New Goat Island Skiff in Brooklyn, NY

**callsign222** · 18th September 2010, 11:13 PM

It is not likely to happen, but screws in the ends of those frames serve an interesting function.

The problem with wood is that it splits - we all know that.

When the piece of wood has plywood glued to two faces it is very unlikely it will split.

Most of the timber in my boats is protected this way.

However when it is glued to plywood on one face only then the question is whether to try and prevent the possiblity of splitting.

The main thing that prevents the gunwales and keel battens from splitting is their large cross section. On a much larger boat I would recommend putting a fastener through the ends of those as well. but the gunwale is so beefy and also it is laminated - so there is little chance of a split starting that will agree with both bits of wood.

So the classic ways of preventing splitting in modern structures are
Glassing - like the tips of the spars and foils.
Laminating with plywood or to plywood - like the mast partner and step and they are quite big anyhow.
Putting in a fastener - like the tops of the frames.

The reason I was worried about the ends of the side arms is that we are relying on three of them to support the side of the boat. They also have a small gluing area - correct for their load. But the smaller glue area does mean that if the side of the boat gets hit from the inside (or from the opposite side) the small cross section could split very easily.

Just imagine getting an axe and splitting one of the side arms. It would take almost zero effort.

So I think the fastener is a small price to pay for some degree of certainty.

The way I think about boat structures is a bit different from many. Most will listen to my argument about the side frame issue and their solution would be to make them bigger or stronger or out of more dense timber.

My way of thinking is always to try to identify the MODE of failure and work out a means of preventing it.

Here the risk is splitting - and a single fastener at the end will prevent it - because timber splits from the end. The only way it can split from the middle is if the grain runs out the side of the piece.

One of the GOOD ways of using fasteners in modern boats. But you can see why my hull fastener list only consists of six - quite a saving.

So before making something stronger ... work out why it may fail and then see if there is a simple way of removing or limiting that possibility.

So, I need more explanation. The top of the side arms that gets the screw is already sandwiched between the ply, the inwale, and in my case, a spacer. The outwale re-enforces the outside of the ply. That's three out of four sides that have a gluing surface. The only one-glued side of the arm is under the gunwale to the seat tops, and that doesn't get a screw anyway. Wouldn't pushing a drill bit and then a screw through the very top of the side arm only increase the risk of splitting/rotting the wood anyway? It seems counter-intuitive.

**Boatmik** · 19th September 2010, 01:22 AM

Howdy,

The weaknesses without the screws being there are

1/ the glue surface area between the tops of the sidearms and the inwales is very small. Would be possible to pull the inwale off the side arm

2/ If that one doesn't break the cross section of the side arms is quite small, so a split through the 19mm dimension can propogate from the top of the side arm towards the bottom end ... because of grain deviations it might not get that far.

As you suggest, making the inwale spacers continuous either side of the side arms would increase the gluing area and reduce the risk of either of these failures. But it would make the distribution of the gunwale spacers tricky to describe and a pain to do.

Also if the side arms were thicker than 19mm or harder (heavier) timber it would reduce the risk of splitting, but with a fair bit of weight and making the approximate bevels where the side frame meets the ply would have to be cut much more accurately if the side frame was thicker - we are relying on the epoxy to fit the gap.

Not to mention the increase in weight.

A screw seems a very simple method to accomplish all the same objectives

Best wishes
MIK

**woodeneye** · 19th September 2010, 05:32 AM

Originally Posted by Boatmik

As you suggest, making the inwale spacers continuous either side of the side arms would increase the gluing area and reduce the risk of either of these failures. But it would make the distribution of the gunwale spacers tricky to describe and a pain to do.

Aah, I see now. Actually, this is sort of what I did. So on my boat, when you look down at the gunwale from the top you don't see the tops of the sidearms as they integrate into the spacers and inwale and it's all epoxied together. I feel a lot better about it now.

**callsign222** · 19th September 2010, 06:12 AM

Thanks Mik, that made more sense, I don't know why, I didn't really get at what you wrote before.

Since all my side arms are backed up by inwale spacers, I'm going to let it slide and see what happens. 30+ days so far and so good. I'm going to do a "Battle Damage" report at the end of the season anyway. There is some weird stuff, but mostly all benign. In regards to the inadvertent bashing that I seem to regularly deliver to my faithful steed, she is holding up quite well.

**callsign222** · 19th September 2010, 06:17 AM

Originally Posted by Boatmik

As you suggest, making the inwale spacers continuous either side of the side arms would increase the gluing area and reduce the risk of either of these failures. But it would make the distribution of the gunwale spacers tricky to describe and a pain to do.

It might be difficult to describe, but it really comes down to some very simple math. It was only a very slight deviation from your suggested inwale spacer length to get uniform spaces and uniform spacers to back up the side arms and also the ply joint amidships.

