Lapstrake Replacement

[Rocky]

Thought I would have seen the answer to this by now, maybe I'm just not picking up on it. Suppose I rammed the dock so hard I had to replace an entire strake halfway between the waterline and the thwart from stem to stern. How would I separate the bad strake from the adjacent ones?

[ 01-27-2003, 04:20 PM: Message edited by: Rocky ]

[RGM]

Very carefully if the boat is out of the water. More than very carefully if the boat will remain in the water during the repair.

[Donn]

Back up and ram it again and again, preferably at the corner of the dock, until the offending strake is ripped off.

[Rocky]

Thanx boys! Hey Donn, I'm think I'm gonna try that options thing. What the hell, it's only money.

[John Blazy]

From your profile I see that you're a truck driver, so I certainly see why you are presenting this as a hypothetical question, and I of course am fully assuming that you have never done this yourself.

Right BUSTER ????!!!! (something about that name)

[Rocky]

Mixers, actually. At least I earn my pay. This whole forum is getting to be less and less about boats and more and more about snide remarks. This is the building/repair section, remember? How bout a straight answer?

[ 01-24-2003, 02:18 PM: Message edited by: Buster ]

[Donn]

How is the plank held on?

[Rocky]

I tried to remove a rib for sanding and varnishing and found it had both screws and nails, so I guess the strakes do too. And some kind of glue or sealant.

[ 01-24-2003, 07:51 PM: Message edited by: Buster ]

[Donn]

It's simple, then. Remove any screws and nails, and defeat the glue. The plank should pull right off.

[Rocky]

OK, let's rephrase the scenario: suppose some overpaid asshole rams me and I have to replace an entire strake.................

[Donn]

Doesn't change the answer. You get rid of whatever is holding it on.

[Rocky]

So you're saying you could just slide it out from under the overlapping one and use it as a template for a replacement?

[Donn]

Yep.

[RGM]

Let's back up here a little bit. First off, how about some details up front. What kind of boat? Length and beam? If it's big, would you consider leaving it in the water during the repair? Construction method (sounds like lapstrake)?Dimensions of planks and frames? How fastened, screws, rivets, nails (apparently a combination)? What material is it made from? What do you have in the way of wood boat repair reference books? How about wood working tools available to you? You got my first answer because you provided essentially zero meaningful information. Details matter. As this thread progresses the blanks are getting filled in. I wasn't trying to be a smart ass.

[John Blazy]

Patience dear Buster. Seriously now, You will clearly get the most awesome answers to your problem from the most comprehensive field of mostly qualified, well experienced group of people that you could possibly get in the short time, instant-gratification miracle of the web. You are in great hands.

Try the search button at the top right, too.

You may not know this, but if I post a harmless funny, then that puts your question at the top of the list giving it way higher chances of being answered by a Bob Cleek or a Dave Fleming. No offense taken - enjoy the forum - JB

[Rocky]

Just under 19 foot, about 6' beam, 5-ply marine fir plywood, on a trailer. Assuming I could (get someone to) make a proper replacement, should it be fir? Or could I just make it out of the chip on my shoulder? smile.gif

[ 01-24-2003, 03:46 PM: Message edited by: Buster ]

[John Blazy]

The "Chip" material sounds very durable :D . But fir marine ply would work as it sounds like its a plywood lapstrake like an old Lyman. However you get the damaged strake off, you gotta dry out the hole, possibly cut out only the bad section (my first choice) and replace using boat epoxy, backing the new member with cleats over the joints (interior) like lath catchers in wall construction. You could screw this all together, then back out the screws after the epoxy sets, though some may suggest glassing over and sealing in the screws. Then feather sand the outside joints to bare wood, and embed glass cloth with epoxy over the joints. Fair the surface with epoxy and microballoons (sanding additive to get with the epoxy), sand and repaint. - JB

[Rocky]

The hull is painted, so it's not about looks. Is there another reason not to use dissimilar woods, eg different flexing characteristics? In reality a patch would be done, as you say. But glass cloth with epoxy? Hmmmmm. I doubt I could separate the strakes without making a mess. The only way to extract that rib in one piece would be to cut around each nail with a small hole saw, which I think I shall do come spring.

[ 01-24-2003, 07:50 PM: Message edited by: Buster ]

[Dale R. Hamilton]

Buster- you should realize this is a little like calling in to Click and Clack. First you're going to get some wise-ass comment. Then you going to get a few irrelevancies like "What color is it".
Only if you persevere will you get the real dope- and there's plenty of it in the forum. Thats the system- the alternative is look it up in some damn book.

