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lenm

Ocracoke 20 in OZ

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Thanks Alan for your detailed reply.

I tried what you suggested and discovered the highs were voids full of epoxy.

I then tried larger pads in conjunction with pressing the sheet down with my hands a bit harder (to help expel any excess/pooling resin) before torquing the screws.

Problem solved!

Also helped tightening the screw in the middle of the planks first then working outwards (helped squeeze the excess resin out the sides).

 

 

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On 11/10/2017 at 8:03 AM, Alan Stewart said:

When it comes time to fair the hull (before sheathing) I would apply some kind of guide coat to the surface such as a light dusting with some contrasting color of rattle can primer (it doesn't take much) or spritzing the boat down with a spray bottle solution of denatured alcohol with some red food coloring in it. The alcohol evaps away leaving the light pigment on the surface. Then once you begin sanding all the small low spots will jump out at you and you can go in with a wide putty knife and apply microspheres to each area, then fair again and it should be ready for glass. You can repeat the coloring again if you wish depending on how far you want to take the surface. 

 

That's what i'd do anyway. 

-Alan

.

 

This is what I've seen done countless times.  Thanks.

 

I mentioned this a while back on another boat building forum and was blasted for even suggesting that any faring material go under the glass.  I shook my head & kept quiet (which is a struggle for me...).

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It is my opinion and observation that applying fairing compound under glass work is not always the best. Shrinkage comes into play when you have a disproportionate amount of resin to the faring balloons that's meant to float across a surface making it easier to sand. By far the thicker filler materials are harder to sand and can cause some craters in the wood, which is normally softer than the thickened resin. A mixture of fairing compounds and a final blend of cabosil is what I normally apply if I have any real deep dish on the woods. Then if need be apply a skin coat of fairing after sanding the harder materials. This is actually done with a soft pad and grinder to knock the surface skin off. Then go back with a DA. or random orbiter.

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On 12 November 2017 at 1:46 AM, Oyster said:

By far the thicker filler materials are harder to sand and can cause some craters in the wood, which is normally softer than the thickened resin. A mixture of fairing compounds and a final blend of cabosil is what I normally apply if I have any real deep dish on the woods. 

Oyster,  may i ask what sort of proportions are you referring to?

3 parts fairing compound to 1 part cabosil?

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I though this day would never arrive, the final plank went on this week!

 

Started trimming up the ply edges today and radius the transom corners (a template worked great).

 

Still a little confused re the best way to finish the ply edges along the shear clamp before the glass goes down.

I.e. creating the bevel -  and how it transitions from the bow to the rear of the boat.

 

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I glassed to the edge of the rough cut ply and will dress that area when I have the deck on and start the rub rail build up.  I other words, I didn't do anything to it at the stage you're at.

 

OH, and congratulations on the whiskey plank.

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re whiskey plank, thanks, I'm glad your build is ahead of mine,  yours and some others are certainly setting a standard to aspire to :-) 

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The rub rail, gunwale, guard or whatever you want to call it is a very critical part of the boat and if not done well can spoil the look of an otherwise good boat. Beyond protecting the boat from accidental bumps against docks and anything else in it's path it is the visual break between the hull and the deck and it is right at eye line and is probably the most critical line on a boat. It is further compounded by the fact that it can be fairly difficult to do especially on boats with a lot of flair.

 

The sheer line needs to be fair, both in plan view and profile. On a boat like we are discussing here we need to protect the wood gunwale. This is normally done with a metal half oval which can be done with solid back or hollow back. I prefer hollow-back on a boat this size because it is about 1/3 the weight and at least 1/3 the cost even though it is not as strong. Hollowback can be improved by rounding the gunwale face so that it is has more bearing on the wood. Once we decide on the width of the protective strip we have a starting point for our gunwale design. The next will be the thickness of our wood followed by how we are going to blend with deck followed by whether we will shape the boat to the gunwale or the gunwale to the boat.

 

I prefer to set the gunwale below the deck edge by a little less than the thickness of the ply decking. I have tried many times to make the gunwale top a continuous smooth line to the deck and have usually been disappointed with the results especially on bright finished boats. If there is any movement in either the deck or gunwale it will show big time, not to mention that the tiniest bit of an unfair line in the sheer will show. On this boat I like to glass the deck and over the edge to the hull. This requires a good round over so that the glass will not bubble.  The raw end grain is well protected from water ingress not to mention the hard use that the deck will get. If after the the deck is rounded over and glassed, you find some slight unfairness while installing the gunwale you can average out the variations by installing the gunwale with a nice, sweet, fair line which the eye will catch. Thus, the slight variations of the rounded over deck edge will not easily be discernable.

