Thread: Another UK GIS (Gizzle in Hants)

Its happened to all of us at some time.

Either another piece or beef it up with some laminations.

Hi all,
The mast has been epoxy-glass sheathed, as has the tip of the dagger board after shaping to the correct profile. I’m going to try and do the main sheathing of both foils at the same time so the rudder blank has been laminated ready for shaping.

All the detail here… http://georgeisted.blogspot.com/

While I could make another Yard with the DF I have but I’m now toying with a Aluminium yard and boom. Fortunately none of this indecisiveness will hold up the hull build as the mast is all but done. I may have a chat with a sail-maker before any final decisions are made.

Most sailmakers will have their own biases - particularly as most are not very familiar with wooden spars on small boats these days.

if they are old enough to remember the transition from wood to alloy there is quite a bias about the bad behaviour of wood as moisture moved around and the weight.

Some of that is resolved now.

Younger chaps might not know much about timber spars at all.

This is one of the reasons for developing the WIKI and also the information sharing on this forum. It is well ahead of most sailmakers and more methodical with mores sources than almost anywhere I can think of.

Best wishes
Michael

Originally Posted by Gizzle

Hi Ian,
The spar blank is 40mm square

Supported at each end there is a deflection of approx 4-5mm under its own weight, with a 10KG bucket a further 21mm of deflection can be measured so a total of around 25-26mm.

Note that my measurements on the "bendy yard" did not include any deflection from its own weight, just from adding the 10KG.

To my untrained eye it seems that this DF may be a little more flexible than we would like.

I'm not planning to do anything further on the rig this weekend while I consider the options. The dagger board is sitting on the bench ready to be planned to shape and some of the bulkheads are marked out and ready to cut from the ply sheets so I have plenty to be getting on with.

I had a play on the spreadsheet with the deflection data and spar sizes you provided.

The numbers for you spar rounded to 38mm dia make reasonable sense. The 100mm deflection makes sense as you said as a combination of being over enthusiastic with the plane and taking it down to about 38mm dia. From this data I get a figure of just over 8GPa for the Elastic Modulus ('stiffness') of your timber, which is at the low end for Douglas Fir. (I would expect plantation pine to have an E of 8 to 9GPa, most Doug Fir should be around 10GPa, and high end old growth 'Spar Grade' Oregon/Doug Fir should be around 11Gpa) The figure of 8 GPa matches your subjective sense that the timber is more flexible than you would like.

Your deflection figure of only 21-25mm for the unrounded blank 40x40mm don't make sense in this context. It implies that that piece of timber is more than twice as stiff as the other piece, and outside the range that any softwood could have. Possible reasons - the square blank is actually bigger than 40x40mm or your deflection measurement was inaccurate, or the supports were closer than 3.5 m apart when you did the deflection measurement.

Either way, data from the Wiki would indicate that the yard shouldn't bend more than 50mm with 10 kg in the middle. If you're sticking to timber, stiffer timber and or making sure the finished diameter stays up around 42 - 43 mm should result in the yard being stiff enough. If you're going with a loose footed sail, then Woodeneye's hollow box section boom is probably the way to go to get a stiff boom without too muck weight.

If my calculations/your measurements on your yard are correct, and your spar timber is relatively low stiffness, then it's probably a good thing you've glassed the bottom 1200 mm of your mast, that should take care of any doubts about it being OK.

Hope this helps, if you want to get a more accurate measurement of the stiffness of your spar timber, I can post how to do so.

Ian

Originally Posted by Boatmik

This is one of the reasons for developing the WIKI and also the information sharing on this forum. It is well ahead of most sailmakers and more methodical with mores sources than almost anywhere I can think of.

Hi Michael,
The Wiki and Forum are both very useful sources of info so many thanks for your efforts in setting them up and answering our (my) inane questions.
G

Originally Posted by IanHowick

I had a play on the spreadsheet with the deflection data and spar sizes you provided.

The numbers for you spar rounded to 38mm dia make reasonable sense. The 100mm deflection makes sense as you said as a combination of being over enthusiastic with the plane and taking it down to about 38mm dia. From this data I get a figure of just over 8GPa for the Elastic Modulus ('stiffness') of your timber, which is at the low end for Douglas Fir. (I would expect plantation pine to have an E of 8 to 9GPa, most Doug Fir should be around 10GPa, and high end old growth 'Spar Grade' Oregon/Doug Fir should be around 11Gpa) The figure of 8 GPa matches your subjective sense that the timber is more flexible than you would like.

