Caledonia Yawl mast dimensions?

[StevenBauer]

So Mary and I are crewing on Chris's CY at the Small Reach Regatta in a couple of weeks and I just heard that he broke his mast on Wednesday. So we have a line on a couple of 18' Fir 2"x6"'s. Do any of you guys have the dimensions of a CY's mainmast?


Steven

[TerryLL]

Yes, I have them, But the plans are out at the site. Will post tomorrow if no one else responds.

[StevenBauer]

Thanks, Terry.

[StevenBauer]

Found 'em! Sometimes it's nice to have an almost complete collection of WoodenBoat Magazines. # 185, 6/7-2005 page 43. Geoff Kerr's article shows all the spar dimensions. Now I'm off to check the birdsmouth spar calculator.

[TerryLL]

Pics of the mast build are required.

Any idea how the mast broke, or how it was built?

[StevenBauer]

Well I guess it was really windy... He said in hindsight he probably should have reefed.

Not the greatest picture but I'll take more tomorrow:


Here is the Doug Fir for the new mast:


I think one of the reasons the mast broke is that it was a little undersized, only 2.75 inches instead of the 3 1/8" the plans call for. We'll work out the details for the new mast soon.

[teresajude]

If the design diameter was 3-1/8" and the as-built dimension was 2-3/4" the mast was badly undersized. A little diameter makes a huge difference on strength; strength is proportional to diameter raised to the fourth power. His mast is 12% undersized, and so has only 60% of the strength of a properly sized mast built of the same material.

For the new mast, if the 2x6's are not rough, he may be tight on material. Best of luck with the new mast.

God bless!
Wayne

[StevenBauer]

Yes, definitely undersized. And no reinforcement up past the partners. The new mast will be much stronger than the old. We're switching from Spruce to Fir, increasing the diameter and stave thickness and adding a core at the base that will go up past the partner. I was talking with Clint about the new mast a little tonight. A hollow mast should have its diameter bumped up 5% and the last one was smaller by 12%.
I think there is plenty of stock here. I can get six staves out of one 2 x 6 so even when I make one extra stave I'll still have half a 2 x 6 left over.



Steven

[Clinton B Chase]

If the design diameter was 3-1/8" and the as-built dimension was 2-3/4" the mast was badly undersized. A little diameter makes a huge difference on strength; strength is proportional to diameter raised to the fourth power. His mast is 12% undersized, and so has only 60% of the strength of a properly sized mast built of the same material.

The CY mast is a great example of why you cannot convert to hollow BM and not do some re-design. Sometimes you need to bump up diameter as much as 10% to get the strength, which I understand to be proportional to diameter to the THIRD power not 4th as cited in quote above. Nevertheless, diameter is important as is the correct wall thickness which of course is a function of the diameter.

I think the original mast diameter is actually too small for the solid version too. A lug mast needs to be rock solid, that is to say no bend. When the lug is set with firm downhaul tension to flatten the sail, improve upwind efficiency, if the mast bends this luff tension releases and the sail loses some shape. Also a CY is a big boat and loaded up with crew (3 up) and a stiff breeze, there will be some real stresses on the mast.

A SOLID mast for a CY should be more like 81-82mm esp. if it is done in Spruce.

[TerryLL]

I'll soon be spar building in my CY project and I've got a question about the main mast. I've got a couple nice sticks of really tight old growth Sitka spruce that I had milled for another boat that will serve for a solid mast.

Would there be any real advantage to building a birdsmouth mast over simply building a solid spar, other than some weight reduction?

[Hwyl]

I know I'll be lambasted but a carbon rig would make so much sense in a lug rigged CY. Easy to rig, stiff besides the righting moment thing.

[teresajude]

The CY mast is a great example of why you cannot convert to hollow BM and not do some re-design. Sometimes you need to bump up diameter as much as 10% to get the strength, which I understand to be proportional to diameter to the THIRD power not 4th as cited in quote above. Nevertheless, diameter is important as is the correct wall thickness which of course is a function of the diameter.

I think the original mast diameter is actually too small for the solid version too. A lug mast needs to be rock solid, that is to say no bend. When the lug is set with firm downhaul tension to flatten the sail, improve upwind efficiency, if the mast bends this luff tension releases and the sail loses some shape. Also a CY is a big boat and loaded up with crew (3 up) and a stiff breeze, there will be some real stresses on the mast.

A SOLID mast for a CY should be more like 81-82mm esp. if it is done in Spruce.

Clint:

Looking at a few references, it looks like bending strength varies with moment of inertia, which is calculated as ((pi * r^4) / 2).

If you are calculating the appropriate dimensions for a birdsmouth spar, using the third power actually understates strength, and so builds in a small additional safety factor.

Regardless, a small change in mast diameter makes a BIG change in mast strength.

Steven:

I hadn't realized you would be making it birdsmouth. It looks like 8 staves 1.3" by 0.65" would give you almost identical strength to the designed solid mast, at an external diameter of 3.33". This would give you a wood weight of about 77% of design weight (obviously glue will add to this number).