[Nicholas Carey]

So, Buster...it sounds like this boat is lapstrake (clinker-built for the Brits and Ozzies.) Right? Each strake is fastened to the frames on which it lands with screws or rivets and and either clench-nailed or rivetted to the lap immediately above it and below it. That...more-or-less...is the way it's usually put together.

Replacing a strake in a lapstrake boat is a little more difficult than it is with a carvel-built boat.

A carvel-built hull has caulking cotton hammered into the seams to make the hull watertight. When the hull planking expands in the water, it expands, compresses the cotton, which acts as a gasket and makes the hull watertight. This makes the hull easier to repair since [simplified smile.gif ] each plank is pretty much a wedge fit.

Lapstrake hulls, on the other hand, depend on the fit between the laps -- how snugly each plank overlaps the next -- for its waterightness. There's no caulking to help. A plank -- strake -- on a lapstrake hull has a 'rolling bevel' planed on the upper outside edge of each plank. The next plank hung overlaps the plank below and lands on the bevel. The overlapping plank must lie tangent (flush) against the bevel on the plank below. It's called a 'rolling bevel' because the bevel 'rolls' over the length of the plank -- its angle changes.

So...to replace an existing plank on a lapstrake hull, you need to cut a new plank that (A) has the same shape and thickness as the old plank, and (B) has a rolling bevel that matches the old plank. Sounds easy, right?

If (big if here), you can get the old plank out in one piece, you should be able to use it as a pattern for the replacement. You should be able to (theoretically, at least, in this the best of all possible worlds) to pick up the bevels off the old plank, using your trusty bevel gauge. Pick up the bevel every few inches along the length of the plank and transfer that bevel to the new plank at exactly the same spot on the plank.

A good way to do this is to use fine Japanese saw like a Dozuki and saw the bevel into the new plank, but make the saw cuts just a hair shallower than the bevel needs to be.

When you're done, you should have saw cuts every few inches along the edge of the new plank defining the shape of the rolling bevel.

Now, get out your handplanes (block plane, mostly, but a spokeshave and a smoother might come in handy depending.) Sharpen them up well. Carefully plane down the bevel just until the saw cuts vanish. Ahh...nothing like the smell of a fresh cedar shaving coming out of the throat of a sharp plane -- it makes me think of...planking up.

Theoretically, the new plank should now just slide right in and fit. Unlikely, but a man can hope :D

So you carefully trim and fit until the plank does fit properly. Just remember its easier to take wood off than it is to put it back on.

Carbon paper can be a good tool for identifying high spots between two mating pieces like this. Slide a sheet of carbon paper between the two parts, carbon-side towards your bevel, press the two parts together and work the joint a bit. Any high spots on the bevel should be marked.

Oh...One last thing... Each strake usually has something called a 'gain' :eek: in the last few inches at each end of the plank. A 'gain' is a tapering rabbet -- a rebate for you Brits and Ozzies -- that enables the strakes to make smooth elegant transition from the overlapped 'shingle' effect you see in most of the hull to a smooth, flush fit at the stem and the transom. To cut the gains, you'll need paring chisels and possibly a fine rabbet plane.

Walter Simmons, of Duck Trap Woodworks (http://www.duck-trap.com/) has written one of the few books on lapstrake repairs that I know of. http://www.duck-trap.com/dtpress.html

The books are probably well worth their weight if you actually needed to make this repair.

Hope this helps.

Cheers,

N.

[ 01-24-2003, 06:49 PM: Message edited by: Nicholas Carey ]

[Rocky]

This sounds daunting. Didn't know about the bevel. I thought they just overlapped like cedar shakes! Sounds like in practice it might actually be easier to replace the entire side. I'd like to ask how the hell one makes strakes anyway, but - I know, I know - I'll go look through the searches first. And John, it's Buster as in "now look, Buster..." Also what I call my dog most of the time.

[ 01-24-2003, 07:44 PM: Message edited by: Buster ]

[Nicholas Carey]

Originally posted by Buster:
This sounds daunting. Didn't know about the bevel. I thought they just overlapped like cedar shakes! Sounds like in practice it might actually be easier to replace the entire side.If you replace the whole side, you'll be bevelling a whole lot more than just one plank.


I'd like to ask how the hell one makes strakes anyway, but...Lapstrake planking...if you're planking up, it all starts with 'lining off'. Since the laps are highly visible, it's really important to get an aesthetically pleasing flow to the plank edges.

Theoretically (there's that word again), establishing the plank lines is fairly straightforward.

