Advice needed: laminating and bending wide pieces of hardwoood (and saving cash)

[stuhaynes]

I'd appreciate advice from more experienced forum members. I've had our boat now for 11 years. She was launched in 1951 on the Thames in London and is mahogany on oak frames. I have changed planks in the hull, and done some steaming, but do not have a natural background in wood. We love the boat very much, she is our home, but she is reaching a point where I am going to have to do, what is for me, a serious level of woodwork.

I have truly been inspired by the work of the boat builders on here, and have learned a terrific amount about manipulating wood. If I can get the largest board I have to change into my head, I believe that I can manage the rest. So here is what I need to do:-

Our wheelhouse / salon leaks because the mahogany is rotting and soft in fairly large areas. I've previously dug out the rot, used Ronseal wood hardener, filled it and painted it. It still leaks.

The culprit is a 16 foot X 14 inch X 3/4 inch piece of curved mahogany. The curve is not massive but I do not have access to a steamer big enough to achieve it in one piece. So, my thoughts are:-

to make up the offending plank by using 3 laminations, each 1/4 inch thick - but 7 inches wide, not 14 (For the 2 outer laminations) The centre lamination would be one at 7 inches wide (between the centre join in the outer 2) and 2 at 3 1/2 inches wide to fill the rest.

I would expect to use the removed plank as a template for the new lamination.

From avidly following the 'boat build' posts I would use epoxy to bind the laminations, but which one? I know West 206 seems popular, but it is expensive. Maybe I won't need enough to worry about the cost?

Also, I can't afford to be puritanical about the timber? If I'm going to paint it, which I am, is there a problem using Sycamore instead of Mahogany? There is a massive difference in price. Pride wise, I'd rather use Mahogany, my pocket book says different.

So what do you think? All input appreciated. Stu.

[Mrleft8]

Sycamore.... Or "London Plane Tree" is one of the most rot prone woods there is..... Don't use that!
If you're going to paint it anyway, I might be inclined to look at pressure treated pine.... Heresy, I know...
But proper Mahogany will probably be your best bet in the long run....
The real question might be: Why is your current mahogany piece rotting? There must be some place for water to get in and not get out....

[Peerie Maa]

Sycamore.... Or "London Plane Tree" is one of the most rot prone woods there is..... Don't use that!
If you're going to paint it anyway, I might be inclined to look at pressure treated pine.... Heresy, I know...
But proper Mahogany will probably be your best bet in the long run....
The real question might be: Why is your current mahogany piece rotting? There must be some place for water to get in and not get out....

Lefty, we had this argument over two pages of a previous thread. English sycamore is not the same as yours nor is it London Plane: http://en.wikipedia.org/wiki/Acer_pseudoplatanus
this is the tree:

not usually used for boat building, and prone to rot in contact with soil, but no data on marine durability.

[Sayla]

The culprit is a 16 foot X 14 inch X 3/4 inch piece of curved mahogany. The curve is not massive but I do not have access to a steamer big enough to achieve it in one piece.

This isn't cheap wood, but should be readily available to you in one piece - it is here. The British had the foresight to plant stacks of it in Fiji about 50 yr ago and now we can buy it. If you can steam it all you need is a planer and a sander, and you don't need to by glue to laminate it, or worry about the glue getting wet and failing either - just replace the piece.

I've got Fijian sweetinia mahogany in the garage attic (which I've just about used up now, and need to buy a pack -cheapest way) - as a single piece purchase from the timber supplier that piece would cost me between 150 & 200 dollars.





sayla

[Todd D]

Since you plan to paint it, why not laminate it from three layers of 6mm plywood or 6 layers of 3mm.

[stuhaynes]

This isn't cheap wood, but should be readily available to you in one piece - it is here. The British had the foresight to plant stacks of it in Fiji about 50 yr ago and now we can buy it. If you can steam it all you need is a planer and a sander, and you don't need to by glue to laminate it, or worry about the glue getting wet and failing either - just replace the piece.

I've got Fijian sweetinia mahogany in the garage attic (which I've just about used up now, and need to buy a pack -cheapest way) - as a single piece purchase from the timber supplier that piece would cost me between 150 & 200 dollars.

sayla

Hi Sayla

Just out of interest, is the wood that you've bought green / air dried / kiln dried? All of the mahogany I've seen / bought is kiln dried and it can be a pig to steam with a homemade ply box and a wallpaper stripper to supply the steam! Stu

[Mrleft8]

What kind of curve are we talking about, and what is the piece used for..... IE: is it weight bearing, or more superstructure?

[Sayla]

Hi Sayla
Just out of interest, is the wood that you've bought green / air dried / kiln dried? All of the mahogany I've seen / bought is kiln dried and it can be a pig to steam with a homemade ply box and a wallpaper stripper to supply the steam! Stu

This stuff is kiln dried (notably dry when working it - use a mask), but it's also available air dried. It actually comes treated as well if you can source it. I've steamed it and I'll admit there isn't much of a bending window once out of the steamer, but it does bend easy when well steamed. As far as work reduction goes, I'd rather steam a piece than laminate.
Your piece is wider than my steamer, so I would make a squarish/cubic thin ply (or whatever) box lined with building insulation and an opening (and exit) like a letterbox, and put my $15 butane Gasmate camp stove with a kettle underneath, and bend it portion-ally over a drum or something as I made my way along the board - still quicker than laminating wide stock - but that's me, I'm not an expert........just trying to get out of work.

I just realised you wrote that you did "not" have access to a steamer big enough (I thought you wrote that you 'did').

Like I wrote - I'd make a box about 2ft square with a letter box opening to feed and exit, lined with scrap building insulation (or not), get a Chinese camping butane gas stove (15$ Aud), and kettle (?5$ Aud), a 4pk of gas cannisters and steam 2ft at a time and feed out and bend it as I went, over a drum or something (while rough sawn) then clean it up with a strong belt sander (if you have one). Or a 4ft long box and do it in half the time.

sayla

[Bill Griffin]

If painting the piece anyway, I agree with Todd D. Pictures?

[Cogeniac]

A 16 foot long board at 3/4 thick will bend pretty readily without any steam. Just how tight a bend are you looking for? If this is a roof piece, I doubt much steaming will be required.

At the boat shop I had Makoto at this last winter they did a Mahogany coaming that was probably about 12 feet long. They used steel straps on both sides and some sort of screw drive business to shorten the inside strap and lengthen the outside strap, so the whole thing would bend. They bent it into a 180 degree hoop with about a 3-4 foot bend radius. THAT required a lot of cooking.

I did the top of my canopy as you were thinking with three layers of 1/4 inch ply epoxied together. I did the lower piece joined in the center, the middle piece with two joints farther outboard, and the top joined at the center again. It worked fine, but I did this more to add stiffness to the canopy curve. I could have easily bent 3/4 ply to that curve.

[Gerarddm]

I'm with Cogeniac. A board that size and thickness should indeed bend w/o steaming. It will probably need some firm help, but go. If the plank curves more at the ends, you might try a re-saw cut at the end,; when you bend, the two (attached) halves will bend more than the single thicker plank would. You'd epoxy the saw cut in situ just as you were attaching the plank.

[AndreasJordahlRhude]

White oak - glued laminated with resorcinol. Standing knee for Old Ironsides.