 

Because this boat has a lot of flare and the deck edge has a lot of shape forward it is easier to shape the hull rather than the gunwale in the bow section. This means that the gunwales only have to be bent rather than bent and twisted. Once I decide on the gunwale section section shape, I plane a vertical surface to width of the gunwale height. This means that the gunwale section can be constant in the forward section and the outside surface will be vertical which will work best as a bumper. Of course, this is easier said than done with the boat still upside down because you do not know how fair the sheer line actually is until you turn the boat over and clean it up. I have spent a lot of time with my head down around my ankles trying to sight the upside down fairness of the sheer line; but it is hard to tell how much the inwale needs shaping for the deck camber and see if the inwale sagged between any of the stations. Where there is tumblehome, I bevel the lower inside edge of the gunwale so that the outside of the gunwale stays vertical like the forward section. You can dress the outside edge of the gunwale slightly after it is installed, if this is necessary to make it look uniform. All of this needs to be decided on before glassing as it is hard and unproductive to plane or re-fair glass later on.

 

I like to bevel the underside of the gunwale up by about 15 - 20 degrees so it matches the rub rail on the outer edge, but you still have a lot of bearing against the planking. This keeps the gunwale from looking visually heavy. On this boat I usually use 1" stainless steel hollow-back with a slight round above and below the metal. This sets the vertical height for the outside and I work out the section shape from there. The top edge can be horizontal or angled slightly up towards the deck. Some builders like to use a lot of filler and fair the underside of the gunwale so that it ends up with a continuous fair line with the hull. This is where you can inject your own personality into the boat.

 

 

Take notice of Oyster's comment on print-thru. I take it one step further, especially if I am going to paint the boat a dark colour. I like to put the boat out in the weather for at least a week before priming to get worst of the print-thru over before painting.

 

 

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Hope you don't mind one more opinion on fairing.  

 

Regardless of how perfect you fair the hull before glassing, you'll be fairing it again after glassing, so I would suggest not going crazy.  

 

Run around the hull with a grinder or DA to get any large humps of resin flattened, then with a relatively long (30 - 36") medium stiff fairing board with 60 grit or coarser paper before making any decisions on filling.  A quick pass will let you know what you have for lows, then check for highs with a batten where you may have gotten a booger behind a plank.  Knock off the high, and only fill where there is a step off between planks that the glass won't follow.  Use cabosil thickened resin.  Grind smooth not fair.  If the planking creates a gentle sine wave pattern leave it.   Glass it.  There will be plenty of sanding, filling, fairing to do now and it will all count.

 

If you are still considering using fairing compound under your glass, do a peel test.  

 

 

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Graham,

Your tips are priceless, thank you so much, that helps a lot.

I shall repay you some day - in the form of a beautiful example of one of your designs on the water.

 

Thanks smccormick,  I built the 36" fairing board today with some 60grit.

I also tried hooking it up to my shop vac for dust control.  It works so well I now don't need to wear a mask!

Bolted the vac head to the fairing board and sitting on top of a 1/2" foam (so the board can still bend/flex fair).

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Happy new year fellow boat builders and hope everyone has a productive 2018.

We are ready for sheathing after a long interruption due to a period of calm oceans and hot ocean currents (great for fishing).

Like the GulfStream in the US we get the East Australian Current - funnelling warm water from the Coral Sea along the East coast of Australia.

 

 

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Thanks smccormick.

Started glassing yesterday (glass tape chines). 

I dont have a helper so the rest of the hull looks to be a big job to pull off solo. 

Thats on the notion that everything is chemically bonded.

It's got me thinking about breaking it up into smaller sections, with unfortunately, more mechanical bonding (will be mechanically bonding to a peel ply finish).

Does anyone have any opinions re mechanical bonding or a good strategy to pull off hull glassing solo??

I cant say i have ever experienced a delamination due to a well prepared mechanical bond, apart from an incident where there was some some surface  contamination.

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Suggest you get expert opinions on this before trying any large areas.  We found that with the heavy bi axial cloth used on the 256 plus working in tropical conditions with short pot life that brushing the epoxy on the back of the cloth made it so much easier to get a nice wet out. Of course after laying the glass down we used a squeegee and put more epoxy on top. Thought by putting this out there you might get some more knowledgable responses.

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Thanks Capriosca, I'm hearing you re heavy fabric and tropical conditions.

Did you use a single 1708 or 2208 on the 256?

 

Currently proposing 2 layers of lighter fabrics (with no mat) due to their fast wet out and the way you can stage the pot life.

Bottom done first then topside the following day.

