Non-foiling trimarans and catamarans - Page 2 - RC Groups
Thread Tools
Nov 17, 2015, 09:50 AM
Registered User
Dick L.'s Avatar
Thanks Doug - still undecided about final bow profile shape - but that isn't related to the build or a performance issue. Bandsaw, some sandpaper and I can radius it at any time.

Also, after posting I took jib down to put away and had thoughts of rigging it like an A Class cat. I just will stay a lot wider than the "real" A cat beam dimensions, so I don't have to fool with moving weights, in place a of a single crew/skipper. Saw some old theory drawings where weigh was suspended out in front of mast but controlled/connected to the main boom. As boom swings out to leeward, the weight in front of mast is moved to windward to counteract. Not sure if it will work or if I will try, but concept was different than what I've seen so far. As I recall, it was in an old issue of Popular Mechanics (1930s - 1940's) add in that it would be in front of cross beam, and not sure I would like it if sailing downwind with possibility of a capsize.

Any thoughts on cross beams? Easy, and round tubes - or shaped and curved raised cross beams?
Sign up now
to remove ads between posts
Nov 17, 2015, 10:10 AM
Registered User
DLord's Avatar
Depends on how much time you have to spend. I've always used round tubes because their strength to weight is so great but curved aero shaped cross arms sure look good. But you can put aerodynamic refinements on round tubes if you want to spend the time-wouldn't add much weight.
You shouldn't so easily dismiss movable ballast -its a hell of a lot of fun to sail with though the winches aren't cheap. Once you try it you'll be surprised how much fun it is.
Nov 19, 2015, 05:06 PM
Registered User
geh458's Avatar

Build Issue


Afternoon, I'm in the process of building a trimaran from RCSails.com, the Firedragon. I'm at the point that I'm ready to glue the hulls and decks together, but I'm not sure how to proceed and could use some suggestions as what procedure will work best, and whether to use CA or Epoxy. If you've got pictures or video's of such a task, that would be great.

Thanks in advance for any help that you can provide.

Gifford
Nov 19, 2015, 05:23 PM
Registered User
DLord's Avatar
I wouldn't use CA-it can be adversely affected by water-use epoxy. If I were you I'd consider building a jig out of balsa or whatever so you can set the hulls and crossarms up perfectly. Hope you have plans?! Make sure to sand the contact surfaces so the epoxy will stick.

This is the massive styrofoam jig I had cut out for my 5.4' long X 6.7' wide trimaran. I took the plan to an architectural styrofoam place and they cut it out quickly and inexpensively. You don't need something this big-just something that will hold the hulls and crossarms in proper position.



Last edited by DLord; Nov 19, 2015 at 05:43 PM.
Nov 24, 2015, 03:24 PM
Registered User
Dick L.'s Avatar
I managed to find a bit of time, and started the glue-up of the second hull. Only got the bulkheads in place and decided to lay the first hull with foam bottom next to the second hull. I then pulled out some old foam crossbeams originally cut to fit my trimaran, and just laid them in place. I think I will go with a plywood cross beam (plywood in vertical orientation) and then glue some foam on to shape and give it a bit of water shedding properties. Interesting in that a third hull (quickly made) could easily be slipped under the middle of these foam beams, and it might work fine as a trimaran.

Anyway, these beams are too wide for this cat, and tacking could become a nightmare. I will layout and cut a new set of beams with not quite so much arch coming off the hull. These beams are 46 inches wide, and I think I will make a new set keeping them to somewhere around 40 inches wide max. I will be giving up some platform stability but hope to reduce the tacking issues of a wide boat. Attached are two photos. One is the "Wide" version and the other a bit closer showing one hull and where a beam would be located.
Nov 30, 2015, 07:06 AM
Registered User
disabled's Avatar
I would suggest you use the proven stuff!

Also available as kits from www.rcsails.com

By the way - all trimaran floats can also be used as cat hulls.

Furthermore:
All these informations are for free use -
and I donīt get any money from rcsails - no business relation,.
Last edited by disabled; Nov 30, 2015 at 07:49 AM.
Nov 30, 2015, 11:14 AM
Registered User
Dick L.'s Avatar
Ernest - unfortunately there is a huge cost in shipping - especially items as large as 48 inches (1.2 meters). Also seems like after Siri left prices have gone up significantly. Finally, as noted in the introduction, I am putting this concept forward for anyone wanting to give multihull sailing a try - but at a significantly lower cost and building effort. The idea of shaping the curved portion of a lower hull could easily translate into other classes as well. Consider the waterline down shape for a Marblehead, 10R etc. Just make templates of waterline - to - waterline and place at appropriate distance, then hot wire rough cut followed up by shaping, and coating with epoxy. A very simple way to build a hull and decide if the end result (probably for local club racing) is adequate. Not too many traveling with large boats by air to regatta formats.
Dec 21, 2015, 10:54 AM
Registered User
Dick L.'s Avatar
Thought I would post the following video related to r/c Multihull racing. This one from France.
Enjoy - and note the boat speed after all the lead (keels) are removed.

breizh multi race 2015 (3 min 35 sec)
Dec 21, 2015, 05:35 PM
Registered User
Dick L.'s Avatar
Managed to find a bit of time between granddaughter's birthday and holidays and managed to get the second hull of the '"Economaran" fabricated and foam added to bottom of second hull, Still need to fine shape hull #1 and do the rough shaping of hull #2. I did go through and lay out locations for mast stays and shrouds. Still have daggerboard trunks to build and locate.
Dec 26, 2015, 03:51 PM
Registered User
glouis's Avatar
Really like the concept Dick and can't wait to see the progress. BTW I know how you feel. Started the restoration of A class sweet9 few months back and while progress was good in the late summer it has hardly progressed since.

