Rebuilding Mast Step Area: Douglas Fir vs Marine Plywood

[arjand]

And just FYI, It will be thickly glassed over so indeed it will be the fiberglass that will be providing the strength (and than a big alum or stainless plate and than the mast foot).

[Seahunter]

Originally Posted by Cheechako

If thickly glassed over, I'd use Western Red Cedar. Cheap, light and wont rot. I still see fence posts up here that are about 50 years old out of untreated red cedar.

Cedar's too soft. It's extremely flexible (hence it's use in planking wood boats) but has no compression ability (except on the end grain) and would ultimately result in catastrophic mechanical failure.

[minaret]

Originally Posted by arjand

Thank you all very much!! Doug Fir is out, now researching the foam. thnx!!!

Good choice. You can laminate ridgid urethane sheet into any thickness you want just using spray adhesive, and then mill/shape it easily. It takes a router nice for radius', sands easy, etc. If you just use 5 lb. foam and then throw a very heavy laminate over it you dont need to worry about compression strength of the foam. If you want to do a lighter lam, move up to 10 lb. or denser foam. Here's where we get ours, a great supplier...

Fiberlay

Price per sheet for 1/2" Airex C70 5lb. urethane-
40216151 - SHEET,BALTEK 1/2" C70.75 RIGID 48"X58" OVERSIZE
$105.51

[minaret]

I like to drill limber holes with a forstner bit and then install 1" fiberglass tubing. I usually leave the tubing sticking out 3/8" extra and lay a little fillet around it with thixo, and lay up onto it while it's wet with some matt. Keeps the whole thing sealed up tight. The foam wont saturate or rot but you'd be suprised how much water can end up living in a structure like this below the waterline. Limber holes are extra important around a mast step for obvious reasons. The other option I've seen is no limber holes, seal up the step up tight and put a pump in there, so water coming down the mast is isolated and doesn't get in the bilge.

[gonesail]

Originally Posted by atoll

the best long term solution would probably be to do the whole job in glass

agree .. something that will not rot .. seen wood under the mast before and yes it rotted.

[arjand]

wow... just going to the Home Depot for PVC duct is looking for trouble? (using WestSystem to glue them in).

[minaret]

Originally Posted by arjand

wow... just going to the Home Depot for PVC duct is looking for trouble? (using WestSystem to glue them in).

If you mean pvc duct for limber holes, it works OK. You can goop in some PVC with Sika or whatever. The reason I like glass tube is that if you glass them in immediately after glassing in the step you can coat everything with gelcoat all at once and it looks great and stays easy to clean. Looks very proffesional, like it was made that way. PVC pipe looks like amateur hour. And eventually it will probably fail. Glass tube is permanent, will never leak, and looks like you actually know what you're doing. Little things like that are why we get paid the big bucks to work on megayachts. The forstner bit is important 'cause it helps you make the cut down in the fillet, so you dont have that last bit in the corner that wont drain and grows mold. Hole saw works too if you put a pilot hole all the way through both sides first for alignment purposes. Glass tube really doesn't take too much longer than PVC anyway, and we always have some kicking around...

[Jim Cate]

G'Day Minaret,

I think that your approach is great, but for us innocents out here, just what is a "forstner bit"? Never have heard that one before...

Cheers

Jim

[minaret]

It's like a hole saw but instead of cutting a plug out, which limits your depth of cut unless you pull the hole saw out and chisel out the cut every inch or so, it shreds everything in the cut into shavings. This means you can make a single cut the depth of the bit's shaft without stopping to break out the center of the cut. I find it much easier to line up something like a limber hole cut with a forstner than a hole saw. Obviously the start side is easy but you need it to come out the other side at exactly the right elevation. If you start a hole saw cut from both sides and meet in the middle it's difficult to keep it straight. If you are doing glass tubes you can do a hole saw cut a little oversize 'cause your gonna glass in anyway and then do the meet in the middle technique and have enough slop to make it work with out having to grind in the cut. Or you can use a jobber length bit the same size as the pilot bit on the hole saw all the way through and then cut from both sides, but then it's hard to get the elevation perfect. Forstner bit solves all that for me.


Irwin Industrial Tool Co 42934 2 1/8in. Forstner Bit#

[Jim Cate]

Originally Posted by minaret

It's like a hole saw but instead of cutting a plug out, which limits your depth of cut unless you pull the hole saw out and chisel out the cut every inch or so, it shreds everything in the cut into shavings. This means you can make a single cut the depth of the bit's shaft without stopping to break out the center of the cut. I find it much easier to line up something like a limber hole cut with a forstner than a hole saw. Obviously the start side is easy but you need it to come out the other side at exactly the right elevation. If you start a hole saw cut from both sides and meet in the middle it's difficult to keep it straight. If you are doing glass tubes you can do a hole saw cut a little oversize 'cause your gonna glass in anyway and then do the meet in the middle technique and have enough slop to make it work with out having to grind in the cut. Or you can use a jobber length bit the same size as the pilot bit on the hole saw all the way through and then cut from both sides, but then it's hard to get the elevation perfect. Forstner bit solves all that for me.


Irwin Industrial Tool Co 42934 2 1/8in. Forstner Bit#

G'Day Minaret,

Thanks for that! I've seen these in use but didn't know their name or a good source for them. Look really useful. How are they in FRP? And can they be readily resharpened?

They don't appear to be much dearer that decent quality holesaws, but they're not cheap. Have to figger out what sizes are critical.

Again, thanks.

Jim

[hummingway]

They cut a much cleaner hole then any holesaw I've ever owned and you don't have to wrestle the stuff out of the middle.

[minaret]

They need to be sharp to cut glass nicely, but they are easy to sharpen. Just dont stop a cut while you're in glass if you can avoid it. They also make nice flat bottomed pocket cuts, and can be used in place of a counterbore when you want to bung a large fastener like a bolt in wood.
Must have gear I think. They dont replace a hole saw though, they have their own niche in the toolbox.

[minaret]

And remember, for hole saws in FRP, use carbide abrasives if you can. So much nicer, no blowout.


http://www.holesaws.com.cn/products/...aw/gritsaw.htm

[arjand]

This is how it looks now, I made an album with more pics.