Following a suggestion, I will start a new thread for my first effort build of a 65cm multihull.
I am currently planning on wood templates, with foam between. Foam will be shaped to same size/curve as each station template. When completed, I will lay up a couple of layers of glass cloth, then remove from what will be termed the “plug”, giving me two half hulls that will provide hollow floats once glued together.
In the photos, I have split the templates horizontal, as my previous experiences with a vertical split made fitting support bulkheads a bit of an issue. As seen in the photos, there will be a “plug” for both the upper and lower portion of the complete float.
The templates are from the GHOST TRAIN plans I posted here, but I may modify the bow and forward underside to represent more modern thinking in multihull design.
Basically - the plan was printed full size, and each of the station templates for the float were cut out and glued on to 1/4 inch thick ply. Once glued, I cut out the rough shape and using a belt sander, sanded the perimeter to final size. Then each station template was cut in horizontal plane so a top and a bottom resulted. Before cutting, be sure to mark the two halves at “Top” and “Bottom”.
I started cutting 2 inch thick house insulation foam to length and a bit oversize, but have an out-of-state trip planned, so won’t get back to this until midweek next week at the earliest.
Back from an early spring vacation, and I used time away for reconsideration.
I was originally going to cut wood templates out of very thin stock, but after a brief experiment, I found it hard to see the template shape - so I went up in thickness to the 1/4 inch originally planned. This provides sufficient space between the foam fillers to be able to see when getting close to final shape.
Instead of 2 inch foam, I measured my half hull templates and found 1 inch foam would be adequate, so rectangular foam blocks were cut in the starting basic size of 1 inch thick by 2.5 inches long by 2 inches wide. A quick check verified this was large enough for all lower float hull templates.
So moving forward -
A. All templates were glued to the end of a block of foam, assuring the 2.5 inch dimension would be from the back of one template to the front of the other.
B. One one template was glued to the end of each piece of foam, a center line was drawn on the top of the foam to aid in alignment when foam blocks were glued up.
C. When done, I measured length of all foam blocks WITH the templates between and I found my first front foam block works out to 2.5 inches as well, and I will probably free hand shaped after the other part of the hull bottom is shaped to fit the templates.
Image 1: Shows all components - foam blocks glued to one wood template. Wood template fitting to end of block. Remaining wood templates yet to be glued. I used plain old wood glue, and this is only going to be a male “plug”.
Image 2: A look at how one wood template and block will align and be glued to preceding block.
Image 3: A closer look at one of the wood templates glued to end of foam block. Note center-line on template which is carried to top of foam to aid in alignment before shaping.
Image 4: Remaining wood templates still to be glued to foam.
Image 5. All blocks and templates laid together (yet to be glued) for overall measurement. On left of photo I still need to add one more 2.5 inch length of foam to be shaped for bow. Once added the overall length with be 25.5 inches or just a touch under 65cm.
More to come as I move forward. I will replicate same process for the top half of the float and follow the above process - just using the “top” half of the templates. Will not replicate photos - as these could be for both top and bottom float halves if so desired.
As noted above, bottom half of float has been glued up with wood stations between the blocks of foam to help provide final cross-beam shape. Because all templates were cut horizontal in the same exact location (line drawn before templates cut) the side view rocker or deck profile will emerge as foam is shaped. I did not glue front bow piece on yet, but photos below show the glued up half-hull.
Image 1: Is a look at the bottom half of the entire length of float after having been glued up.
Image 2: Is a look at the top of same float.
Image 3: Same as image 2, but I have added drawn lines where I will cut top view profile of the float.
This afternoon, I had a few minutes to start shaping the foam to match the wood templates. I used a belt sander (80 grit) to quickly remove the majority of foam, and get it close to the wood templates, and then switched over to hand sanding with 80 grit to continue to rough shape. Since the foam sands easier than the wood, there isn’t much chance of messing up the wood templates, but it is easy to put a hollow where you don’t want it. Not to worry, and any low spots can be filled with wallboard compound and when dry sanded in a more careful manner. Since this is a plug and will be covered by tape to allow epoxy/glass removal, one doesn’t have to worry about moisture issues.
Image #1: Shows the difference between foam shaping from nothing (left side of photo) to nearly matching the wood template on right side of photo.
