Sprits and Snotters.

A ‘WABI”’ spring projects post.

In a couple of posts i have been talking about modifying my Hunter Liberty’s rig with a long term plan of making new spars and converting her from cat-ketch to cat-yawl.   One of the driving forces for that is to make the cockpit more ergonomic and principally to get the mizzen boom out of my way.  As it is now the boom is just at shoulder height and always in the way when i am at anchor or just working in the cockpit.  The long term plan would be to have a smaller mizzen and move it aft and then have a lot more area in the mains’l instead.

The intermediate experiment i am actually working with and making the parts for right now is to change from conventional booms to down-angled sprits  (booms) on both masts. With the mizzen that would mean the mast end (tack) of the mizzen sprit-boom would be above head height and with a topping lift would raise the ‘boom’ out of the way when topped-up.   The similar plan with the main (forward) rig is to also remove the existing boom, which is too high, move the sail track down the mast by nearly a foot and also have a down-angled sprit-boom there as well.

That might potentially improve the boat’s behaviour at anchor as well by getting rid of the deep mains’l stack-pack bag which i have always disliked.  As it is, with a lot of area and mounted as it is quite high it represents a lot of unwanted sail area forward at anchor and is one of the main reasons that the boat sheers around so much.  What i would do for sail storage forward is have the sail carried low in it’s track and have the sprit such that it could be lowered to deck level.

To explain the terms here for those not familiar with these older small boat rigs i’d best pull up some pictures to demonstrate the differences between sprit rig and sprit-booms. For those that know them in the UK our Thames barges are usually rigged with a vertical (near vertical) sprit which is permanently rigged and gives a big, powerful, almost square mains’l. The mains’l isn’t reefed as such vertically but rather it is ‘brailed’ into the mast.          The same rig on small boats is often rigged with a sliding sprit and can be reefed by sliding the sprit down the mast.

Thames barge ‘Thistle, i think, with sprit rig but mains’l brailed up.

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Small boat sprit rig.

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Neither of the above 2 rigs are what i am referring to here.  The sharpie in the picture below has sprit-booms and very much the arrangement i am going to experiment with. The way that sprit-booms work is that if they are down-angled from the tack with the attachment point some distance above the point of LP (longest perpendicular) then the sprit also has a similar effect to a vang in that tension in it’s ‘snotter’ tackle applies a force stretching the foot out and also down.  Just to mention that ‘snotter’ is the proper term for the tackle that can be seen between the sprit and the mast.  The critical part here is to get the angle of the sprit very close to what is needed to give enough outhaul and vang effect at the same time.  Small adjustments could then be made by moving the whole sail up or down the track slightly/

While uncommon in the UK in small boats the sprit-boom rig is well known on boats like Sharpies as seen below and seems to work well with free-standing masts. The little sharpie below has down-angled sprit-booms which have both an outhaul (foot tension) function and a vang/downhaul effect.  A later and logical development along the same lines is the wishbone boom as seen on many ‘freedom’ rigs as used by Gary Hoyt on his designs.   Making wishbones for WABI”’ is also a potential option.   A purely horizontal sprit-boom as rigged on Spirit of Bermuda doesn’t have a vang effect so sailing efficiency is lost off the wind.

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Spirit of Bermuda, while being a magnificent boat and a great experience for the young Bermudians she takes to sea has a horizontal sprit-boom on the aft rig that tends to ‘kite’ up in a breeze.  I love the look of this boat and those radically raked masts, and she is one of the few ‘big’ boats alongside ‘Grayhound’ that i would pay real money to go sail on.

2014 Newport Bermuda Race start from Newport, Rhode Island. SPIRIT OF BERMUDA, 3-masted Bermudian sloop owned by the Bermuda Sloop Foundation

So….the project.

Sprit-booms on small boats don’t need to be as big as a conventional boom on the same boat because the loads are completely different.  Unlike a conventional boom with a powerful vang tackle (mine used to be a 5 : 1 tackle) the sprit doesn’t use one and so doesn’t have to act like a beam with as stress near the centre.  The primary loads should only be found at either end and the load balanced thus at the clew the mainsheet should be attached as near to the first reef/clew point.

