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.