Thread: Start Building Another Dutch GIS

Ralph, I have to say I am a bit skeptical that you really needed to beef the structure up by 6mm...that is a lot. The good news is that you can always plane down the outside of the box to make it lighter. I wonder if Ralph could do a flex test after the glue up. If we measured a certain weight off the regular box construction per the plans we might really know if his will be overbuilt. I'd flex it and go by feel but that is quite subjective. Oh well, too late, it is a done deal...all glued up. It will certainly be a big mast.

Remember, others, that Mik designed this mast for three guys hiking out hard in a blow, so it is built tough as it is...how often will you be in these conditions? Think about that before beefing up scantlings. The yard and boom can be played with a little bit (there has been some discussion here about that) based on wood type and how the sail is rigged/laced.

I'm not discouraging people to do what they feel is right, but I will say that it takes a lot of experience to really know what you are doing, so others should stick to MIK's plan. Consult MIK preferably before doing anything major, and feel free to consult other designers, too. If your local wood species are different then spec'd in the plans, it probably will mean little for construction of the mast. Wouldn't you say, MIK? The spars may need slight beefing up if using a softer/less dense wood...but that mast should be OK as drawn for most woods we'd use in a spar, except maybe for cedars and the lightest pines.

I'll reiterate that it takes a heck of a designer to design a boat as refined as the Goat. No design is perfect; there are trade-offs in every case. But people will not regret following a plan as good as MIK's.

Rant over.

Clint

Hi Ralph,

The mast will be OK at 12mm thick boards whatever the species (almost - would rather they were not balsa, cedar or paulownia, but anything above those will be fine).

I am sure you are aware of the glue discussion below ... so I apologise if I am going over stuff you know well already.

The PVA glue is not gap filling and relies on higher clamping pressures than epoxy, so this needs to be taken into account with good workmanship and planning.

There are some areas that are difficult to clamp too ... so epoxy should be preferred in these places (eg when the bottom goes on.

The places where the gap filling properties are important are the chines and when the bulkheads are glued to the sides of the boat in particular. So I would probably recommend that anything that you can construct on the flat will be OK for the PVA providing the fits and clamping are perfect. I still regard these glues as experimental as the manufacturers will not recommend them for boats that might be in the water or contain water for extended periods. The epoxy outside will help for sure ... but still experimental.

However when doing the assembly of the hull into 3D I would really like to see epoxy being used between the bulkheads and the hull sides and to glue the bottom on. For these joins you would not need to use anything but temporary fasteners.

The two mistakes that people make with alternative glues apart from looser fits and not enough clamping is they don't put enough glue on the pieces and they clean up too soon. Give the joint 15 minutes to soak up any glue into the wood and it will pull some of the excess back into the join.

Best wishes
Michael.

Hi Clint, Hi MIK

I actually fully agree with your comments.

Using 18mm fir is probably an overkill, but that's available in large quantities and greater length since it's used a lot in building houses. I was actually thinking to make a larger box section than 8x8 so you could plane it down to a thinner size, but making it this way now gives me an opportunity to make it rounder and perhaps plane it down to smaller diameters higher up if needed. ( reduced windage and looks perhaps less boxy )
Anyway; making a mast this way costs me less than 60 Euro incl glue and epoxy, so it's worthwile to try and perhaps retry at other specs?
I would be very interested in any kind of flex indicator or measurement?

PVA indeed only for flat surfaces !, and I would probably not use it if I would keep GIS in water all year round. I agree it's "experimental" in marine use, but in my experience ( my father and I have a long history in amateur boating and (re) building ) it lasts very well if sufficiently protected with paint ( in former days ) or epoxy.

And again: I fully agree; GIS exactly as designed by MIK is an excellent design !
I really like the looks, it's well-though simplicity and Joost convinced me with the great capabilities of this design.

Square box section of the mast is ready. Foot at 81x81 mm top at 55x55 mm. Weight now 10.3 kg, balanspoint at 214 from foot......not too bad. Rounding and some extra taper towards the top could bring this down to less than 9kg (?) and bring balanspoint furter down

Clint, It's certainly very stiff now and could easily take my weight ( around 90kg) between top and foot.

MIK, you have designed some taper at the foot, is that to get some conical fit if you step the mast? Or just to cut weight were possible?

Pictures, lots of clamps to get sufficient pressure on PVA glue. As you see there a lot of material to plane round.

Best Regards

Ralph

Mastsides have been planed down a bit towards the top ( from 18mm at the foot towards 15mm at the top ) and box is rounded. I have kept the foot as a square 80x80 box to fit in the deck later.

Weight of the bare mast is now down to 8.9 kg. After sanding and epoxy coating it probably will be up a bit.
Balans point is relatively low at 2.00 from foot.
After planing and rounding it feels more flexibel now, but it is still a very strong mast and easily keeps a 90kg weight if supported at foot and top.

