laminated mast using two or more species?

[pdq123]

Merry Xmas, all!

With all the cold weather lately, I've been doodling in my notebooks again. My current sketch topic is a coastal cruiser design, basically a plywood dory type. A laminated wood mast seems like it would be a good approach. But any wood thats light enough for a solid or nearly solid mast isn't going to offer the hardness and strength I want in way of fasteners. For example, consider a solid laminated mast of rectangular cross section, with layers of flat stock oriented fore and aft. Here's one layup configuration;

(port)

oak
D fir
D fir
D fir
oak
D fir
D fir
D fir
oak

(stbd)

Oak on the outer laminae not only for holding the fasteners for shroud tangs, spreaders, etc, but also because the bending stresses will be highest there. Oak also on the center laminae because of the fastenings for the mainsail track. I'd not wedded to Douglas Fir and Oak as the two woods, they just happen to offer roughly reasonable densities and general properties. This way, the mechanical properties of the mast can be tailored to the loads placed on it, with an easier construction task than fiberglass or aluminum.

Aside from materials cost, glueline reliability, and labor, the only show stopper I can think of is differential movement. It seems to me that if the layers are thin enough, movement isn't an issue; plywood being one example, also cold-molded hulls. If each layer is 1/2" of flatsawn stock, and the mast is sealed with epoxy or other wonderglop and painted with a good epoxy or PU paint, will movement really be an issue?

[gonzo]

All the glue will make the mast heavier. A strip of a harder wood to hold fasteners is common practice. For example under the sail track.

A simple way around the anchor pullout problem is to notch out the mast for hard wood " PLUGS " while it is still straight sided. It was done on a lot of ST. Lawrence River rowing skiffs. Some of the masts are +50 and still in use. It looks a little different, but very serviceable and repairable.

[Eric Sponberg]

PDQ,

If you are using epoxy resin or glue, it will not stick to the oak very well. One should never use oak and epoxy because it will delaminate quickly over time. Spruce is the most common and recommended species for spars because it is strong and stiff for its weight. For fastenings, you can follow the methods of the Gougeon Brothers (WEST System) for potting screws and bolts in epoxy.

Eric

[pdq123]

Thanks for the replies.

Doh! Forgot about oak's badness w.r.t. gluing. Not a mast question, but how is black locust for gluing? Its often recommended as an oak replacement, but I've never seen talk of gluing locust and I didn't find anything via Google.

Try www.hardwood.org---It really has great info on all American woods. Could help this thread.----------------------------------------There is nothing wrong with the web site. Do a search.

[tschienque]

Having attended Gougeons workshops and seen tests conducted with 3/8 welded eye bolt screwed into cheap 2x4 stock blocks.

We (attendees) after having been informed about "hardware bonding"/potting were left to create our own samples to test following day.

Hydraulic press was set up to pull fittings out of block

• baseline block with eyebolt simply screwed in failed at approx 500lbs
• eyebolt threads coated with epoxy resin failed at about 900lbs
• attendees samples failed at 800-2100lbs

This was just with overnight cure. Holdoing should be improved when full cure is achieved.

Gougeon technical staff stated no sample had exceeded 3000lbs of pull, stating eyebolt failure (deformation of eye) at that level as main cause.

Highly recommended!

[pdq123]

I looked at the WEST system page and the brief descriptions of the "cast-in-place" method.

tschienque, did those eyebolts have regular woodscrew type threads?

[tschienque]

Originally Posted by pdq123

tschienque, did those eyebolts have regular woodscrew type threads?

Yes it was threaded like a wood screw (a welded eye headed lag screw would be best description) .