Take a look at this little gem ... (homebuild F16)

Every few weeks or so I do a round of all the new (catamaran) sailing related things on the internet. It is an activity that had to do as the F16 class chairman (to keep tab on things) but sort of continued doing after finishing that role.

And this time I was very pleasantly surprised to find this new item on our own F16 website !

Link to Nick's photo gallery on <...="_blank">www.formula16.org</a>

It is about Nicks new boat and he seems to have worked out a very interesting way of building a foam cored modern hullshape. I find this concept extremely interesting, especially for a possible application in building a F12 hull.

So please Nick (or Ncik) tell us more, what are you experiences so far ? Does it work out as intended. Is it a viable new way of allowing a homebuilder to make his own competitive F16 hulls. We all are aware that the sourcing of marine grad ply is getting harder and harder. So maybe this is a good alternative ?

Wouter

Yes Farrier has used this system and moved it along a little in his homebuild plans by going vertical rather than horizontal, the foam just goes around the corners better. A Dutch guy has even gone one step further and used infusion resin which I think looks very clever, have a look at http://www.fram.nl/. <img src="http://www.catsailor.com/forums/images/graemlins/smile.gif" alt="" />

It's coming along well, the decks were glued on last weekend and the top skin is going on the decks this weekend. Then a quick fair and paint and put it all back together.

I'm pretty happy with how it's going, a few notes on things I'd do differently in terms of construction though...

- Thinner foam, more frames.
- I had planned to use 6 or 8mm Corecell but none was available at the time of ordering. Ended up buying 10mm Airex. It was difficult to heat and bend into shape. Maybe that's because it was so thick and the heat didn't transfer through the foam well or maybe it was my technique (although it got quicker with practice). It has also ended up being heavier than I wanted, original weight estimate with thinner cores was 5kg underweight for each hull, that has been eaten away with the thicker core. The minimum number of frames I have in this hull is satisfatory for the thicker core, but more would be needed with a thinner core, probably twice as many.

- The reason I built it in a female framed mould was because I wanted to install as much of the internal structure before pulling it out of the mould. I have had previous experience with a hull that was difficult to maintain the shape of. When it came off a male mould without any internal structure it was very wobbly. The MDF framed mould was very cheap to get CNC cut.

- Leaving the bow open enabled a reasonably easy method to skin the inside right to the bow and join it with glue and an exterior tape later. I don't like adding lots of useless foam in the form of a sacrificial bow here, just a personal preference. The method worked really well, it wasn't hard to join the bow and maintain a fair hull shape.

- Foam fibreglass construction automatically complies with the 50L flotation per hull. Each of my hulls has 60L of foam in it. (PS. I don't understand the point of this rule. Is it for safety? This seems pointless with a redundant second hull to keep crew afloat in the case of a big leak, plus only stupid ppl don't wear life-jackets. Or is it to restrict builders/designers to closed hulls, ie. no **** boats? Can someone please explain...)


There's not much more I can think was different to any other boat build. There were a couple of structural items that I did maybe a little differently to standard boat building practice. I don't think those photos are up yet, except for the tapered plywood beam mounts.

Infusion is great if you do it properly. This requires experience and a female mould of some description. I didn't want to build a female mould and would think that doing so would be beyond most home-builders, in terms of both cost and skill. Don't forget that the whole point of home-building is to reduce the cost. Building a female mould generally costs more than a simple frame mould. Although infusion does look good and can produce lighter hulls. I've heard stories from a large production stink-boat builder reducing the weight of some small parts to a fifth of the original by converting from choppy gun open mould to infused production.

Excluding tools, I've spent about $2000-$2500 on materials including some carbon double bias I haven't used. This is to just build the hulls. Compared to buying a pair of foam glass/kevlar mosquito hulls at about $7000-$8000 (from memory), I think it is very good value. Plus I've learnt a bucket-load about boat building while I've done it.

I'd better get back to work.

