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Carbon Spindrift 10


William
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For want of a decent local plywood supplier I will be building in 5mm nidacore honeycomb sandwich, carbon outside, vectran and glass inside. If I can get my hands on some affordable basalt fabric I am sure I will find a few panels for it to feature. It is certainly not going to be as enjoyable as building in wood but at least I will get to learn a few new skills along the way. A lighter boat is almost a guarantee, but that all depends on how many laminates will give me the impact toughness I require. 

 

I do have a partial sheet of nice 6mm ply and will cut the transom, mast partners and a few other small parts from that.

 

The nidacore sheets are 7ft x 4ft, which, as fortune would have it, is just long enough to cut the main hull panels from 3 sheets, one being halved and butt-joined to the full sheets just like the plans for plywood.

 

 

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An extra 1.5mm would have been perfect as it would have given me exactly the same panel stiffness as 6mm ply with only one layer of 6oz carbon outside and 6oz Vectran inside. 

Unfortunately the next Nidacore size up is 10mm which is overkill, unnecessary weight and cost.

Larger boats (e.g. Mirror) have been built with 4mm ply although I am not prepared to go that flimsy.

 

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I have a couple of questions relating to the interior layout (non-nesting version) -

How does the boat trim while rowing two-up? With the passenger (120lbs) sitting on the lazarette it looks like the transom might be dragging too low unless I move the thwart a bit further forward.

What do you typically store in the lazarette while sailing? I am a big guy so for the sake of not overloading the stern, would it be more useful to have the storage space under the thwart?

Any thoughts on rather using the Spindrift 12's deck design up front, i.e. level with the gunnels? 

 

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The Minipaw uses a longitudinal seat and can have 2 sets of rowlocks, thus balancing with 1 or 2.  Any small boat will need 2 stations to really balance with a changing number of passengers. I don't think this is practical in the Spindrifts, or shall I say I haven't figured it out.

I wouldn't raise the forward seat/partner on the cat version.  With 3 or 4 rowing it is used as a seat.

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Butt-joint on the nidacore. Glassed one side first, flipped the whole thing over after about 12 hours, flexed the joint half open and filled the half-open cells with thickened epoxy and then added the last bit off glass to complete the joint. 

 

The tissue-like scrim is quite thirsty and requires about 30-50% more epoxy that plywood to wet-out. Part of the problem is that it does not allow easy re-distribution of the epoxy once it is on the surface, resulting in the inevitable over-saturated areas. That is why the peel-ply is there, helping to absorb some of the excess.

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Once the panels were marked I applied a layer of epoxy to what will be the inner surfaces before cutting them out. The epoxy allows a cleaner cut using a utility knife but the main reason is to add some stiffness to the scrim. Without it, curving the core results in the scrim crumpling over each cell on the compression side, giving an uneven surface. Adding stiffness to the inside also moves the neutral bending axis and increases the tension on the outer scrim for an even smoother surface to work on. 

 

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6 hours ago, Walt S. said:

William,

 

Have you thought of vacuum bagging these panels? The vacuum-bagged surfboards I've used were much lighter than the ones glassed with layup.  

http://www.westsystem.com/wp-content/uploads/VacuumBag-7th-Ed.pdf

 

I have thought about it but since all the cells are technically open I dismissed the idea, reasoning that the vacuum will simply suck the resin into the cells. But now that you brought it up again I think it is worth investigating a bit further. 

One reference I found used a light vacuum to press down the dry core onto pre-wetted glass. Since the polyester scrim adds no strength apart from something for the epoxy to bond to on the actual cell walls, I cannot see the need for full wet-out of the entire scrim surface. As long as the glass itself is properly saturated and evenly bonded along all the cell walls. 

 

I have tried this on test pieces with wood strips, wetting out only the wood and pressing it down evenly on the dry nidacore. Another interesting test was to use thin abs sheet, dissolve its surface with a few brush strokes of nothing but acetone and press it just like that against the dry core. It gave a very nice bond. Heavy, naturally, but an interesting option if you want the impact resistance of rotomolded polyethylene without the lack of stiffness.