1) Mash epoxy into wood with squeegee and wait till tacky.

2) roll out and epoxy a 8oz woven hybrid (0/90) basalt

3) squeegee and wail till tacky

4) roll out and epoxy a 12oz double bias (45/45) eglass

5) Squeegee

6) peel ply

 

Alternatively,  just 2 x layers of the 12oz double bias (45/45)

 

As you mention, would be good to hear a more knowledgeable persons opinion, albeit, I've already asked a hundred questions already :-)

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Lenm, a couple of things I have learned along the way:

 

Glassing will take far longer to complete than you will ever think reasonable.

 

Do one strip of glass at a time, bow to stern.  Wait for it to kick and grind a nice bevel to accept the next strip with 36 grit, except for the keel overlap..  Don't grind into the wood.  If there is a slight step off, smooth with thicken epoxy while laminating the next strip rather than divot the planking.   Grind the second piece overlap flat with the surface.  Essentially a scarf.  This will pay dividends galore when fairing. 

 

Secondary bonding is fine for our work, as long as the overlap is prepared correctly.  It's done all the time with satisfactory results.

 

Get the slowest hardener you can for the resin system you're using.  Even if you wait until the fall to do the work, you'll appreciate the long working time and easy pace.  I went with a 7-8 hour working time hardener, laminating was a casual event rather than a fire drill.

 

Biax without csm can be pulled out of shape easily when positioning.  If you have a tacky surface, applying and smoothing 1700 will be frustrating.  Even 1708 will be a pain.  Applying prewetted biax is an order of magnitude more frustrating.  The design calls for a single layer of 1208 on your model I think. 

 

If you have a very slow cure, position the glass on the surface dry, fasten the top edge if you have to.  Roll up the glass length wise about 3/4 of the way.  Saturate the substrate, roll the glass down, then roll the top edge down and do the same, then finish wetting out and squeegee.  This will be a disaster with a short pot life.  With a short pot life, either wet the planking, let cure and grind, then apply or just wet through the glass.  Don't mess around with brushing, much too slow.  Dump a bucket of resin on the surface while squeegeeing it around.  Easier said than done on some surfaces but you'll get the hang of it.  For the bottom and large relatively horizontal surfaces get a squeegee with a long handle, so you can stand up and reach to the keel.

 

I doubled the glass on the bottom of my build for the extra impact resistance, It was around a 54 lb penalty and worth it to me.  If you look at the keel and chine overlap and the small distance between them, it really is a small area to fill to get double coverage.  I can draw a laminate diagram if you are interested.   Order of events important to minimize work and fairing.

 

Doing 2 layers of lighter glass rather than one will double your work and introduce another bond line.  Getting a really slow hardener or waiting for it to cool would save a lot of work.  

 

Any surface where the next step is fairing, I would suggest applying fairing compound onto the green resin rather than peel ply.  It's cheaper, lighter and saves a couple steps.

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Smccormick,

Thanks for taking the time to describe all this.

 Some great ideas, and if you have time to share your laminate diagram that would be much appreciated.

I just spoke with the tech rep and looks like we can get hold of a hardner with a 2hr pot life and 8hr thin work time.

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'Tested' a few samples today in order to get an observation of how ply compares to other typical sandwich panels in an impact. 

Under 'uncontrolled' conditions, I dropped a 20mm, 1.5kg metal rod from a height of 2 metres onto 3 different configurations.

75mm wide panels were span 150mm (not clamped).

1) 13mm end grain balsa core with 18oz double bias each side 0/90 (vacuum bagged.

2) 15mm H80 foam with 18oz double bias each side 0/90 (vacuum bagged).

3) 9mm marine ply (meranti) with 12oz double bias each side 45/45 (hand laminated).

 

Results

1) Balsa - large dent at impact site. Front/outside skin sheared. core fractured and sheared. large de-lamination of back/inside skin.

2) Foam - large dent at impact site. Front/outside skin sheared. core squashed and bent only. inside skin intact.

3) plywood - very minor dent at impact site. no damage to core. inside skin intact.

 

Then took the panels up to complete failure (unmeasured)

Comments

1) Balsa - inside skin holds structure from a complete shear. Core severely fractured in multiple places.

2) foam - inside skin holds structure from a complete shear. core severely squashed and bent.

3) plywood -  Core layers separate completely.  Wood fibres parallel to the shear direction 'roll' causing failure.  fibreglass skins stay bonded to ply.

 

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Do you have an approximate amount of force need to fully break each sample? Though the plywood was the thinnest, I suspect it took the most to bring to failure, with the H-80 a distant second?

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