clothespin scarf

[Lee Winstone]

Hi Ian, thankyou for your comprehensive instructions on scarfing. I certainly have more confidence in tackling the project now. One thing I probably should have mentioned is that on my Tahiti Ketch the original main mast was keel stepped. The previous owner converted it to deck stepped with a galv pipe compression post to keel. There are no backstays, fixed or running (gaff rig). The aft shrouds are only about a foot back from heel of mast which concerns me. With jib, staysail and main hoisted in a following sea I am always worried that mast may fall forward with all that pressure due to the very slight angle of the rear shrouds. I have heard that if they are positioned any further aft they will interfere with the gaff when running. This is one of the reasons that I wish to scarf extra length onto mast to return it to original design of keel stepped mast. In your experience, do you think deck stepped mast without backstays is a reasonable rig for gaff? I still need to scarf mast as I wish to run cutter rig and need the extra length for jib and extended bowsprit. Your input would be greatly appreciated. Kind regards Lee.

[Ian McColgin]

Ahoy Lee,

You may want to either get a professional opinion from Brion or a local pro, or perhaps dare to open a copy of Skene's Elements of Yacht Design to check some mast scantlings. A keel stepped mast can be built more lightly than deck stepped and thus you'll want to consider if the mast is too slight in it's deck stepped configuration. Probably it's ok as it was most likely over-built anyway but worth the check.

If the mast is robust enough to be deck stepped you have some choises. I think you want running backstays in any case. They help tension the head stay and will take some of the wobble out of the masthead in a jumpy sea, both on and off the wind. The sail will help keep the mast up when on the wind but especially in a sea, there's a lot of motion at the truck if you've only shrouds. And running backs will ameliorate downwind dread.

Pros and cons of each. Keel stepped is stronger and stiffer as the mast is held at both butt and partners. This may or may not be a good thing.

Keel stepped has a somewhat greater chance of surviving a rigging failure, especially, depending on the stay that fails, you can alter course fast enough to take the strain off. But you really should be inspecting the rig often enough that you note problems before they are breakage. Most rigging failures that actually happen are preventable.

Rigging failures that happen far off-shore on well-maintained boats happen in such dire circumstances that I think there's little difference deck or keel stepped. If you have a catastrophic roll-over that's taking your rig apart anyway, perhaps it's better to not have such a big hole in the coachroof or deck. But then maybe the tabernacle would make a hole. Who knows? If you've lost the rig, is it easier to jury rig with the option of keel stepping whatever you make. And if so, what's to prevent you from removing whatever may be left of the tabernacle and reopening the partners?

As you may be guessing, I don't hold much with simply deck stepped for a cruising boat. To get the full virtue of deck stepping, a tabernacle of sufficient height that you can step and strike the mast floating in a calm is worth the work especially if your cruising involves low bridges, long canal trips like across Europe, or maintenance .

Deck-stepping should eliminate any overhead leaks at the partners.

With today's rigging, there is no reason deck-stepped cannot be as ultimatly seaworthy in the long run. So, your decision, if not forced by the mast's scantlings, is just that, a choise. All my own boats, most obviously my current 6 ton catboat, wewre keel stepped. But my previous boat, Granuaile, 20 ton 55 foot Marco Polo three masted schooner, was planned to convert to tabernacle-deck stepping in a planned major rebuild, sadly thwarted by her loss dragging her mooring into the breakwater in a peculiarly vitriolic northeaster. Marmalade, my catboat, has a hugely heavy solid stick and even were it hollow, an essentially unstayed mast needs deep planting.

I think that with the weight of a solid spar, if that's what you have, and gaff rig, I'd do keel stepped because that's probably too heavy to handle from a tabernacle anyway and keel stepped is cleaner from an engineering point of view and more elegant emotionally.

I take it this is a solid spar but either way, you'll likely be adding a both ends if you go keel stepped and just the top if staying deck stepped as you probably can and should carry a bit more taper aloft. I can't really address this and it's a most important point to get right so again, Brion or someone like him or Skene's if you're brave. Key thing is to design the whole mast as it should be and then figure out how much to add at one or both ends.

G'luck

Ian

[Ian McColgin]

Ahoy Lee,

Added thought on staying: Usually the aft lowers should come in about at the throat and, as you play with your rig with some professional help adding a staysail inside the jib, this is a grand spot for the staysail stay to land. These stays cannot bother the gaff with full sail, though they could limit your travel when reefed. On schooners where I confronted this problem, I didn't worry much as the leeward shrouds go slack anyway.

By the way, that gaff can get well out with sail twist and you'll want the spreaders hinged such that they can move fore and aft without stressing the base. The spreaders must not be overlong. Imagine a straight line chainplate to mast tang. If more than half the spreader is inboard of where that line intersects the spreader, the geometry is such that the shortest distance, which the rig will assume under tension, is the correct allignment. This, by the way, is also important for the dolphin striker if you have one, except that should be free to move athwartships.

Wait a minute. The bit about spreader length. That's how I learned and always assumed but I don't know that for an empiracle fact. Perhaps Brion would comment.

Any way, fear not pulling the lowers back a little if it makes you feel good.

If you're adding mast height, consider designing for a topsail. This is going to tower above the jib stay tang. Whether part of the single pole or seperate as a top mast, it should be light and disposable. Let it fail first. It helps the topmast or topmast section to build in a bit of foreward bow to be straightened when the topsail is set, thus giving nice leach tension.

G'luck

Ian