We must remember that there are multiple ways of building a F16 hull. Not all are using the foam cored laminate method. I myself have a ply hull. Here the ply skin will only provide some 1.5 kg of bouyancy per hull. As such the pure ply hull will barely float itself when submerged. In the past fully glassed hulls have been made and these will indeed sink when filled with water.

The ideas behind many of such rules in the F16 framework is to garantee that the boat remains sailable in case of accidents, so that the crew can sail themselfs to safety unaided. You can't sail a catamaran back with one completely sunken hull, the rig will then by laying on the watersurface. Not always does a crew have a recue boat around. Most of the time the owners will sail recreationally with only very limited help nearby. We wanted the F16's to be safe boats to own and operate. Fast and high performance but still safe and dependable. I agree the damaged baot will sail badly but at least you can limp back into port without outside assistance.

In you case if you can proof that your foam core is closed cell and of sufficient volume then you can satisfy the F16 bouyancy requirement that way. I don't see any reason why you couldn't. You have satisfied the spirit of the rule.

Personally it seems you did it in a smart way because you have used the bouyancy requirement in a constructive way so the weight added by this foam is now utilized twice, i.e. it is not dead weight you carrying around for as long as the hulls are undamaged. In your case you have made the hull skin stiffer as well. I think that an excellent example of how clever engineering can optimize a boat design under the Formula 16 rules. A line of thought I always wanted to engrane in the F16 rules personally. Giving enough freedom in the rules to allow for smart double application of required components. In my own hulls the foam floatation aren't simply floatation blocks without a secondary functions but are primairily the (stiffening) bulkheads and the floatation devices in a secondary sense.

Wouter

Further to the flotation query -

At the first UK 'Nationals' I was unfortunate enough to hit a submerged object hard enough to literally rip the port dagger and case out of the bottom of my Stealth. It is a tribute to JohnPs' building/design and the F16 rules on flotation that I was able to sail the (submerged) boat back to the beach - from about a mile out - in lumpy conditions and 12-17 knot winds.

It's just commonsense to have a minimum buoyancy requirement for a boat design.

Is subdivision of a hull with watertight bulkheads satisfactory? It was another alternative I was looking into before realising the foam core was enough.

The main bulkhead under the forward beam was going to be watertight with a bung at the bottom to enable drainage after sailing. This would make two compartments in each hull with about 150-200L each.

Watertight compartments are a common feature in dinghies and are compulsory on larger commercial vessels.

Nick,

I'm very interest in how this way of building a hull can be translated in relatively easy homebuilding of F12 hulls. For these hulls we don't need much. Just large rounded edges on the keel, the rest may well remain flat panels bended in one plane only (multichine).

I'm not even sure we need vacuum bagging for the F12 hull. The hull is very small and it only need it to be 17 kg or less to get at the overall weight of 60 kg ready to sail. In my current design the bow is not loaded up at all and there are no daggerboards or skegs that would require local reinforcements. Pretty much what I'm looking for is a Arafure cadet hull but with large rounded corners on the panel intersection lines at the keel.

The unstayed rig is supported by compression rods that go back to a point on the inner gunwhale somewhere between the mainbeam and rearbeam. So that, together with the beam landings and the sterns would be the only points that need to take some loading. The compression rods will be loaded up with some 600 kg (same as the bridle points on the F16)

How do you feel your building method would suit being used for F12 hulls in this respect.

Wouter

Is Styrofoam closed cell? It can't be used on commercial boats that require positive flotation foam in Australia, there's only one approved foam, Microlen. It's similar to the foam in life-jackets.

If you don't mind taking a heat gun to the foam, you can make any shape with enough time. It took me about a week of evenings to do the bottoms of each hull. The sides were done in about 30 mins each hull.

One alternative for a simple hull build, I would consider making the hulls with chines using thicker foam with one skin already on the inside then once all the structure is in, torture board (sand) some round into the chines before glassing the outside, if you want a round hull. I like how the paper tiger is made though, leaving the chines in. It looks alright and goes well for a small cat.

If you want a really easy build, consider a similar method to stitch and glue for plywood, but with just the foam, or just one skin on the foam, then laminate once the desired shape is achieved.