It’s difficult to find exact dimensions for sprit-booms because i can’t quite find a design with sail area similar to mine that has a sail-plan and spar dimensions so i have had to try and extrapolate up and down from other designs.  The size required for the sprit-boom which is often nothing more than a square section stick seems to be around 60mm x 40mm which does look small but , as i have explained above, it’s doing the job in a different way and i am just used to IOR influenced booms.

I am making the mizzen sprit-boom first as that’s the one i am going to work out the details with and rig first.  You might be shocked but the base material is a length of CLS timber, reasonably straight grained and only having small knots.  Cost, i think was less than a tenner !. The main costs will be the fittings as the eye-bolts and cheek blocks are about the same amount each as the spar itself.    If it works out well enough then i might get a couple of nice pieces of straight Douglas fir although the price from a specialist marine timber supplier is at least 8 times as much as the structural CLS timber from the builders merchant.

Rather than try and describe all the technical details such as how the clew is attached, how the snotter works at the mast and how the whole thing is reefed, take a look at this video of a CLC ‘core-sound’ 17 and it’s rig because this is where i have taken a lot of the details from.     Carlita’s rig isn’t that much smaller than mine and it will be quickly apparent how small a section the sprit-booms can be.   As with ‘Carlita‘ seen here it should be possible to reef the mains’l from the cockpit which has always been difficult to achieve with WABI”’.  Reefing the mizzen should obviously be easy as i am standing next to it most of the time.     The relevant section starts at around 16 minutes in : (owners video)

Project progress.

January : basic materials bought in for the sprits and sorting through the bits boxes to see what useful bits-n-pieces i can reuse for the project ….my mate AL calls this ‘available parts technology ‘ !  . At this stage i know i need some cheek blocks, jammers and some eye-bolts.    I have also stripped the mizzen rig on the Liberty ready to move it because i am also moving it onto the aft face of the cockpit bulkhead at the same time.

On the bench.

The spars themselves are extremely simple, just a length of timber tapered at either end and here with eye-bolts mounted top and aft for the clew and forward, inboard face for the mast (snotter tackle) end.  The 2 mast ends are different because the mizzen will be mounted on mast-right and the main on mast-left.   Not fitted yet are the cheek blocks, jammers and cleats for the reefs as at this stage i still have to work out where they go. At the end of day 1 of the actual project the sprit-booms are ready to soft-fit.

Mast ends…eye bolts to take the snotter tackles.

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Clew ends. Sail clews will be simply laced into the eye bolts.

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Clew ends, each sail will have one of the small ‘S’ hooks laced into the clew ring, the outhaul effect is created at the mast end by the snotter tackle.

At the beginning of February i took both the sprits down to the boat and temporary-fitted both just to check them for approximate length/ fitting angle and to work out where the snotter tackles would fasten to the masts.  They then go back to the workshop for smoothing off and a bit of paint and varnish.  I did the first fit by making up temporary lashing strops around the masts to use what blocks i had available.  In the final version the snotter tackles will hang off eyelets riveted into the mast.   Although i gave myself a reasonable amount of spar ahead of each mast it’s possible that i have guessed each sprit a tad too short.

When i get a chance to take a second look i intend to re-rig the sprits with the sail clews lashed directly to the eye bolts as that will give me just enough space at the mast end to allow the snotter tackles space to work with going ‘2 blocks’.  As i write, it had been my intention today to go down to the yard and try the second fit….as it is it’s both raining steadily and blowing briskly, i don’t mind getting wet but i wouldn’t be able to have the sails up to test out the systems.

As a first impression, from the dry-fit, the mizzen sprit looks great as it’s mast end seems to want to sit well above my head height and all it would need will be a topping lift to raise the clew end with.  With the main mast and it’s sprit, it almost certainly needs to have the sail mounted lower on the mast and i think requires me to move the whole track down the mast or find a small additional section of track.  My next job is to get both masts off the boat as there are other jobs to do at the same time but in terms of this job to see if the external mast track could be moved easily….i think it should be as long as most of the rivet holes are at regular, even spaces.

