OK … to make it easier for someone to build a multihull, a person would provide the easiest way for a new builder to be able to start in with little if no effort. No need to know and get lost in plans and lines … no need for a person to have a large drawing board and try to plot all the dimensions … and no need to do anything except use a simple pair of scissors and some copy paper (or PC printer) to get started.

If you really want people to build to your ideas, Ernst, please go out of your way and provide (as I suggested in a different post) a set of cross section lines similar to the ones that follow. At least they will be useful.

For the new builder (a quick set of building directions):

  • Print out the following line drawings of the sections. Enlarge so that the height/width equals the actual size desired. At this point, if you have done a few boats, you can begin to play with changes in design, hull width and height, etc. For the beginner - reproduce at a 1:1 ratio.
  • Print enough copies so you can cut out enough sections.
  • Spray glue and attach to heavy chip board or thin 3-4mm plywood.
  • Number and cut out the sections. (Note - you are looking at both halves of the hull/float) I think there are 10 or 11 sections.
  • Space them along a building board at the appropriate space between sections to give you an overall length of 48 inches. They are about 4 inches apart as I recall.
  • Make sure the “datum” line on each section lines up - this will insure the rocker of the hull/float is correct)
  • Cover each section with plastic tape to prevent strips from being glued to the section templates.
  • Proceed just like you would with a strip built monohull (1 Meter, IOM, etc.)

Download Attachment: [ WRTm40coque.jpg](http://www.rcsailing.net/forum1/data/dick lemke/200541312826_WRTm40coque.jpg)

Download Attachment: [ WRTm40bras.jpg](http://www.rcsailing.net/forum1/data/dick lemke/200541312842_WRTm40bras.jpg)

Download Attachment: [ WRTm40float.jpg](http://www.rcsailing.net/forum1/data/dick lemke/200541312852_WRTm40float.jpg)

Download Attachment: [ WRTm40mainhull.jpg](http://www.rcsailing.net/forum1/data/dick lemke/20054131295_WRTm40mainhull.jpg)

If you print out the side/top view of the hull, and enlarge it (or print multiple letter size sheets with the lines) to an overall length of 48 inches (1.2 meters) you can scale directly from the side view for height and location of the cross sections. Depending on your printer, you might need to play with copier enlarge/reduce to bring the height in to the desired overall height. This in turn will also bring all other sizes of the cross section in line for the scale to which you are building.

Anyway - the reader can determine which method they prefer to use to build an F-48. This one where printing and copying and cutting out is the method, or you can use Ernst’s method and do a lofting project first in order to get thse type of cross sections.

awesome dick, thank you…

Hey - you’re welcome!

Now for my next magic trick … for those who don’t want to spend the entire summer laying up three hulls via balsa strips …

Foam covered with glass !!! Taa Daa !

Use the same templates from above - but this time you are going to use the parts you normally would throw away. (The female or negative part of the template cut-out.)

These must be all cut so they end exactly at the half-hull line (vertical).

  • Layout the side and top view on a piece of 2 inch thick pink/blue/gray house insulation foam. (Extruded kind - not the white expanded kind)
  • Use bandsaw, hacksaw, framing saw, etc. and cut out the general side and top view.
  • Mark off the location of the templates along what will be the outside of the half-hull.
  • Glue up and cut out the same number of section templates as before - but save the “OUTSIDE” part of the cut, not the normal inside. (Actually save both)
  • Number the sections and number the lines on the foam.
  • If you want to be cool and quick, use a Dremel and sharpen the curved edge that represents the outside of the hull ON THE CUTOUT TEMPLATE. (female side)
  • locate the proper station line on the foam and make sure you are using that template.
  • Carefully - but firmly press down on the template, forcing the sharp edge down onto the foam. Pressing down “should” leave a cut line in the foam when you remove the female template outline. Don’t worry about crushed foam that may have been mashed instead of cut.
  • Using a plane, belt sander with 80 grit paper, an electric hand plane, or even a “Sure-Form” type file begin removing the foam. Do this directly over the line that was pressed into the foam. It helps if you have an area of foam removed of about 3 inches wide directly over the template line you pressed into the foam.
  • Keep removing foam and be careful You want to remove the foam ONLY down to where the line stops. This will leave you with a place at each template location that has a curve to match that of the female template.
  • Once you have all template lines shaped down so it is almost impossible to see the line - use the same technique to remove the foam BETWEEN the section areas already shaped.
  • Use your eye to blend in so there are no bumps between section lines, and no hollows at the section lines. A thin piece of flexible wood, about 1/2 meter long with sandpaper will help keep from sanding in hollows.
  • When done, you should wind up with one half (vertical) of the main hull or float.
  • Repeate 5 more times so you have both hull halfs and both float half hulls.
  • Use a medium grade of sandpaper to gently shape and sand to remove any coarse sanding marks. Use about 100 grit - it doesn’t have to be really smooth - but you want to remove any hollows or high spots.
  • Glue both halves (left and right) of the float together. You can use regular yellow wood glue. It will eventually be inside and protected from water.
  • Once glued together, cover with a single layer of 1/2 or 3/4 oz. cloth. Just to prevent dents of the foam. You MUST USE EPOXY as polyester resin will melt the foam. Give a coat with enough resin to adhere and wet out the cloth. Don’t worry about cloth weave. After cure, give a second coat and try to only use enough to fill weave. Once this cures, you will need to fair any areas where you missed a hollow. Fair, sand, fair, sand and so forth.
  • For the main hull, you may want to hollow out an area for radio gear and rudder linkage, etc, BEFORE gluing half-hulls together. Then simply finsh like th floats.
  • Locate where cross beams will attach, and cut out or drill oversize holes. Fill holes with epoxy and you can imbed nut/bolt before cure. Just be sure to lubricate bolt (not nut) so you can remove it after epoxy cures. Basically you will have a solid epoxy plug with a nut at bottom and threaded center hole to match your connecting bolts that have been removed.