Or for a well rounded bottom, mould up just the bottom of the hull to the point where the flat sides start. Once this is made (with a single skin flange to attach the sides to), install some well thought out frames (pre-fabricated frames with flanges would be awesome), glue the pre-laminated flat sides on, then glue on the deck. This may be a good alternative for any cat build actually, anything that has relatively flat sides. You've got me thinking now, damnit, I was just about to get some sleep!

Nick,

Did you have to heat both sides of the foam to get it to set well to the curved shape ?

I'm estimating you used 120 kg/m^3 density foam, is that correct ?

How well does the foam bend under load ? Or is it very stiff unless it is properly heated ?

Wouter

Why not cut the foam in to "strips" and glue them together, like strip planking?

"Why not cut the foam in to "strips" and glue them together, like strip planking?"

Besides the extra time and material involved...Added weight of the resin and filler...it doesn't take long for the weight to add up...it happens faster than you would think.

Regards,
Bob

I tried to heat both sides on the first couple of pieces, but by the end, I could get by with only one side needing heat. It was 10mm thick foam so it required quite a bit of heat, you'll see the slight burn marks in some of the photos.

It was a gradual process, heat and bend, heat and bend, heat and bend, until it fit in the mould without too much force. Once it's a close fit, screw it into place and hot glue onto the mould. Just before glassing, all the screws get removed.

I think it was 80-90kg/m^3 foam. Any lighter and it dints too easily, higher weights aren't necessary on these size boats.

The Airex I used was quite stiff. There is no way of putting large compound curves (bending in multiple directions) into it without heat. I had planned to use thinner foam because it would be easier to form. The relatively flat sides went on very easily. The foam was a little brittle if you tried to bend it too quickly (heated or not), and I cracked it 2 or 3 times.

It wasn't a problem to work with the foam, infact I'm more confident working with foam and glass/carbon than I would be working with plywood. If you make a mistake or create/find a defect, it can easily be fixed.

Strip planking the foam is a possible way to build in foam/glass composite. I've helped build a moth that way, but only the sides, the bottom was heat formed sheets.

We found that strip planking such a small boat with 6mm foam was a nightmare! When glassing, the seams between the planks would crack under the pressure of a brushed or squeegee. A lot more frames and stiffeners were needed in the mould. The fairness of the final glassed hull wasn't good, you could see the edge of each plank poking out. It required a bit of careful filling and sanding.

AMC Moth Crew

Hi, I've been thinking of doing this and presto!
The kelsal method is usually just one side of the hull. Any reason for not doing vertical joins? How uniform did the aerocell bend when heated? Infusion can be done within female moulds it's just a way of getting the resin uniformly over the cloth and being able to lay up cloth in a dry state. It also reduces the wet lay-up time and vacuum bagging to one step. It should create a much stronger bond between the glass and resin and the foam.

I LOVE photos any more? <img src="http://www.catsailor.com/forums/images/graemlins/smile.gif" alt="" />
Keep us informed <img src="http://www.catsailor.com/forums/images/graemlins/cool.gif" alt="" />

The foam didn't bend uniformly with heat the way I did it. Had to do bits at a time, working fore and aft along the sheet.

Could only heat about a foot at a time with a standard heat gun, then only bend that foot of material. Then move along the sheet and heat and bend the next foot. Sometimes you'd have to go back and take out some unfairness.

It was a time consuming process but worth doing properly to obtain a better finish at the end.

What is the kelsal method? What do you mean by vertical joins.

Kelsall boats website http://www.kssboat.com.
Instead of joining hull to deck, its joining the left half to the right half. I did have a URL to some photos and will post as soon as I can remember

I still don't understand the Kelsall method, does it just involve cutting small wedges out of the bottom of the flat panel transversely and then rolling the side sheets around the bottom frames? The website was very vague and very difficult to read. Was he also claiming he invented infusion layup technology!? This sounds suss.

I think most of the commercial small cats are built with the port and stbd halves joined down the centre.

