Thread: Another UK GIS (Gizzle in Hants)

Originally Posted by Gizzle

Question for the team – is there any value in adding a fillet of thickened epoxy on the inside of the mast or is this just adding additional weight and strength that is not required? I would only be able to do it on one side anyway so I’m thinking not to bother.

Fillets are not in the plans, so you can leave out that weight-adding exercise!

Good chaps! Well done!

MIK

Thanks chaps, no fillets added.

I fitted the fourth side of the mast last night. I'm hoping that once the kids are in bed I will have time to plane down the wide staves tonight + put the taper in the bottom of the mast.

You are going to give yourself a pat on the back when you finish the hull and the spars will be sitting there waiting!

Hi all,
A bit more progress on the build, full details on the blog (http://georgeisted.blogspot.com/2011/01/another-weekend-has-come-and-gone.html).

To summarise I have marked out the first of the hull panels using Michael’s “faring batten around a bunch of nails” method that worked well. I have also thicknessed and then cut out the daggerboard ready to plane down to the correct profile. I have also rounded (if that is the correct term) the yard that was tapered but still square in section.

The yard now seems VERY flexible, especially as the aft end. I wish to measure this bend against the data collected in the lug rig Wiki, can someone confirm the best way to do this and how much weight needs to be applied. Is it as simple as holding the yard at each end and applying weight at the middle then measure deflection?

Best wishes

Good progress! The yard gets supported at each end (as close to the end as you can) and then a 10kg (22lb) weight is suspended from the middle. I'm still not sure how stiff the yard should be. If your sail is cut to the match the flex characteristics of your yard then I'm sure the boat will sail well. All of the talk about the stiffer yards is to eek out maximum performance. I wonder how much all of the tweaking helps over a good stock rig and if it's worth the effort. I am getting ready to order a sail and have just about convinced myself that the stock setup with it's simplicity and a well cut sail is the way to go.

Steward at Dabbler sails has his own yard measuring technique and when I talked to him about yard flex he indicated that it was less important than having a sail made to match the flex of the yard. This is his yard flex measuring procedure. Note that it is slightly different from what is being used in the GoatWiki. Sailmakers - Dabbler Sails - Sail Lofts - Sails for small boats - Sail Makers

Originally Posted by Gizzle

The yard now seems VERY flexible, especially as the aft end.

I would be interested in how it feels compared to my yards. If I support the yard at both ends and flex it by hand pressure. The yards go down about 1" or an inch and a half. Sort of bend then stop.

Does it feel like that or softer. Sorry don't have a Scow yard to hand to properly test it. 10kg sounds a lot to me to stress a yard with.

I also feel too soft a yard is going to be too unstable too soon, even if the sail/yard are cut to match.

Brian

Hi Brian

It's hard to say from that description Brian. Your hand pressure could be exerting 10 or 20kg, but from the pics of your boat sailing, you have a stiff yard.

I agree about the flexible yard becoming unstable. I found that up to about 8 knots (not much) the flexible yard was OK. After that the the yard just keeps flexing when it needs to become firmer to support the leach. I think when the sailmakers talk about flex, they are only interested in the curve they need to match from throat to peak. Once that curve is maxed out by the yard bend and the yard wants to bend more than that, further pressure turns the sail into little more than a rag with no shape. Instead of a nice curve ), the leach instead acquires a > shape.

In this video, the Pooduck skiff has a stiff yard and sailing in a fresh breeze. You can see how the yard is working by falling away to depower the sail in the gusts. However, the sail still holds its shape.
[ame=http://www.youtube.com/watch?v=KnEBACCkI-g]YouTube - wooden skiff[/ame]

Here is the link to to WIKI on MIK's site http://www.storerboatplans.com/wp/de...r-google-docs/

Thanks for the quick responses chaps.

I have just been out to the garage to get some measurements, it's about -2C so I didn't stay out too long.

With both end of the Doug Fir yard supported and a 10KG bucket of water hanging in the middle I'm getting 103mm of flex, that seems to be a lot more than it should be.

The GIS Wiki gives examples of approx 50mm or so but it doesn't say what weight was used so I'm assuming it was 10KG.

The weight of the yard (before epoxy coating and varnishing) is 2KG so the finished spar would prob be circa 2.1 - 2.2KG.

The only thing I can think of is that I have mis-measured and removed too much material while shaping to size, either that of I have been supplied with some particularly flexible DF.

For interest I also took the weight of the mast, it is not epoxy coated or varnished yet and came in at 9KG which seems about normal for the hollow square mast.

As a comparison I could measure the flex of the spar blank (before tapering) as I have an identical one for the boom that has not been touched yet. Bit cold to go out and do it now though.

More than likely that it is very flexible Fir, George.

The only way to mess up the shape with so many reference points is to plane past them.

I would probably leave the boom tapered but square with 10mm rounded corners.

Best wishes, MIK.

My yard is made from cypress. It weighs 2.5kg and deflects 50mm with 10kg hung from the middle. I have not sent this data to the Wiki because I'm not sure if I'm going to use this yard. If I want to go to a significantly stiffer one then alu or carbon are the only options since it's already a tank and going bigger in diameter would make the wooden one way too heavy. The cypress cost $15 so it's pretty price competitive with the $600 carbon sticks.

If you need to stiffen a yard, I would use unidirectional glass on the top of the yard. No need to make another or start again.

Unidirectional carbon tape is available at little cost for 3m or so. Would look neat and sexy just running along the top of the yard. It's what I planned to do if my carbon/glass yard was too soft. It turned out very similar to the alloy yard that the sail was cut for.

Only £3.68 plus vat a metre. Will be narrower one available. http://www.cfsnet.co.uk/acatalog/CFS..._Tape_378.html

Soller in the US do loads of nice things. http://www.solarcomposites.com/compo...ni-fabric.html

Bending a yard 100mm seems a bit extreme to me.

Brian

Thanks for all the responses, much appreciated. I’m not happy with the amount of flex so Brian’s suggestion of carbon tape may be the way to go.

Brian – I’m thinking that I could run one long carbon tape along the length of the yard, trimmed to match the taper. If that does not reduce the flex enough I can lay up a second layer wrapping around from the other side. Thoughts?

Regarding the boom, I plan to go for a loose footed sail to allow more control over the draft at the bottom of the sail. Therefore I’m thinking that tapering the boom is not required and I will just round the corners?

Hi, if after taping it's still not stiff enough, the perhaps all the way round, but it's the top of the spar that's in tension, so the uni-directional carbon can do it's job, and I would double tape the top. Underneath is in compression so no need there, but I guess top and bottom would be more lie an I beam?

My son has recently made spars for his build and he was surprised at how much more flexible the spars were after taking from square to round. MIK's suggestion of just softening the edges makes lots of sense, as usual!

Hope I am going to get a sail in the Goat.

Brian