Thread: Boat ribs

Howdy,

Depends if they are sawn frames or steam bent frames.

Often, these days, people will laminate replacements as it is simpler and faster with less setup (fewer odd things to find and make work) and less risk of things going wrong. It also widens up the timber choices.

If steam bending timber it needs to be green unless the bend is very slight.

Best wishes
Michael Storer.

Thanks Boatmik, yes in conversations outside this forum people are talking to me about laminating and it makes good sense. As you say it makes it easy to get the timber.

My understanding is you prepare your strips, apply the epoxy, wrap in plastic?, lay next to the rib your sistering, adjust as needed, and then temporaraly fasten till dry. Then remove, clean up, and fasten. How does that sound? Any suggestions appreciated.

Its a classic little fishing boat out of Koiroit Ceek williamstown with pram hood etc, and does have steamed ribs.

Jimmy

Attached is the best way to install a rib repair. The laminate you've described will work, but this method just gives you the shape, not the attachment. Sistering works, though it's "clumsy" to say the least and often depends on location to be preformed well. The scrafed in repair (shown) under paint is invisible and under varnish clearly shows someone cared about the quality of the repair, rather then the ease of it. The adhesive of choice is epoxy, for both the laminate and the repair.

I'm getting my money's worth from this forum, thank you. Mine is a small boat and ribs are only 12 mm thick do you think a scarfed repair is possible?

At this thickness would it be best to replace the ribs completely one at a time?

I assume with a scarfed repair you still need to bend the new section rather than cutting a curved section, so grain strength is maintained. As is logical my ribs are fractured at the point of maximum curve so i guess I would need to give it a go and see if I can get an insert in place.

How would you cut the diagonals, lots of care and a good panel saw?

Sistering has its place too.

MIK )

Sistering is a technique that works, it's fairly cheap in labor, though it adds weight and looks cumbersome and cobbled together.

I assumed you were going to laminate the repairs, which means you'll bend thin stock into the shape of the curve. Since you're 12 mm thick, three 4 mm layers or better yet, four 3 mm layers per rib would make a very nice repair as they'd be easy to bend in and brace.

The typical technique is to "cast" them right along side of the broken one. This naturally assumes the local area around the broken rib isn't deformed as a result of the break. If it is, then it has to be braced or proped back to where it belongs or you'll cast the repair to the distorted shape.

Clean the area very well, so regular plastic packaging tape can be applied and stick. Place lots of tape around so you don't get epoxy on things you rather not. Arrange the blocking and bracing necessary to hold the 3 or 4 repair pieces in place. Do several dry runs, so you have this part worked out. Butter up the wooden strips and brace them into position on the tape. When cured, they'll pop right out, the same shape as the hull. Remove the tape and consider how you'll attach them, sistered or scarfed. Sistered, all you need to do is trim up the ends, maybe the sides and fasten them to the planking. Scarfed, they'll need to be "fitted" which means cutting the "ramps", but with epoxy this isn't an exact science, just cobble the ramps as best as you can, the epoxy will fill the gaps and make you look like a pro under paint.

One last note a sister repair is typically much longer then a scarfed repair. This is because you can employ the use of the old rib with the scarf, but the sister has to "bridge" the damaged area and have enough "bearing" on surrounding planking to hold it's shape, which generally requires a longer repair piece.

Perfect

MIK

Perfect, then call my other half and reminder her . . .

When i re ribbed my 15 ft clincker, after much talk with local fishermen and a go at green spotted gum that i think was too thick for the size of my boat, I settled on using celerytop pine from Mathews Timber in Melbourne. To help prevent splitting I planed the corner of the top edges after determining what way it bent easier in relation to the grain. An alternative to steaming that worked well for this project was having a solid steel tube 6 inch diameter, welded one end and propped on an angle filled with water. Light a fire under and bring to the boil, add a splash of kero to the water and it boils at a higher temp. This is exactly how a 40ft long 2 inch thick plack of spotted gum was bent into place on the Alma Doepel when i helped the shipwrights do some work on her hull 20 years ago. Hammer a nail into one end of the celery rib so it catches on the end of the pipe and doesn't fall right in. Place a heshien bag or something simmilar over the end of the pipe and boil away for 20 minutes. Wear gloves when handeling the hot timber. Its also worth mentioning, that if a few ribs in a row need replacing only remove the rib you are replacing to help keep the shape of the boat intact and as Par said, you might need to apply some counter force to the outside of the hull to stop it loosing shape when bending the rib pushes on the hull.

