Mast for a catboat

[tsugak]

I just recently purchased an older Herman 17' catboat. Although it is a fiberglass boat the mast, gaff and boom are douglas fir. Unfortuantely the current mast is way overbuilt and extremely heavy at 6 1/2" dia. and 1 1/4" thick birds mouth construction. This is not the original mast. I wish to remake the mast at a more modest diameter, like around 5" with douglas fir again in birds mouth style construction. How thin can I make the staves and still have a strong mast? One additional piece of information. Unlike most catboat that only have one fore stay this boat has an additional port and starboard chain plate, which although are not being used on this mast, could be used to offer additional support to the new mast. This makes me think I could get away with a somewhat lighter mast. I also plan on making a tabernacle for this mast as well, hence my desire to make it as light as possible without compromising strength.

[michigangeorge]

tsugak, I cannot help you with sizing but would like to comment on your rigging. A free standing, keel stepped, mast will bend to leeward a bit when under high loading - a good thing. Your tabernackle mounted mast will require shrouds and will not bend to leeward but will be placed under compression loading. The narrow shroud base further exacerbates this situation. To my mind this would require an even heavier construction, not lighter. The SOLID spar on my 18' cat is 6 3/4" so your existing spar size seems about right. I would consult a Naval Architect before proceeding.
You may also want to consider how the tabernackle and shrouds will interact with things such as gaff and boom jaws,hoops, boom travel and chafing.

[Ian McColgin]

michigangeorge is on the right track. A deck stepped mast must be stronger, considerably stronger, than a keel stepped. Even with a couple of shrouds. Remember, you have no backstays.

There are catboats with what amount to lifting tabernacles where the mast rotates up on a pivot at the top of the tabernacle and once verticle is then lowered through the partners and to the step. The process is dangerous with the boat afloat as even a small passing wake can get the mast whipping side to side when it's not well supported. The best versions of this step the mast while the boat's on the trailor. If you go this route, remember to look up. Most boat ramps are safely designed but every year a few people fry themselves banging their masts against a power line.

Were I you, I'd stick with your perfectly good stick, don't have shrouds if the mast doesn't need them, and engineer a way to get it up without going to deck stepped.

G'luck

[wizbang 13]

6 1/2" hollow mast may seem big laying em the sawhorses, but it will shrink as the breeze comes up.
Same thing happens with ground tackle!

[tsugak]

Well, its seems like I'm barking up the wrong mast! Thanks for the excellent replies. One of the reasons I bought this particular catboat was to get as much boat as I could but still be fairly trailerable. I live on the coast of Maine and want to do some trailering as there are so many wonderful places to sail from. Having a tabernacle mast is key to doing this. If I'm reading the tea leaves right it appears that an aluminum mast with tabernacle is the best choice for my intentions. The current mast I have for the boat is a beast and trying to raise and lower it at a boat launch, even with a tabernacle would be a real challenge. I was looking forward to making a wooden mast but I do know that Marshall Marine makes a nice aluminum tabernacle one.

[JimConlin]

The issue is not the material of the mast, nor its weight, but the geometry of its support.
Because of the location of catboats' masts, supporting them with stays is problematic and tabernacles provide no support.
Stepping through to the keel is probably necessary.

[Ian McColgin]

I'm not aware of a tabernacle from Marshall but their sanderling, about your size, has a mast that itself is hinged. The gaff and furled sail are below the mast hinge so the whole thing is right there, very handy and slick. It really is a keel stepped mast, but jointed. Could be just the thing if you don't mind the cost.

G'luck

[rbgarr]

IIRC the Marshall Marine tabernacle is for the 15' version of their boats. Is the sail area for your boat similar to that one? I imagine Marshall will advise you on that point.

