Roof, Sheeting points


Posted by Paul

Just when you thought you might be through cutting holes in the boat. And just when you thought there was nothing else to add to the structure…well not really, I have known about having to make sheeting points and a radar mount for some time. And having faired the roof to the second highbuild stage I can attest to how slippery the surface is, so steps up onto the roof were always going to be a necessary part of the build. The sheeting point contraption makes a great place to create the steps up.

So sheeting points. There are 4 bi-rig 1230’s being made and we all have different ideas on where the lines will run and where the booms will sheet to. The original Schionning plans called for the sheets to lead down to blocks on the side decks directly below the mid point of the boom in the exact fore/aft position, in order to sheet the booms as closely to the centre line as possible, hence the term for this; close hauled. This trim is needed to sail to windward. One idea was to not sail to windward, its uncomfortable and cruisers generally like to sail with the wind than into it. But its not a serious option. The tighter you can haul in the boom the higher you can point into the wind. There is one minor problem with the idea of deck mounted blocks, one of the booms swings out over the roof (depending on which tack it could be either) and the roof extension or bimini is in the way of this. On a traditional centre mounted rig you have a traveller that can slide to either side of the boat in order to aid in trim, we cant have these because we dont have the width of the boat to mount them to and of course half the trim on certain points is out over the water on one side or the other and the other boom being over the roof. One solution is to not have a roof covering the cockpit. Not a great idea for me. Another idea was  to mount stainless steel rub rails on the roof edge and have the sheet deflect off the roof edge, also not an ideal solution.

The solution most of us settled on was to raise the sheeting point so that the sheets cleared the roof on either tack, and from there we all vary on where we will winch the sheets in. One of us is going for a central winch so is leading his sheets over the roof then down to the central winch at the middle of his rear seats, similar to where many single masted boats have their central winch. Another has mounted winches on his roof on either side and sheets are hauled there, and whilst I originally considered having my winches on the roof, I eventually decided to have the winches on the side deck, because from there the same winches can service the halyards, the daggerboards and the outboards up and down, meaning just 2 winches could service the boat. It is also a comfortable platform from within the cockpit to work the winches.

sheer web design

The engineered sheeting arms and legs consisted of foam plugs, leading and trailing edge shapes to be glued to a centre web (which consisted of a ply core and carbon either side) and then carbon layers over the foil. The design also called for the arms to be over a meter long with the sheeting points at the ends. The length accounted for in 2 ways, first they arms would protrude into the deck side about 100mm more and mounted up the roof higher making the arms about 150mm longer to accommodate the curved roof, so in all about 250mm longer than I planned mine to be, this shorter length should mean my arms dont need to be as strong, because the longer the arm the greater the load at the end. The original engineering also called for the centre web to be extended another 400mm and to cut holes in the cabin side and glass these web (called sheer webs) extensions to the bulkhead on the inside of the main cabin.

I initially thought that because my arms and legs were not hollow I would not need the sheer webs, but decided it would be fairly easy to cut slots in my arms and legs and glass solid glass strips into them extending out 400mm (and into the legs about the same amount). I am so glad I did, because the amount of force these extensions apply to the lever of the arms is incredible. I felt this force when dry mounting the arms, I could hold the entire weight of the arm by just my finger and thumb squeezing the end of the sheer web to the bulkhead. Makes sense I guess, just leverage at work.

We had the same engineers as designed the masts and posts look at our sheeting options and design a solution so that the sheets clear the roof and they designed sheeting arms with legs that attach to the cabin sides and roof. The sheeting point arms and legs were designed from carbon fibre in a wing foil shape but unfortunately I ran out of money to have them built. The foil shape is mostly cosmetic though, so using the layup diagrams I decided to make them from ply and glass. Since running out of money  I have had a policy of use what I have left wherever I can. I planned to make my sheeting arms more flat so as to use the surface top as a step, not possible with the wing form. To compensate for them not being carbon I used way more glass (mostly uni) than the layups called for, but as to how much I am guessing at about double the amount of glass to carbon to get the same strength, and of course I have a solid ply core to help. As a consequence the sheeting arms and legs seem to be way over engineered and quite heavy. Probably 10 kilograms heavier than the carbon alternatives, so I have 20kgs more weight than I otherwise would have. But at least I can feel confident they wont ever be compromised by the loads they will need to withstand and they will make great top steps onto the roof.

