Thread: Start Building Another Dutch GIS

Howdy,

When I built Beth I was still thinking about the way we always built boats in the 70s - very few used epoxy for sealing.

All I can say is that before I sanded down BETH and epoxied as much of her as reasonable she was about four times the maintenance of a full epoxy sealed boat.

I never resolved the problems with the plywood bottom which was an inferior ply which sucked water in from every edge - I think it had a fair few voids too.

Really crappy stuff. If it had been epoxied it would have been a non issue.

MIK

I have finished the inwales. Things have been planed flat and rounded with a router.
There is still a lot of sanding to be done, but the overall looks are there.

Attachment 123021 .

I have decided not to make additional knees in both transom corners. The notched construction makes it very strong as it is and the aft deck will eliminate any possible flex.

Attachment 123022

In the bow I have made a knee from ply, connecting both inwales.

Attachment 123023

I personally like te looks of these slightly wider and flatter inwales and gunwales.........and what a great looking design from the bow !!

Attachment 123024 .

(just tidies up the formatting by putting each attachment on a separate line - MIK)

I have also finished the bottum runners. I have made them from one 18x25 mm fir batten covered with 15mm hardwood. I have tapered the fir batten towards the bow Attachment 123025 and a little less towards the stern Attachment 123026 to give them a nicer look.
I fixed these runners with screws from the inside and removed them after the epoxy has cured. This to enable planing the hardwood off in case of damage or repair. I also made a long filet on both sides to make it as smooth as possible.
After gluing I have planed them flat and used a router to round them. Attachment 123027 .
I have made them a bit longer towards the transom. This will give maximum protection in case the transom hits ground ashore. Attachment 123028
I have also made a small hardwood bow runner to have extra protection hitting a concrete trailer ramp. Attachment 123029 .

I still need to sand everything flat, but for me this looks quite okay

Howdy,

I recommend the knees strongly. They spread the loads of anything that might hit the gunwale over about 10 times the area in that corner as well as providing geometric support for the hull to resist twist.

The reason the Goat structure works is that the gunwale/inwale structure is light but massively stiff and the light hull is effectively "hung" off the gunwale.

I dont' think you can expect a 25mm join to handle the potential loads, no matter how well "locked in" it is by other structure.

I don't think you will go sailing on the first day and it will break, but I think sometime in the history of the boat it is very likely to be broken.

Best wishes
Michael

Originally Posted by Watermaat

I have decided not to make additional knees in both transom corners. The notched construction makes it very strong as it is and the aft deck will eliminate any possible flex.

Mmmm. I like your work and appreciate your skills, but I must agree with Mick that the transom knees as per plan should not be eliminated, especially as you will also be using an outboard motor. The triangle is a fundamental aspect of engineering design and if the designer puts them there, you can be sure they are not superfluous.

I understand your requirements for certain mods, and this is entirely up to you based on your perceived usage of the boat. However, I think that a few of us watching your build with interest were hoping to see some meaningful performance trialling between the NL Goats, but those hopes appear to be slipping away somewhat due to the added weight disadvantage that your boat will inevitably carry.

If you were building your GIS as a knockabout for young kids that you know would not give it the best of treatment, then fine, no problems and I think I would also go down that path. But you have exceptional woodworking skills and the great thing with timber boats is that you can quite easily take care of any knocks and damage along the way

Hello Ralph,

I would also put the knees in to take any stress loads especially when using the outboard. The knees don't weigh much anyway.

Hi Woodeneye,

My Goat will probably be the lighter one, as my GIS is almost 100% standard (just a couple of minor and very light weight reinforcements under the thwart and the aft deck, the dagger board case gusset has been doubled up, and the inside of the dagger board case has been glassed).

On Ralph's GIS, the weight added by the glass on the bottom, heavier bottom runners and other modifications like the boxed in midseat is probably still less then 10 kg. We should weigh both boats when Ralph is finished with the build to have exact figures.

On a side note: it has been confirmed that the mast weights will be quite the same. Ralph's boom and yard are heavier but also a lot stiffer. I have ordered some fine grained oregon pine to make a second set of stiffer ones (50-55 mm diameter) this winter.

Best wishes,

Joost

Originally Posted by Joost

On a side note: it has been confirmed that the mast weights will be quite the same. Ralph's boom and yard are heavier but also a lot stiffer. I have ordered some fine grained oregon pine to make a second set of stiffer ones (50-55 mm diameter) this winter.

