A quick update - F-48 build

Apologies to those who may have seen this posted on another forum. Have two different groups on different forums and discussion has been about hull lay-up specs.

Well - tonight the first hull skin came off the port side, main hull foam plug. After a bit of coaxing, and some help with a thin, flat stick the “skin” reluctantly let go of the male foam plug which had been covered with plastic packaging tape for release. It still took a bit of work but was finally in my hands - along with a couple of glass cuts on fingers suffered in the removal process.

After a series of traded correspondence with a U.K. builder, he convinced me the strength of a hull was in it’s final shape and not necessarily in the number of glass layers. My mind agreed with him - but my heart said “better add another layer to be safe”. Well, this was my first opportunity to test his theory/view, so I followed his (and my mind’s) instructions. The skin consists of only one layer of epoxy/glass of 4 oz. Weight (about 113 gr. for you metric folks). Boy can that hull “oil can”! After a single layer of glass, fairing was added to any low spots along the sides.

A small piece of wood will serve as a glued in keel/deck “locator” so both hull half sections can be aligned and glued together and then bulkheads will be added from double sided glass covered 3/4 inch foam (about 19 mm). These will be located to accept the deck mounting of the cross beams. I probably will build the daggerboard trunk and the radio board from light ply - or carbon fiber. Also I need to install the rudder and arrange any required deck fitting hard points.

In all due respect to my U.K. friend - I will probably lay in some additional layers of glass in areas around bulkheads, daggerboard trunk and rudder assembly - as well as along the deck where sheets exit and beams attach. It may eventually turn out stiff and strong like the builder said - but damn it is “scary” flexible right now. In the photos, you can see the skin (with light fairing) next to the tape covered foam plug. I’ll be taking it in to work to get weight of both plug and skin and then just the skin only. With foam being planned to be left inside the floats and yet so light in weight (5 oz. - no glass), I’m curious just how light only the skin is - knowing of course some weight will be added back in.

If this completes as I hope it will, the main hull will be hollow and floats will be glass covered foam. I am still debating if I should keel step my mast in a series of tubes so I can shift fore/aft - or if I should deck step the mast on a “T” shaped rail with mast base slotted and pinned to the rail. Right now I have a series of very high aspect ratio “M” Class sails - but have fabric to build my own of various sizes - mostly smaller suits for high wind days. Actually the M sails look out of place on the trimaran because they are so skinny and tall. Also need to build a small storm suit which will be a jib attached about 5/8 up the mast and with a small main. Want to keep it low aspect ratio to be able to control in heavier winds.

In the photos you can see both main hull halves and the two floats leaning against the wall, and then photo of the main hull (port side) plug with “skin” removed. The skin will be returned to the foam plug until it is time to glue both halves together. No sense in tempting fate by leaving that skin of glass off the plug - and just waiting to be stepped on.

I’ve been meaning to ask you this for a long time. When you mold the hulls using your method how much wieght do you think you add in the finishing. I seems to me that you would need a lot of sanding and filler to arrive at a smooth hull. Any time I have glassed something externally I have had to do a ton of sanding and filling and I’ve sanded through the glass more than once too. Patches aren’t light.

Hello Don

I hope to find out when I get to weighing the thing.

After a couple of posts, and the fact my 48 inch float only weighed 5 oz. without glass, I questioned if leaving foam inside and just dropping on a layer of 1/2 to 2 oz. cloth would make sense. If I remove foam, then the glass hull would need to be thicker/stronger since there is no backing. That in turn adds back the weight that left with the foam.

I am finding that the fairing doesn’t “seem” to add too much, but I try to get the plug as smooth as possible first. Second is I fair with it on the plug. I tried (once) to do it off the plug and nearly slit my wrists after that escapade!

Yes - it is a bunch of work/time to finish the exterior, but it is, after all, a one-off. I sure wouldn’t do more than two this way. Once you do that many, the plug/mold method is more economical time-wise. Given that these designs aren’t mature yet, the ability to change shapes for performance (good and bad improvements) allow a quick way to do it. Sanding foam is much quicker than the balsa strip glue-up option for the plug, And one could obviously make a mold, but that is just an extra step. A few German builders aren’t even covering with glass! They take the foam, shape it, add a plywood deck for attachment and then cover everything with the tape. Assemble, sail, bring in, disassemble, remove tape, reshape hull(s) and repeat.

I guess, down the road when I am happy with the performance, I would move to a balsa (or veneer cold-mold) for the final version. Even my 1 Meter needs to have board and rig moved back a bit - but that is a hollow main hull and I just hate to think of Dremel tool cutting and modifications.