If you bump the staves to 1.4" x 0.7", the strength goes up to 40% higher than the designed solid mast, with an external diameter just over 3.5". The wood weight for this version is about 90% of the design weight.

You are correct about wood use. You can easily get 6 staves out of a standard 2x6, assuming a standard 1/8" kerf.

Good luck and God bless!
Wayne

[StevenBauer]

Thanks, Wayne. Good stuff. Current thought is 1.25" x .75" with a diameter if just over 3.25". With a core for the bottom 3' this will be a much stronger mast than the previous one. Which is the second one that Chris has broken. He has had the dubious honor of yelling out the "Cut away the wreckage" command twice now, but I guess he's gotten that out of his system.

Gareth, when Bill Boyd broke his second Caledonia mast that is just what he did - switched to carbon fiber.

[StevenBauer]

I'll soon be spar building in my CY project and I've got a question about the main mast. I've got a couple nice sticks of really tight old growth Sitka spruce that I had milled for another boat that will serve for a solid mast.

Would there be any real advantage to building a birdsmouth mast over simply building a solid spar, other than some weight reduction?

Just that it is faster and easier.


Steven

[TerryLL]

Just that it is faster and easier.


Steven

Yup. I can see knocking out a birdmouth mast would be a a quick couple hours, but that solid spar might take me half the week. And all that epoxy would sure be cheaper than disposing of all those shavings off the solid stick.

[Clinton B Chase]

The hollow BM CY mast should be 10-20% lighter. A finished one will be around 22 and the solid could be 28 pounds (these would be Spruce #s for the nice stuff I use). That 5 lbs of weight saving matters when you need to step the mast!

And it is an efficient way to build it but it takes practice and a few masts to start getting it down!

Clint

[teresajude]

Thanks, Wayne. Good stuff. Current thought is 1.25" x .75" with a diameter if just over 3.25". With a core for the bottom 3' this will be a much stronger mast than the previous one. Which is the second one that Chris has broken. He has had the dubious honor of yelling out the "Cut away the wreckage" command twice now, but I guess he's gotten that out of his system.

Gareth, when Bill Boyd broke his second Caledonia mast that is just what he did - switched to carbon fiber.

Steven:

Just based on numbers, it looks like you are right on the money. That should be right at Iain's design strength. It will also be almost twice as strong as the previous mast. Hopefully it won't break.

God bless!
Wayne

[TerryLL]

The hollow BM CY mast should be 10-20% lighter. A finished one will be around 22 and the solid could be 28 pounds (these would be Spruce #s for the nice stuff I use). That 5 lbs of weight saving matters when you need to step the mast!

And it is an efficient way to build it but it takes practice and a few masts to start getting it down!

Clint

Thanks Clint.

Even though I'm getting old and feeble, I think I can handle the extra 6 pounds.

But the efficiency part I don't get. Seems to me the BM uses up more wood than the solid stick, when you add up all the scraps left over when the job is done, plus the epoxy. I suppose if all you had on hand is 4/4 stock, then the BM would be the obvious choice.

Since I have enough Sitka to do all the spars as solid, I more than likely will forgo learning the BM technique this time around.

[Clinton B Chase]

Terry, Only on one boat, a Shellback Dinghy, have I been able to take out a solid rig then immediately take out the hollow rig, same sail and everything else. It was quite noticeable the weight decrease aloft, more than I expected. With larger boats, the weight savings is only greater because the rig is larger, too.

On a recent mast I finished for a large dory, I estimate the weight to be about 25% less than the solid. People picked it up at the shows and almost tossed it into the air, they expected much more heft than they got! Makes a difference for older folks and I think that is why some go CF. That is fine, but the look of the wood mast is gone. Hard to maintain a traditional look and feel to the boat, though one can fudge a wood grain paint job over CF. That said, like wood, you can make a CF spar, but the laminate schedule and diameter has to be right such that the stiffness is what is needed. A lug mast needs to be wicked stiff, especially one requiring a firm downhaul for decent performance, which is any lug meant to go upwind. A downwind rig can have more flex and be OK.

Regarding usage of stock, a BM mast definitely can use less wood. The nice thing is that you can rip around knots. If ripping from a clear board, depending how the staves are gotten out, a lot less wood is actually going into the stick. It would be nice to get a CY with a solid and a hollow mast and compare.

Thanks Clint.

Even though I'm getting old and feeble, I think I can handle the extra 6 pounds.

But the efficiency part I don't get. Seems to me the BM uses up more wood than the solid stick, when you add up all the scraps left over when the job is done, plus the epoxy. I suppose if all you had on hand is 4/4 stock, then the BM would be the obvious choice.

Since I have enough Sitka to do all the spars as solid, I more than likely will forgo learning the BM technique this time around.

[TerryLL]

Clint,

As always, your advice is appreciated, so I'll take another look. Perhaps Steven will post a ton of pics to help educate me.