Best wishes,

Joost

Hi Joost,
What I'll do this weekend is work out some simple measurements to take for the spars so that we can compile some information for putting these up on the Storer forums. If we can eventually arrive at some parameters that we can say, "OK this much flex works but that much flex is a bit too much or not enough", then we will have some valuable data to work with and provide to our sailmakers as well.

Originally Posted by woodeneye

Hi Joost,
What I'll do this weekend is work out some simple measurements to take for the spars so that we can compile some information for putting these up on the Storer forums. If we can eventually arrive at some parameters that we can say, "OK this much flex works but that much flex is a bit too much or not enough", then we will have some valuable data to work with and provide to our sailmakers as well.

What could work is a simple set-up were the spars are supported horizontally on both ends ( on sawhorses or any other support to hold them above ground level ) , put a certain weight in the center ( hanging on a piece of rope ) and measure the distance to the ground. It would be nice to standardize the weight ( 20kg seems effective? )
I have used a digital scale like this Attachment 123066 , but just a simple fixed weight could do the job very well.
For my yard that is 50mm bend with 20kg , I have used that to order my sail. My sail-supplier checked this with Richard Harvey's GIS and found 40 mm bend with 11kg ( all approx. ) and he decided to use less curve in his sail.
NB for fine-tuning you can allways plane down a yard, but it's complicated to make them stiffer to match an existing sail.

I think it is very worthwile to have the bending caracteristics of the yard and boom measured and standardized in a way. It's makes it much more simple to play with different wood and diameters.

Originally Posted by Boatmik

Howdy,

I recommend the knees strongly. They spread the loads of anything that might hit the gunwale over about 10 times the area in that corner as well as providing geometric support for the hull to resist twist.

The reason the Goat structure works is that the gunwale/inwale structure is light but massively stiff and the light hull is effectively "hung" off the gunwale.

I dont' think you can expect a 25mm join to handle the potential loads, no matter how well "locked in" it is by other structure.

I don't think you will go sailing on the first day and it will break, but I think sometime in the history of the boat it is very likely to be broken.

Best wishes
Michael

Oke MIK , I will give that another thought..........allthough my gunwale/inwale structure is quite a bit wider as designed ( 83 mm finished wide and 26 finished height ) and feels stiff as a rock now. But I could add a nice knee to be shure nothing goes wrong when there is a heavy side impact.

Hi Woodeneye, regarding the overall weight I am with Joost's guess. It will not be more than 10kg. That's a small penalty handling ashore, but it will hardly make any difference sailing ( except in strictly one-design competition ) . The runners are not heavier as designed ( 30x25 hardwood plan, 32x24 finished with softwood underlayment ) and the only real differences are the boxed middle seat ( approx 2kg, checked by scale ) and extra glass.
I like building with wood.......but I don't like repairs . I will be very happy if I am able to ground my GIS on a concrete ramp ( after a nice day of single-handed sailing ) , take my trailer and lift her out of the water without being worried about too much wear and damage
Besides that, any real damage on bare wood, means intensive drying before you can go on encapsuling with epoxy......

Hi all,

I just measured the bending of my spars, suspended at the ends (they are still some cm longer and can so easily placed on sawhorses with the given ends) and weighted in the middle for the sailmaker.
My son has some lead pigs with 6,25 kg each, so I used up to for (6,25 kg, 12,5 kg, 18,75 kg, 25 kg).
The yard bends for each pig 4 cm, so with 25 kg it bends 16 cm.
The boom is somewhat stiffer and bends 3,5 cm per pig, 13,5 cm with 25 kg.

Joost, Ralph, are these numbers in the same range with your spars?
MIK, are these numbers according to your intended bend?


Best from Bonn - Jörn

Originally Posted by joern

Hi all,

I just measured the bending of my spars, suspended at the ends (they are still some cm longer and can so easily placed on sawhorses with the given ends) and weighted in the middle for the sailmaker.
My son has some lead pigs with 6,25 kg each, so I used up to for (6,25 kg, 12,5 kg, 18,75 kg, 25 kg).
The yard bends for each pig 4 cm, so with 25 kg it bends 16 cm.
The boom is somewhat stiffer and bends 3,5 cm per pig, 13,5 cm with 25 kg.

Joost, Ralph, are these numbers in the same range with your spars?
MIK, are these numbers according to your intended bend?