The other thing is the reverse bow. I get the idea on full size tri and the effect is quite visible in video but do they give the same advantage in RC scale? besides the modern look?
btw it is a genuine question not a criticism - just in case-
Dec 27, 2015, 11:27 AM
Registered User
disabled's Avatar
Quote:
Originally Posted by glouis
Really like the concept Dick and can't wait to see the progress. BTW I know how you feel. Started the restoration of A class sweet9 few months back and while progress was good in the late summer it has hardly progressed since.

The other thing is the reverse bow. I get the idea on full size tri and the effect is quite visible in video but do they give the same advantage in RC scale? besides the modern look?
btw it is a genuine question not a criticism - just in case-
Hi glouis,
reverse bow in rc scale:
Have a look here:
MOD40 at Flevo Cup 2015 (3 min 8 sec)

It definitely works!
Dec 27, 2015, 04:53 PM
Registered User
Dick L.'s Avatar
@ Glouis -
At a risk of being considered a "troll" - An interesting question was raised on the IOM Forum topic of design, with an unanswered question about what is next in design, since so many have moved to a "Skinny" design. I feel it is being answered by the multihull classes - big and small.

For how long did it take the M Class to recognize important performance changes as the M Class boats became more narrow? To this same thought, NACRA on their full size catamarans began to breach common thought when the INTER line of boats came to market. They had extremely narrow bows and one could easily see how well they sliced through waves. However at the same time, one could see the newer skippers/owners getting caught in irons trying to tack on windy days when all of the freeboard in the bows continued to be an issue. When the A Class boats changed to the reverse bows (rounded or simply raked) many found tacking easier as the tall bows were not there to fight the wind. Given many cat designs come from the drawing boards (computers ???) of the Melvin and Morelli firm, and seeing their change in design from the Inter series, through the Infusion series to the bows of their current designs - including the AC boats, I (personal opinion) feel they must have found a performance breakthrough that has increased early planing of the hulls, the ability to foil, and if they do drop a bow into the water, less chance of the dreaded "pitchpole".

I often wonder if (with a few minor rule changes) a very thin IOM based on a single catamaran hull, but using a shroudless mast, wouldn't prove competitive. If multihulls are fast, why consider staying with a wide bow and deck - considering the need to part the water - both when going forward and when emerging from beneath a wave?

As to the question of scale - if one considers the scale of true waves (as in the video above) I subscribe that any reduction in "pounding over waves with subsequent "hobbyhorsing" results in greater linear performance by going through the waves and keeping airflow attached to the sail and supporting the ongoing drive of the sails.

Not an engineering answer - only a personal feeling after some observations.

Cheers.
Last edited by Dick L.; Dec 27, 2015 at 04:55 PM. Reason: spelling
Dec 28, 2015, 09:46 AM
Registered User
Dick-it is an interesting thought experiment but you are forgetting that the IOM has a minimum weight, maximum depth and a one design sail plan. Narrow boats were around for a long time, the problem was getting a hull shape that could handle the rig and weight and not become overly tender or unable to tack. The trick to the current crop of fast IOMs is the overall hull form not simply the width.
Dec 28, 2015, 12:45 PM
Registered User
Dick L.'s Avatar
Tom - could be - but of your three important parts to the IOM "Rule" the minimum weight and the sail plan are not factors in my mind. I would consider the maximum depth as the major factor, and it "might" be the limiting factor, although, since it is impossible to even find someone's IOM to sail against, there is a lot of design room left open for experimentation. Can't discard discussion of theory unless there is experimentation to support or reject design ideas.
Unfortunately, with the current rules today, neither the IOM or the "M" Class has much appeal to me - except for "day sailing" with friends and having a boat to loan out. Too bad that AMYA doesn't support and promote an OOAK type of regatta (One Of A Kind) and see what "things" might emerge from a basement or garage. Possible the next big breakthrough in performance is just out there waiting to be unleashed and to be seen.

Dec 28, 2015, 07:23 PM
Registered User
glouis's Avatar
thank you Ernst and Dick for your response. I didn't think these reverse bow would make that much difference for our scale even in 2m.

it seems it does but would like to see that mini40 sailing in windier conditions.

I see your point Dick. For me the IOM is purely for racing with others and it is convenient in size. the competition is quite close and demands the right tuning now that other boat designers have closed the gap with the BP. I personally race a Goth XP designed by Frank Russell. I like his lines though I struggle with speed but tend to outpoint pretty much anyone so I'm working on this as it is not ideal.

I got into the A class which is fun to sail but at a completely different level as from the IOM in that their sheer mass and size requires to sail them more like full size ones.

But my love for multis is still there - so much can be done and while the competition is restricted to some countries the designs and building is not.


Thread Tools