Building Shesha, a Hunter Valley GIS, Australia

[Boatmik]

excellent.

Maybe I can help you destructively test it in a few weeks!

MIK

[woodeneye]

excellent.

Maybe I can help you destructively test it in a few weeks!

MIK

Naaah, this one's fulla muscle, no chance of destructing this baby! But we could have fun trying anyway

[woodeneye]

I was too late posting the missing data so could not edit my previous post about the new boom data. No problem, here it is again...

The weight seems more than it feels, but it's right. After all it has larger dimensions and uses 12mm vs 10mm timber. The good part is that it's twice as stiff as the old one. (Flex for the old boom was 17mm)

Summary:

Material - Superlight Meranti 3600x66x12mm (Bunnings) and Paulownia infills
Finished Length - 3600mm
Finished width - 55mm
Finished depth - 65mm
Front taper - 20mm to zero over 800mm
Rear taper - 20mm to zero over 1000mm
Weight - 3.3kg
Flex - 8mm (using 10kg weight)

[woodeneye]

I have been having trouble with the rudder blade being pulled backwards on high speed reaches and runs, and this makes for difficult control and some hairy moments due to the pressure on the tiller.

I tried a different type of bungie cord with a flat profile but it too wasn't successful. I'm now trying this solution. It's a nylon strap with velcro strips attached. The strap itself is also attached to the rudder case with velcro to prevent it riding up which would let the blade lift back.

The plan is that the strap will prevent the blade lifting backwards, but hopefully the velcro will still let go if the blade hits the bottom.

Attachment 157212

[Joost]

Hello Bruce,

I only seem to have the issue of the rudder blade being pulled backwards if I have not been careful making sure that the bungie cord is right at the bottom of the rudder case just above the bottom timber reinforcement.

- I am using quite strong 6 mm bungie cord that only stretches under a lot of pressure.
- One thing I am considering is a small stainless steel eye on the front of the rudder case to prevent it from riding up on the rudder case.

Best regards,

Joost

[IanHowick]

Summary:

Material - Superlight Meranti 3600x66x12mm (Bunnings) and Paulownia infills
Finished Length - 3600mm
Finished width - 55mm
Finished depth - 65mm
Front taper - 20mm to zero over 800mm
Rear taper - 20mm to zero over 1000mm
Weight - 3.3kg
Flex - 8mm (using 10kg weight)

Great to have this data!

Can you include the exact span you used when you supported the boom at either end and hung 10kg on it?

ie the the boom is 3600mm long but it is likely the support points were perhaps 150mm in from each end when the weight was on it, so actual span is quite possibly 3300mm or less.

Sorry to be pedantic, but there is a power of three on the span on stiffness calcs so about 25% difference between 8mm defection at a span of 3600mm and 8mm deflection at a span of 3300.

Thanks,

Ian

[woodeneye]

Great to have this data!

Can you include the exact span you used when you supported the boom at either end and hung 10kg on it?

ie the the boom is 3600mm long but it is likely the support points were perhaps 150mm in from each end when the weight was on it, so actual span is quite possibly 3300mm or less.

Sorry to be pedantic, but there is a power of three on the span on stiffness calcs so about 25% difference between 8mm defection at a span of 3600mm and 8mm deflection at a span of 3300.

Thanks,

Ian

Hi Ian, yes I'm aware of the need to measure with the very ends only supported.

Span was 3560mm, ie. it was supported by 20mm at each end.

One mod that I will doing is increasing the outhaul ratio to 4:1. I found that the 2:1 wasn't enough for the big foot of the Goat sail.

Harken 421outhaul.jpg

[woodeneye]

Hello Bruce,

I only seem to have the issue of the rudder blade being pulled backwards if I have not been careful making sure that the bungie cord is right at the bottom of the rudder case just above the bottom timber reinforcement.

- I am using quite strong 6 mm bungie cord that only stretches under a lot of pressure.
- One thing I am considering is a small stainless steel eye on the front of the rudder case to prevent it from riding up on the rudder case.

Best regards,

Joost

Hi Joost

I have been using bigger cord than yours, ie. 2x10mm strong bungie cord at the bottom of the case, and it still can't hold the rudder blade even when tightly tied. I used 6mm bolts for my rudder, so by comparison with the bungie diameter in the pic you can see that 6mm will be much too small. The bungie is tight on the case even before I put the rudder in. The cord is moved up high now only because of the strap.

I'm hoping the strap with 60mm of velcro will provide enough static holding power, but will break the hold if it takes a decent hit. If I pull on it quite hard from the bottom of the blade the strap will snap off, so it should work OK in practice. If it doesn't I might be replacing my transom!

[Joost]

Hello Bruce,

I might actually have been using 8 mm, thinking about it. Not sure why your rudder case is giving problems. I have the elastic band 2 turns around the case. It is quite tight but what also may help keep the rudder in place is the fact that the rudder case width the same as the rudder thus giving quite a bit of friction (especially with the vanish on both the inside of the case and the foil itself).

Anyway, good luck fixing the matter.

Best regards,

Joost

[Boatmik]

Hi Ian, yes I'm aware of the need to measure with the very ends only supported.

Span was 3560mm, ie. it was supported by 20mm at each end.

One mod that I will doing is increasing the outhaul ratio to 4:1. I found that the 2:1 wasn't enough for the big foot of the Goat sail.

Harken 421outhaul.jpg

Cute how the fitting companies draw their most expensive fittings for their illustrations!
HEHE

It is quite a bit of overkill for a line that is going to be adjusted a dozen times in a race! For those not familiar with our methods.
MIK

[woodeneye]

Cute how the fitting companies draw their most expensive fittings for their illustrations!
HEHE

It is quite a bit of overkill for a line that is going to be adjusted a dozen times in a race! For those not familiar with our methods.
MIK

I like their drawings only for the ideas! My 4:1 outhaul will have cost under $20 as I've used those cute little Riley RM302 blocks for about $3.50 each and cleated off with a $6 clamcleat with integrated fairlead.

If you want a laugh, have a look at what the Laser fraternity call their "turbo pack" vang which sells for over $600. The sad thing is that unless they have the "approved" stuff, they cannot legally enter in a club race.

I spent this morning setting up the new boom. I'm really happy with it as it is nice and stiff and hardly bends at all under sheet and vang loads. The new outhaul has more power so will be easier to adjust when the breeze is up. I've also installed two webbing straps on the boom to help prevent the dreaded sheet loops from hooking on the skipper and causing the inevitable swim. All I have to do now is epoxy in the screws to ensure a watertight seal.

[IanHowick]

Thanks for the data on your boom, I'm curious to see if my more complicated construction comes in any lighter or stiffer, but think you have got it just right in terms of simple and effective construction for max stiffness at a reasonable weight.

Regarding the rudder blade pulling back - I agree with Joost, the bottom bungee should be as low as possible, and held so that it can't ride up when some pressure comes on. Otherwise, a little bit of movement and the bungee moves up, it becomes less effective, so keeps moving up and it just gets worse and worse.


What about a 9mm hole through the rudder box just below the bottom gudgeon? (Positioned so it goes through the spacer). Thread the bungee through the hole and around the back of the rudder blade. It will have at least double the holding power relative to where that bottom bungee is in this picture and won't be able to ride up when pressure comes on the rudder.

Reefing when underway:

How about this sort of arrangement at the tack:
Reefing - Tack end

A hole vertically through the boom just in front of where the tack attaches. Tie a 3mm spectra line to the tack reefing eyelet and run it down throught that hole then back to a cleat further back on the bottom of the boom. When reefing, drop the sail, heave that line down tight and cleat it off, then sort out the reefed clew attachment as normal.

A single line running down from the reefing eyelet to the tack, rather than the usual line attached to the boom, running up to the eyelet and then back down to save windage and because you don't need the 2 to 1 as the sail is in the boat so there is no pressure on the line while you are pulling it tight.

Aim is to be able to sort out the reef and get underway without having to go forward of the middle seat.

Ian

[Boatmik]

For general sailing the system seems to work quite well. I have sometimes thought of adding a small plastic fairlead or saddle to keep the bungee in the right place - so it doesn't slide up.

MIK

[woodeneye]

Thanks for the data on your boom, I'm curious to see if my more complicated construction comes in any lighter or stiffer, but think you have got it just right in terms of simple and effective construction for max stiffness at a reasonable weight.

Regarding the rudder blade pulling back - I agree with Joost, the bottom bungee should be as low as possible, and held so that it can't ride up when some pressure comes on. Otherwise, a little bit of movement and the bungee moves up, it becomes less effective, so keeps moving up and it just gets worse and worse.

I had a fantastic sail today on Grahamstown dam to test the new boom. I'm really happy with it, and the new 4:1 outhaul works a treat. The boom is stiff enough!

When you push the rudder blade down, the bungie goes down to the bottom where it should have maximum holding power. However, the blade is forced up with the pressure when you are going fast and it rides back up. The pic of the bungie was just for the photo, and not where it is when sailing.

The velcro strap was not a success today as it was really hot and the velcro glue just melted and it slipped off. I just knew it had to be sewn, but I don't have a sewing machine, so I was kinda hoping that the velcro product was good enough to stick!

I'm a bit worried that such a big hole through the rudder case spacer to accommodate the bungie might weaken it, so perhaps as MIK suggests, a small saddle instead? A third bungie just might do the trick too. What about a shallow groove on the trailing edge that engages the blade when it's pushed down. Not too deep though, as that would cause problems lifting the blade. Maybe just a shallow notch that stops the bungie riding up?

Today I was the only boat out on Grahamstown dam. Unbelievable. This is the best sailing water in the area! It was just awesome with a lovely 10-15 knot southerly breeze. Later at about 3pm, there was a spell where the anemometer recorded 25 knots, but it was short-lived and I was already heading in, close hauled to get home and the dagger board only half down. The really good bit was that it was a southerly, and the clubhouse is on the southern shore. This means that where I was sailing, the water was dead FLAT. What do you reckon a skiff does in a nice breeze and on flat water? Lets just say that it was the kind of conditions you dream about and makes you WHOOOP because she just gets up and planes so easily on flat water and a little breeze. The other great thing is that the boat and skipper stays completely dry, although a little splash or two was great because it was so humid.

Funnily enough, there was no humming harmonic today as I had described in a post to the GIS thread. Weird. (Maybe it was weed around the foils? I mean the sort that floats around in dams!)

I have an easy little mod to carry out from today's sail, and that is to install a split foam noodle to the upper cut-out of BH3. When hiking, I find it's comfy to hook my front foot under there. This evening my feet are feeling the results of that ply edge, even though I was wearing wetsuit booties .

[woodeneye]

Reefing when underway:

How about this sort of arrangement at the tack:
Reefing - Tack end

A hole vertically through the boom just in front of where the tack attaches. Tie a 3mm spectra line to the tack reefing eyelet and run it down throught that hole then back to a cleat further back on the bottom of the boom. When reefing, drop the sail, heave that line down tight and cleat it off, then sort out the reefed clew attachment as normal.

A single line running down from the reefing eyelet to the tack, rather than the usual line attached to the boom, running up to the eyelet and then back down to save windage and because you don't need the 2 to 1 as the sail is in the boat so there is no pressure on the line while you are pulling it tight.

Aim is to be able to sort out the reef and get underway without having to go forward of the middle seat.

Ian

Hi Ian, A good thought that! I think that will work OK, but it is also a complication that you would need to live with for the rest of the time that you don't need to reef. With reefing, there is a lot of loose material that needs to be rolled up and tucked away so that it doesn't catch the wind and fly away or collect water from all the spray/rain. A nice tight reef onto the boom is the aim. Do you have any thoughts about what you will be doing there?

My sail has the first reef point too high up, so I'm always going to be reluctant to set a reef. I'll get this sorted out next winter when the sailmakers are quiet. Also, my luff is starting to stretch, so I'm going to need some dyneema cord or tape sewn into the luff to fix this. It is amazing how much tension is applied to the luff. I guess I have upped the ante with my vang as well as the downhaul.

Oh I nearly forgot to let you know that I've moved the downhaul attachment further forward. It is now in front of the tack. The reason for this is so that I can pull the boom back even further for beating, which I need to do in order to induce some weather helm. You will just need to experiment where it needs to be for your boat as likely you won't have the lee helm issue that I get.

The other thing I've changed is to sheet from the very end of the boom. As I have my traveler right at the back attached to the knees, when beating and the boom is pulled pulled right back, the tackle is now more in line. As well, the position of the forward block is over the CB case. This sheeting arrangement works very well as it gives me plenty of room and there is less chance of getting the tiller extension hooked up when tacking or gybing. Also, now that I have the vang, I have started to practice playing the sheet that comes off the boom, rather than the one that comes off the block on the seat. It takes some getting used to, but it does allow for much faster trimming and pumping to keep the boat on the plane. As I have a ratchet block on my traveler as well, I can still hold it without getting tired quickly. However, with the front block so far forward on the boom, it's not very crew friendly, so will need to move it back a bit if I take on a crew member.