Thread: GIS Build in Queenstown New Zealand

That sounds great.

I am very happy with your approach.

The only weakness of the paulownia as spacers is they might tend to split at lower stresses. However, I don't think it will be a general problem - just require fasteners through the inwale/side frames and also in the area the traveller will be lashed on.

MIK

MIK

Originally Posted by Boatmik

That sounds great.

I am very happy with your approach.

The only weakness of the paulownia as spacers is they might tend to split at lower stresses. However, I don't think it will be a general problem - just require fasteners through the inwale/side frames and also in the area the traveller will be lashed on.

MIK

MIK

I think I can allay any fears there, as I used Paulownia spacers and I have no structural screws in my boat at all. One of the virtues of Paulownia is that it does resist splitting.

After I had finished the boat, I realised I was supposed to leave the screws in the side frames where they attach to the gunwales, but its a very strong structure anyway and probably not necessary.

My traveller is attached via eyes with big 2.5" screws that go right through the inwale into the gunwale, so I'm not expecting that to come off!

On a day out on Lake Macquarie with my brother recently, we hit shallows at speed with full sail in about 15 knots of wind with the board 3/4 down and we came to a sudden dead stop. It's a wonder the cb case wasn't ripped right out with the impact. However the only damage was to the trailing edge of the Paulownia dagger board which hit the back of the cb case and crunched it in about 1". The trailing edge was of Tasmanian Oak, a local ubiquitous hardwood. I also have to repair the ply at the back of the case where the board hit. Other than that, I've checked the hull over carefully and it's 100%! My brother said if it had been a Paper Tiger, the whole boat would have opened up like a tin can as he has seen this happen.

The other damage was physical. I broke my thumb when we were thrown violently forward. As we hit, I was thrown overboard and when I grabbed the gunwale to stop myself my thumb got caught in between the spacers and was wrenched the wrong way. It's still very sore and swollen so my sailing has been curtailed for a while. Maybe the extra wide spacers you're planning are a very good idea?!

I used Paulownia for all the framing, chinelogs, inwale spacers, cb and rudder stock spacers, and the bow stem as well. It's also used as the infills in my mast and boom. It's good stuff, and I'm very comfortable with it's use in my boat. Oh yeah, the design is good too!

Hi Woodeneye, whoops, that was probably the day I urged you to take your brother to the lake. Sorry about your thumb.
Regards, Brad.

Originally Posted by Jazzman

Hi Woodeneye, whoops, that was probably the day I urged you to take your brother to the lake. Sorry about your thumb.
Regards, Brad.

Yup, same day...

Originally Posted by Boatmik

That sounds great.

I am very happy with your approach.

The only weakness of the paulownia as spacers is they might tend to split at lower stresses. However, I don't think it will be a general problem - just require fasteners through the inwale/side frames and also in the area the traveller will be lashed on.

MIK

MIK

Thanks, Mik

I'd already thought that I'll probably do the inwale spacer at the traveller position on either side out of Vic Ash. Also small blocks of Vic Ash either side of the side frames where they come through and meet the inwales. My side frames will be Paulownia, but with 5 or 6 mm Vic Ash laminated on the inboard edge so should be very strong and light with a hard edge to take knocks.

I like the idea of going both stronger and lighter by making structures with lighter cores and thin, higher density timber on the outside to take the load. There's many places on a boat you need a medium (450-500kg/m^2) density timber, Paulownia would be too weak/soft, a smaller section of higher density timber would also be weaker due to the thinner section, but if you use a light core that problem is overcome.

I think it should let us move to timbers such as Vic Ash/Tasie Oak and Paulownia which will (presumably) remain available and away from reliance on old growth timber from Canada. Not sure you could do a wooden mast this way, but I guess the Australian Hoop pine would work there.

Attached is a picture of how I'm thinking of doing my boom.

Ian

Good idea for the caps on the boom as this will provide sideways stiffness as well.

Mine is lacking stiffness in a heavy breeze, which I'm trying to correct with carbon tow as per MIK's suggestion. I'll let you know if that works.

Hi woodeneye, do you have the dimensions/construction/timber type of your boom handy?

Is it lacking stiffness in the vertical and/or the horizontal direction?

Some flex figures for now and/or after you get it stiff enough would be good. (Just put it between two saw horses, sit on it, see how much it deflects at the midpoint. Doesn't matter how much weight you put on it, enough to make it bend (not enough to break it!) as long as the weight and deflection are recorded.

Thanks, Ian

Originally Posted by IanHowick

Hi woodeneye, do you have the dimensions/construction/timber type of your boom handy?

Is it lacking stiffness in the vertical and/or the horizontal direction?

Some flex figures for now and/or after you get it stiff enough would be good. (Just put it between two saw horses, sit on it, see how much it deflects at the midpoint. Doesn't matter how much weight you put on it, enough to make it bend (not enough to break it!) as long as the weight and deflection are recorded.