Image #2: A photo of the front 1/3 of the float hull rough sanded to “close” shape.
Image #3: Another photo of the rough shaped/sanded hull near the bow. (Actually station Number 2 and aft). Once all have been rough sanded, I will pull out the 150 grit to get a bit smoother foam finish, although it isn’t too necessary to have it glass smooth - just no bumps or hollows.
ADDED-Image #4: Bottom half of a the float, rough sanded to general shape and viewing from stern toward bow.
Moving on with the float plug build ……………
Photo #1: Just a look at the entire length of the float plug for the R65M (multihull). Bottom of float has been rough shaped to match wood templates. Deck has been glued up for length and is now ready for rough shaping to match wood templates. Had to use 2 inch thick foam for bow as templates were taller than 1 inch as used for stern.
[COLOR=black]Photo #2: Front view of wood template #2 that shows planned float hull shape at this location. Bottom has been shaped to match template - top is ready for shaping. There will be one more section of foam added in front of this template that will bring float to desired total overall length, and will be shaped from this float oval shape at station #2 to a pointed bow shape [/COLOR]
Began the process to shape the “other” half of the float plug. I held both halves together with clamp so you can visualize how the two half-hull fiberglass floats will come together.
If you want to follow this process, the foam “could” be left inside the glass, but then I would recommend using thinner wood station templates.
IMAGE #1: View of both halves held together by clamp
IMAGE #2: Close up of station template #2 (bow) showing top and bottom half rough shape.
Keep it coming Dick, always interesting to see how others do their builds.
Thanks Ray - will try.
Unfortunately a full time day job, household chores for the “better half”, and a couple of grandchildren makes any time precious (and valuable). Mother’s Day weekend here, so little if anything accomplished.
Work continues on the plug to be used for trimaran floats.
Future steps yet to accomplish: fair both halves of plug, attach each half to a section of wood for support, cover each half with plastic packaging tape to act as release surface for epoxy/glass, using glass “tape” (3 inch wide and 9 oz weight ) for initial glass hull, consider adding fabric (as in Claudio’s method) but may not due to additional added weight, add finish layer of 1/2 oz. glass, glue top and bottom halves together, fill glass weave, fair, paint. Somewhere in there I also need to add some bulkheads to attach cross beams and a “hard” point to attach side shrouds inside each of the floats.
Photo #1: Side view of top and bottom half of the plug for floats. White is filler added to fair off any hollows in the foam, and to provide a hard surface upon which to apply tape. Bow section still to be added.
Photo #2: Top front view looking down on float plug. Still more fairing and sanding to do, but foam bow section has been shaped to rough dimensions and added to both upper and lower half of the plug. View looking down also illustrates good multihull design (thank you Andy McCulloch) with narrow beam to length ratio (a 2 inch wide maximum float beam compared to a 25-1/2 inch overall length) meaning this slender float design requires very little effort to move water out of the way when sailing, as compared to fatter or shorter hulls which must move lots more water out of the way.
Good job, Dick
I enjoy your report.
I am planning to build my own 65M tri next winter - so I will use the opportunity to learn from you!
looking good dick! What weight glass are you planning on using for this build? I was thinking of using a couple layers of 3/4 ounce, probably like 5 or 6. But, more than likely I’ll use 2 layers, or maybe 1 of something bigger.
In the past, I’ve used two layers of 4 oz. with specific extra layers in locations where needed. Until I lay one up, and judge it’s strength/stiffness - I’m “considering” a layer of 9 oz. cloth (actually tape) with a skin of 1/2 oz external. Will probably lay in a strip of 4 oz. internally for bulkhead area to spread stress over bigger area. That would be optimum, but if the first layer looks too flexible, I would add a second layer of 4 oz. (to exterior) and then add the 1/2 oz. In place of 4 oz., I might try Claudio’s fabric ideas as the second layer as a possibility too.
Here are my thoughts. The hull is basically an oval of sorts. Once the top and bottom are joined, the cross section should add a good deal of inherent strength based on cross section shape (like an egg). Thus, the glass becomes more for keeping water out, with a secondary purpose to provide design shape.