For main hull attachment, I suggest three bolts for each cross beam. For the floats, I would suggest at least two per attachment point. Obviously you can always glue the cross beams in place, but won’t be able to dismantle for travel!

Go to Jean Margail’s site for photos that will help explain this process. It’s a longer description than above strip method, but if you are all set up to go, you should be able to shape and cover a set of hulls in a weekend of steady work. Takes longer to explain than to do. I guess I could say …“Shape foam, cover with epoxy/glass cloth!” [:D]

Anyway, this really is an easy way to build, especially if you don’t have wood working tools, or a lot of time to strip build. Just remember the final size of 48" x 48" when done. After completion, I can email you a view of the rig/sail and a rudder and board outline as well.

I also want to note that this method (covering foam) will be heavier than strips, but I really don’t think you will notice much lack of performance. And, if you liked it and wnat a lighter boat, you can always use these hulls as a plug for a mold. Then layup a glass or carbon hull if you really need light weight.

With April 2005 (US) pricing, I am guessing you could easily build a set of trimaran hulls for about $100 US as follows:

<u>WEST Epoxy </u>
1 qt. resin, 1 Pt. slow hardener @ $60
1 sheet - 2 Inches thick x 4’ x 8’ @ $16
<u>Thin plywood </u>for templates @ $8
2 yards 3/4 oz. (50" wide) @ $10
sandpaper, stir sticks, gloves, etc. @ $10

Replace the foam with balsa wood if you want to strip build BUT add you will add a lot more time/labor to glue up all the strips.

I guess the queston is:

$100 for hull and 2 floats
$ 20 for 2 carbon crossbeam tubes
$150 for RMG winch
$100 for AM 2 channel radio, receiver and rudder servo
$200 for rig and professional paneled sails.
$ 50 for rudder and daggerboard

[:-thumbu] Thats just a bit over $600 and I would guess it would blow away any IOM, US1M, and probably most “M” Class boats which cost $1,000 - $1,700 (or more )!

<center>Go On - you know you want to try it! Give it a go!</center>

Magic Dick [;)]


_/ if it isn’t broken, don’t fix it! _


Thank you, Sir! [:-bouncy]

Thanks for describing the process of carving a foam plug. That’s what stumped me when I received the plans from Traplet a few years ago. Since then I’ve done some glass over foam work with my wingmasts, which I vacuum bag to get uniform surfaces & bonding. When you glass over these cores, do you simply drape the cloth, or do you think vacuum bagging would be of some assistance?
ps; Have you had a chance to get the MultiOne out yet?
pps; Gotta run. Going to see “Sting” tonight[:-jump][:-jump][:-jump2][:-jump2]. I think he’s great! Thought some of you Brits & Blokes from Down Under would get a kick out of that.


I tested both ways on two wingmasts.
The vacuum bagged one was way lighter and more stable.
The vacuum helps to bond the glass and the foam together with much less resin than you need for the same stability without vacuum.

After this experience I started bagging pretty much everything. Even the smallest parts.

I can highly recommend it.


Bill -

I use what I call a “dry” wet layup, and never found any instances of voids or air bubbles.

