Small trimaran / microcruiser

G'day all,

Well after much lurking have finally got to the point where I have something solid to show. Not much, but it's a start, and starting is half the drama, apparently.....

So, my rationale goes like this:
- decided on a multi rather than a mono (you all know why) and then decided on a tri with folding akas for trailing/low marina costs etc
- couldn't afford to build the boat I want (Farrier Command 10m)
- realised I couldn't afford my second choice (Scarab 18) without saving for a number of years
- so option C) is to 'mix and match and adapt'..... and Richard Woods 'Strike 16' with beach cat hulls got me thinking....

I already had an International 420 ex-racing dinghy. It being 14ft long (4.2m) I researched ama designs and quickly realised it would be quicker and cheaper to buy an old beach cat and use the hulls.

A Paper Tiger fitted the bill: reasonably plentiful, reasonably cheap, symmetrical hull design, fairly large volume floats, cheap to buy.

So the I420 forms the basis of the vaka, the PT hulls will be the amas.

Basic idea is to strip the deck off the I420, raise the sheer a cuppla hundred mm, then build a new deck/cockpit/saloon - sitting headroom only, so will be kinda like a tri-hull version of a Hartley 14 TS.

Done some basic 'rough' design sketches and measurements and a single large bunk will fit, with benches for sink, stove etc.

Beams I'm not certain about yet - may build them from ply/glass/epoxy, or may utilise the beams off the PT and modify them to what I want. Am also keen to make them folding, and have some ideas of my own for this....horizontal folding a la Quornings, but forward not backward fold, with beams folding into a socket for additional strength/resistance against main forces (ie not relying solely on the bolt/pivot)....

Plan is to get it on the water within 12 months and gunkhole the east coast of Oz. But no promises.... lol

And before those with leaden boots tramp all over me, I *know* a flat bottomed, wide-hulled ex-racing dinghy is not the *ideal* hull shape for the vaka; I know a 14' boat is not going to be comfortable sailing inshore or camping in for long periods; I know I still have a lot to learn......

So please be gentle, dear readers. I post this with some trepidation, mainly to encourage other lurkers, as much for my own personal gratification, but also to seek suggestions / solutions to any problems I may have along the way.

So if you are willing to contribute to my education in a *positive* manner, feel free to post and/or bookmark this thread.

 

Good stuff, It'll be interesting to see what you come up with. Its good to see old boats given a new life. Keep the updates coming.

Cheers,
Dave

 

Good luck with your project. At least your making a start, so you can work up in size.

Warwick

 

There have been many monohull conversions.
Just be sure to move the ama's out far enough for there to be some benefit, 8 ft overall is hardly worth all the effort.
Raise the ama's so there is little or nothing in the water at rest, to reduce the drag in light air.
The best reason for going trimaran is to increase sail area for more performance.
If you don't the increased weight and wetted surface will actually decrease performance most of the time.
Check diytri.com for a folding trimaran. innovative but the author does say they increase the weight of the boat, and I am not convinced they are very weight efficient as designed, but an interesting start.

You might also look at the Trika 540 from a German Designer, Metz (I believe). I personally would put the folding pivots further outboard so the akas will not fold into the cockpit.

There are multiple newer and older boats that fold like the Cross 18, but that will not let you fold on the water.

So long as you recognize the inherent limitations from using a wide dingy as a starting point you can have something that works, just not fast.

Good luck, and I want to see the progress also.

 

Buzzman - you are following exactly the same development concepts I used - see pictures on the recent "OK -Farrier" thread and on my post at http://www.boatdesign.net/forums/multihulls/hybrid-6-3-metre-cruising-trimaran-32810.html .

Contact me off-forum and we can compare notes

Alan

 

Another angle would be a fast towing luggage dink for beach cat sailors. Tow your camping stuff behind, make camp then blast around the area....

 

Now that's out of the box.
But it obviously should be a catamaran dink, to not slow you down.
Probably a tow bar from the center of the rear beam to allow it to turn and not slow you down on the tacks.

 

upcmr
Yeah, seen Dr Frank Smoots work...in fact his folding tri gave me the idea I'm going to experiment with, but reversed, so amas fold forwards.