[tsugak]

Ok, I need to clarify here. Maybe my terminology is a bit off. When I say tabernacle I'm referring to a keel stepped mast, hinged right above the gooseneck. I though this was the definition of a tabernacle. Is this correct? My thought, again was to make a birds mouth wooden mast, have a stainless steel hinge arrangement made, cutting the mast above the gooseneck, and stepping off the keel as usual. I thought the port and starboard shrouds would allow for a lighter weight mast to be made. Does this clarify things? By the way, Marshall does make a hinged aluminum mast for their Sanderling. I talked with Jeoff Marshal about it. I saw one a someones boat, made very well and works slick. I would still prefer a wooden mast if I can keep it light and manageable to raise and lower.

[rbgarr]

IMO, you're describing a hinged mast in that case. The width of the base for the shrouds that far forward on a catboat has always seemed negligible to me, unless spreaders are installed, and even then I don't think they help all that much. I've seen shrouds without spreaders on catboats hook inside the gaff jaws as the mast bends to leeward.

[Thorne]

Tabernacle -

http://www.catboats.org/cats4sale/cats145.htm

Hinged mast on Sanderling -

http://www.marshallcat.com/m18hinge.htm

[michigangeorge]

tsugak, send me your email via private messages. I just remembered I saved some photos of a hoisting mechanism which may work for you. If I had Thorne's skills I would post them here but I have no patience for this technology.
George

[tsugak]

Well, when I look at these two pictures they basically seem the same to me just different methods of hinging the mast. I assume with the top picture the mast below the pivot point goes all the way down to the keel. Here is a picture of a hinged mast, (tabernacle?) on a wooden mast...mmm, how do you post a picture from your computer, does this forum only allow posting pics from a web address?

[Mad Scientist]

...mmm, how do you post a picture from your computer, does this forum only allow posting pics from a web address?

Yes, that's what you need. Thorne is our resident expert on the technique. He recently posted an updated photo posting procedure. I've forgotten which catergory it's under...might be Misc. Boat Related.

Tom

[wizbang 13]

That Sanderling looks wacky to me. Wooden wedges and 18" away is a space age hinge. I guess it must work? Is that rig unstayed?

[BillyBudd]

My Chebacco cat-yawl has a nearly 20' mast (birdsmouth out of eastern spruce with strips per WB mag. specs re: width and depth, but with important stiffeners within) weighed 44 lbs. before adding on wood ears, halyards and such. Bolger designed the neatest way to raise the mast -- he drew in a slit in the roof to allow the mast to be put in on a low angle with the butt against the inner stem. One walks up the deck with the mast in hand/shoulder (the butt slides down the curve of the inner stem to the sole) and when vertical it is simply a few inches straight up and then down into the mast step on the keel. Ker-plop. The partners on deck with wedges secures the mast along with putting a cap over the slit. Wedges as well as at the mast step, complete the raising. No shrouds whatsoever. For this to work on your boat, the mast opening in the deck/roof needs room aft for the mast to angle into the hull.

[Thorne]

Did someone mention my name?

Basically a "tabernacle" hinges the mast right at or near the deck, no spars or stays below the hinge, and can be made nearly all from wood. Tabernacles are common on some boat designs, the most famous being the big Norfolk wherries in the UK that could sail up to a low bridge, lower the mast while under way, coast under the bridge and then raise the mast again -- all without stopping. These sort of tabernacles were often counter-weighted with a fair amount of lead on the end of the mast to allow easier raising/lowering while moving.




Although this bit of ecclesiastical furniture is also called a 'tabernacle' -- who knew?


A "hinged mast" can have spars below the hinge, and usually requires a fair amount of modern tech, metal parts, etc.

Here's how to post photos on this forum:

FIRST - Don't attach photos. Only a tiny version will display.

SECOND - Post the photos on the web. Use your own website or a free image hosting service like www.flickr.com, picturetrail, photobucket, etc.

Once posted on the web, right-click the photo to "Copy Image Location", or drag the photo to another browser window, then copy the URL (web address). You can test by pasting the photo URL into the location field (http://* ) of a web browser and see if the photo displays. Remember that this process will not work for photos only located on your computer, or uploaded to members-only Yahoo groups.

