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Old 11-06-2007, 23:14   #1
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Where should I cut the hull timber ?

Hi,
I am about to do some repairs on the hull of a 4 year old wooden motor boat (12m long) that I recently bought.

While preparing the hull I noticed that about four of the planks towards the stern and suffering from rot and I need to replace some. The affected area is about one square foot. I am going to take a picture of the damaged bit today but I have included a shot of the boat to give an idea.

I took off a bit of the wood and found that it was attached with galvanised nails. I am hoping to get silicon bronze screws and possible use glue as well to replace about four planks.

When cutting out the existing planks, should I try and cut on a rib so that I can then easily screw the end of the new plank into the rib, or should I cut in the middle somewhere and make some kind of joint ?

I do not have a workshop - just some simple wood working tools.
If I cut in between ribs - should I put an extra "patch" of wood on the inside of the hull behind the joint - with glue and screws ?

Obviously I am a complete novice ! But I want to learn, so I'll really appreciate your advice.

Thanks
Dave
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Old 12-06-2007, 00:20   #2
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Hi Dave
Seeing what you are working on helps. Looks like you could end up with a nice boat. Good lines. How wide are your ribs? And how far apart? Also what kind of access do you have from the inside? There are several ways to tackle this. 1. Butt joint on the rib if it is wide enough. No two joints on the same rib. 2. A scarf joint done at a long angle on the rib. 3. A scarf joint done between ribs with a backing plank. Do you have any rotting in the ribs? Are the ribs bent or sawn? How wide are the planks?
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Old 12-06-2007, 02:12   #3
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Good questions ...

I hope to go over to the boat today and I'll measure up and take some photos.

Hopefully that will help you to help me !

As for the boat - yes I thought it had nice lines even though I am a newbie. I have some photos of when it was new as well. I will post some in a seperate thread.

Thanks
Dave
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Old 12-06-2007, 05:44   #4
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i would never cut a plank to land on a rib period. the plank buts should go between the ribs with backing blocks a little wider than the plank you are repairing so the block bears on the upper and lower adjacent planks. there should be atleast 5 fastenings per each plank end that you have cut and are replacing. if you can get red lead putty you should seal the ends of the planks and coat the contact points on the butt block and the planks. a small amount of a polysufide sealer in-between the plank but ends will stop any water from getting into the seam. if it is only the plank ends that are rotted why can't you scarf a 12 to 1 aftre the rot and scarf new ends on the effected planks? i understand that you are a novice as you cited in your post, but these repairs are not above you if you think about what you are doing and take your time to execute the job slowly and with due caution!
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Old 12-06-2007, 05:56   #5
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I suspect that Mike's proscription against plank ends landing on ribs might be to prevent splitting.
I wonder if the fastenings for the backing blocks might present the same hazard?
Should the plank ends (wherever they land) be scarfed, or is a butt-joint adequate?
If scarfed - in one axis (which), or both?
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Old 12-06-2007, 09:54   #6
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Ok - I just got back from the boat.

Here are the photos.

The measure is in metric. There are two ribs bolted together each is 4.5cm - total 9cm. As can be seen the ribs in one place are a little damaged with rot.

The interior is sound but shows chinks of light. I guess these will close up with swelling ?
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Old 12-06-2007, 12:16   #7
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I hope that you can make something of these photos !

I tapped all the wood on the interier and it all seems very dry and solid excep for abit a round where the rot is - which is about a sq foot.

As mentioned before due to being out of the water for 8 months ( and the tmp now is getting pretty hot ! ) there are a lot of seams between the planks opening up.

I assume that if I soak the boat these will seal up ok as the wood and cotton swell up ?
What I mean is - I dont have to scrape out all the cotton caulk and re-caulk do I ? ( the boat is only 3 - 4 yrs old )

Does it make any difference whether I saok it with sea water or fresh water ?

Relating to the last photo. That photo shows one of the many seams that have opened up between the "above water line" planks.

Will these swell up and fill themselves again as well ?
( they have their cotton stuffing intact. )
So should I just leave them alone for now ?

I will try and soak the whole of the boat befopre launch to see what happens.

BTW
The ribs are 8cm in depth and 4.5 cm wide but as they are usually 2 bolted together, the thickness is 8.5 - 9cm.
This means that they can take longer screws than 1.5 " if nec. The nails that have been used are 3" galvanised wire nails.

Thanks for your advice.
Dave
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Old 12-06-2007, 12:57   #8
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Planking butts should not terminate on frames. This has been mentioned earlier in this thread. There are also rules about number of butt joints per frame space and specs for scarf joints. It's not hard to do, but might be considered complicated.

I think you should read up on this subject before attempting repairs.

Try this

http://www.daviscoltd.com/nams/Documents/nvic7-95.pdf

Rick in Florida
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Old 12-06-2007, 16:57   #9
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The USCG site is easier to read & navigate.
Guidance on Inspection, Repair, and Maintenance of Wooden Hulls
US Coast Guard NVIC 7-95

