+ Reply to Thread
Page 1 of 5 123 ... LastLast
Results 1 to 10 of 41

Thread: 2 metre catamaran build

  1. #1
    Join Date
    Sep 2008
    Location
    United Kingdom
    Posts
    187

    Default 2 metre catamaran build

    In the spirit of Claudio, Dick, Siri et al I though I would start a thread to provide occasional updates on my 2metre catamaran build. The boat' hulls are based on the lines for the centre hull of the Midnight Oil trimaran, I squeezed them horizontally and stretched them a little vertically.

    THe hulls will be moulded over a male plug, which I have constructed from thick plywood - the lines in the ply are excellent for sighting along to check symmetry and fairness. The plug is split into two halves along a horizontal plane parallel to the waterline. As these are "Mk 2" versions I'm currently tidying up the plug - I've reduced the freeboard at the bow and have rounded the stern over. I've just rubbed down the whole plug down ready for finishing.

    Another change I'm making is to mould in the recess for the crossbeam. On the previous version I moulded the hulls and then cut into them and glued in a recess but this added weight and wasn't as strong as I expect moulded in recesses to be. If you look at the pictures of the plug you'll see a curout in the top of the hull. I'll show how I make the final recesses in a future post.

    For now here are some pictures of the plug "as is".

    Ray
    Attached Thumbnails Attached Thumbnails Click image for larger version

Name:	2009_0613catamaran0006.JPG‎
Views:	552
Size:	1.49 MB
ID:	3351   Click image for larger version

Name:	2009_0613catamaran0007.JPG‎
Views:	431
Size:	1.53 MB
ID:	3352   Click image for larger version

Name:	2009_0613catamaran0004.JPG‎
Views:	369
Size:	1.49 MB
ID:	3353   Click image for larger version

Name:	2009_0613catamaran0005.JPG‎
Views:	367
Size:	1.47 MB
ID:	3354  

  2. #2
    Join Date
    Sep 2008
    Location
    United Kingdom
    Posts
    187

    Default Re: 2 metre catamaran build

    Having decided to mould-in the recesses for the crossbeam I introduced the need to build left and right-handed hulls (the crossbeam is 'arched'). I decided to achieve this by having removable inserts for the recesses, i.e. an interchangable part to the plug.

    The first thing I needed was a building board to keep everything true. I actually used a thick piece of kitchen worktop. I then set four pieces of studding into the building board, checked for sqareness and accuracy. The studds are positioned to be on the centre lines of the hulls.

    The top half of the plug already had vertical holes drilled and this enabled the top part of the plug to slide down onto the studs. I then used soem aluminium section and carefully drilled holes to locate over the studding and also to align with the fixing bolt holes in the crossbeam. This enables me to horizintally align the crossbeam. The pictures should explain it better.

    I then used some packaging tape to act as a release barrier on the plug and the bottom of the crossbeam (I used several layers on the crossbeam to build it up to the thickness of the laminate when it gets layed-up. I also used some PVA release agent over the tape. After aligning everything on the jig I filled the void between the hull plug and the bottom of the crossbeam with glassfibre/polyester resin paste.

    Ray
    Attached Thumbnails Attached Thumbnails Click image for larger version

Name:	2009_0614catamaran0006.JPG‎
Views:	246
Size:	1.46 MB
ID:	3355   Click image for larger version

Name:	2009_0614catamaran0004.JPG‎
Views:	245
Size:	1.49 MB
ID:	3356  

  3. #3
    Join Date
    Sep 2008
    Location
    United Kingdom
    Posts
    187

    Default Re: 2 metre catamaran build

    Having filled the void with the paste it looks a bit of a mess at this stage. After the glassfibre paste has cured a liitle effort saw the crossbeam release. The resulting glassfibre insert had some voids but these should be fillable. Following some hardwork the insert is cut back fair with the plug and released from the plug. Not perfect but usable.

    I reckon it took about an hour of effort to get the insert to this stage. Of course there's another one to make.