Thank you Hallam that sounds just the shot. I'm desperately trying to tool up as I have 2 weeks at home over Xmas for the first time in years. I have the pipe, tools and fasteners, the timber is all i need. Will ring 'em tommorrow

Howdy,

The way that a water/hydrocarbon solvent mix will work is that the solvent with the lowest boiling point will start boiling first before the other does and evaporate off. The temperature will not usually be able to rise much above the boiling temp of the water until it all evaporates.

When the water is mostly gone the kero will get up to its normal boiling point (around 150deg)

That's the way you do solvent extractions in chemistry. We had a temperature readout so you knew what was evaporating at the time. We were putting heat into the system quite slowly, but I would expect the temperature trends to be the same. Someone could check by boiling some water on the stove with a thermometer and adding a splash of kero and seeing if the temp goes up any or much.

It doesnt' mean the method doesn't work, but the kero probably doesn't make any/much difference. I could be wrong of course, but a splash of kero won't make a lot of difference and a large proportion could be quite exciting (bazooka).

Or often with "folk methods" there can be some other good reason for doing it, but the wrong explanation is given. For example steel used to be quenched in young boy's urine. This means that some nitrates may get incorporated in the surface increasing the toughness and durability. Also the higher impurities mean that the urine is likely to be more effective in contacting and cooling the blade. Clearly an old blokes urine would probably work just as well, but the young boy was chosen to give the blade more "vigour".

Steam is far and away the best way because it is much hotter than boiling water or boiling kerosene. Probably looking several hundred degrees even with a basic setup. That's why steam burns are so serious and steaming vegetables can be way faster than boiling them.

Steam is very much more efficient for bending as it gets to a much higher temperature than water. Water will never raise above the 100C (just like pure kero won't be able to get above 150) but the steam will be able to get well above that.

The heat does the job, but the moisture is important as it prevents the wood drying and becoming brittle. Green timber is important because the moisture inside makes sure the timber is not brittle and also helps the heat move into the timber more efficiently as the internal water turns into steam, but if the timber is full of air then the air is a very good insulator.

Best wishes
Michael Storer

Mik has brought up two good points, the first is the use of kerosene in a boiling mix for bending wood. This is an old school trick and the kerosene is falsely believed to help in rot prevention, more then raising the boiling temperature. It's was quite common for traditional builders, to slather this stuff all over everything going into a boat. The technique is all but frowned on now, partly because of the fire hazard, but mostly because of it's limited effectiveness as a wood preserver.

Now the old school wood type are up in arms, but testing has easily and repeatedly born this out. Not that petroleum products don't help, they do, but you'll want oils lower down in the cracking tower then kerosene and preferably drawn in (vehicle) with petroleum products from even further up the cracking tower then kerosene.

The reason steam bending is preferred is two fold, heat and wet heat, which steam has in abundance. The heat helps soften up the cellular walls in the wood fibers, promoting bending without tearing them. The moisture makes the cells swell up and partly fill with a combination of very hot gasses and moisture, which prevents the 6 sided cells from collapsing, as they are distorted in the bending process. Lastly a by product of the steaming process is it steralizes the wood on a cellular level. This kills off mold, fungus and animals, that might be living in the wood, leaving the steamed result much less prone to rot.

As a rule boiling is used on easy curves, but the serious stuff needs to be steamed.

Just thought of this.....before you buy you timber. A visit to Joe Pompei yesterday reminded me when i saw the frame up of a boat he is building. I remembered quarter sawn or vertical grain bends with a less likelihood of splitting than slab cut or horizontal grain.Also you have to work quick once you have the timber out of the steamer and it's really a two person job. One on the inside with a drill, roves and dolly, and the other on the outside with the hammer and copper nails.

Re the kerro etc i haven't done the job often enough to know anything other than what some of the old fellas have told me so it's good to have a few myth busters with more experience on the thechy side of the job throwing in their two bobs worth

Hi MCJ,

The key is to make sure your timber is sawn on the back off ie with the annual rings parallel to the wide surface. By far the easiest way to go is to use thin laminates of dry timber say 2.5 mm to 3.0 mm thick bent and joined in situ with marine epoxy glue. Standard joinery approaches apply to preparing the laminates. Good luck; this is not a job for novices.


Old Pete