Your deflection figure of only 21-25mm for the unrounded blank 40x40mm don't make sense in this context. It implies that that piece of timber is more than twice as stiff as the other piece, and outside the range that any softwood could have. Possible reasons - the square blank is actually bigger than 40x40mm or your deflection measurement was inaccurate, or the supports were closer than 3.5 m apart when you did the deflection measurement.

Either way, data from the Wiki would indicate that the yard shouldn't bend more than 50mm with 10 kg in the middle. If you're sticking to timber, stiffer timber and or making sure the finished diameter stays up around 42 - 43 mm should result in the yard being stiff enough. If you're going with a loose footed sail, then Woodeneye's hollow box section boom is probably the way to go to get a stiff boom without too muck weight.

If my calculations/your measurements on your yard are correct, and your spar timber is relatively low stiffness, then it's probably a good thing you've glassed the bottom 1200 mm of your mast, that should take care of any doubts about it being OK.

Hope this helps, if you want to get a more accurate measurement of the stiffness of your spar timber, I can post how to do so.

Ian

Hi Ian, thanks very much for taking the time to do this, much appreciated.

Regarding the "bendy yard" it was not all rounded to 38mm, the plans show that the spar should be tapered at both ends so it was 38mm at it's widest part, tapering down to significantly less than this at the aft end (maybe 25mm with my over zealous planeing).

Re the spar blank it is deffo 40x40 and the deflection is as put in the prev mail over a 3500mm span.

The mast actually seems really stuff, I sat on it between two trestles and it didn't seem to move much at all.

Cheers

I spoke with forum member Andrew Denman (bloggs1968) today at his stall at the Hobart Wooden Boat Festival about a solution for stiffening our yards for much less that a carbon spar would cost.

The product is a sleeve made of unidirectional carbon fibre combined with Spandex to form an expandable sleeve which is slipped over the spar and then epoxied into place. Apparently, the stiffness of the yard that they trialled the product on was increased by 50%. They have various sized and modulus sleeves available which are sold by the foot(!), so you need to get out your calculator.

It could be a great solution for us, and it's not all that expensive compared with the cost of a carbon spar.

* Soller Composites * Carbon UNI & Biaxial Tape Page

Bruce, thanks for that post and link.

Interesting that they had good results. I was thinking about your post saying you had no increase in stiffness when you tried it. Something that is odd about carbon tubes like mine is just how flexible they are as you apply load. Much less stiff than wood or alloy at first. Then as you reach a certain loaded up point they stiffen up and stop bending. Perhaps your earlier trials were bending in that starting mode and only just loading up by the time you were taking measurements.

Originally Posted by keyhavenpotter

Bruce, thanks for that post and link.

Interesting that they had good results. I was thinking about your post saying you had no increase in stiffness when you tried it. Something that is odd about carbon tubes like mine is just how flexible they are as you apply load. Much less stiff than wood or alloy at first. Then as you reach a certain loaded up point they stiffen up and stop bending. Perhaps your earlier trials were bending in that starting mode and only just loading up by the time you were taking measurements.

Yes that's the case. I think by the time the carbon on my spar got loaded up, it would have broken.

With this sleeve product, I think the go would be the high modulus stuff.

Originally Posted by woodeneye

I spoke with forum member Andrew Denman (bloggs1968) today at his stall at the Hobart Wooden Boat Festival about a solution for stiffening our yards for much less that a carbon spar would cost.

The product is a sleeve made of unidirectional carbon fibre combined with Spandex to form an expandable sleeve which is slipped over the spar and then epoxied into place. Apparently, the stiffness of the yard that they trialled the product on was increased by 50%. They have various sized and modulus sleeves available which are sold by the foot(!), so you need to get out your calculator.

It could be a great solution for us, and it's not all that expensive compared with the cost of a carbon spar.

I'm not that convinced by the sense of this route. My feeling regarding carbon is along the lines of 'go hard or go home' I.E. Go to a full carbon spar made of mandrel wound pre-preg carbon, or stick to wood. A professionally made mandrel wound pre-preg spar can give you the same performance/stiffness at a 60 - 65% weight saving. Big cost increase, big weight reduction, plus saving of your time fiddling.

