Wood- Technical question.

[duncanmack]

I have a couple of problems with wood.
1 It can't be welded.
2. I don't know very much about it.

Having said that the problems are actually with replacing the rubbing strakes and the main beam under the companionway on a Hurley 30/90 - I know she's a MAB but she's mine and I love her dearly. I reckon you guys will know more about wood than the avarage MAB owner and should give better advice.

I've been offered some green oak. I know it will be easy to bend for the strakes, but will it shrink as it dries and if so, by how much? Is it a bad idea? The strakes will be 10m finished length and about 70mm by 35mm. Will it bend or should I laminate them?
Is it sensible to use this for the beam under the comanionway (2840mmx160mmx25mm) . The main track is bolted through it and it's glassed on to the hull at either end. Will it shrink?

Should I get something else?
Recommendations/advice gladly received.

 

[Captain Coochie]

I dont work with unseasoned ( green ) timber but from what i know about it it will shrink and may well split aswell . Depends what it wants to do really .
alot of church roofs where built with green oak or other unseasoned timber so they could bend the arches and work the joints easier . I suppose they just allowed for shrinkage in the joints . If its for a rubbing strake then it will only shrink along the width so you should be ok joining it length ways , it should bend in as its quite thin so no need to laminate it .
Back to the church roof thing , there is a church oop north where the timber moved in the worst way it could and the spire ended up twisted . Its still like that to this day .

 

[absit_omen]

I worked on green oak last week making capstan cheeks. Don't know if it has shrunk but it has certainly split in spite of loads of linseed on it - applied daily. However, does not matter as it adds to character /forums/images/graemlins/smile.gif

I would go for teak, or iroko if you can't afford it.

 

[burgundyben]

I'd say Iroko for the strakes and mahogany for the beam, really could do with a better description of the beam, its purpose and shape.

you're in the right place.

 

[exfinnsailor]

Used green oak on a verandah I built .. As previous .. It splits .. Twists .. and does its own thing .. Have just laid a new patio using Iron Wood .. Its rock hard it ruins drills .. it splits .. it does not bend .. and the splinters are something else .. /forums/images/graemlins/smile.gif .. Looks great though ..

 

[Lakesailor]

Well I used Iroko on the dinghy gunwhale and it was a bugger to steam and bend. But probably not as much bend required for your rubbing strakes. If you can get teak, I'd go with that for them.
Beam? Don't know but probably seasoned oak.

 

[duncanmack]

[ QUOTE ]
I'd say Iroko for the strakes and mahogany for the beam, really could do with a better description of the beam, its purpose and shape.

you're in the right place.

[/ QUOTE ]


Straight beam, dimensions as given. Difficult to describe though it doesn't seem to be critical to the structure. I'll take a photo of it on Tuesday and post it. It is a case of a picture being worth a thousand words! /forums/images/graemlins/grin.gif

 

[Cliveshep]

Oak of the sizes you mentioned needs to be seasoned for about a year outside, covered over but not covered up, air allowed to circulate for natural air drying. Putting some hefty weights on it might discourage it from twisting too much. You can of course beg someone to kiln dry it for you but.........that dries it too much.

Moving on to steaming, once seasoned you'll have to steam it to bend it. Here's the rub, once you steam it it'll take up moisture and expand, shrinking back over a period of weeks as it dries out again. Dare I suggest.........for the deck beam, steam it as it is and make a beam overlength and temporarily marry it up to the existing one to give you some deck support and let it dry out during this year with the intention of properly fitting it next year? With the rubbing strakes, I'd just go ahead and use it, oak often shakes like billy-o anyway as it dries so there is no guarantee you won't have some splits to deal with.

All of the above is based on your own words "I've been OFFERED some green oak" which says to me it is a freebie, much to be desired compared with buying teak or mahogany but that's only my opinion.

 

[misty56]

I am a fan of oak for the right jobs, but I don't think it's right for either application you mention.

In general, oak (given your source I'm presuming it's a Quercus spp of domestic origin) is notoriously variable in quality and you must take great care to avoid any sapwood (the paler, softer part on the edges of the planks) if present. It's unlikely you would do this on a boat, but never use ferrous fasteners with oak--it's quite acidic.


More specific to you, Oak contains a lot of tannin, which will leave nice dark streaks (which are bloody nearly impossible to remove) on your topsides if you use it for the rubbing strakes.

I would not personally use oak to replace the glassed-in beam either. Oak is not stable, and it will twist with variations in heat and humidity, but it is very strong indeed and may well simply break the glassing--possibly in such a way as you can't see the damage. You're not needing a lot of wood, and I'd suggest Iroko or mahogany there (Swietana spp, NOT one of the fake mahogs like keruing.) Elm would do nicely too, though it doesn't like being wetted and dried--but in your application should be okay.

 

[monkey_trousers]

curious about the none ferrous comment for fasteners. Just about to replace a few deck beams on the panser, the oak is arriving this week

the larch deck is nailed through to the oak beams using iron nails, can't get much more ferrous than that...

they been there for 70 years, and have indeed 'reacted' with the oak, but in a good way, the flipping things are totally and utterly immovable, the one I did manage to pull, was as hard as well, iron! cut it in half to see what it was like and the nail was totally solid right through

as for green or seasoned... I'd always assumed seasoned is best, and thats what we've just bought, but have heard contrasting opinions, one builder reckons green is best, for beams especially, and doubly so if there's any steaming involved

depending on the dimensions, and with a little nosing around, have you though about trying to source a bit of grown oak, rather than having to bend a bit?? can't imagine your deck beam is going to have a massive curve in it or be a huge muckle great big affair, track down a bit of seasoned grown oak and you've gotten rid of heaps of your problems already, will just a bit of sweat and drudgery with a plane to knock it into shape

 

[laurance]

In the days when commercial vessels were built out of timber it was generally green: easier to cut, chisel and bend. The trick was was to get it into its natural element without delay.
All timber will eventually balance its moisture content with the environment it is used in and between seasonal variations. Working with green timber the aim is slow drying, thus if you fit your rubbing strakes now and then sail of to the Med for the season then expect them to shake and perhaps split.

 

[Kukri]

Up to a point, Lord Copper.

Please cite some evidence for this as it goes against everything that I have ever heard or read.