the scarph is even with the top of the ramps. Then go at it with the jointer plane. By holding the plane at angles where the heel is always on one of the ramps you can keep the correct angle. Becasue my plane was a little shorter I screwed in a cross peice flush with the ramps to help with the angle in the middle. The top of each ramp is rubbed with beeswax to keep the action smooth.

You can't rely completely on the jig to get the best results, it just gets you close. Once your down to the scarph line you'll want to take a look at whats going on and adjust your cuts to even it out where needed

Make your base for the ramps a bit wider than I did so you'll have a good place on either side of the ramps to clamp the jig down without interfereing with your plane.

Give the wooden clamp bar at the back of the jig a slight taper to each end to help it hold across its entire length. Other wise it will bow up in th emiddel and yo uwont get good pressure.

[ 01-11-2006, 04:48 PM: Message edited by: dmede ]

[Peter Malcolm Jardine]

That's a great little jig.

[dmede]

Thanks, but I can't take credit for the idea. Unfortunatley I forgot where I read about it so I can't give credit for it either