Thread: GIS spars

Mik -

Thought I'd describe my understanding of your dimensions for the timber/ply hollow boom:

Overall Dimensions: 45mm (wide) by 70mm (deep) x 3658mm (long); tapered; squared end sections (45mm x 45mm)

Sides: 4 or 6mm ply

Top Timber: 12mm x the size to give the boom an overall width of about 45mm.

Bottom Timber: 12mm x the size to give the boom an overall width of about 45mm


The join in the ply can be butt-strapped with the normal width strap - 20 times the ply thickness.

Top and bottom faces of wood and the sides of ply - so made of 4 pieces - no extra cleating.

No taper looking from the top.

Taper:

No taper looking from the top

Forward taper: Taper to square section (45mm x 45mm) from 450mm from end
Aft taper: Graceful taper to square section (45mm x 45mm) from beginning at 2440 from front end to aft end

Corners radiused to match the ply thickness.

Did I get it right? I've got 6mm ply on hand so that is what I will use.

Like I said, I'll get started on this "side" project tomorrow.

Originally Posted by Joost

I don't know the exact figures, but can confirm that the spars have a far larger diameter (something like 55 - 60 mm perhaps). Oughtred usually draws loose footed sails for his boats, so that explains the fatter boom. To compensate for the boom, I imagine that the yard had to be beefed up as well.

I can confirm that these dimensions are about right...the CY is a bigger boat...much heavier, and takes more people aboard, so you need stiffer spars...it is hard to compare these two boats. The Arctic Tern has the same sail area than GIS and the yard maxes out at 57-58mm and the boom nearly 76mm. Not only does the boom have a footless sail, but there is only one sheeting point set up on a 3 to 1 purchase.

With MIK's help, I've come to understand that it is the stability of the boat that dictates how fat the spars are...I've sailed a CY a couple times and can attest to it's weight and stability.

I hope to have a Goat at next years SRR and will enjoy sailing past them with my flexible spars and rowing past them, too, when the wind subsides.

Originally Posted by Compass Project

I hope to have a Goat at next years SRR and will enjoy sailing past them with my flexible spars and rowing past them, too, when the wind subsides.

You'll be pulling hard on those oars Clint, the CY carries an outboard

So, how should I respond to this suggestion?

How about using a modern rig? (pic)

Glenn is a pretty hardcore racer and has sailing Finns a few years now.

Originally Posted by woodeneye

You'll be pulling hard on those oars Clint, the CY carries an outboard

I believe that use of an outboard is forbidden in the SRR...

Originally Posted by Joost

I believe that use of an outboard is forbidden in the SRR...

Sorry for my ignorance, but what is an SRR???? Sail, Row and Rampage perhaps?

Small Reach Regatta organised by Wooden Boat:

WoodenBoat Publications, WoodenBoat Magazine, Professional BoatBuilder Magazine, Small Boats Magazine and Getting Started in Boats.

"There are no hard-and-fast rules imposed on boat types or lengths, but in general this fleet will consist of traditional rowing and sailing boats between 15′ and 20′ LOA capable of putting in to a beach and relaunching without assistance. Depending on wind and weather (which may include fog, rain, or times of no wind), rowing may be an important part of the activities. Boats equipped with auxiliary outboards are asked to refrain from using them unless safety demands otherwise. In general, full-keel and fixed fin-keel boats are excluded. Oars-only boats are OK, but be aware that the courses can be as long as 15 miles. Wooden construction, whether traditional plank-on-frame, cold-molded, or plywood, is highly encouraged, as are owner-built boats, but fiberglass boats are also acceptable if they are of traditional sail-and-oar type. A fleet of motorized chase boats will accompany the fleet."

The SRR is more low key than the European RAIDs, I think, in that we are not racing. BUT, when two boats get together, guess what, we are racing. Mostly, people love the beach lunches and getting together to look at other people's boats and learning some new things.

If things go to plan, I will have my dory there with a lug rig using the flexi spars approach (the dory being my own design, currently being built by someone else) and I hope to have a GIS there, too, and my rowboat, Drake. We'll see how it all pans out!

Originally Posted by BobWes

Mik -

Thought I'd describe my understanding of your dimensions for the timber/ply hollow boom:

Overall Dimensions: 45mm (wide) by 70mm (deep) x 3658mm (long); tapered; squared end sections (45mm x 45mm)

Sides: 4 or 6mm ply

Top Timber: 12mm x the size to give the boom an overall width of about 45mm.

Bottom Timber: 12mm x the size to give the boom an overall width of about 45mm


The join in the ply can be butt-strapped with the normal width strap - 20 times the ply thickness.

Top and bottom faces of wood and the sides of ply - so made of 4 pieces - no extra cleating.

No taper looking from the top.

Taper:

No taper looking from the top

Forward taper: Taper to square section (45mm x 45mm) from 450mm from end
Aft taper: Graceful taper to square section (45mm x 45mm) from beginning at 2440 from front end to aft end

Corners radiused to match the ply thickness.

Did I get it right? I've got 6mm ply on hand so that is what I will use.

Like I said, I'll get started on this "side" project tomorrow.

Sounds very interesting !! It might be a very light and stiff boom, following the KISS priciple I like so much ( or is it GIS principle ) Would be nice to get some pictures.
Would WRC do the job for the top and bottum part?

I do also see some benefits in the fact that a flat padding ( in stead of round leather ) would be sufficient to eliminate damage to the mast.

MIK, any idea if a similar construction would work to get a very light yard? Something like 40x45 square in the center tapered towards 40x25 on both ends?

That same question - would WRC work? - went through my mind, too.