 

I don't have any vacuum bagging equipment, and to use it on this particular build would not be practical for the major hull panels. It would require cutting out the fabric to the individual panel shapes and bonding them together again with tape as one would with plywood. It would require much more fabric in total to fit the parts individually. To get the most economical use of the 1m wide carbon fabric, my plan is to stitch the hull into its basic shape and lay up lengthwise with a generous overlap along the keel. It will also give me continuous fibres from the bottom panels onto the topsides, for whatever that is worth in additional stiffness.

 

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Having set up a spreadsheet to calculate the wood-replacement layup schedule, I started thinking about the spars.

To replace the boom would require a rather generous amount of UD carbon to match the bending strength and stiffness of solid spruce. A rough estimate indicated a weight saving of about 50%, or 1kg. Such a small saving might not seem worth all the extra work and cost  as far as overall weight reduction goes, but I was surprised at the impact it has on stability. 

I calculated moments and center of buoyancy at 5 degrees heel and with the boom sheeted out 15deg from the centerline. The reduction of the 1kg that far to leeward adds the same amount of stability as the addition of 2kg of ballast at the tip of the centerboard.

On a reach with the boom out 45deg and the board pulled up by 1ft, the equivalent tip ballast would be 6.7kg.

 

The values a trivial and might not even be noticeable on a boat with such a stable hull-form such as the S10, but it is worth keeping in mind for those designs that never give the stomach muscles a break!

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The recent supermoon gave us higher that usual tides, so this morning we explored some nooks of the estuary that are not normally accessible. The canoe is a 12ft adaptation of the B and B canoes that I recently completed. 

 

Then on to open the butterfly and go 3D. I don't plan on doing a full series of build videos like I did for the little canoe but I did take some timelapse of today's progress. The camera's battery died before I got everything fully stitched but at least it captured the essence of the whole exercise.  

Stitching is with thin galvanised binding wire. No drilling required to make holes but to puncture the cured layer of epoxy did require the use of a scriber. Hole placement was done such that the wire pulled up against a hex-cell wall.

Working with the floppy core panels was as cumbersome as I thought it would be, ditto for getting fair chines while stitching. Having built the canoe out of 2.7mm ply at least gave me some experience in using gravity and well-placed supports to help tune the shape. Adding the ash gunnels went a long way in getting the right curve on the topsides. 

 

I was expecting some discontinuities at the bulkheads and was prepared to disassemble and add glass tape on either side of each free edge to provide more stiffness, but I am very happy with how it turned out. It still needs to be flipped (or raised) so that I can tighten the keel stitches and fair the rocker. 

You can tell from the photos that I have modified the sheer line.

 

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  • 2 weeks later...

Chines are all taped inside.

Time to flip and get the outer skin on, but first I had to clean up the chines on the outside.

 

I used a wood file to rasp open the core cells on the edge of the bottom panel and filled them with thickened epoxy. 

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After curing it was easy to clean it up with the same wood file, but I soon also started using a plane which worked surprisingly well.

The remaining holes and hollows were filled up before adding tape to the edges.

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I tackled the Vectran with a brand new pair of scissors. It made it about two feet into the fabric before it started gnawing and never really recovered. Another less serrated pair worked slightly better but it was a pair of serrated tin snips that proved to be the real solution, cutting MUCH faster and giving a very clean cut.

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The Vectran turned out to be plain weave instead of twill, and being a very stiff fabric it was impossible to bend some of it over the chines. I had also cut out a slot where the daggerboard will protrude so that I do not have to struggle cutting through the vectran once the skin has cured.

 

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Carbon tape on the chines and then the whole lot got covered with some 5oz glass. The glass is 1m wide, just enough for one half hull at a time with a bit of overlap on the keel.

 

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  • 3 weeks later...

Ash gunnels, not full thickness but enough to give a fair curve to the sheer for now. 

Just finished laminating the carbon inside. It was difficult to tell dry areas from those already wetted out, but a good deal easier to wet out than the Vectran!

I added the straps to maintain the correct beam just in case the topsides get too rigid once the carbon skin cures.

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