Thanks, Ian

Th boom was made of stock sized 40X10mm radiata pine. So it finished at 60x40. The sides were clear stock but the top and bottom caps were finger jointed. It's tapered down to 45mm at the ends. Spacers are paulownia with the front of the boom having a continuous spacer of about 800mm (from memory) to stiffen the downhaul area.

With 10kg, the deflection is 15mm. At the time I thought this was relatively stiff, but it's not nearly stiff enough. I'm hoping the tow will bring this down to 5mm or less, but I'm not sure if this is just wishful thinking.

When the breeze is above 15knots, the boom bends horizontally as well, so again, I hope the tow will provide stiffness here too.

Most of the bend was caused by the mainsheet tension, not the downhaul, so my thoughts now are not to taper the boom at the ends at all. Looking at the recent RC44 series, I noticed the carbon booms are much like the old Finn style planks, so are vertically stiff all the way to the clew.
Attachment 147301 Attachment 147302

Attachment 147303

Originally Posted by woodeneye

I think I can allay any fears there, as I used Paulownia spacers and I have no structural screws in my boat at all. One of the virtues of Paulownia is that it does resist splitting.

After I had finished the boat, I realised I was supposed to leave the screws in the side frames where they attach to the gunwales, but its a very strong structure anyway and probably not necessary.

Howdy,

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.

Best wishes
Michael

Originally Posted by Boatmik

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

Great FMEA (Failure Modes and Effects Analysis)! I knew I liked your Goat for good reason...

Originally Posted by woodeneye

With 10kg, the deflection is 15mm. At the time I thought this was relatively stiff, but it's not nearly stiff enough.

Thanks for those numbers, I can work with them to see if I can make a structure with triple the above stiffness.

Originally Posted by woodeneye

I'm hoping the tow will bring this down to 5mm or less, but I'm not sure if this is just wishful thinking.

You might need quite a lot of carbon tow to make the stiffness three times what it is now, but I'm not sure how to calculate how much you would need.

Much easier to calculate how thick a layer of Vic Ash or similar you would need to laminate on the top and bottom of the existing boom to triple it's stiffness.

Interesting your thoughts/experience regarding boom stiffness, from memory your current boom is at least twice as stiff as Joost's solid round section, and you want it three times stiffer again. You must be working that boat of yours pretty hard!

Ian

Originally Posted by IanHowick

You must be working that boat of yours pretty hard!
Ian

It's really only when you are two up (both experienced sailors) with full sail in a decent blow that you'd need the kind of stiffness that I'm after. Realistically this is outside of normal usage, but then I want it sorted for when these sailing opportunities arise. For ordinary sailing up to 15 knots my boom is fine. If single handed, I would of course reef my sail, so it would be OK for that sailing. However, my yard is way too flexible in all kinds of breeze except ultra light.

Overall, this has been a lesson to me for using crappy timber (radiata pine) for the yard and boom. I went with quality timbers in the boat, mast and foils, so what possessed me to choose radiata for important items like the yard and boom is a mystery to me now!

Originally Posted by woodeneye

On a day out on Lake Macquarie with my brother recently, we hit shallows at speed with full sail in about 15 knots of wind with the board 3/4 down and we came to a sudden dead stop. It's a wonder the cb case wasn't ripped right out with the impact. However the only damage was to the trailing edge of the Paulownia dagger board which hit the back of the cb case and crunched it in about 1". The trailing edge was of Tasmanian Oak, a local ubiquitous hardwood. I also have to repair the ply at the back of the case where the board hit. Other than that, I've checked the hull over carefully and it's 100%! My brother said if it had been a Paper Tiger, the whole boat would have opened up like a tin can as he has seen this happen.

The other damage was physical. I broke my thumb when we were thrown violently forward. As we hit, I was thrown overboard and when I grabbed the gunwale to stop myself my thumb got caught in between the spacers and was wrenched the wrong way. It's still very sore and swollen so my sailing has been curtailed for a while. Maybe the extra wide spacers you're planning are a very good idea?!

Didn't your Mom tell you to keep your fingers out of doorjambs and other tight places? Jeezo, Bruce! Careful, but better your thumb than your noggin'.

Here's a pic of 4 sudden stops, and corresponding daggerboard damage. Cherry trailing stem up against cherry spacer in the CB case. A strip of dense yet yielding foam on the aft spacer is ideal. I can only imagine if I brought the daggerboard down to 1/16th of an inch.... (impact 1 and 3 are temporarily filled with epoxy, 2 and 4 still too fresh, the wood hasn't had a chance to dry in the past week...)

My rudder, however, still looks brand new!

EDIT actually, most of the damage is not coming from the trailing edge of the case, but where the bottom ply meets the aft spacer. The spacer comes down at an angle, but I finished my ply vertically flat, which made a little lip for the trailing edge to really bam up against. It has since been squished flat and more parallel with th aft spacer, but that small neglected area still wreaked and continues to wreak considerable damage.

What that dagger board really says is that it's seen adventure. No doubt each of those dings has a memory attached to it?