[StevenBauer]

Terry, a different Steve has a buch of good pics up on the thread that Chris started over on the Caledonia Yawl Forum

[TerryLL]

Terry, a different Steve has a buch of good pics up on the thread that Chris started over on the Caledonia Yawl Forum

Found them, thanks.

[StevenBauer]

We've been chipping away at the mast project. Tuesday night after work Chris drove up and we milled out the staves. Clint helped gt the size just right. And let us use his shop, too. Thanks, Clint.



Wednesday I cut all the birdsmouths into the staves:

[StevenBauer]

Then tonight Chris came back up and we tapered the staves and made he plug for the base and made the molds and glued up the mast.

Using a batten to mark the taper on the pattern stave:



http://i146.photobucket.com/albums/r...s/85c84865.mp4


After planing the pattern stave we used it to mark the other 7 staves.

[StevenBauer]

I'll post more pics tomorrow. it's after 3 now and the burst of energy I got from waking up to pick up kids from the last Harry Potter movie is fading fast...

[Brian Palmer]

[QUOTE=StevenBauer;3053251]

Please excuse the interruption, but what is the story with the giant wagon wheels?

Brian

[TerryLL]

Great photos Steven.

Is the base plug straight or tapered, and is there a plug at the head?

[StevenBauer]

Those aren't Wagon Wheels! They are Mast Moving Wheels. Maybe you were hibernating last February when this thread was new. (winking smiley here): http://forum.woodenboat.com/showthread.php?127095

The mast has no taper at the bottom. Yet. We leave the staves full width at the bottom and glue in an octagonal plug when we glue the mast. In the CY the partner is about 29" from the step so we made a plug about 48" long with the top foot cut at an angle to protect against stress at the top of the plug. After the glue up the foot of the mast will be tapered. Chris has a piece if Lignum Vitae to make a plug for the top. We'll probably drill out the top and turn the LV on the lathe to fit the drilled end. Then when a dumb sheave is drilled and shaped the LV will take the wear.

When we came back from a bite to eat we cut the last few staves on the bandsaw before planing. This saved a little work.


So we were just about ready for glue time.

[StevenBauer]

Of course being the perfectionist that he is Clint had to break out the laser and check out our work:



I'm going to take off the clamps today and maybe start planing down the edges.

So far we spent 2 hours planing stock, 1.5 hours cutting the birdsmouths and a whole evening planing tapers, making molds and gluing up the mast. Chris might take it back to NH to finish the sanding and varnishing.

[TerryLL]

Great thread Steven! Thanks.

[StevenBauer]

You're welcome! I took the clamps off this afternoon and planed the mast to 16 sides. About 45 minutes. I still need to taper the bottom.

3/4 of the way there:








Now it's time to go sailing! Full moon tonight! Maybe stay out on the bay for some night sailing.


Steven

[hikingchrs]

Thank you so much Steven and Clint. It looks awsome

[Clinton B Chase]

Chris is going to have the nicest CY mast out there. Thanks for the opportunity to design the mast and see the results in short order with the hard work you and especially Steven put in!

Every project is a learning experience.

It will be nice to have Steven sailing with you and the mast in a couple weeks for the on-water feedback.

[StevenBauer]

So Chris stopped by this morning to pick up our gear for the Small Reach Regatta and I got to see tha mast after sanding and varnishing:Now lunch is over so it's back on the scooters for the second half of the ride. actually only about 70 more miles from Rockport to Lemoine.

[StevenBauer]

Here's the new mast in action at the Small Reach Regatta:

We all agreed the boat handled better with the stronger mast.


Steven

[bloggs68]

Looks great guys. What was the finished weight of the mast?

regards,

AD

[hikingchrs]

I have not weighed the mast, but the preformance is much better than my privous masts... my boat points much higher then it prioviosly did. While at the Small Reach Regatta I looked directly up the mast while Steven changed directions in a heavy blow, the mast deflected only a half inch or so... the undersized mast I had before would have bent a at least a couple inches. As Clint had explained to me the tension on the luff is realeased when the mast bends, without tension on the luff the windward preformance is decreased. Also during the priovous mast build I was working alone on a hot day and the epoxy kicked off when the mast was not straight so I had a bannana... Clints U shaped supports where far faster and more accurate. my new mast is increadably straight. Even though my old mast was undersized the break started at the point I had mounted the cleat for the halyard, the new masts plug goes higher than the cleat mounting point.... I however decied that I did not want to drill screw holes... I made a wooden cleat and mounted it with epoxy... I was worried about it breaking off but it seems very soild.

[Clinton B Chase]

Andrew, I would say this one is 25 pounds. Normally, I can get them to around 20 in Spruce, but Chris was fine with trading off some weight for the extra strength. We did not want to mess around!

The wall thickness was probably around 21% and with the Doug Fir as well. So this sucker is strong and stiff. The boat sailed noticeably better...quite remarkable.

[TerryLL]

I hope you don't mind if I steal this rub rail detail and use it on my CY build. Very darn sweet is what it is.