Keep you updated

Ralph

Howdy,

That will improve the strong wind performance considerably by reducing pitching from the extra overall weight and the weight near the top.

I am happy with that - good work!

Michael

Originally Posted by Watermaat

waterproof white construction glue ( Class 4 PVAc-dispersion ). With proper woodsurfaces and sufficient clamps this makes excellent bonding and works very clean ( you can wipe glue away with water, it dries within few hours ) .
I only use more expensive epoxy for sealing and protecting the whole construction, some glassing and some roughly made joints.

Ralph, your mast looks great!

PVAs are very strong. For the past 20 years I have been using yellow x-linked PVAs for cricket bats, handles/splices and also for repairs and lots of other things including antique furniture repairs, because it is reversible with a bit of heat. It really is the perfect glue for that use. I think as long as you seal your mast carefully it will be fine.

For boat building though, I have to say that there are other better choices than the PVA if you don't want to use epoxy. One of the problems with PVA glues is that they "creep", and this becomes exacerbated if the joint is exposed to temps below 10degC (very likely in NED!). Ordinarily this creep is not usually a problem but you may find that your paint finish could develop fine cracking around glue joints in the hull. This is because over time the glue tends to creep out of the joint and push up a small ridge. There is no way to prevent this characteristic. Sure, the glue is plenty strong enough and the joints won't fail, but the creep would eliminate it from use on the hull for my mind. If you are set against using epoxy then I think PU glue will be a better choice than the cross linked PVA you are thinking of using. But just like the PVA, PU is not gap filling so it should only be used on tightly fitted joints.

I hope this helps.

Looking forward to watching progress on your Goat!

Thanks MIK,

Next Saturday I will have a test-sail with Joost and I will bring my scale ( digital and pretty accurate ) to check his mast-weight. I guess the original 12 mm oregon box section will still be lighter.

NB your remarks on using a good hand-plane have been very helpfull ! I have been used to an electric plane and course beltsander for speed. I re-sharpened an old ( but still good ) stanley and indeed it does a great job with much more control !
I still use the electric plane for removing the bulk, but the hand-job is more rewarding.

Would you still recommend to wrap glas around the bottum-part of this mast? I agree that a small band of glas around the top is very helpfull, but have my doubts about the foot?

Best Regards

Ralph

Thanks Woodeneye,

Thanks for your tips !
I am not really "against" epoxy, but working with it in smaller quantities for just a little jobs gives a lot of waist and mess if you compare that with f.e. a 1comp PVA . I did use 1-comp PU a lot, but that still gives a lot of mess to clean afterwards and I was not impressed by the strength of it if you really use it's gapfilling properties ( if the fit is pretty bad, it fills but does not make a strong connection )
2-comp PU is probably good, but in that case I would go for epoxy to be able to combine it with coating.

I try to stick at PVA for smaller jobs ( f.e. making GIS bulkheads, rudder, perhaps even centerboard/rudder blanks ) and some longers parts ( mast, laminated boom and gaff, chines on sides ) when surface is really flat and I can put sufficient pressure.

I did not realize this "creep" at low temperature, allthough there is a "warning" not to use it if it construction is "regular" under 0 degr celsius. But it is still recommended for professional outsite waterproof use ( and used a lot ! ) in construction in our area ?
( It does not freeze that much in the Netherlands )
I will certainly keep this in mind for anything on the outside of the hull or under painted surfaces.

For the rest ( fitting bulkheads, bottum, dekpanels a.s.o) I defenitely use epoxy!

Best Regards
Ralph

Joost and I had a test sail today with his GIS and a loooooong chat about it.

And finally we did check his original 12mm oregon box-mast's weight; 9.25 kg fully varnished incl halyard "ready to step" ; Very good lightweight !
My bare 18-15 mm fir box-mast is now 8.9kg but epoxy, varnish and halyard will ad at least another 1 kg or a bit more. Perhaps I plane wall-thicknes down a bit further, or just leave it as with a nice reserve in strength and wall-thickness.

We had avarage light winds but some nice gusts. GIS sails really easy and nice and has a remarkable smooth steering balance. Speeds up quickly in a gust, but she still gives you plenty of time to react.

I think her sail could use a bit more power, the thin bendable boom works well running, but eliminates neccessairy depth in the bottum part of the sail close winded, even in light weather. Joost has a nice USA Duckworks sail. You could probably order a sail with more profile in the bottum part, but I think that current boom just flexes more and still makes that flat.
I think that a stiffer boom would improve the shape and control over it, regardless if you would lash your sail around it ( just a standard depth and don't bother about tuning ) , or have it loose footed ( more tuning ). I am currently making a rounded "plank on edge" boom 70 x 35 , with it's height tapered towards 40 at both ends. On the side it seems as flexible as the original boom, on the edge it's very much stiffer. As soon as this one has some epoxy coating, Joost will give it a try with his boat ( since mine will not be ready very soon )
I will post some pictures soon

For the rest: Great boat! I don't have any doubt that an experienced sailer could handle her single handed very well, just put a reef in time and she will get you anywere.( within reasanoble expectations ) Joost already has proofed, she is a very good raid boat. With some minor adjustments, she could be a very good single handed raid boat as well.