NVIC 7-95

Specifically Chaper 5 (E)
BUTT JOINTS IN PLANKING
Planking butts should not terminate on frames in normal construction. They should be located between frames on proper butt blocks, though in light construction with narrow strakes, they may sometimes be found as glued scarf joints at the frames and in some construction with massive framing they may be found butted on the frames. As a rule of thumb, butts in adjacent planks should be at least three frame spaces apart for transversely framed, longitudinally planked vessels.
Those butts which fall in the same frame bay should be separated by at least three solid strakes. This is not always possible, especially at the end of the vessel, but serves to illustrate the principle of keeping butts separated as much as possible. Where frame spacing is unusual the following rule may be used as a guide.
Butts in adjacent strakes should be no closer together than 5 feet. If there is a solid strake between, they should be no closer than 4 feet. Butts should be shifted so that three or more do not fall on a diagonal line.
To be effective a butt block must have adequate size (See page C-12). If the frame spacing allows, its length should be at least 12 times the planking thickness. Its thickness should be one to one and a half times the planking thickness and its width at least 1" greater than the strake width. Prior to installation it is recommended that the faying surface of the butt block and strakes be coated with a wood preservative. The top of the butt block should be curved or chamfered to allow for water run off. Avoid butting the block hard against the frames to minimize decay.
The fastenings of the strake to the butt block should be of equal strength to that of original butts. The fastening size should be equal or larger and no fewer number of fastenings should be allowed. Through bolts or machine screws are preferred fastenings in butt blocks because the joint will achieve maximum strength. Care should be exercised to avoid over tightening so as not to crush the planking or split the butt block.
Plywood butt blocks should be avoided because plywood has somewhat less strength than the "along the grain" strength of the basic wood from which it is made. Plywood is also prone to delamination and rot precipitation.
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Old 12-06-2007, 18:10   #10
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the main reason you don't put a seam but on a frame is that it stresses the frame at that point, and visually it createsa hard spot on the plank line that has to be planed off in order to get a fair curve in hull shape. what the but blocks do is pull the plank ends into alignment with the rest of the planking if the ends are properly fastened to the but blocks. i apologize for not elaborating more, but i did not want to run on as i have a propensity to do that. (known as i don't know when to shut up, and keep beating a subject up).

dave if there is a well stocked library or you could ask around for a book on plank on frame construction either Bud Macintosh, or Howard Chappelle, or I believe the other is Ian Nicholson. these books will tell you all you need to know about this subject and then some. they are actually quite good for (must have) reference material for the wooden boat owner and repair person.
i've been here and done that will a few woodies good luck
oh and by the way dave use the bleach sparingly as it will attack the wood fibre. start highly diluted and let it work if it does then slowly increase the strength untill you get the desired results. this is not an over nite process you have to watch it while you do other things around the area. when you start to get the desired affect immediately rinse with fresh water to neutralize the bleach. then let the wood dry and try the finish in a non conspicous area.
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Old 12-06-2007, 19:36   #11
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Gord May and mike d just stole my thunder so I would only add that the book How to Build a Wooden Boat by Bud McIntosh is available from wbstore@woodenboat.com $36.00 U.S. Excellent illistrations by Sam Manning. This book is one of the best on the subject from a lifelong proffessional boatbuilder. There are right and wrong ways of repairing wooden boats and the differance may not always be obvious to the novice. I think a good referance book would be a good idea.

This boat may leak alarmingly so when you launch her, being out of the water so long in a warm climate. Common practice is to leave her in the slings, on the ways car, or on the trailer, however you launch, for several days to give the planks time to take up and get the leaks to a managable level. I recently read an article about boat restoration and the authors used roofing tar in the below the waterline seams. The reason being that the boats were out of the water so long during the restoration that the seams really opened up. A flexible seam compound allows the planks to swell up and the excess compound pushes out from the seam. During the next haulout it was easy to trim off the excess compound. Not for the topsides as the tar will bleed thru the paint.

I don't think it will matter if you use fresh or salt water to soak it as it is just for a short time but salt is best. Fresh water leaking into the boat thru the decks is a major cause of rot in wooden boats. The salt water actually acts as a preservative.
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Old 12-06-2007, 22:05   #12
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Thanks for all the advice (again)
I am going to read through that pdf on repairing wooden boats.
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Old 12-06-2007, 22:32   #13
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Cutting this scarf joint ...

OK I have read that repair.pdf - actually it was the same one I read 3 days ago about the screws - but there is no harm in reading it twice

Now, in the repairs section it says that glued "plain scarf" joint is strong.
And I assume that this should NOT be on a frame (rib).

So my big question is - how do I make that sloping (or diagonal) cut in the plank that is on the boat AND on the one that is to be placed against it ?

I have a jigsaw which can do angles - but I don't know if it will keep a stable angle through out the cut. Actually I am pretty sure it won't.

Also on the plank on the boat will have adjacent planks so I would have to drill a hole first to get the jigsaw blade in - and that wont be at the correct angle - it will just be a mess !! (:

The other tool I have is a circular saw ( in US it may have another name) but again - how can I cut the plank that is in situ on the boat when it has adjacent planks ?

The diagrams of scarf joints are all very well - but how can I possible cut one ? If anyone knows - please help !!
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Old 12-06-2007, 22:38   #14
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try wooden boat products instead of the email address I posted in the previous post. This is the correct address for their store.
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Old 12-06-2007, 23:51   #15
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Dave - from your pics it looks like there would be plenty of room to in sert a jigsaw blade through the opened seam first then follow your cut line. You can buy wide blades for the jigsaw that will help keep a straight track. Just go slow and steady. When you fashion your replacement piece, cut the scarf too large to start and then by positioning the piece against the scarf in the plank already on the boat, you can trim either the scarf or the edge of the plank with a plane as required or sander etc to winnow down the wood in the needed areas to produce a good fit. Continue with backing board, screws and glue to finish. The scarf joint will also swell together during the take-up when you launch. BTW - those seams look to be previously caulked and are quite wide. You should consider pulling the old caulking and puting in new.

Good luck, Randy
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