Scarf direction?

[paxtonm]

Hello everyone,

Even though I can get WRC long enough to not need scarf joints, the thought of ripping 18-foot planks on my table saw gives me pause. I'm working in a pretty tight space, and that's a lot of wood to have to feed. So, I'm thinking about buying 10-foot planks, cutting those to the right dimensions for gunnels and stringers, and scarfing them all up. I'm probably over-analyzing (first time doing SOF) but I've been wondering about the best orientation for the scarf joints, or if it even matters.

Take the gunnels: if they're 1.5 inches high and 5/8 inch thick, would it be best to have the scarf run diagonally across the long side or the short? I'm thinking long side as it would be a longer glue joint, and the wood would bend mostly across the scarf.

I've already done up a jig, using Jeff's suggestions.

Thanks in advance,

Mark

[P Doug (WA)]

Mark, I asked this same question when I got started with my build. Here is the thread I asked it in and the responses I received. Hope it helps.

http://messing-about.com/forums/topic/7724-more-questions/page__hl__scarf__fromsearch__1

[Hirilonde]

I bought 18 footers for my kayak, and 13 for my wife's. I opened the garage door and moved my saw a little. I used a step ladder as an outfeed bracket. Very easy and no scarfs to make. I only use scarf joints when I have to. Not because of strength, because scarf joints are more than strong. I am just lazy.

[chris.lewis.425]

I think there's another solution to this issue that I'm trying out. I used a 4:1 scarf and then placed the scarf joint on a frame so that it's not only glued, but also lashed on both sides. The wood will break long before the glue joint when supported this way.

My two cents.

Chris in Seattle

[paxtonm]

Thanks everyone. Maybe I will try 18 footers. The purchase is tomorrow, then ripping and rounding over corners. Lashing starts Saturday.

[Hirilonde]

I think there's another solution to this issue that I'm trying out. I used a 4:1 scarf and then placed the scarf joint on a frame so that it's not only glued, but also lashed on both sides. The wood will break long before the glue joint when supported this way. My two cents. Chris in Seattle

Even if it is strong enough, and I seriously question whether it is, it is not as strong as an 8:1. And nothing bends more fair than a stand alone scarf joint with the possible exception of no joint at all.

The excepted practice in the marine industry is a minumum of 8:1 and for spars and other high load applications 12:1.

[Kudzu]

I think there's another solution to this issue that I'm trying out. I used a 4:1 scarf and then placed the scarf joint on a frame so that it's not only glued, but also lashed on both sides.

Sorry but I can not recommend this. It may work, but it is just a short cut. If you're going to cut a 4:1 why not just do it right and cut it at 8:1.

[chris.lewis.425]

Point taken - "Short Cut" A good pun!

Scarf length - Small workspace and small table saw. I tried hand cutting them longer without success.

My curves are quite fair and I did a test on a scrap before I started to make sure it was strong (wood failed well before the glue joint) and flexible (no flat spots in the curve). Landing them on the frame also adds considerable strength.

Considering our forebearers in this art used driftwoood and animal parts, I'm thinking there's a fair latitude when it comes to putting together a working boat. There are plenty of skin boat enthusiasts who that feel plywood is heresy, yet we're all building good looking, usable boats. They even argue over oak or bamboo ribs. Nylon or Polyester, Varnish or Paint...

I hope there's room for everyone here. I'll let everyone know how it goes. I'm certainly not trying to talk anyone into it and I understand your wish to promote the standards.

I'm happy to venture out (own boat design and TJI strongback even!) and see how it actually plays out. Just a stubborn independent streak I guess.

Chris in Seattle

[PAR]

The scarf should also face away from any water flow. Simply put, the joint should be facing in such a way that water can't be driven into it from flow, gravity, etc. On a rub rail, this means the forward portion of the rub rail overlaps the aft piece and the joint slope is from inboard to outboard (forward to aft). This way, if water was to get at the joint, it would slide along the taper and drip outboard of the boat. If the joint was facing the the other way, it would permit water to follow the faying surfaces into the boat.