Basically -

  1. Suspend the foam - or place on a piece of plastic sheeting (visqueen). This allows the cloth to hang down beyond the hull.
  2. I use a metal handle brush like they use for applying solder acid/paste on copper pipes. If you watch, you can buy 2 boxes of 144 each (as I recall) for about $13.00 or so. I buy 1/4 inch wide and 1/2 inch wide and assume they are disposable. I like them because they have stiff bristles (more on that below).
  3. I will mix up epoxy in quantities that I know I can spread before the batch starts to go off. Usually it is one or two full pumps (quart can size) into a plastic butter dish. After stirring to make sure resin and hardener are mixed well, I dip the brush and “paint” on the epoxy resin starting from the middle and working both lengthways and downwards.
  4. Don’t paint on thick - and then use the stiff bristles and “stipple” the epoxy into and through the cloth. Stipple is tapping the bristles directly onto the cloth with only the tip of the brush bristles touching the surface. It is <u>NOT</u> back and forth like painting a wall.
  5. As the cloth begins to wet out, the color of the foam shows through and the white color of the glass turns to the color of the foam - which indicates a good bond. If you use too much epoxy at this point the glass can “float” on a layer of resin. It probably will adhere OK, but too much resin is just adding weight. This is much as what happens before vacuum bagging. The cloth could be floating.
  6. As you work outwards, you can also work the wrinkle out as well. I have an old pair of fabric scissors that I use to cut slits up from the edge if needed to allow glass to lay flat or take up a strange or compound curve. Use old shears as they will eventually load up with epoxy and will have to be dipped in solvent to clean.
  7. After stippling and applying epoxy to all areas of the hull - allow to set about 10 minutes, then look closely for any white spots which indicate the glass has lifted from the foam. If using pink colored foam, the glass should have an even pink color to it, without white spots. If you have spots, you will need to add a bit more resin and stipple a bit harder to make sure epoxy goes through.
  8. When done, you should be able to see and feel the weave of the cloth (4 oz. or heavier). Let the epoxy cure. Then go back and paint on another coat of epoxy - just enough to fill the weave of the cloth. Let it cure and then proceed to fill/fair/sand/prime/paint.

Some prefer to give one light coat to foam to “seal” it and let cure, then follow the above steps. The feeling is sealing the foam first will prevent epoxy starvation later. Also, some will place cloth and “pour” a ribbon of resin and use a squeegee, credit card, or even heavy cardboard to spread it around. I use this second method/process for large areas like on a kayak hull, but beginners often scrape too hard - leaving a too dry of coating or the don’t scrape hard enough leaving the resin “ponding” under the cloth. Hard to explain, but soon experience will be a guide.

If you have vacuum bagging supplies, pump or vac equipment and feel comfortable, I would strongly recommend using that process as gravity does a heck of a better job squeezing out excess resin and holding cloth tightly against the foam (or foam plug). Bagging by far is the ideal method - no doubt! My method is more for the guys who want to do a “One-Off” and experiment and don’t want to buy the supplies and pump to try bagging. I don’t have a dedicated pump, and either a vacuum cleaner or my air compressor running for at least 3 hours while epoxy kicks off is something the wife/neighbors don’t appreciate. If you can build or get hold of an old refrigeration compressor, they can be converted for very few dollars and are infinitely quieter.

Maybe I will take some scrap foam and do the first step so I can cut into small pieces and mail for those who prefer to actually see the results instead of reading about them via words. Then you will say - aahhhh - now I understand what I should be looking for!

Hope this added detail helps.


I am using a refrigerator pump too. I think they are of pretty much the same design worldwide and give over 90% vacuum if properly sealed. On some junkyards you can just rip it out of an old fridge for free. But better look for a newer refrigerator model (the older coolants damage the Ozone layer). 0$ - 5$

I use thick standard plastic foil from the home depot and silicon sealing compound to make the bags. Comes for 5$ for several bigger bags.

Rigid plastic hose 6mm. 5$

The most expensive part is the Vacuum gauge. I got mine for 24$. Indispensable for finding leaks… and there will be leaks.

idealy you use breather cloth and “tear of” cloth (don’t know the technical term in english…)

Its actually quite easy to do and after three or four times practice, its no effort at all.


<blockquote id=“quote”><font size=“1” face=“Verdana, Arial, Helvetica” id=“quote”>quote:<hr height=“1” noshade id=“quote”>Originally posted by Bill Korsgard

Have you had a chance to get the MultiOne out yet?
<hr height=“1” noshade id=“quote”></blockquote id=“quote”></font id=“quote”>
Hi Bill

I still have that pesky leak that I just can’t fix. It seems to be coming from around the board trunk, perhaps part way up one of the edge seams. With warmer weather here, I am going to try mixing up some epoxy and letting it run down between forward trunk wall and rear of forward bulkhead. I think that is where it is leaking. I tried taping off with a plastic straw and adding a bit of internal pressure and some soapsuds on and around rudder post and trunk. Had a few bubbles exit the trunk, but even with flashlight I couldn’t see far up the trunk.

If I really get angry, the daggerboard may become a permanent fixture and I know I will seal the leak that way !