    Ray
    Attached Thumbnails Attached Thumbnails Click image for larger version

Name:	2009_0614catamaran0007.JPG‎
Views:	178
Size:	1.39 MB
ID:	3357   Click image for larger version

Name:	2009_0614catamaran0008.JPG‎
Views:	190
Size:	1.43 MB
ID:	3358   Click image for larger version

Name:	2009_0614catamaran0009.JPG‎
Views:	206
Size:	1.51 MB
ID:	3359  

  4. #4
    Join Date
    Sep 2008
    Location
    United Kingdom
    Posts
    187

    Default Re: 2 metre catamaran build

    Work is mainly progressing on finishing the plug and I should start waxing it prior to moulding over the weekend - not very exciting.

    I'm still moving forward on other components though and have just about finished the riuders and fins. I build these using blue foam cores, cut with a hot wire by a guy who makes model plane wing cores.

    To keep the fins/rudders the same, I start by vary carefully aligning and glueing in carbon tubes to accept the rudder stock or fin mounts to one of the cores. I then joining the foam cores together, again being careful to ensure alignment, before glueing the carbon tubes to the second core - I use this approach because everything is kept in alignment properly. After fairing in the carbon tubes I laminate over the core with a couple of layers of 200g carbon fibre. Once cured I seperate the two fins rudders.

    Below is a picture of the fin cores, showing the carbon tubes prior to lamination. Second picture is an almost completed rudder, complete with 'inverted wing' across the bottom (this is actually a balsa core laminated with carbon).

    Each rudder weighs 40g (about 1.5ozs) and each fin 50g.

    Ray
    Attached Thumbnails Attached Thumbnails Click image for larger version

Name:	2009_0206Catamaran0002.JPG‎
Views:	191
Size:	1.73 MB
ID:	3391   Click image for larger version

Name:	2009_0619catamaran0001.JPG‎
Views:	236
Size:	1.64 MB
ID:	3392  
    Last edited by nautibuoy; 06-20-2009 at 02:54 AM. Reason: typo/clarification

  5. #5
    Join Date
    Aug 2003
    Location
    Minnesota USA
    Posts
    3,811

    Default Re: 2 metre catamaran build

    Hi Ray

    I realize it's massive, but is a single cross-beam going to provide sufficient stiffness and resist twisting between the two hulls?

    The old FREIGHT TRAIN design with single "wing" cross-beam suffered from torsional twist, and even my big cat with two beams still had issues.

    Just wondering if the issue has been considered?

    Looks good and I like your idea of using vertical ply for plug hull shape, and you were right about the under-beam filler photo. Looks like someone "sneezed" and it came out blue.

  6. #6
    Join Date
    Sep 2008
    Location
    United Kingdom
    Posts
    187

    Default Re: 2 metre catamaran build

    Hi Dick, I don't have the technology to prove that the cross beam will be stiff enough before building it so ultimately the proof will be in the pudding, however, I've done the right thngs; its curved, it has a fairly thick cross section, there's a lot of unidirectional carbon along the beam but also cloth at 45deg and 90deg to provide torsional stiffness and the mating area where it bolts to the hulls is fairly large.

    My mini40 tri has single swept back beams and they seem upto the job - it was built by Mike Dann who knows what he's doing and I've also used him as a sounding board ideas on the big cat too.

    Ray
    Last edited by nautibuoy; 06-20-2009 at 02:56 AM.

  7. #7
    Join Date
    Aug 2003
    Location
    Minnesota USA
    Posts
    3,811

    Default Re: 2 metre catamaran build

    OK - just curious. As I mentioned, my big cat was 5.5 meters long and not quite 3.5 meters wide. With two cross beams, I could lift the bow on port hull, but starboard hull stayed on the sand beach. Finally found a way clamp the cross beams to the hulls much tighter than the two SS straps, and it stiffened up a lot, so at least both bows would rise if only one lifted.

    Hey, forgot to add - Love the idea of a master plug with variable inserts depending in idea and designs. Great idea to build the plug that way.

