CS 17 Start

[smacrae]

Have started my CS 17. Actually, the work to date has been building a boatyard, sewing a tarp to cover said boatyard and glueing up a blank for the centreboard. Ripped up a length of 6x2 spotted gum and laminated it as per the plans. It was an old floor joist I've had kicking around for about 20 years - it's now very well seasoned and hard as the hobs! My ply arrives next week.

Questions:

The plans specify 3" tape; is cutting your own tape a reasonable alternative? I have heard the selvedge edge of the tape creates some problems.

What sort of fibreglass cloth should be used? Woven rovings, chopped strand?

Masts: I have an 8x2 length of clear western red cedar (17 foot long). If ripped, laminated and sheathed in glass, would it make an adequate mast?

With thanks

Steve

[Melissa Goudeseune]

Some answers:

I used 3" tape on the Minipaw. As you described, the edge is a blessing and a curse. The tape doesn't unravel when being handled, but it does create a ridge which should be faired or ground down with a scraper.

With careful handling, cutting your own tape from cloth should be just fine. Charlie posted a thread yesterday about "circular cutting wheels" which make cutting fiberglass MUCH easier than using scissors.

I would stay FAR away from the chopped-strand mat fiberglass. It's normally used in a multi-layer layup, alternating with woven roving. It will also absorb lots of epoxy, which will only serve to make your boat heavier and more expensive. Stick with woven roving or biaxial at the most.

I'm not sure about the 8x2 dimensions you refer to for the mast. Inches, centimetres? Birdsmouth would probably be the best lamination for a wooden mast. Charlie's a much better source for info on birdsmouth construction, but I doubt that glassing it would really be necessary. Also, there may be better woods than cedar for a mast. Charlie?

Michel

[Charlie Jones]

I would think that would make a strong enough mast BUT I'd worry somewhat about the softness of it holding fastings, most particularly in the way of the snotter attachements.

I've build all the birdsmouth masts I've done using Douglas fir. Six masts, one boom and one bowsprit so far. Being totally unfamiliar with what woods are available down under, I'd suggest something that matches that- the fir that is.

And no- there is no real need to glass the spar.

Cutting your own tape would work fine. I really don't know though which is more work. Cleaning up the threads that invariably get loose when using self cut tape, or using a carbide scraper to do away tath that selvedge edge on the tape. For me it's kinda a toss-up. Of course using self cut tape also means shorter pieces- sure is nice to just roll out a long strip to do a chine or whatever.

Also- on exterior surfaces, and on interior ones too where you can easily reach, a flap disc in an angle grinder makes very short work of that tape edge too.

There's no need for mat in a Core Sound boat. Cloth and tape does it all.

[mustangermatt]

I would recommend aganst using red cedar for a spar. The fiber length is much shorter than spruce or fir. Also the fibers seperate REALLY easily. Thats one of the reasons it makes such great kindling :-)

It works really well for planking though.

[smacrae]

Thanks for your answers.

My apologies re units of measurement: the dreaded imperial/metric challenge. In Oz, most builders, timber yards (that's "lumber" to you) deal in millimetres or metres. We also put our larger measurement first. So a board might be 4800 x 150 x 50 mm or in your old fashioned terminology 16' x 2" x 6". There was a lot of grumbling in Australia when we changed from imperial to metric, but once you've worked in metric, using millimetres as your base unit, the advantages become obvious.

We have Douglas fir over here. We call it Oregon. Like all timber, top grade clear stuff is becoming harder to find and more expensive.

Looks like both self cut and factory made tape have their places. Am unfamiliar with carbide scrapers - presumably these are readily available from hardware stores as are the cutters Charlie mentioned.

When birdsmouthing long lengths I would presume that a tilting arbour table saw would be useful. For those of us without such luxuries, what other methods are available?

[Frank Hagan]

If the Oregon Fir is very expensive there, look for a local wood that can be used, although I seem to remember Australians saying they used Oregon or spruce because, even with the shipping costs, Oregon was a better deal than the other straight grained woods they had a choice of.

You can make the birdsmouth cut with router bits. See http://www.timbecon.com.au/products/torquata-jointing-bits-435_0.aspx which looks like a company "down under" to me. You'd want the bit that makes 8 sides. Need a router table for this though ... you wouldn't be able to balance the router on the edge of the timber and cut the v-shaped groove.

[Charlie Jones]

And the cutter I spoke of is a fabric cutter. Available in most any decent sewing center. Called a Rotary cutter. Get one with a carbide or tungsten carbide cutter wheel. I have since found out that sharpeners are also available.

[smacrae]

Thank you once again for your replies. Quite a learning curve this boat building. I can see why it is so hard to stop at one!

I've ordered a birdsmouth bit from Timbecon (thanks Frank) and am hoping to pick up a rotary cutter in Cairns on Monday. (thanks Charlie)

More mast questions: I want to use a sail track, so any tapering must be smooth. Does that mean I have to taper the eight sheaves that make up the mast?

Secondly, is rounding off the mast a matter of planing the corners, or do I build a 20 foot long lathe or some other jig?

[Charlie Jones]

You just plane the corners. On larger spars I start with an electric hhand plane, then go to a jointer. On smaller sticks I just use a bench plane, then the jointer. You could do it all with just a smoothing ( bench ) plane. Not hard.