Rationale is that sailing forwards, most force on amas (and akas) is rearwards (and upwards), so if the aka folds into a socket facing backwards this spreads the load and reduces stress on the pivot. That's the theory.

Will have to pivot outboard of the hull sheer, so amas tuck in underneath or beside the vaka hull, similar to the Trika 540, which I'd also seen.

The 420 is designed for 2 sailors, and cracks along when sailed flat (bodies leaning well out to counterbalance) so won't be 'too' bad as a flat sailing tri for one+plus extra baggage.....I hope.

Will probably extend the mast by half a metre or so, then if I needs a bigger main I can get one later when funds allow. Mast will need strengthening probably due to increased forces caused by less heeling/more resistance.

Stock 420 sail area is 140 ft2 / 13.01 m2. So may need a bit more.

'Nother option is a prodder and a gennie/headsail to overlap the fractional jib.....dunno if that will work.....

Forget the towed dinghy, unless you want it to whack you in the back of the head with every following sea......

Don't have the math smarts to do the necessary calcs, so it's all a bit 'rule of thumb'....might need to enlarge volume of amas, but PT has fairly big floats....

 

Richard Woods 15' tri folds fwd I believe, at least that was his plan before he released the design. Haven't looked in some time.

The 420 does move well, but will never compare to a catamaran, except possibly in extremely light air.
But I don't think you are looking to race, so that doesn't mean anything.

Sorry but I don't believe your comment about spreading the load at the pivot. The load at the pivot is the same in either case, the load at the inner end is also the same, but how you support it can be significantly different. If Frank ever breaks the line holding the unfolded crossarm in position you will have a perfect reason for reversing the folding!

 

Yes, seen Richards Strike 15...but had the idea *first*....

Nah. Not planning to race. Microcuiser. Still hope to do a bit better than hull speed. lol

 

I used to tow a canoe with my mono and in some conditions the canoe would surf faster....we sized a small drogue to use on the canoe in those conditions and it worked great. The "campcat" (non registered trademark) would be sized with a folding top to use as the tent as well as storage. With a folding wheel option to go from the beach onto the shore of course. The tow bar is probably the way to go. Then it all functions as one articulated boat.

 

Yeah, take your point...what I meant was the load on the stay....like you say, if Frank's rope breaks at speed or in a seaway it might be interesting to say the least, main reason I opted for forward folding.

I'm thinking rope to haul it into position, then a wire stay with perhaps Hyfield lever for ease of lcok-in and tension, from outer end of forward aka to hull abaft the rear aka.

I will want it to be able to fold away from the dock (or ramp) so it needs to be some reasonably quick release.

 

Buzzman, I have the same idea with an old 505 and Mosquito hulls for amas.
It won't be as fast as either of it's original donor boats, but that's not why I'd do it, like you.
The towable catamaran-type dinghy exists, look up Mark Gumpbrecht's designs, he has an 8fter and a 12fter.

Steve

 

Tri with beach cat amas

Dear Gentlemen,

I wish you the best of luck with your projects, but I think it would be better if you combine the beach cat with a mainhull that is designed for the use as a multihull. Even if it is drawn with a very simple (sharpie) hull form this will provoide much better sailing abilities than with the hull of a dinghy.

The work will be only a little more, because stabilising the this single layer grp skin of a dinghy hull (in the case of the 420) is a lot of manhours.

What the cost concerns it is the qustion what you have lying in your backyard. If you have to buy an 420 or a 505, the money invested would be the same as for a couple of plywood sheets and some gallons of epoxy. Or you sell the dinghy and buy materials for it.

Take a look at this project:

http://husky6.blogspot.com.au/2013/05/i-started-thinking-about-trimaran-in.html

Note the building time from zero to the present state ... after work building. Ok, this boat is meant as a cruiser racer without cabin, but small cruising boats could be designed accordingly.

Best Regards, Michel

 

Michel
I pointed out the 420 was already in the backyard - it isn't in saleable condition (broken mast) and is therefore cheap and available and a challenge.
Don't want to spend any money on it than I absolutely have to.
I know it will be better with a narrower hull...said so already.
It's not happening.
Next project...