Best from Bonn - Jörn

Hi Joern,

My yard is much stiffer with around 5 cm bend with 20 kg central , but that's still oversized and I need to start sailing with my new sail before I can check final flexibility I need.
My sailmaker has measured 4.3 mm with 11 kg on the hallyard block on a standard GIS ( that seems less flexible as yours? )
Perhaps Joost could do a measurement, since his original yard is made very close to designed specs ?
My boom is a different story, since I have chosen for a loose-footed sail and therefore it needs to be as stiff as possible.

In general I do not dare to give any recommendations, since I did not sail yet with my GIS.
I have made my yard less flexible and have my sail made for a stiffer yard and to be used loose-footed on a (stiff ) boom. I think that could work very well ( that's why I made it this way ) BUT time will tell if I am right or wrong

Hi Jörn,

I don't have any figure. With the Goat, I worked from what I already had with BETH and made the changes because of the greater stability and greater sail area.

I have no ideal figure for the bend.

With the home made sails I have been designing the edge shaping has been based on our trialling of four different sails and two mast designs for the sprit rigged PDR and the lug rigged PDR sail (which worked perfectly off the drawing board).

But these came much later than the GIS spars and sail.

A good rule of thumb is if the spar of the same dimension - particularly thickness and taper - is 20% heavier it will be about 20% stiffer.

The main point is that the standard spars work fine for normal purposes.

But you chaps are moving off onto a whole new level and I am really interested to see what you will find. It will be completely ground breaking (unless Brian Pearson knows of something) in terms of finding optimised stiffnesses for a lug rig.

Very exciting!

Michael

Originally Posted by Boatmik

Hi Jörn,

I don't have any figure. With the Goat, I worked from what I already had with BETH and made the changes because of the greater stability and greater sail area.

I have no ideal figure for the bend.

With the home made sails I have been designing the edge shaping has been based on our trialling of four different sails and two mast designs for the sprit rigged PDR and the lug rigged PDR sail (which worked perfectly off the drawing board).

But these came much later than the GIS spars and sail.

A good rule of thumb is if the spar of the same dimension - particularly thickness and taper - is 20% heavier it will be about 20% stiffer.

The main point is that the standard spars work fine for normal purposes.

But you chaps are moving off onto a whole new level and I am really interested to see what you will find. It will be completely ground breaking (unless Brian Pearson knows of something) in terms of finding optimised stiffnesses for a lug rig.

Very exciting!

Michael

Indeed; exciting to see at what level we could improve GIS's performance.

Few weeks ago Joost and I had a nice discussion with a 12ft dingy owner about their racing-trim. It's a standing lug, but there is much similarity with GIS rig ( about same size, shorter / heavier boat ) . Attachment 123142 Attachment 123143
These yards and booms have a larger diameter. In racing they use 2 yards with different flex. They also vary the point where the hallyard is attached to the yard. The guy told us that he planed down an old yard to make it a heavy weather yard in case there was too much wind and he did not have an extra crew to compensate.
It's nice to see how these old racers have developped so far over years and years. I am impressed by their beautifull lug rigs and sails and various solutions how to adapt these to different weather conditions and crew weight.

If you limit yourself to an experimental GIS yard and boom, it's a fairly inexpensive way to fine-tune and optimize GIS performance. Given a good design sail ( and most sailmakers will be able to supply that ) the flex of the yard and boom is THE mayor factor of performance in a well build GIS. In that perspective it's very nice that MIK already put so much effort in foil-shape, which is another mayor factor......but there is not much to gain there. Mast-weight seems to settle in below 10kg range, which is good and light enough. Little weight differences in the hull are not very important ( same is stated by those 12-ft dinghy racers ) and if you take care of a smooth hull finish there is not much to gain there too.

If you are a first-time builder or do not want to build different yards or booms; stay close to designed specs! I have seen Joost GIS and overall performance under various conditions is just great, as he has shown in Caledonian.
But if you are as mad as some of us.........

Okay I have made those knees, since everybody bothers me with that..........
These copper nails are only there to keep them in place untill the epoxy has cured.
The holes in the inwale corners are there to have a very simple ( and light ) way to attach ropes. Attachment 123153, Attachment 123154 .

I have also put the decks on, to have an overall impression of my GIS. Those knees do not look too bad on it.......... Attachment 123155, Attachment 123156