Heck - I may be completely wrong on this, but the 1 Meter was 2 layers of 4 oz. and is (I admit) subject to “oil-canning” if you squeeze the sides of the hull. Obviously with this one, similar to the one on the other build/blog, if you plan to leave the foam inside, then only the lightest weight glass fabric would be needed… if at all. Remember, some of the German guys are sailing foam Mini40’s with hull and floats covered with plastic tape!
Hey, Floats of foam covered in plastic tape! Quick and dirty, just the way I would like it for a development hull.
Any updates on your build, Dick? The daggone tai’s are taking us to school here (just kidding siri!) I had my son this weekend, so I didn’t get any done on mine, but about to hit the shop.
Not much - filling, sanding and filling again.
Because I am building to a known and proven design, I want to take time on the plugs so they will be ready to give me a decent set of epoxy/glass take-offs. Not in a rush as I have two more RG-65 monohulls to build/finish. The tri is simply a diversion for when I waiting for something to cure/harden/dry on the single hull boats.
Same here, just in between working on my sons new star 45. Finished planking it last night, may take the night off of it and build the two floats for the tri though.
Looks good, what’s your projected weight of the tri?
Haven’t given it a thought as yet.
Now wife has me “enrolled” in a kitchen and dining room floor replacement project, so my only interaction with any of my r/c boats is as I walk past the work bench toward the table saw.
I don’t know - The rooms looked so small, the flooring boxes so tall when stacked. :mad: [sigh]
I’ve seen your post on my thread at RCGroups. Thanks for your help with the tiling of the pdfs. How is your Tri coming along? Can’t wait to see the first videos. You guys need to hurry otherwise sail no. 2 will be mine as well.
If someone still needs the plans for the RT65, an updated version with tiled plans and seperate shadows is available for free download at
Well - the wood floor in kitchen and dining room is complete. Also did a furnace and central air replacement - which is why things on the 65 Multihull haven’t been moving along as fast as I would have liked.
Tonight I managed to mount the top half of the float “plug” to a piece of wood, allowing sufficient overhangs to let glass cloth “drape” beyond the plug. Plug had been filled and sanded with wallboard joint compound/filler to provide a surface that could be lightly sanded and it filled any low spots or holes/dents.
With the “plug” attached to the wood support (beam), a layer of plastic packaging tape was applied over the foam “plug” - laid up at about a 30 degree angle to let it conform to compound bending around the exterior of the “plug” and tried to eliminate as many creases as possible for a smooth, shinny, non-stick surface.
A length of 9 oz. glass tape was cut - 3 inch wide by just slightly longer than the “plug” length. Epoxy with slow hardener was mixed and using a small brush, dabs of epoxy were spread directly on the plastic tape at various points - to hold glass in position while more epoxy was applied, spread and worked into the weave. Glass is carefully applied assuring it overhangs both sides of “plug” and again, using stiff bristle brush epoxy is “stippled” into the fiberglass cloth. Once all fiberglass cloth was saturated (wetted out, but not shinny with the weave completely filled (I call it a dry coat) I took more plastic tape and simply laid it over the wet fiberglass. I saw Claudio do it with plastic trash bags on his AC boat thread and thought I would try it. Supposed to do two things…
- Hold glass tape against the plug similar to vacuum bag, but with only mechanical pressure.
- With the covering tape being plastic, it should (??) make the exterior surface of the glass covering the top half of the float hull pretty smooth and (hopefully) needing only minor filling and sanding.
Until it cures and I remove the exterior layer of plastic tape, I won’t know how well it worked (or didn’t) and will then decide if a second layer of glass should be added (4 oz. weigh) - or just add the 1/2 oz. glass for final finish - all depends on how firm the hull feels. Once I can slide the glass off the “plug” I will be able to weigh it to answer questions - and perhaps project a sailing weight.
In the photos, a second part of the hull (the bottom) awaits sanding, adding tape and laying up glass. It is the white/pink shape and looking closely you can see the wood ply cross sections used to shape the foam.
Before gluing the top and bottom halves of the float together I will need to add a couple of bulkheads (pink foam epoxy coated and also some “hard points” to fasten cross beam to float. Still trying to determine if I make it a “break-apart” platform, or glue everything together and deal with transport/storage issues later.