Ncik, the "Kelsall method" is not entirely unlike how the ply Blades are built only modified for composites.

Basic process is:

1. Pre-laminate Developed flat panels.
2. Stand the two (port and stbd) on a table with the deck shear line defined with blocks.
3. Join the panel on centreline
4. Force the cl down into the desired rocker.
5. Clamp into position.
6. add internal structure
7. add decks.

Despite what Bill seams to think it doesn't allow you to forgo a hull deck joint.

In reply to some other questions and comments up thread...

When strip planking with foam apply a layer of uni to one or both sides (depending on allowable stiffness) of the foam before cutting it into strips. This allows you to make full length strips and the added stiffness removes a lot of the issue with fairness and seams etc.

Your heated foam system is the way I would have gone too, if you set up a vac bag over the foam and increase the level of suction as you work you'll find it much easier to work the foam into the right shape. Obviously having a second person with a heat gun helps too.

More photos please.

I don't think I could apply a vacuum without a female mould. My mould is just mdf frames with some stringers.

I have some basic resistance vs speed values for my hull if anyone is interested. Things to note though:

1. One hull only.
2. The hull is upright. (No heel)
3. There is no sinkage or trim. (It is fixed in space at the design waterline and the waves rise and fall around it.)
- Hydrostatic nor hydrodynamic effects are accounted for to support the hull
4. There is no leeway angle.
5. Speed is in knots.
6. Resistance is in Newtons. (divide by 9.81 to give kilograms)
7. The results are not validated. They're just for fun.
8. It was done in Michlet so all its standard restrictions apply

Speed Resistance
1.0, 1.57
2.0, 5.89
3.0, 12.86
4.0, 25.77
5.0, 42.48
6.0, 83.01
7.0, 114.35
8.0, 138.48
9.0, 161.14
10.0, 184.42
11.0, 208.78
12.0, 234.25
13.0, 260.70
14.0, 288.10
15.0, 316.38
16.0, 345.56
17.0, 375.63
18.0, 406.69
19.0, 438.72
20.0, 471.73
21.0, 505.78
22.0, 540.96
23.0, 577.16
24.0, 614.63
25.0, 653.11

I used FreeShip to do all the hardwork of creating the Michlet "in.mlt" file. Was done in about 1.5-2hours including reading the manuals to figure out how they both work. Also got a couple of wave plots saved and opened in FreeShip, but was only playing with these and hence only did them at lower speeds.

you can.. by using the foam and epoxy/micro mix as the vac barrier... Extend the foam below the gunwale line.. apply glass to the gunwale line and put the bag over.. double sided tape in the extra zone... well hope you get the idea...

I'd be dubious about the support offered to the foam by my mould with a vaccum applied to it. I reckon the foam would deflect.

There would have to be some more photos by now nick <img src="http://www.catsailor.com/forums/images/graemlins/smile.gif" alt="" />
Hows the project going?

Nah, sorry, no photos since I started fairing. I'll get some soon though.

The decks and hull sides are faired, hull bottoms were started yesterday. Fairing is one problem with the method of construction I've used. It is very time consuming.

Also started laying up the new centreboards. NACA 66-010 section, about 1.7m long (about 1.2m below hull), 240mm chord (so aspect ratio of about 5), rectangular planform (easier to make mould). They are this long so that we can pull board out to find a nice balance for the conditions.

When carrying out this exercise are you using Salt or Fresh water. I predominately race on the sea so when I go inland I'm sure that I can notice a difference with the boat due to less buoyancy. Or is it just the fact that when I capsize the water tastes different?

You are building a F16 right ?

Then those boards have FAR to much surface area. You have more surface are then any of the F18's.

All other F16's are between 0.144 and 0.188 sq. mtr surface area per board and you are at 1.2 * 0.240 = 0.288.

As a comparison the F18's have an area per board of 0.200 - 0.255 with the larger area belonging to the older designs.

I expect your boat to feel like it will trip over the boards easily, as the FX-one had as a tendency. These boards were the same size as the Tiger F18 (initially). You have even more then that.

As such I expect you to pull up the boards by 1/3 most of the time ending up at :

Area : 0.192
Depth : 0.8
aspect ratio : 3.33

I have made this prediction before with the nacra I-17's and since a few years their class rules allow the boards to be shortened by 30 % after they too found that singlehanded sailing with too much board area makes the boat feel like it is tripping.

Wouter

sea water

Oh yeah, i know they're too big, but I'd prefer to be oversize than undersize. It won't be hard to cut them down later once I know what I want.

They're gonna be huge, nearly as tall as me!

This is not being "just oversized" this is being rediculiously too large.

You have to cut off so much board that it with result in a big hit in aspect ratio. Why do it ?

You'll end up with a pretty mediocre design after the testing and cutting.

If anything start with a 200 mm width and a 1000 mm board instead. That 0.200 sq.mtr is oversized without going overboard and if this has to be cut shorter then you still have asn aspect ratio of at least 4 or heigher (200 mm by 800 mm)

Wouter

The plates on my boat project approm 1m below the bottom of the Hull, but I do not have them with me so cannot measure them. I could ask John to do so if you want a comparisonm for the longer plates

Hi all,

don't know about you guy's, but I hate having the boards up above deck line. They get in the way of moving around the boat and hurt like anything when you slide up the hull and hit them <img src="http://www.catsailor.com/forums/images/graemlins/blush.gif" alt="" />.

I don't (so far) find it a problem as when they are up, it's so windy I'm either on the wire or at the back of the boat. So far, it looks to me like they are better when the wind is below about F4, and then I just (when I remember <img src="http://www.catsailor.com/forums/images/graemlins/smirk.gif" alt="" /> ) pull them up a little.

I agree the higher aspect boards are a complete waste of effort... <img src="http://www.catsailor.com/forums/images/graemlins/grin.gif" alt="" />

Well, if that's the way you feel...

These are a set of experimental boards with which I can test a couple of theories.

If these ideas don't work I can easily modify the boards or easily build new ones. My centreboard cases are rectangular so they don't require too much modification. I will cost me about AU$200 to build this set out of carbon.

Plus I don't think they will be too far off the money. The chord length is a fraction longer (10-25mm) than what seems to be around atm, the board length can be adjusted to suit. Aspect ratio isn't everything, I think the Taipan boards have a ratio of about 1.5-2, just from looking at them.

I agree that they do get in the way when they're up...but it's sail area! <img src="http://www.catsailor.com/forums/images/graemlins/grin.gif" alt="" />

As long as you are aware of this then it is all fine.

Good luck,

Wouter

Nick,

you are a brave man going where you are. Even if the boards turn out to be too long and not fast, the class will have final and real-life information about how large boards should be. Theory and experience from other classes is one good, but a full scale test is even better.

Ncik,

How long are these plates ?

Mine project approx 1050mm below the hull on my Stealth.

I think they are about 200mm wide, not sure what the cord is.

Should be about 1.1m below the hull, with a chord of 240mm and thickness of 24mm.

Sound very similar to mine, but mine (I think) are slightly smaller cord. Hopefully get the measurements soon.

Yes in an emergency I suppose you could even use them as dishes. … <img src="http://www.catsailor.com/forums/images/graemlins/grin.gif" alt="" />

I would suggest the reason styrofoam is banned is because of its flamability and toxic smoke production.
With an engine and flamable liquid the percentage risk from fire as opposed to sinking is increased.

From a rough glance at the news it would appear in WA the number of fires on powered boats equals the number sinking, groundings swampings combined. (please note this is a personal observation and not a statistic)

It's interesting to see that petrol inboard engines are essentially banned on commercial vessels with the new rules coming into effect soon, no doubt because of the risk of fire and explosion.

If you want statistics...
Australian Boating Incidents 2005

Particular attention should be paid to capsizes and falling overboard...they accounted for 50% of fatalities.

Particular attention should also be paid to recreational boat use..they accounted for 79% of fatalities.