Courtesy of YouTube
http://www.youtube.com/watch?v=QZDS3miKQCc
Ahhhhhhhhhh ! 
Dick,
Very interesting video, thanks.
One interesting thing I noticed and had been thinking about - the lack of rocker along the ākeel lineā of the floats on Broceliande. As I have been making my Water Resist floats I had been thinking that the rocker up front was going to allow more ānose downā attitude than if it was straighter.
Also wondering why the main hull has so much volume on a rc model. If the floats get away with enough volume to carry the whole weight with spare, why not the smame volume for the main hull (lighter)
I have nearly finished main hull, floats and compound beams (in fact I started again - new items going for light weight) Will organise a post soon with some pics and details.
Jon
That was foremost comment made by Mike Friend of his PULSE design - having rocker made āhobby-horsingā more pronounced - but it als allowed the hull to tack easier as the bow was up and out and didnāt āpushā water as boat turned.
I was looking at photos of a few of the catamrans that they fly in by helicopter to inland lakes - somewhere in the 32-40 foot range and tey are using a pod full length like a mini-hull, on which to fasten the sprit pole, a place to douse/store asy spins, and just another way to reinforce the hulls to make them stiffer (shorter cross beams from pod to hull instead of hull to hull). Will try to find some photos again to post for reference.
I think the cat is still the way to go - but because you either have a center pod, or weight distribution issues, the main hull of a tri makes for a much nicer ālookingā boat.
Anxious to see your photos.
Dick,
I was waiting until I got things more complete, but here are the first set of photos.
A series ofphotos of construction of āWater Resistā hull from expanded styrene(slightly larger than 1/8ā bead size) over a couple of posts.
- Rectangular section bandsawn hull (235 grams) Slightly visible is the partial cut through aft rudder section.
- Lines drawn on foam ā transferred from sections.
- first bevel sanded (using coarse grit ā 36 ā paper on attached to a long board)
- first bevel close up
- 2nd bevel ā sanding looks rough, and still oversize.
- finished close up (190 grams) Note centre lines kept!
I hope 6 attachments are OK
Jon
Next set,
Next I cut the hull into 6 pieces. From the rear I cut at the ābulkheadā in front of rudder post, then at rear cross beam, front cossbeam, halfway to bow, and just aft of bow.
- These were taped with masking tape so I could hollow out the section with a hot wire.(except short bow piece)
- Hollowed out section ā about 16 mm thick walls - roughly half weight. I was surprised how solid these sections were, and would go thinner next time.
3, 4, 5 Photos of hull joined back together ( 145 grams). With thin (3mm) dense foam āring framesā at beam positions, a full bulkhead forward of rudder post, beam positions, rudder post and forestay positions reinforced with dense foam. (160 grams!). If you sqeeze with one hand, the sides do not flex (but would ultimately go ābangā)
And again,
- Close up looking aft of front beam/hull and inside main hatch. Shows dense reinforcing foam around beam position.
- Beam attachment ā shows a beam in position over styrene plus dense reiforcing foam float hull. 4mm hole (enlarged for head) drilled through beam.
- Beam lifted off float showing threaded insert glued in position. Have glassed bottom half of float ā top glassed soon.
Hull glassed top (about 100 g cloth) and bottom now weighs 400 grams (about 14 oz)
Beams of laminated dense extruded foam carbon on top weigh about 75 grams with all reinforcing points done. Carbon still to go on bottoms.
I will update when I have completed the hulls and beams. (also working on mast/booms/fittings/etc)
Jon
Wow - in all of my hot wire cutting and foam shaping, I never gave a thought to hollowing out the hull like you did! :headache:
Well done - man, I love these forums - so much info to be shared ! I plan on passing on to the guys here just getting ready to start.
One question. When hollowing out, did you have to cut through the bulkhead wall to get the wire inside - or did you use a single small metal rod like one would use a welding rod to heat and cut? I could see easy reglue at cut line to reinforce the foam.
Nice job - and addresses the problems of a retro fit of bulkheads into a hollow hull like I am currently faced. Thank you for sharing Jon.
Jon-
I also have been trying to figure this one outā¦ is it not a matter of hydrodynamics/boyancy not acting as greatly on such a small object? For instance, with RC airplanes, a scale copy wouldnāt fly like the real thing ā they need to be exaggerated a bit. Iāve just assumed that this was the case - can someone with more knowledge comment on this? Iāve had great interest in the brossard trimaran - in fact iāve been in contact with them about getting some line drawings in order to more accurately replicate it. I love the shape of the hulls on that boat (and the others similar to it). Itās very trim and sleek. Iām particularly confused as to why the floats on RC tris are so different than those on the large tris. Most of the large ones go from vertical ovals (like catamaran hull) to a rounded-diamond shape in the rear ā it seems that all the RC tris are pretty much egg shape throughout their length. I may be mistaken on but this is just what iāve noticedā¦
You are probably right - and that may be āinspiredā by a lack of many different designs within the R/C multihull community. In my prototype design for IMPULSE (my 1 Meter tri) I go from a vertical thin bow to a rather round stern for hull and for floats. I probably could have made it more pronounced, but at the time (3 years ago) it was a design that had bounced around long enough āinsideā so was time to create it āoutsideā of my head. Even today I am critical of a few aspects of the design - but the biggest is moving the rig back even further. At the time it was in a pretty radical position back as far as it was. Today, the beach cats are leading the way with rig and platform almost in the last 1/3 of boat length.
Ahhh - maybe the next one, perhaps - I will modify more ?
Dick,
I did it the easy way (?) - cut through the masking tape on centre line of keel with a knife and then hotwired down centre line of keel to inside. I could not face undoing hotwire for each section, pass it through a hole and re-connect.(I hollowed out the floats as well)
Jon
eikelben,
I think some of the differences are to make the small tri more āsafe sailingā. A full size boat can be designed for speed, and not necessarily to be easy to sail. The crew then has to work hard - steering over every wave, trimming sails constantly, and changing sails sizes to suit the conditions. An rc boat needs to be more āsea goingā usually at the expense of speed.
My thoughts on the rounded floats are that they will allow some side slip when the boat heels over (with a central centre board and rudder now partially in the air) to de-power slightly. Maybe not as fast, but safer.
Jon