I generally plane the corners flat so I have an 8 sided spar, then start rounding. You can leave one flat flat for the sail track or round the entire spar.

You can start a taper at any point by simply tapering the side of each stave opposite the mouth. The formulas on Frank site will let you figure how much. I rough cut with a band saw, but a jig saw would work OR you can draw lines and just plane it down. Use the first one as a giude and make the other 7 match.

Here's three pics of a 22 foot mast I built for a gaffer in Florida. First one shows all the staves cut and ready for epoxy. This mast was straight for 17 feet, then tapered from 3 1/2 inches to 2 inches at the mast head.

Second shot is the staves all glued up. I use bicycle inner tubes as clamps. Just spiral wrap stretching tightly as you go. Check to be sure everything is straight while the epoxy is still uncured. You can lay it on a flat concrete floor and get a straight side by the way.

Third pics is from where I split the spar open to add the internal blocking. I left the opposing mouths un glued - actually added packing tape in them so the COULDN'T get glued. Then opened up the two halves, added the blocking cut to fit closely, then glued it back together finally. On a small spar this wouldn't be neseccary since you can drill the ends and insert solid wood that way. On a 12 foot stick you don't need anythings in way of shrouds, etc. This mast required solid blocking inside where the gaff jaws sat and where the shrouds attached.

At any rate, you can get some idea of the process. I have built an 6 foot bowsprit ( using a table saw) in a flat three hours working time, not counting epoxy cure time of course. And that was to the round, sanded, ready for finish condition.

[Charlie Jones]

oh - and one more shot- the finished spar being load tested

[Dale Niemann]

One other thing you might consider. Once I finished planing the birdsmouth top section on my CS17, I put a small drum sander (1 1/2 inches diameter) in my portable drill and inverted (turned inside out) a 24 inch sandpaper belt and used it to sand the spar. It worked very well. I think I started with about 80 grit and just increased it until I was satisfied with the finish. I then epoxied and varnished it.

[Charlie Jones]

Getting mechanised eh? I made a ""plane" from some plywood and a chunk of PVC. It's sized to take a standard sheet of sandpaper. I use spray adhesive on the insides, then just peel off the sheet to change grits. Actually I have several- they are pretty cheap to make

[Frank Hagan]

Charlie, you are a genius!

[smacrae]

Not only a genius, but ingenious! Can hardly wait to build my mast!

What a wonderful medium the WWW is for disseminating ideas across the world and cultures. It's such a shame that others choose to use it for darker purposes. The knowledge you blokes share is humbling - I only hope that soon I will be able to give rather than just take.

Another question: Charlie, you mentioned "The formulas on Frank site". For the life of me I can't find this formula - could you lead me to it, please?

The plans mention a composite aluminium/timber mast. From an aesthetic point of view I would prefer all timber. Any recommendations?

with thanks from the apprentice

[Guest Oyster]

People also use the aluminum and paint the masts to simulate wood or to remove the metal look. I think I recall someone even laminating wood to the masts, as a skin.

[Charlie Jones]

If X is the stave width, then Diameter = 2.5X and stave thickness =.5X

So if a mast is to be 3 1/2 in diameter, the staves would be 3 .5/2.5 or 1.4 inches or roughly 1 3/8 inches. It isn't totally critical . The stave thickness would then be 1.4/.5 or roughly .75 or 3/4 inch. Again, it isn't totally critical. A 16th off on either of those will work just fine.

I've found that that formula will put you very close though and it gives excellent strength to weight.

[Norman Colter]

Steve,

Go back a page and check out The launch of P22 #19. John Manchester left a link to Franks site. It's a five page download that gives you a lot of useful info.

Charlie, thanks for the tutorial. I had figured that i'd need some sort of solid support where the mast hinges on the tabernacle. Now I know how to get it in there

Norm

[Frank Hagan]

Another question: Charlie' date=' you mentioned "[i']The formulas on Frank site[/i]". For the life of me I can't find this formula - could you lead me to it, please?

Heh ... I never copied that page over, and I should have. Its on my site about building my Weekender, which is the site that got me started on the Web. Its at http://users2.ev1.net/~fshagan/bm.htm

I downloaded the info again and will make it an Article for messing-about.com. I'm disappointed the Google Search box I added for the site search really doesn't return good results, but gives you links that take you to a forum index page; its hard to see which of the 25 forum postings has your info. :cry:

But entering "bird's mouth mast" at http://www.boardtracker.com shows these useful links in our forum pages:

http://www.messing-about.com/forum/viewtopic.php?t=2489

http://www.messing-about.com/forum/viewtopic.php?t=3053

http://www.messing-about.com/forum/viewtopic.php?t=1618

http://www.messing-about.com/forum/viewtopic.php?t=2233

I'll have to see how I can add a BoardTracker search box to the header so that we can get some useful searching done here!

[Frank Hagan]

OK, added a search box up there for people to use ... it works much better than the built in search function the Forums have, and much better than Google (which really isn't designed to index forum posts). Type "bird's mouth mast" in there and click "Search" to see all the posts here on the subject.

[smacrae]

Good on ya, Frank: the search engine works well. It will certainly stop me posting queries that have been already adequately covered.