So goes it with “development” classes - we are never satisfied and are always looking for a breakthrough. Thankfully the class rules are very minimal to allow this experimentation. :rolleyes:

OK - the weighing results are in … rather interesting - but still need to monitor as build progresses. Here ya go Don

This is one half of the main hull…

Glass only = 5.1 oz. (144.6 gr.)
Foam only = 5.5 oz. (155.9 gr.)
Total = 10.6 oz. (300.5 gr.) - this would be if I leave the foam inside - but I could then reduce the glass from 4 oz. to something much less as a simple covering.

By projecting out - a hollow main hull of glass would be a minimum of 10 oz. and a foam inside glass main hull would be a minimum of 20 oz. - plus weight of fixtures, radio gear, rig and sails, beams, rudder, board, etc. so I can see it easily pushing 2 lb. ( .9 kg) and the floats (2) would be perhaps 1 lb. for a total sailing weight at 3 lb. (1.3 kg) minimum. This is just estimates, so as I continue, I can easily be more but what the heck - as good a target as anything. Just have to have faith the design and glass is to (primarily) keep water out ! Can’t overbuild! Can’t overbuild! etc. etc. :lol:

That German method sounds like a good idea to me. I was thinking about building up the back half rocker on my modified Mistral to try and reduce the weather helm. I was going to use bondo but I could just use form and tape. Reversable and easy, may not even have to glue the foam to the hull. Thanks for the idea

Hey - those Germans come up with some neat ideas - and I are one - well at least 1/2 of me is. :smiley:

Not to be outdone, some of the UK fellows have used the water pipe insulation tubes for their floats. They just shape a point on them and hold by tape. It allows them to test the float to find optimum point for rocker. Sail, bring in, bend float slightly, sail again - then repeat. Sure cuts down on the work until you find the best possible shape. Then that rocker profile gets transferred to paper, lines drawn and a final float design built. Looks - well, what can I say, prehistoric, but sure saves time and energy to get it right. Some are just leaving the pipe insulation floats - never bothering to build “good looking ones”. :lol:

The German engineering motto:

Warum so einfach, wenn man es so wunderbar kompliziert machen kann?

Why so simple when you can make it so beautifully complicated.



The Germans want it efficient - at any price
The Americans want it cheap
The Japanese want it to be reliable.
The English want it simple
The French want it ingenious
The Swedes want it safe
The New Zealanders want it light
The Russians want it to be maintainable with a big hammer
The Dutch want it watertight
The Italians want it painted bright red and to go Vrrrrm, vrrrrm, vrrrm.


As Purchasing Director for government this list has been expanded to a framed document on my office wall. (hows that for irony) :scared:

I only modified it slightly with a last line that reads … “So what is it that you want … today?”

Don - here is a sample of what I was talking about - skip the glass and just shape, cover with tape and test !


My pleasure, sir!:zbeer:

A couple of emails arrived asking how the F-48 build was going, so thought I would post.

Boy - it’s amazing at how on-site engineering triumphs over paper plans !

In my case, I started out to have hollow glass hulls. After laying them up and weighing (see above) and feeling how soft (as in “oil can”) the sides were, I stepped back, and decided to change tacks a bit. (Call it a header)

After consideration, I think I will follow the concept proposed in another thread here, and retain the foam, but just hollow out the inside for radio gear, dagger-board trunk and steering connections. The slight gain in weight by retaining the foam will offset my concerns about a self destruct in waves. Since I had previously decided to leave the solid foam in the floats, I will only gain about 10 oz. more by doing the same in the main hull.

The following photo is just after cutting the first foam beam. At one time I was going to use laminated wood beams (as shown by rear beam), but after seeing them on the boat,they just didn’t look right. So I will build a set of foam beams with thin ply spine, shape and glass. Once I see how they look, I can make my choice, saving the ones “not” selected for a future build. The front beam in the photo was only cut to the “wing” shape, and now must be shaped looking down. It won’t be the same width the entire beam.

Also of note, is that I shortened up the total beam of boat. While 1.2 meters (48 inches) is maximum class rule I am going to reduce to see if it helps in tacking. The yellow color of the measuring tape just behind front beam is set to 1 meter for size comparison. Overall outside of floats beam will probably be right around 42-44 inches instead of 48 inches.

While I already have a carbon fiber (tapered tube) for mast, I am also considering building a large wing mast from wood so I can include a trailing edge sail track yet still taper the side profile of the wing mast. I also have plans for a single flap solid wing, but will save that for later and after I see what kind of performance this one will make.

Thanks for the update Dick. It is looking great.

I received some sample “styrofoam” in 1 lb and 2 lb densities. I wil try to shape each to see which is easiest to machine and form with hand tools.

BTW, I have gone back to the Ghost Train plans. The sides of the main hull are pretty much straight as is the bottom and top so the main hull can easlily be cut with a hot wire and the bulk of the float can be cut with a wire as well.