(In Flickr - You usually have to first click the photo to bring up the black-framed viewer, then click the "View All Sizes" link near the top right. Then you can get the URL by right-clicking the image. If you don't want the largest size (displayed) you can then click another option in the "Available sizes" links above the image.)

THIRD - ONE TIME PROCEDURE TO SET UP ENHANCED INTERFACE:
1. Click the "Private Messages" link in the browser window in the top left of the menu bar.

2. Click the "General Settings" link about 2/3 down the left column under "My Account".

3. At the bottom of the next page in "Misc Options", select "Enhanced Interface - Full WYSIWYG Editing" from the Message Editor Interface options. Click the Save Changes button.

FOURTH - DO THIS EVERY TIME TO POST IMAGES IN THREADS:
A. Once the above Enhanced Interface has been set up, in any "Reply" window you can click the "insert image" icon --> a little yellow square icon with a dot at each corner, a tiny tree in the center.

Depending on browser version and Reply/Edit status, this may bring up a simple window to paste the URL into, or the "Add an Image" window described below.

B. If the window titled "Add an Image" comes up, click the "From URL" tab, paste the URL of the photo in the field, deselect the box for "Retrieve remote file and reference locally", then click the "INSERT IMAGE" button. The Forum software will resize some large images, so look at your post to see the actual displayed images.

YouTube video on how to select the image URL in Firefox, navigate the "Add an Image" tabs and paste the image URL -
http://www.youtube.com/watch?v=AkfB_...layer_embedded

[tsugak]

Billy, where can I get the specs for the stave w & h measurements you said are in WB magazine? Also, what is the diameter of your mast, do you know what the stave thickness is?

Thorne, thanks for the tabernacle info and pictures as well as how to post pics. A little involved but I'll give it a try.

In reading about birds mouth masts there seems to be some discussion about the taper and whether its done before the mast is glued up or after. The issue being, that if the individual staves are tapered before glueing then the wall thickness stays the same, where as if tapered afterwards then the wall thickness is reduced at the top of the mast where you don't need it so much, which translates into less weight high up. This supposing to be a good thing. What do folks think about this concept? I was thinking about a little of both, some tapering before glue up and some afterwards.

[DanBurrill]

Thorne, you beat me to it with the pictures of Norfolk Wherries. (I'm pretty sure the first picture is Albion before she had her keel replaced with a custom steel I-beam that's restored her sheer, the second is Maud, that I first saw not long after she'd been raised from the bed of Ranworth Broad, when she was in the late Tim Whelpton's yard at Upton - I'm not sure how much original timber is in her now, but it can't be much. Still a wonderful vessel though.)

It would be difficult to replicate the system used by Norfolk Wherries and pleasure yachts in a Catboat that wasn't designed from scratch to accommodate it, as the bottom of the mast would foul the inside of the stem when raised or lowered (shortening the mast would increase the amount of lead needed to counterbalance the mast, probably to a point where the design was unworkable). You'll notice from the pictures posted that Albion and Maud have forestays but no shrouds (you'll also notice the size of Maud's tabernacle knees - the main deck beam and tabernacle of Albion are now reinforced with inch thick stainless steel plates to help deal with the enormous stress this imposes on the boat).

[boattruck]

Ts, I think you could accomplish what you are hoping for in an arrangement much like Thorns first cat boat picture, a fixed lower section, likely metal ( cast off section of an aluminum spar? Chopped and channeled and reenforced as needed...) then a nice light birds mouth spar built to suit above. A massive pin to hinge the upper section on, a head stay would make it all work if you could get the requisit lateral strength in your tabernacle...then you've got to struggle with the logistics of the boom and gooseneck etc...as to the taper I'm of the before school, but it wouldnt hurt to try the 'both' approach, Let us know what you come up with, Cheers, BT

[rbgarr]

The Marsgall Sanderling with hinged mast has no shrouds: http://www.marshallcat.com/M18Lines.htm

If you don't want to go through the Thorne method for posting the occasional single photo, try tinypic.com.