The first step in construction of my sheeting arms was to decide on a shape. As usual, I used cardboard templates and experimented with shape until I had one that pleased me. The others will have a tapering wing, so I tried to shape mine in a similar fashion. A flat surface but with rounded edges and shaped like a tapering wing with a slightly swept back trailing edge and highly swept leading edge creating the taper shape. So from the get go I was dealing with angles everywhere. From the initial shapes to the angle of the edges that attach to the cabin side and roof. These angles include the face angle of the cabin wall to the leg angle (the engineering did not specify an actual angle just that it must be a minimum 50 degrees) the cabin wall to the the sweep angle and the exact lengths of each and each had to be precise so that the edges all meet correctly. I set it out using and adjustable set square and spirit levels and set it out on the floor before cutting.

various angles of the sheeting wings and legs

The manufacture of the legs started with cutting the ply to initial shape. Then sandwiching 10 layers of glass (7 x 450g uni, 3 x 457 double bias) between 2 sheets of ply, 1 x 20mm, 1 x 25mm. The glass was compressed between the ply to set by screwing it all to the bench with long screws and the excess glass trimmed once set leaving a heavy arm about 50mm thick. The excess glass was trimmed and final shape cut with a circular saw in one action and then I rounded the edges with a router and sanded smooth with an orbital sander ready for the next stage, closing it all in more glasss. Before glassing the outer skins, with a circular saw I cut a slot about 300mm long and 4mm thick, the thickness of the solid glass strips I had and I then glued them into the structure as sheer webs as per the initial design. Once set the surface overhangs were ground flat ready for the exterior glass. I then glassed the sandwich in by wrapping about 5 layers of glass (3 uni, 2 double bias). When laying the glass in the spine and around the surface I slightly opposed the thread of each layer to ensure strength in different directions. I downgraded the amount of glass on the outside based on just how heavy the structures were, originally I was going to put 10 layers on the outside too. I cut the hole at the end of each arm to house the hawse using a hole saw at each end and then jigsaw between them. I regret I didnt finish the glassing with peel ply as it would have meant I didnt need to grind the glass skin but wrapping peel ply around curved surfaces is difficult so I skipped and just put up with the dust of grinding the surface ready for more glass when attaching to the boat.

sheeting wing first sandwich sheeting wing legs sandwiched sheeting wing shaped

The slots for the shear web extensions were cut using just a drill. I started with holes along the line they needed to be at, one top one bottom, then filled the rest in with more holes then pulled the drill bit like a saw blade joining the holes. This ensured that the slot was hard up against the bulkhead on the inside so that the web extension sat snugly against it. The slot ends up a little larger than it needs to be but thats ok, the balsa is decored anyway and glass will cover the oversized slot.

sheer webs for sheeting wings sheeting leg with sheer web sheeting wings sheer webs glued

Although I am still to experiment with exact rope angles, my idea is to run a block from the underside of the boom to the top of the sheeting arm (in the same way as a regular boom to traveller would work) and then the single line would fall off the last sheave and down through a hawse pipe mounted at the end of the arm to direct the line down to a turning block on the deck and back to the winch. The idea of the hawse is similar to having the rub rail on the side of the roof, but only a single line will rub on the steel surface instead of up to 3, and that line will be under far less load than the lines from above the block to the boom, the load reduced by the double or more likely triple block. So the likely hood of friction damage to the line is somewhat reduced when the load is reduced. I decided on a hawse rather than a turning block because the standing triple block angle will change dependant on the tack and angle of the boom to the fixed sheeting point so the angle that the final working line coming off the last block will change, so I thought it much easier to lead the lines through a hawse that doesnt care so much what angle the line hits it, whereas a fixed block can jam if the line comes at it at a difficult angle, and the line can run off the groove in the sheave and jam in the block.

sheeting wing and leg dry fit sheeting point dry fit starboard sheeting point first dry fit

I originally considered cutting a single hawse pipe in half leaving the outside open, but the stainless hawse pipes were only $30 each and having the line captured means it cannot jump out of the hawse. And it is much neater and easier mounting the entire hawse within the sheet arm and then just rounding off the overhang left than it would have been to create the end of the arm with the half hawse neatly mounted in it. It just means I have about 40mm more protruding out into the cabin side walkway than I otherwise would have had. On that, everything in life in building a boat is a compromise. If I mount the sheeting block directly below the centre line of the masts on each hull the sheeting arm protrudes out into the walkway even further, and I envisaged bumping into it with my hips or other tender areas (otherwise known as the family jewels) so decided to confine the end of the arm to be inside the directly plumb line above where the cabin side starts. This means the foot cannot fall inside where the sheet arm ends. It will still be possible to hit the arm but now the foot naturally guides the hips (or other parts) past it.

sheeting wing shaped 1 sheeting wing sheer web slot

This means that my sheeting point is about 100mm inside the point where the ideal, directly below point would be. It might mean I lose a degree of pointing ability, but I doubt it. If it came to that I could always run a snubber line around the sheet line to a point inboard to help with sheeting in that extra 100mm, but seriously, how often is pointing as high as possible going to windward, going to be a critical issue? Remember, gentlemen cruisers dont sail to windward.