    I have some old shelving removed and looking at the end section (looks like a ladder) am thinking it could make a great building board/surface/strong-back for a 2 meter. Darn it - now you have me thinking of a possible cat myself. !

  8. #8
    Join Date
    Sep 2008
    Location
    United Kingdom
    Posts
    187

    Default Re: 2 metre catamaran build

    Thanks for the feedback Dick; I know you're sold on the small multihulls that you and Siri and that is great but it would be interesting to see you buld a 2metre boat using your foam core approach. My personal preference is for larger boats on the basis that the meduiums in which we operate (water and air) don't scale and have an increasing impact as you go smaller.

    Regarding the crossbeam, as you indicate with your comments about your 5.5metre cat the way cross beams mate with the hulls is important and I observe pictures of model multihulls using small round cross section crossbeams mating with small round recesses on the hulls and this can allow relative movement between the beam and the hull, as I think you found, Also these small cross section beams can themselves be subject to torsional flex, which makes the situation worse.

    I'm confident that my crossbeam will not be prone to movement between it and the hulls. I would like to demonstrate the beams strength (I've though about standing on it for example) but its a lot of work to make another one if it turns into 'testing to destruction' so I'll do the testing on the boat.

    Of course, the crossbeam is only part of the issue and even if you get that perfect it'll still be let down if the hulls are too flexible. I've got some ideas on that score that time may reveal.

    Ray

  9. #9
    Join Date
    Sep 2008
    Location
    United Kingdom
    Posts
    187

    Default Re: 2 metre catamaran build

    The plug is progressing well. I've finished shaping and have applied a couple of coats of finishing epoxy, applied with a foam roller, and I'll start waxing as soon as that has cured. The epoxy really shows the lines from the plywood that I used for the plug and that are so useful for checking fairness and symmetry.

    I've also laid up an experimental piece using Claudio's cotton fabric decorative technique. I'll update tomorrow when it has cured.

    Ray
    Attached Thumbnails Attached Thumbnails Click image for larger version

Name:	2009_0623catamaran0001.JPG‎
Views:	229
Size:	1.46 MB
ID:	3405   Click image for larger version

Name:	2009_0623catamaran0003.JPG‎
Views:	274
Size:	1.50 MB
ID:	3406  

  10. #10
    Join Date
    Sep 2008
    Location
    United Kingdom
    Posts
    187

    Default Re: 2 metre catamaran build

    Incidentally, on the half of the plug for the bottom of the hull you might notice two black marks on the centreline, one near the stern and one about midships. These are in fact holes through the plug; when building the plug I glued in tubes at the locations of the fin and rudder and again the lines in the plywood are excellent for checking alignment. When I mould over the plug the holes will be plugged with some dowel and plasticene but after moulding the plugs will be removed and, whilst the moulding is still on the plug, the tubes in the plug will be used as a jig for drilling and aligning the rudder and fin mounting tubes. I have used the same approach on the top of the plug for locating the mountings for the crossbeam mounting bolts. I find this approach easier than trying to locate and align the tubes on a finished moulding that may not have any simple reference points.

    Ray

+ Reply to Thread

Similar Threads

  1. Build Log first sailboat build - footy Razor
    By jusval in forum General Discussion (Footy)
    Replies: 63
    Last Post: 03-13-2010, 08:40 PM
  2. 2 metre Catamaran
    By nautibuoy in forum General Discussion
    Replies: 2
    Last Post: 02-11-2009, 02:59 PM
  3. Wanted Pop-Up Mfg Catamaran
    By dedwards in forum Classifieds
    Replies: 4
    Last Post: 06-21-2008, 12:21 PM
  4. Catamaran
    By Shaun RSA in forum General Discussions (MultiHull/MultiOne)
    Replies: 13
    Last Post: 07-12-2007, 11:05 AM
  5. Ian's New Catamaran
    By Dick Lemke in forum General Discussions (MultiHull/MultiOne)
    Replies: 5
    Last Post: 01-06-2005, 10:21 PM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts