Thread: GIS Yawl Conversion/variation

My Yawl conversion:

When I started building, I didn't plan on doing the yawl version, but was convinced by Mik's comments after he completed the Texas 500 with John Goodman.

I'd already done the hatch in the front buoyancy compartment in a way the precluded putting in a second forward mat step. I was also reluctant to do anything that could compromise the front and rear buoyancy compartments, so I decided to leave the main mast where it was and adjust the underwater COE by making my daggerboard more adjustable fore and aft. I kept the bottom of the slot at original length and position, but make it wider at the top, I extended the top of the slot about 2 1/2 inches both front and back. You can see my ability to adjust daggerboard angle in these two pictures:

This shows my centerboard nearly upright, held in place with a bungee from the rear, this is how I have it when I'm not using the mizzen, and on the left, angled back about 45 degrees, held in place with a bungee from the front. This is how I have it when I'm using the mizzen:

Adjustable daggerboard.jpg

This has worked well, the boat balances well under mainsail alone, balance was also good with the mizzen up and the centerboard angled back, though I didn't try going to weather triple reefed. (Though it did go well enough to weather in conditions that required a second reef plus mizzen on a previous outing)

More when I get a chance, pictures of the mizzen setup on the transom are attached, I'll put some more description of how I mounted the mizzen on top of the rear buoyancy compartment, hopefully soon.

Ian

More on my mizzen setup:

GIS Yawl1.jpg

Mizzen.jpg

My mizzen mast is fiberglass, wound on a tapered mandrel with a sleeve in the middle so it comes apart into two short pieces and weighs just on 2 kg. Boomkin and mizzen boom are also tapered fiberglass tubes, they were wound on oar shaft mandrels.

I did my mizzen with a boom jawed boom rather than a sprit boom as I wanted to be able to reef it and couldn't figure out how to do so easily with a sprit boom. A 3mm sprectra line goes from the clew reef point down to a loop on the boom, forward to the tack end of the boom, through a hole from bottom to top in the boom jaws, up to the tack reef point then back down and though a hole on the other side of the boom jaws where there is a wooden cleat. I have downhaul and vang on the boom made with tape and friction buckles. My halyard attaches to a wooden cleat on the front side of the mizzen mast. Sounds complicated, but with everything on the mast, setup is just putting the mizzen mast and boomkin in place, doing up the partner lashing and pulling the two friction buckles tight and it's ready to go. My halyard is only long enough to let the mizzen down to it's reef point, and has a stopper knot on it's end. Reefing the mizzen is very quick - just release the halyard, bring down the tack and clew by pulling on the reefing line and cleating it off on the side of the boom jaws, then retighten the two friction buckles.

I figure if I want to take the mizzen down, I take the whole mizzen rig down, my mizzen mast is fibreglass and sleeved in two pieces so it can go right up the front if I don't want it.

These pictures show the boom jaws, downhaul and vang and reefing line at the tack end of the boom:
Mizzen downhaul and vang.jpg

Mizzen Boom Jaws.jpg

My mizzen sheet goes through inside the hollow fiberglass boomkin. There are hardwood plugs at both ends of the boomkin where the sheet enters and exits the boomkin. The boomkin is in two pieces with a sleeve just behind where it exits the transom so I don't have to undo the lashing when I take it off, the rear part just slides out and stows in the boat, leaving a short stub sticking out of the transom.
Boomkin-Mizzen Sheet.jpg

This shows my mizzen mast step and partner, and boomkin arrangement from the inside. I'm happy with how this has worked out without compromising the rear buoyancy chamber. I did some engineering on how strong this all is, I'm confident my transom is strong enough to take this. I couldn't see any undue flexing under sailing loads, and it all survived a crash capsize while surfing fast downwind.
Mizzen Step and Boomkin.jpg

You can also see my wooden flush hatch in the top of the rear buoyancy compartment. These have worked well, the middle buoyancy compartment on the in-water side when I last capsized had a third of a cup of water in it when I got home, the others were dry and dusty. I'll experiment with a little more bungee tension and some glue where the rubber sealing strip joins, but I guess I'll still be putting the down sleeping bag in a dry bag if I'm out on the salt water.

By the way, this is my original build thread with more info on the variations I've put into this boat:

https://www.woodworkforums.com/f169/g...ealand-115452/

For completeness, the innovation that didn't work was the drainage tubes from the front of the rear buoyancy compartment through to the transom. The rocker meant they had to enter the the front of the rear buoyancy compartment at too great a height to let much water out in a capsize. I've got them taped up, but they would probably prove useful if I came through surf and ended up with the boat full of water on the beach.



Ian

Very useful Info Ian!

What were the final dimensions of the centre seat buoyancy? Did bulkhead #3 stay in the same position?

Quite apart from the interesting technical details - a great story of a nice sail.

One thing with Mizzens ... one thing I understood from reading was that if you sheet the mizzen in really tight the boat will sit head to wind. This is true but it is a bad idea.

The downside of pointing directly into the wind is that you will get the wind on one side of the mainsail and then the other making the stability hard to predict. Lurches one way then the other

However just a little bit of slack in the mizzen sheet will keep the boat with one side more predominantly toward the wind - much more comfortable and predictable.

Sounds like you had it set up just right.

MIK

My comments in blue, Mik's in black:

Originally Posted by Boatmik

Very useful Info Ian!

What were the final dimensions of the centre seat buoyancy? Did bulkhead #3 stay in the same position?
The centre seat buoyancy is 800 mm long (fore and aft dimension) I moved bulkhead #3 back 150 mm. (Don't worry, I adjusted its size for the new position so the hull shape is identical to your plans!) Not sure I should reveal my technique(s) for doing this here or not - let me know.

Quite apart from the interesting technical details - a great story of a nice sail.

One thing with Mizzens ... one thing I understood from reading was that if you sheet the mizzen in really tight the boat will sit head to wind. This is true but it is a bad idea.

The downside of pointing directly into the wind is that you will get the wind on one side of the mainsail and then the other making the stability hard to predict. Lurches one way then the other

However just a little bit of slack in the mizzen sheet will keep the boat with one side more predominantly toward the wind - much more comfortable and predictable.

Sounds like you had it set up just right.
Yes, I was running downwind when I capsized, so the mizzen sheet was eased but cleated off. I was impressed with how the boat behaved through the recovery. I was going fast, capsized downwind/down wave. I was triple reefed and still overpowered, so it was quite windy. The boat ended up on it's side, side on to wind and waves with the rig on the downwind and wave side, but showed no sign of inverting in this situation. Low enough in the water to not drift faster than I could have swum after it, high enough to not have too much water in once it came up. I got on the dagger board and as it came up it pivoted into the wind and sat in the perfect position with the wind from diagonally forward, mizzen catching the wind, main on the other side to me and flapping. Once I was in the boat, I could sheet in the mizzen, and drop the main right in the boat. I have a bungee tiller minder, when set it stops the tiller going completely sideways. As well as mizzen sheeting, tiller position makes a big difference to how the boat lies to the wind when hove to (and which direction you can sail the boat backwards under mizzen alone).

MIK

I am very impressed with how hard it is to invert the GIS with the sealed buoyant masts and yard. My previous capsize was with a crew, post capsize he was standing on the submerged gunwale and hanging on to the mast to keep himself as much out of the water as possible (we didn't have wetsuits on and water was about 11 celsius). I of course couldn't right the boat till he got off there and into the water, but the boat refused to invert as he stayed there as I went around to get on the daggerboard. A huge improvement in that regard on the Sunbursts I used to sail on Otago Harbor with alu mast and holes for the halyards.

I may try a big block of styrofoam covered in PVC or canvas tied down forward of the daggerboard case, nearly filling that space to further limit the water in the boat in a capsize. I'm also thinking about a tether from me to the boat if I'm out on my own, the main danger in a capsize would be getting separated from the boat. Not sure how long to make it, reading Frank Dye, he seems to believe in having a lifeline quite long to cut chances of getting caught up in the sail/rigging, though thats less of an issue with no stays. I'm thinking nylon so it sinks out of the way, long enough so I can go around the back of the boat, get on the daggerboard, then back in the boat from that side without the line restricting that.

Ian.

From one GIS yawl owner to another, congratulations on a great looking GIS yawl.

In one of your pictures of the daggerboard I see an oar in the background with an attached oar lock that seem to drop down into the gunnels between the spacer blocks.
Can you comment on how they are built and how well this system works?

If experimenting with a tether or lifeline, I would look at surfboard tethers/legropes ... not necessarily on your leg.

They might be able to be bought in a range of lengths. But maybe or maybe not long enough for moving around the boat.

The advantage I can see (unless the tech has changed) is that they have a shorter surgical rubber outer that would keep things compact but it is quite stretchable. But a cord up the middle that limits the length to a longer preset length.

It also keeps the leash thicker, stiffer and less likely to get tangled as a rope one would tend to do

In the old days people used to make their own from surgical rubber tube and VB cord. A custom length would be possible.

I might be wrong but my feeling is that lots of rope hanging around in the cockpit is a recipe for inconvenience at the least.

MIK

Originally Posted by john goodman

From one GIS yawl owner to another, congratulations on a great looking GIS yawl.

In one of your pictures of the daggerboard I see an oar in the background with an attached oar lock that seem to drop down into the gunnels between the spacer blocks.
Can you comment on how they are built and how well this system works?

It works, but the oar lock set-up isn't complete. Yes, they do drop down into the spaces between the gunwales. I'll post more on them when I've got them sorted properly, plan is to 3D print some swivels and use with sleeves and collars off the competition style oars so that the blade angle and feather angle on the return are set as they are for a competition set-up. It'll be interesting to see if it's a good plan or not.

Ian

Originally Posted by Boatmik

If experimenting with a tether or lifeline, I would look at surfboard tethers/legropes ... not necessarily on your leg.

They might be able to be bought in a range of lengths. But maybe or maybe not long enough for moving around the boat.

The advantage I can see (unless the tech has changed) is that they have a shorter surgical rubber outer that would keep things compact but it is quite stretchable. But a cord up the middle that limits the length to a longer preset length.

It also keeps the leash thicker, stiffer and less likely to get tangled as a rope one would tend to do

In the old days people used to make their own from surgical rubber tube and VB cord. A custom length would be possible.

I might be wrong but my feeling is that lots of rope hanging around in the cockpit is a recipe for inconvenience at the least.

MIK

Yes, I'll play with a few ideas. More ropes floating around in the cockpit would be a pain, but it seems to me the biggest danger that it would be hard to recover from out there would be getting separated from the boat either falling out or having it blow away as you go around to get to the daggerboard after capsize.

Ian

It is the old balance.

If you have a boat that will come up dry after capsize it will blow relatively quickly on its side

if you have a boat that won't blow away easily it will scoop up a lot of water as it comes upright.

MIK

Some things I want to try next:

A really small lugsail - perhaps yard and boom only 1.5 m long, area 3 square metres or so, reefable down to 2 square metres. I could then then run with 2 square metre main and 1 square metre mizzen if I need to.

Fiddle with the halyard and downhaul arrangement so that I can let the mainsheet go and let the mainsail stream over the bow if I am getting overpowered running downwind. I tried bringing the boom right around to the bow with the boat rigged in the front garden, it was binding and wouldn't go that far when the downhaul was tight, so I need to experiment with this a bit more, both reefed and unreefed so that becomes an option.

Make up some sandbags I can tie down in the bottom of those middle buoyancy compartments. I'd be curious to see what effect say 60 kg in the bottom of the boat has on handling in windier conditions. I'm about 70 kg, the boat rigged and all wouldn't be much more, so total displacement on the water is a fraction of any other 16 ft boat anyone is sailing.

I'm keen to do some cruising on some of the big lakes south of here; Lakes Te Anau and Manapouri, but they're like spiders with long arms extending in several directions, so conditions can get quite extreme at times, so I really have to get the boat sorted.

Ian





This is one of my favorite images from this area:

Originally Posted by IanHowick

Fiddle with the halyard and downhaul arrangement so that I can let the mainsheet go and let the mainsail stream over the bow if I am getting overpowered running downwind. I tried bringing the boom right around to the bow with the boat rigged in the front garden, it was binding and wouldn't go that far when the downhaul was tight, so I need to experiment with this a bit more, both reefed and unreefed so that becomes an option.

I'm keen to do some cruising on some of the big lakes south of here; Lakes Te Anau and Manapouri, but they're like spiders with long arms extending in several directions, so conditions can get quite extreme at times, so I really have to get the boat sorted.

Ian

This is one of my favorite images from this area:

Howdy Ian,

If you do allow the sail over the bow one thing to know is the right way to retrim the sail when you want to get going again.

I've seen some spectacular capsizes on BETH when lending her to other people before I started to tie in a stopper knot in the mainsheet to prevent the boom going out further than 90 degrees plus a bit.

The trick - when the sail is blowing out in front of the boat is - DON'T touch the mainsheet to start with. Wear the boat around so it is beam on to the wind. Then trim in the mainsail.

The problem is the heeling forces are large and counter intuitive so the boat blows over very easily. But if the boat is on a beam reach or towards a beam reach ... then it become quite predictable in comparison.

This might be necessary also if the mizzen is released in the same way. Though if you want to stow the mizzen from the blowing forward position you can release the snotter and roll the sail up from the leach around the sprit boom. Then a single lashing holds it tight against the mast.

MIK

Originally Posted by IanHowick

It works, but the oar lock set-up isn't complete. Yes, they do drop down into the spaces between the gunwales. I'll post more on them when I've got them sorted properly, plan is to 3D print some swivels and use with sleeves and collars off the competition style oars so that the blade angle and feather angle on the return are set as they are for a competition set-up. It'll be interesting to see if it's a good plan or not.

Ian

You will need fastenings through the inwale through the spacer block and into the gunwale on both sides of the selected inwale space.

I can't find the right photo ... so you have probably thought about this already

MIK

Originally Posted by IanHowick

Make up some sandbags I can tie down in the bottom of those middle buoyancy compartments. I'd be curious to see what effect say 60 kg in the bottom of the boat has on handling in windier conditions. I'm about 70 kg, the boat rigged and all wouldn't be much more, so total displacement on the water is a fraction of any other 16 ft boat anyone is sailing.

While it would be a lot of work to make, I think a heavy metal center board would be more nice than having sand bags. Actually, I got a better idea: a board made out of concrete, filled with a lot of iron and then wrapped with a cloth and epoxy would be quite easy to make.

Originally Posted by engblom

While it would be a lot of work to make, I think a heavy metal center board would be more nice than having sand bags. Actually, I got a better idea: a board made out of concrete, filled with a lot of iron and then wrapped with a cloth and epoxy would be quite easy to make.

I'm not convinced. I think a heavy centerboard (i.e. remaining in place and pivoting up into a slot) could be an option in boats this size, but if you make a daggerboard heavy enough to help with stability it will be really difficult to pick up and drop into place, you'll likely embarrass yourself at the dock on most occasions either dropping it so it puts a hole in the bottom of the boat, falling over as you try to balance in the boat as you lift it up to drop it into place, or capsizing the boat and ending up in the water hanging on to that heavy thing. I get the impression that people who have tried a heavy daggerboard have quickly gone back to their conventional one. It would be good if someone can point to some first hand accounts of trying a heavy daggerboard on a boat of similar size, I'm not sure I'm prepared to go to all the trouble of making a heavy daggerboard without having heard of a positive experience from someone, it must have been tried.

Sandbags at least will be quick and easy to make and try, and throw overboard if I find they're not helpful.

Ian