Mizzen sprit-boom rigged.

Rigged loose before tensioning the snotter, with the snotter loose the whole sail and boom can rotate around the mast…..might be useful to have an extra long mizzen sheet. The sprit angle looks a bit flat here but quickly changes with more tension in the tackle.

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With the tackle on, the sprit sits well above head height and i can even scramble underneath it onto the side deck.

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Mizzen snotter tackle and temporary strop around mast to work out the position and sprit angle.   One thing i noted is that the soft timber will need surface protection where it rides on the mast.  As i write this section of the post the sprit boom is already on the bench having some GRP bandage epoxied on.

Mizzen snotter tackle temporarily set up with a strop around the mast.

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The mains’l is temporarily back on the mast although the boom is off, the old stackpack bag minus battens is now serving usefully as a simple sail cover and it might even be possible to keep it for that job….just needs a zip repair and a good scrub !

Mid February, progress and details.

I will describe the rig as it is now mast by mast and starting with the mainsail.

The fore-mast has been down (and up again) , been stripped of all it’s existing set-up including taking the goosenck off and taking away the annoyingly complex lazy-jack system that went with the stack-packs.  Rather than removing the entire bolt rope track and moving it down the mast i found something vaguely similar from a supplier in the USA and imported a short length of that.  That’s been bonded onto the mast surface and i am just waiting for some long rivets to complete the job.  The new track length will take the foot of the sail almost to deck height which means it can stow very low.

At the masthead i rigged a new turning block for a single, simple topping lift and rove the line for that.  With the mast down i drilled and riveted the lacing eyes that will take the snotter tackle and it’s turning/lead block.  Mast heaved back into position and re-bolted back through the forward bulkhead.  Sprit boom then rigged with it’s snotter tackle, topping lift and temporary blocks for it’s new sheet.  Not done at this stage is the fitting of the reef turning blocks and jammers.

Mains’l sprit boom and snotter tackle.

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Mizzen.

The mizzen has actually been more work because as well as taking it down : it’s more awkward to lower than the main-mast….i have also moved it from it’s original position. The original position as seen in the video and countless shots of the boat is essentially at one side of the companionway and with it’s pivot mount set on the fore and aft face of the companionway/cabin bulkhead.  That means that as originally built the pivot can’t be used when lowering the mast.  What i have done is moved the whole rig back about 4 inches and taken it about the same amount off the centreline to port.  The new positions for the heel fitting and mast pivot are on the cockpit sole and aft face of the cabin bulkhead respectively.

When i first re-stepped the mizzen in this position with the pivot plate directly bolted through the cabin bulkhead it made the mast too vertical and didn’t look at all right. The temporary fix is a large spacer block which moves the pivot point aft about 4 inches and to my eye the rake now looks about right again.  Tonight, as i write the edit, i have just finished making a pattern for a new spacer piece which i will have made up in spiffy stainless steel.

The mizzen snotter tackle is on but needs some messing about with yet, the sprit itself is on but on the day i rigged it there was too much wind on the river and blowing from astern so i couldn’t hoist the sail to check everything.

Both sprits obviously bear against their respective masts so i have added a wear patch and a layer of leather to each wear-point.

The mizzen sail is back in it’s track and the old stack-pack bag will be going back on minus it’s battens as a soft sail bag.  The similar stack-pack bag for the mainsail is off having a repair.

Another job today was to contact a local sailmaker with a view to having new sails made specifically for this rig set-up in mind.  I could use the old sails for knocking around with but i would like the new ones made with a better shape and more reefs.

Jobs left to do at this stage before taking the boat for a sail are : rig the new sheets and work out where the reef lines will go, fasten the mast track on, drop the mizzen mast temporarily and spray coat the mounting block until the new spacer is made.

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State of progress just before scheduling post.  Mizzen in new position and raked aft.

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On video too..

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