If you look at various options for DIY reinforcing a timber spar with carbon, the best weight saving you can expect compared to the equivalent stiffness wooden spar is of the order of 20 - 25%, at both extra cost and effort fiddling with the carbon on the wood. ( That possible 20+% weight reduction for the same stiffness/stiffness increase for the same weight is probably on the optimistic side of things when I think about woodeneye's experience adding carbon and keyhavenpotters comments on how carbon bends differently to wood.)

Another issue with DIY carbon on wood is reliability. Too much resin in the laminate and it's heavier, get one spot not adequately saturated and it could break there if it's in a stressed area. Also, you can add stiffnesses of components of a structure together reasonably sensibly, but you can't always add ultimate strengths of different components of a structure in the same way - one component may fail first, then the other part will follow - I think a lot of carbon reinforced aluminium rudders fell off in one Fastness race as a result.

If you stick to wood, there are some good (efficient) options:

50% increase in stiffness in a wooden spar can be achieved by just increasing the diameter by 10% - going from 40mm round to 44mm round, which would increase weight by 20%. I'm guessing adding a carbon sleeve would add about the same weight as the simple diameter increase.

If you're prepared to go to hollow birdsmouth at say 50mm outside dia and 25
% wall, then you can increase stiffness by nearly 70% and decrease weight by 32%.

Not arguing for spending lots of money on professionally made carbon spars - I like efficient wood solutions and efficient carbon solutions, but half and half doesn't make sense to me.

Ian

Hi Ian, thanks for your thoughts. I do tend to agree with you. It's just that the sleeves present a cheap option for stiffening an already made spar without the cost/time expense of making a new one or going to all carbon.

Last year in South Africa I saw a very big birdsmouth wooden mast successfully stiffened with carbon rod. The mast was routed out, the carbon inlaid and then capped with a wooden veneer so you couldn't tell. Apparently this is a common mod over there for "around the world" boats that are having problems with their wooden masts.

Of course, you cannot beat the preferred option of designing and building a timber spar to the correct stiffness in the first place.

Yes, absolutely, adding glass (or carbon) can be a good option if you're stuck with something you already have that's not stiff enough, but if you're starting from scratch, it's better to go one way or the other and design it strong enough from the start.

Glass added to wood makes sense from the point of view of adding surface hardness and or cross grain strength/resistance to splitting, so can be worth adding to say the ends and halyard/vang etc attachment points of a yard or boom, and through the base/partner area on an unstayed mast.

If you do the calcs on putting glass all the way up a wooden mast or other spar to 'make it stronger' it's actually lighter to design it stronger in all wood from the beginning.

Ian

Originally Posted by woodeneye

Last year in South Africa I saw a very big birdsmouth wooden mast successfully stiffened with carbon rod. The mast was routed out, the carbon inlaid and then capped with a wooden veneer so you couldn't tell. Apparently this is a common mod over there for "around the world" boats that are having problems with their wooden masts.

I do wonder if some of these 'stiffening exercises' actually help much - has someone done a before and after test?

(Later edit - then again, perhaps your South African friends have real engineers on the job and can show theoretical calculations of the stiffness and strength gains backed up with stiffness measurements before and after their surgery on these spars - it would be interesting to see.)

Test doesn't have to be destructive, just deflection for weight in the way you did before and after adding carbon to your wooden yard. Hugely useful to have this actual data rather than speculation, both when it doesn't work (carbon tow on your yard) and how much it does work ("50% increase in stiffness from one of these carbon sleeves around a ?mm wooden spar" as Denman Marine was able to state. Their value is about what I would expect, but good to see they tested it.)


Ian

I imagine it was several rods - one each face of birdsmouth?

Otherwise you will just get the increase in stiffness of the rod itself - and a 19mm rod is not going to compare with even a fraction of the stiffness of a 200mm mast.

Like Ian says, there is also the risk of materials with different elongations.

Mast bends a bit, the stiff carbon is up to its maximum load and the wood is still relaxed because it has not been bent enough yet.

As the carbon is fully loaded, it breaks, transferring the load (And the energy of the shock loading) to the wood which then breaks too.

In rough terms anyway.

Best wishes
MIK

Nope, I have not fallen off the side of the earth, just been busy with other projects (like preparing my boat for a race to the Azores) so the mighty goatster has taken a back seat.

That said I have managed to finish shaping the rudder blade and got a coat of glass and epoxy on the daggerboard. brings up the colour of the wood nicely. I think it may end up with a varnish finish rather than paint.

more here... Tales of a Weekend Wood-Butcher

TTFN