sheeting point mounted level sheeting points level starboard sheeting wing port dry fit 1

sheeting points as seen from aft sheer webs glued to bulkhead starboard cabin roof with sheeting wings visible

sheeting points glued in starboard sheeting points glued in port fairing removed to glass sheeting points in

I glued the sheeting legs in first then once they had set I glued the arms to the cabin sides and legs. I used Techniglue rather than epoxy and microfibres, its the same glue as used when I glued the mullions into the cabin roof. Its properties include being more flexible than epoxy, which can be brittle and crack, and this flexibility will stop it from cracking under the loads applied by the forces on the sheets especially during gybes where the booms crash across from one side to the other. I also screwed the arms down into the legs and buried the screws (deeply countersunk the heads) and filled over them. The combination of the screws and a clamp on the ends of the sheer web extensions ensured it set exactly in place. Needless to say I measured many times, applied the spirit levels many times and was satisfied with the final placement. And of course before I could glue them in I had to grind away all the bog and fairing work done to that point, you may recall though, I was not as diligent in this area, knowing this grind back was coming. This extra work obviously begs the question why fair first? Well 2 reasons, first its hard to fair around structure, much easier to fair unobstructed. And second, it provides a fair area either side to fair back to. And hopefully, my glassing does not exceed the height of the fairing. It might because I will be adding a lot of glass to secure it all, but if it does I will just fair to that new high. (This fair first, grind away, glass in and re-fair is also the method used when doing the stanchions, its just too hard otherwise to fair around them using long boards.)

During making the sheeting points I also worked on the radar riser. This entailed getting up onto the roof many times, and a few times I nearly slid off again. Which accelerated my desire to have steps up there. So again I employed the cardboard cutouts and made stencils until I had the shapes I wanted. Shapes that did not intrude into the deck area, did not get in the way of the sheet as it travels from the hawse down to the deck, and ensures a decent foot fall both up and down. Here is my first take on it.

first roof step shape templates

Same method when making the stencil for the radar riser. I had an idea what I wanted it to look like, a retro design and lightweight but strong and I needed it to be made from material I had. I presented a couple of ideas to Jo, let here choose the shape she liked and went with that. Its made from 2 pvc pipes and 2 sheets of ply cut to shape and glued together. Then some foam and a piece of cedar to finish the shape. The wiring will travel down inside this hollow mount and through the roof into the cockpit then through the bulkhead into the saloon (inside the pantry and through the furniture to the various points needed). The riser will house 5 items, the radar dome, gps antenna, vhf antenna, a navigation light and through the same roof conduits will also travel the solar panel wiring. The riser will be made to be removable so that I can keep the height down for transport or should servicing or rewiring need to be done.

first rough radar stand 1 first rough radar stand radar stand panels glued

radar stand panels glued and shaped radar stand shaped radar riser taking shape

Eventually once all of the shaping has finished the entire riser will be glassed. I intend to add a boomerang shape to the top to mount the 2 antenna either side, the middle will have the nav light mounted on a further pedestal above it. The base is designed to fit on the roof beam and the poly pipe will fit over a smaller poly pipe that is glued through the roof. The bottom will also have a right angle flange glassed in either side (using the roof as the mold for this) and be bolted through the roof beam. The wiring will enter the poly pipe under the boomerang or radar shelf, which hopefully minimises the chance of water ingress (although the solar wires will enter from the base) and further minimise the chance of water getting through to the roof conduit. If water does manage to get past all these barriers any drips will occur in the cockpit. As can be seen from the circles drawn on the side, I eventually want to cut these circles out and glass in poly pipe to finish the design, further reduce weight and also reduce the windage of the structure.

So thats it, thats where I am up to at the end of 2014 as I enter the tenth year of building. Who is to say it will be the last. I truly hope it is, but if it isnt, I will write all about it for another year after that. Thanks so much for sticking with me, many of you sending encouraging messages that are truly appreciated. Keep them coming. As many of us are at this time of year, I am grateful for the opportunity to be able to attempt a task like this, we are, by the lottery of the location of our birth are gifted so much more than so many others. We are not religious but if you are, we wish you whatever it is you would wish on others. If not, enjoy the break and be nicer to each other. Life truly is great. Next year could be it. Cheers.

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2 thoughts on “Appendages

  1. Gerald

    Nice 1 Paul, it’s great to see progress, it’s about the journey and and not the destination at the moment, in a few years when you guys are on some idyllic mooring in Fiji you will think back and appreciate the work you’ve put in even more.

    I’ve been following your build for so long now I didn’t realize it was 10 years though, Good on you for sticking it out.


  2. webmaster

    Thanks for sticking with me Gerald. It will be a decade in November, it would be fitting dont you think, that if I can launch this year, that I do so on the anniversary? I hope each year that this will be the one, and with so little construction left (the rest of the rear steps and davits and some ply winch pads is pretty much it now) and just the external fairing to go, maybe just maybe I can finally launch this year.

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