1) open tinypic
2) hit 'browse', choosing the source file/location on your computer and select the photo you want to post
3) open that photo, select size and click 'upload' on tiny pic (they'll ask you to type in a security anti-spam phrase)
4) select and copy 'message board' addressing option
5) paste in your WB post

I usually drag and drop the photo I want to my desktop before opening tinypic. It's just easier for me.

[BillyBudd]

Billy, where can I get the specs for the stave w & h measurements you said are in WB magazine? Also, what is the diameter of your mast, do you know what the stave thickness is?

Thorne, thanks for the tabernacle info and pictures as well as how to post pics. A little involved but I'll give it a try.

In reading about birds mouth masts there seems to be some discussion about the taper and whether its done before the mast is glued up or after. The issue being, that if the individual staves are tapered before glueing then the wall thickness stays the same, where as if tapered afterwards then the wall thickness is reduced at the top of the mast where you don't need it so much, which translates into less weight high up. This supposing to be a good thing. What do folks think about this concept? I was thinking about a little of both, some tapering before glue up and some afterwards.

What you want is WB mag. no. 149. -- July/August 1999. I followed the instructions in the article "A New Twist on Round Hollow Spars." I cut tapers before assembly. Moreover, based on reports of cracked masts from one boat where no reinforcements were installed, I put inside the hollow a solid chunk of spruce where the gaff, mast, deck partners would possibly cause the mast to have undue stresses. But...not really solid, that chunk of spruce since I put a hole in it and ran a very small plastic pipe from butt to tip of mast with wires in it for an anchor light at tip. I also coated the entire interior of the mast with epoxy. To do all this, I slipped through the assembly, while still quite wet and gooey, 6 mil plastic sheeting. Then I tightened up the bands. The next day, bands all loosened, a few pries here and there and the two mast halves separated. Then I placed the stiffeners within, coated everything inside, re-epoxied the joints that had been protected from joining by the plastic sheeting, and re-banded. I should also mention that with a full-length of plastic pipe (wire conduit) within, that there was no potential for through-bolting. Instead I installed wood "ears" held in place with many silicon bronze wood screws. To get clear wood, multiple scarfs of the long sort required. Hard to find reasonably clear local (MA) spruce and it took me several years of sweet talking to local sawyers to come up with it. My mast probably about 4" in diameter but thickened for the lower. below deck, portion by adding (4) 45 deg. add-ons to remake a square shape. In looking in my copy of the I see that I penciled in this: 4" x 0.4 = 1.6" = width. 4" x .2 = 0.8" = 3/4+". But you really need the magazine to know what I'm talking about.

BTW, I learned about hollow birdsmouth masts from the two guys shown in the article. They were at a WB Show at Mystic Seaport Museum some years back and were looking at me as they balanced a 10' +/- spar on just a couple of fingertips...enticing me into their wonderful discovery.... Great guys!

At 44 lbs. for this assembly, I don't quibble about a pound saved, but would really be with a switch after myself if the mast cracked at the top because I was trying for an especially light mast. The mast takes a bit of stress--we can hear it creak in its wedges during a good blow and a great run. Follow the WB mag. instructions -- they worked for me. 4 season on the mast so far.

[cybuilder]

http://boats.duncan.com/cyforum/viewtopic.php?f=2&t=647
See this thread for more good birds-mouth resources and construction photos of my spars.

All this talk of tabernacles and mast hinges has me confused now. I always assumed the two terms were synonymous. Can somebody explain the practical differences?

[Thorne]

All this talk of tabernacles and mast hinges has me confused now. I always assumed the two terms were synonymous. Can somebody explain the practical differences?

See post 17 above.

[BillyBudd]

In Post #22 I said I used 6 mil plastic sheeting to keep the 2 halves of the mast separate. Not so. It was Saran Wrap (Cling Wrap in Oz) and it was a mess to get out. The idea was to keep the sharp indent of the birdsmouth.

[Ian McColgin]

Post #11