Pictures of my fir "plank on edge" GIS boom, rounded but not finished yet.

Pictures are taken from front. When the boom is standing on his edge, it is up-site-down. In use top of boom is a straight line, bottum is curved. Max 3.5 x 7.0 cm, short taper towards front end at 3.5 x 5.0 and long taper towards aft at 3.5 x 4.0. Bare weight 3.9 kg, expected to be finished at around 4.5 kg (?)

This boom is very stiff in vertical direction and has similar flex as designed boom horizontal. It might be possible to plane it down a bit later to get a better weight (?)

I need to drill holes at both ends for ropes.....and lots of sanding and epoxy, but than it's ready for Joost to do some "testdriving"

Are you guys doing anything different with the yard. It seems to me that the yard should be stiffer in proportion to the boom being stiffened. With the yard, I find that it doesn't take much downhaul tension to flex the yard a lot, and I think that being able to really tension that downhaul is crucial to windward sailing.

I used Spruce to the original dimensions and am beefing up my yard to account for the less dense nature of our Spruce. However, I may go more because for a lug of the same sail area on one of Oughtred's boats, he goes with a max diameter of 63mm for the boom and 52mm for the yard. That is for a sail with 102SF of area. I understand that the stiffer the spar the less energy it can absorb from things like gusts and hard gybes.

Any comments would be useful...can you guys reiterate the maximum dim's of JOOST's new spars? Thanks.
Clint

Hello Clint,

Two things:
1. I think that much depends on the type of wood.
2. Oughtred specifies big diameter booms as his sail are usually set loose footed rather than laced to the boom.
3. In my experience you always need to put a lot of tension on the downhaul with a balanced lug rig; just more tension when the wind gets stronger.

I have not made a new yard yet as I first wanted to try out the L-type boom. Next to this, MIK informed me that the yard doesn’t necessarily have to be beefed up if the boom is made stiffer. My yard is exactly according to the specs (40 mm max diameter) given by MIK and made of good spar quality oregon pine.

The L-type boom has not worked out for me (I have provided MIK with extensive feedback). I am going to try the new rectangular boom that Watermaat is currently making on my GIS when it is more or less finished to see what it does for my sail (both loose footed and laced to the boom).

Joost

Hi Clint,

I do not know if the yard should be stiffer, for my new to build yard I will be using more or less MIK's recommendations, perhaps a bit larger since I use fir in stead of oregon and it's easier to plane things down later than beef it up
I would not automatically use a stiffer yard with rigid boom, in that case you increase both luff and leach tension a lot and probably loose too much flexibility.

I do agree with Joost that luff tension should be pretty high, luff simply needs to be straight in all conditions.
The depth of your sail ( the drive power ) is depending on bottum leach tension and leach tension aft. I personally think that a pretty rigid boom and pretty flexible yard gives most possibilities to have a rig that both gives power and is sufficient flexible ( and self-flattening ) in gusts. The rigid boom enables sufficient depth since it does not bend and does not flatten the bottum part of the sail ( where you want to keep power) The flexible yard bends and flattens the top part of the sail ( where you want to get rid of power ) Nice thing in GIS is that you can put a reef to lower your centre of power and with a rigid boom you can still have sufficient depth in bottum part of the sail.

I did a lot of Finn sailing, where they have used flexible mast for over 50 yrs ( wood, aluminium and now carbon ) I see a lot of similarity with GIS.
Basically GIS mast is equal to the stiff bottum-part of a Finn mast ( or to be more precize both GIS and Finn luff's should be straight in the bottum part ) and the yard is equal to the flexible top of a Finn mast, both give flexibility and flatten top of the sail. In a Finn they use a plank-on-edge boom and and you play a lot with bottum leach tension to create depth or flatten the bottum of the sail.
In a Finn the right sail-mastcurve and leach tension results in a 10m2 rig that can be used from Bf 1 - Bf 6/7 without a single reef.

I do not know how rigid a yard needs to be to have an optimum for GIS, but I guess MIK did a good job with his designed specs. For real fine tuning the flexibility of the yard should be depending on crew-weigth, sail shape and wind-water conditions. For an Oughtred with different weight and different stability that's different again..............in a Finn you order a 2750 Euro custom carbon mast at your exact body-weight and need two 1250 Euro sails exactly made to match that mast to cover all conditions .........that's much more than my overall GIS budget and I could build a few extra Storer designs with that

When I start sailing with GIS I will probably experiment a little with yard flexibility, but I want my boom to be ( more or less ) rigid at the lowest possible weight.
But this is all due to my "racing background disorder"..............don't bother too much if you just want to enjoy a nice sail with a nice boat and follow MIK's design.

Regards
Ralph