You've already cut the keel rabbet and the stem rabbet. You sprung a batten to layour the sheerline. And you know how many strakes will be hung on each side of the hull -- or at least you need to decide now.

Starting with the amidships station mold you measure the distance along the station mold from the keel rabbet's vertical edge to the sheerline -- say, for the sake of argument, 90 ins.

Divide that by the number of strakes (say 15) to get the plank width at this station mold. 15 divided into 90 ins gives you 6 ins. That's the width of each strake at this station mold. Mark on the station mold the plank edges measuring up from the keel rabbet. Repeat for each station mold. Note that you only do one side -- we're striving for bi-fold symmetry here. When you're done, you should be able to spring a batten along the tick marks on each station mold to lay out your plank lines.

In practice though, it's not quite so simple. First, you might not want strakes of uniform width -- you might want the strakes below the waterline to be wider. Second, you'll probably need to do some adjustments to make it fair.

Repair, of course, is a different kettle of fish entirely. That's why preserving the old strake, whole, if you can is important.

Get the books.

Cheers.

[Tasybear]

Nicholas has given a very thorough and practical direction on how to proceed with the problem.
Advice I would gratefully follow if such a calamity (contingency) occurs to my folkboat.
Thanks Nicholas

[Donn]

Now, if you change the title of the topic to something like "strake replacement" it would be easier to find with the search thingy.

[Allen Foote]

smile.gif Nice posts Nicholas smile.gif

[TomRobb]

Rocky, I'd rethink the hole-saw method :eek:
If screws, unscrew them.
If rivits, grind off the peened end and punch ten out as they went in.
If clench nails, maybe use one of those cutting plyers like thingys, un-clench them, and pull them out.
Or possibly a hacksaw blade between the strakes to cut them.
Why would you want to swiss cheeze the planks you're not replacing? :confused:
(Sorry I called you Buster - another senior moment :rolleyes: )

[ 01-27-2003, 11:02 AM: Message edited by: TomRobb ]

[Rocky]

One of those cylindrical things, like a 1/4". Also got a thingie from a guy at the wooden boat show in Mystic last year for removing stripped screws. Or I'll probably do what I usually do - nothing! How far in do rivets or nails go? Not all the way through, surely?

[ 01-27-2003, 11:54 AM: Message edited by: Rocky ]

[TomRobb]

Rivits & clench nails gog clear through. Screws do not. Try to get the screws out the normal way before resorting to hack & slash surgery.

[Bruce Hooke]

In my experience with removing parts of wooden boats, it's usually a matter of starting in one place and slowly working away at anything holding the part in place. So, you start with the obivous things like screws, then work on the rivets and nails, and then, when it still doesn't budge, start poking around to figure out what you missed. It is not a job for the hasty. If you get tempted to start ripping away at stuff take a break and come back latter. You want to do your best to get the old plank out without causing any damage to the adjacent planks or the ribs, and, if at all possible, with the old plank in good enough condition that it can be used as a pattern for the new one. It can be done but it takes patience and persistence.

One good reason to use the same material as what was originally used is so that you will know that the replacement has the necessary structural strength to do the job it needs to do to keep the boat together. Also, especially with plywood, cheaper grades of plywood will make themselves evident right through the paint.

One final thought...if most of the plank is still so securely attached to the adjacent planks that it looks like it will be very hard to break whatever adhesive material was put in the joint, then are you sure you really need to replace the entire plank. It's rare that an entire plank is damaged in a collision of any sort, so replacing only the damaged section might be an easier way to go...

[Nicholas Carey]

Originally posted by Bruce Hooke:
It's rare that an entire plank is damaged in a collision of any sort, so replacing only the damaged section might be an easier way to go...Not on a lapstrake hull -- you'd have to scarf the ends of the patch in. A little hard to do that with the overlaps. And butt block would be dicey since they'll put a hard spot in the strake. Lapstrake hulls are relatively flexible. That hard spot will tend to concentrate forces and eventually fail.

[Mr. Know It All]

Sometimes the wood swells around the head of the countersunk screw. Ream the hole out before trying to remove the screw. A good pair of vice grips have saved my sanity more than once. What Bruce and Nick and the rest of the guys have said already.
Peace----> Kevin in Ohio

[Alan D. Hyde]

Chris-Craft Sea Skiffs were originally built with butt blocks on their strakes, and they do fine.

Danenberg has done a bunch of articles on this subject in Classic Boating. They are available from its publisher.

There is a Fein tool (Multi-master??) that he uses to cut out the old strakes.

Alan