What wood to use as cross beam on Catamaran.

[philipmclaren1]

Hi I am renovating a Catamaran and the main cross beams under deck are rotten, the beams were pine sheathed in fibreglass.
My Catamaran is 36 years old and I'm thinking, should I replace with pine and get a good few years, or should I use hard wood?
Hardwood seem the best option for durability but pine seems cheaper and more easily sourced.

[UNCIVILIZED]

I would think that anything meeting or exceeding Pine's physical properties would do. With the nod to species which are more rot resistant. And were it me, I'd likely build laminated beams, instead of solid ones. Using thinner layers of wood glued together with epoxy, & then sealed/sheathed.

[Bill O]

Not certain which Falmouth you are located (MA or UK). If you are in MA. look around for white oak which is a very rot resistant wood. A little heavier than pine, but doubt you'll ever need to replace due to rot. Do not use red oak. You can easily tell the difference by taking a small piece and blowing trough the end grain into a glass of water. Red oak will bubble and no bubbles w/white.

Should be fairly inexpensive as it's an indigenous species on the east coast of the US.

As suggested you could laminate the boards together to get the desired thickness and increase strength. I'm not a big fan of fully encasing wood in f/g, as it will eventually rot by trapping in the moisture.

Cheers,
Bill O.

[Cheechako]

You want something light. Are they solid or box beam construction? If you can get it out there I'd use Spruce #1 choice. Light and strong. Used for masts and bowsprits.
Douglas Fir would be good but a bit heavier. (not Hemlock or "hem fir")
If a laminated construction with epoxy etc Cedar might be nice. All are more Pac NW woods though. Hardwoods are not that rot resistant, but as mentioned White Oak (only white!) is traditional, although heavy.
There are pines that are rot resistant... I think southern yellow pine/long leaf pine? Not that familiar with them.

[philipmclaren1]

I went for some me hardwood I sourced locally, it's a bit heavier but hopefully not to much.

[philipmclaren1]

Used marine ply floor, just got to glass it in now [emoji31]

[Stumble]

Frankly I just wouldn't use wood. You probably couldn't even convince me to use aluminum. I would go strait for a large carbon tube. Given the amount of work it would take to replace the material cost difference is going to be pretty minimal, and the weight and stiffness gains would be pretty substantial.

It would take a bit of engineering, but you could probably scavenge a used carbon mast off of a much bigger boat for not much. Depending on where you are a repair shop for big sleds or yachts probably has a stockpile of old broken carbon rigs in the back somewhere.

[Flyingriki]

I fly a composite homebuilt. Our spars are a fiberglass box beam and can take a hell of a lot of load. Carbon potentially much more so. Why wood?