I have three choices for the timbers:

WRC which would need to be scarfed and planed to the 12mm thickness
DF which would only need to be milled (sawed and planed) to width and thickness
Spruce (inexpensive finger joined material): which would need to be cut to the width and planed to thickness

Since I don't have another GIS close enough nearby to sail side-by-side comparisons, I will also make a boom as per the plans. Not ideal, but the best I can do at the moment.

I'll definitely take photos to document the construction

I am not sure if I can help on this thread, but I thought if I shared some observations and finding from racing with a lug rig it might add ideas.

I have sailed for over 35 years and when I first raced a lug rig Scow I was way off the back of the fleet. It takes about two years for experienced sailors to learn the foibles of racing the lug rig. Pottering no problems, racing is a different matter. This first boat had 50mm alloy tubes for mast, boom and yard and a fairly flat sail.

Then by good fortune a nice Lymington Scow came along. An older one but a beauty, the fastest ever made! She was balanced and the sail set was exceptional. Here she is with my favourite photo, posted before I am afraid.



I don't think it is possible to set a lug sail any better - i have never managed it since!

The boom and yard were both different to standard - they were old tubes John had throwing about when I bought her. They were windsurfing masts. The yard tapered from 40mm to 20mm at the tip and the boom tapered about 50mm at the front to about 30mm at the clew.

Downhaul is 6:1 and the exact amount of downhaul had to be applied and then the kicker pulled on and the sail would "spring" into life. More downhaul or less and the boat would feel dead. The rig was great upwind but a bit one dimensional in that it was slow off the wind and reaching. I just dare not adjust it on the water. Good upwind was the main thing racing.

My next Scow was a bare hull fitted out as I wished. I kept the sail and bought a set of carbon tubes. 50mm mast and boom and 40 to 20mm taper yard. Getting this sail to set on these spars has been a really big struggle.

These thin wall carbon tubes bend in a completely different way to wood or alloy. As you push sideways on the tube there is no stiffness at all until about 40mm of deflection and then they stiffen up. But they will continue to bend as greater loads are applied.

I now have a really bendy rig - nothing is certain any more. Too much tension can be applied and it kills the sail unless the winds are heavy. I am never certain of settings but it can be made to work really well. I have just today collected my trophies for this season - three series wins and best Scow sailor of the year! So - four glasses to toast with. It feels like a struggle though with sail setting never certain.

Light winds are weakest - but that may be me and the hull i am now using.
Medium is fine. Biggest difference is reaching and running. I can let off tension without worry and I find the rig much quicker now.

Strong winds she is very good, which seems odd when even the sailmaker insists the sail is cut for a stiff non bending boom and mast. In strong winds I have a lot of yard, mast and boom bend. The boom has a PVC luff groove glued to the tube so the bend flattens the sail foot considerably.

I feel the flattening of the sail is of greater benefit than the coming together of the tack and clew created by bending the boom. This could easily be rectified with a clew outhaul anyway. No Scows use an adjustable clew so I feel my bending boom, both my Scows have had bendy booms, is helping more than hindering - but who knows?

All the Scows on the south coast use stays, unheard of any where else. It seems natural to me. What it means in strong winds is that as I apply more and more downhaul, then the mast bends away from me in the middle. With my sail set on the port side of the mast, it bends sufficiently for the sail to set without touching the mast on port tack - a major benefit!

Hope some of this is of use in your Goat spar discussion. My summary is that if you want to sail upwind with any efficiency for racing, you need at least 6:1 downhaul and decent blocks that work under these loads. You need a sail cut for the yard. Boom settings seem much less important. Then spend years learning so you can constantly disagree with your sailing friends about how to set the lug rig - we do all the time. It's the reason we enjoy it so much.

Brian

I am not sure if I can help on this thread, but I thought if I shared some observations and finding from racing with a lug rig it might add ideas.

Brian - I am quite certain you can help! And your post proves it.

I've never sailed a lug rig and I am planning to race my Goat so any and all observations, findings, comments, rigging suggestions and the like are very welcome. Some of it doesn't make sense and probably won't until I'm sailing the lug, but I appreciate you sharing your knowledge.

Thanks. Keep the info coming.

Originally Posted by Watermaat

Sounds very interesting !! It might be a very light and stiff boom, following the KISS priciple I like so much ( or is it GIS principle ) Would be nice to get some pictures.
Would WRC do the job for the top and bottum part?

I do also see some benefits in the fact that a flat padding ( in stead of round leather ) would be sufficient to eliminate damage to the mast.

MIK, any idea if a similar construction would work to get a very light yard? Something like 40x45 square in the center tapered towards 40x25 on both ends?

Howdy,

It does make the best sense for the boom as the boom can be quite big and not get in the way of performance - note the jumbo booms on quite small racing boats.

Basically the bigger you make it the better it will be (within reason) with a hollow box boom.

The yard is quite different. It kinda forces in the direction of a small cross section to get the bend and windage properties wanted.

MIK

Originally Posted by BobWes

That same question - would WRC work? - went through my mind, too.

I have three choices for the timbers:

WRC which would need to be scarfed and planed to the 12mm thickness
DF which would only need to be milled (sawed and planed) to width and thickness
Spruce (inexpensive finger joined material): which would need to be cut to the width and planed to thickness

Since I don't have another GIS close enough nearby to sail side-by-side comparisons, I will also make a boom as per the plans. Not ideal, but the best I can do at the moment.

I'll definitely take photos to document the construction

I would tend to go with the two traditional spar making timbers - spruce or fir because their grain is straight and they are not too heavy.

If the cedar was really nice straight grain it would probably be OK too. Problem with cedar is that the grain sometimes wanders badly from side to side so the timber can split as if a big scarf joint has been made and not glued properly.

Thinking ... though the ply would prevent that from happening ... hmmm - might be nice to try with cedar.

MIK