For all the glue I somehow left behind in her construction and other visual atrocities, I somehow was very anal to not have any stand alone side-arms. The lack of a systematic pattern and symmetry in inwale spacers and side arms slayed me for some reason, and was a problem that had to be solved.

**BobWes** · 19th September 2010, 11:56 AM

Oh, great...

The more I read, the less I like the job I did building my GIS. I won't even try to explain that right now. Suffice it to say the list of "do-overs" to be done next spring in Michigan is growing longer.

**MiddleAgesMan** · 19th September 2010, 12:27 PM

My spacers do not contact the side arm tops at all, but I never intended to omit the screws.

In my case I was focused on keeping a fair curve around the sheer and a large mass of wood all glued together seems like it would change the bend.

There are good reasons to do it per the plans and good reasons to do what Callsign and Woodeneye did, so don't sweat the small stuff, Bob.

**callsign222** · 19th September 2010, 12:52 PM

The backed up side arms are the same size as a spacer would be, so no mass of wood, but I see what you mean.

Coincidentally, I had more problems with my sheer around BH3, the ply and the side arms extended out at different angles. I had to pinch in the sheer to join the side arms. So I found a smooth sheer, and filled in the gap with some epoxy-- then BH3 side arm got half a spacer on each side. A little complicated, and in retrospect I could've used a wood shim, but it all worked well distance wise with the other spacers, side arms, and butt-joint of the ply.

I'm not sure why my sheer did this, I wonder if it was the plywood itself, everything else fit together really nice.

**alzuger** · 19th September 2010, 01:15 PM

I wouldn't stress too much Bob, little aesthetic details are all well and good on land or on the internet, but most likely none of us will be worried about them when leaning out hard, while tearing through the chop and hoping not to catch the dagger board again on lurking submerged rocks. That's what were supposed to do with these things when we are done making them pretty right? Ride them hard and put them away wet.

-Al

Oh yeah, I haven't made the final decision, but I think I might let the missing sticks ride for the time being. She seems pretty rigid as is, after all, once the gunwales are on and it is all glued up it becomes a very stiff monocoque structure with most of the stresses bourne relatively evenly throughout the plywood skin. I can imagine a structural failure as a result of a very strong localized impact near the missing timber like MIK said about the buoyancy tank corner punching through, but if you hit anything hard enough it will fail eventually. I'm going to put a few more hours in tomorrow, and i'll post some pics.

Also I was thinking about going up to Portland Maine with a buddy of mine for the weekend of Oct 16-17. He's from there, and if I can build and register a trailer I might bring the boat. Anyone up for some cold dinghy sailing?

**callsign222** · 19th September 2010, 01:23 PM

I had tentative plans with Clint on Squam in NH, but two Goats in Portland and meeting you would be hard to resist-- or maybe I could do both... hmmmmmmmm. Or maybe Clint could finish his GIS and we'd have three.... hmmmmmmmm...

Keep me in mind. I'm going to be away until Oct. 10th, I'll drop you a line that week to see what's going on on your end.

That's what were supposed to do with these things when we are done making them pretty right? Ride them hard and put them away wet.

Nice, that's the spirit. And preferably salty, dirty, banged up, and full of stories!

**alzuger** · 19th September 2010, 01:32 PM

I could do Squam Lake if you guys are ok with me crashing your party. I'lll actually be staying in Hollis ME, which is only a little over 60 miles away.

It could be a lot of fun, and I might learn something to boot!

**callsign222** · 19th September 2010, 01:36 PM

Ditch your friend at the NH/ME border and spend the weekend with me. He can hitchhike.

We'll figure something out, and it will be groovy.

**alzuger** · 19th September 2010, 01:40 PM

Sounds good, I'll be there!

**BobWes** · 19th September 2010, 02:43 PM

I'll be testing that "don't sweat the small stuff" theory...

Only the side-arms at BH-3 extend up to the gunwale and is bracketed with spacers. The rest of the side-arms come up short.

I didn't use any screws.

**Boatmik** · 19th September 2010, 11:02 PM

Originally Posted by callsign222

It might be difficult to describe, but it really comes down to some very simple math. It was only a very slight deviation from your suggested inwale spacer length to get uniform spaces and uniform spacers to back up the side arms and also the ply joint amidships.

For all the glue I somehow left behind in her construction and other visual atrocities, I somehow was very anal to not have any stand alone side-arms. The lack of a systematic pattern and symmetry in inwale spacers and side arms slayed me for some reason, and was a problem that had to be solved.

I agree actually, it is pretty simple to work out. However it is much simpler and easier to explain if the spacings don't need to be controlled so accurately. MIK

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