Trimaran Design using a Hobie as a donor boat

After looking at the tremilino I was thinking the best way to go for my first
trimaran project would be to use a hobie 18 as a donor boat for the amas and rig. The center hull could be based on the F22 design. I was thinking of a hard chine ply construction for the first one.

So, would a tri perform better if the cockpit was in center?

 

Tri

See my last post under trimaran design. For what it's worth in your considerations I just bought a 19.5' Hobie Miracle hull and it's all up weight was 99 pounds and it is symetrical.Total estimated hull volume(displ.) would be in the vicinity of 2100lb.'s +. It would be a good ama depending on the weight of your proposed boat. I think that if you're NOT going to consider foils for lift like on the Exploder , Catri and ORMA tris you should tend toward an ama close to the same length as your main hull.

 

Thanks Doug,

The exploder is a hot boat. I would consider lifting foils like a catry; I have sailed on a catry 27 and I loved the ride! I was just trying to keep my first home build as simple as possible. I still have to mull over all of the multihull design calculations in order to get an understanding for these things... Is there any formula or calc threads I should look up. Are there any books that would help me as well?

thanks again,

Raps

 

tri's

R, there are lots of books: google "Trimaran Sailboat Design Books". Also, do exhaustive research on other designers boats-there are nuggets all over the various forums. For instance, what Henrik first said about the CB of the ama vs the CG of the boat when the main hull flies is important especially when considering a non foil boat. You can tell by just a cursory look that there are many design philosophies particularly where length/beam ratio of the ama's and main hull are concerned as well as the overall beam vs the length of the boat.Power to carry sail(and where to put it), canting masts, rudder t-foils,ama volume with and without foil assist,ama length, staggered hulls etc. are all subjects important to and sometimes controversial in the design of high performance trimarans. It has always astonished me that, to my knowledge, no one has yet designed and built a powered up small(around 20') tri( beach cat killer) that takes full advantage of the power tri's have. The closest I've yet seen in a small boat is the Expoder and I just found that the other day. To do a modern state of the art powered up high performance all out racing tri you MUST consider at least foil assist-in my opinion.Another major design area for high performance tri's is the consideration of planing ama's similar to hulls on Parliers cat-if you can solve the low speed drag problem.
In addition to reading and extensive research you'd do well to compile all the statisics you can on the various existing trimaran designs in your size range and work out all the comparitive ratios you can like SA/D, Bruce number etc. If you do all this you will, at least, be able to narrow down a set of specs that gives you a performance/comfort level close to what you want. This assumes you have some basic knowledge of sailboat design.
Keep in mind that the higher the performance level you decide to try to achieve the more you may need the help of a professional naval architect/marine engineer.
Good luck and keep us posted!

 

Good advice! I have already contacted a multi hull designer on this forum, but i haven't heard from him yet. good idea about the spreadsheet... I'll get started. I'm hoping to start building in the fall, so i have some time.

 

tri

R, one last thing: try to make sure that if you are going for a high performance tri your designer is also a marine engineer or works closely with one-do NOT underestimate the importance of this...

 

Tri From Cat Design Process

There are a whole bunch of things to consider in a design of this style, Raps. Put some time into the consideration process of how you'd like to sail the boat once completed.

If the donor boat has daggerboards in the hulls, then what system of lifting and deploying will be used while sailing? Who will be the designated tramp monkey who will scuttle across from the windward to lee side of the boat to raise and/or lower the boards while they are loaded? Will they be agile and strong enough to perform the job while the boat is being tacked or gybed?

Should you be rounding-up a set of hulls from a Tornado or Prindle 19-6 instead, so that you may enjoy the benefit and ease of use presented by the centerboards in those types of hulls? Perhaps the whole centerboard thing is also a big pain and hulls with integrated fin keels, such as those on the Nacra 570 would be even more appropriate for your needs?

It's not as simple as punching in a bunch of performance items and calling it good.

Because the boat is being pulled together from a couple of sources, the integration of the parts needs to be done with a degree of methodical thought in order to get the most from the various parts acting as a whole.

I'd really suggest that you lean towards the more easily doable and less high performance side of the equation for a first project. This will allow you to get a good handle on what is going on both in the building shop and out on the water. Later, you can take what you have learned and apply that knowledge to something a bit more "expressive".

This is my .02 after having built several of these boat types and having another in the shop right now. These boats can be really fun, quite fast and built from easily obtained, affordable sources without hanging it out there at the thin edge of what "may" be possible with tricked-out foils.

A 22-23' main hull would be very nicely sized with a good margin of sailing safety when paired with a set of 20 beach cat hulls if they are positioned correctly in relation to the hull you will need to build. This general relationship will give you very good performance, an amazing degree of utility and it will be easy to fabricate with modest boatbuilding skills.

You could pick-up a very nice, used beach cat in this size range for anywhere from $3-5,000 with rig, sailing hardware and trailer and be half way to your trimaran.

The images attached show the Russ Brown/Paul Bieker Trinado that was engineered by Bieker and built by Brown. Russ is a son of multihull icon, Jim Brown and Paul is a very highly regarded N.A. out of Seattle. The main hull is 24' LOA and is paired with Tornado hulls. All reports I have seen say the boat was fast, has a strip built hull below the waterline with plywood sides and a foam/Kevlar aft deck. Total boat weight was 1100 lbs. When you have a boat that quick and that light with clean hulls, you don't need the extra business involved with canting foils and all the loads they would push through the very simple beams.

If you won't likely be trying to set any records... Keep it simple, have a blast and don't make it more work than it needs to be.

Chris

 

Thanks for the response Chris and Doug. My dream boat is something like an F32. But for budget reasons that will not happen for a bit. I'll race my laser 28 and teach my wife to sail on the trimaran. I want to camp over the weekends and have a good time with the boat. The tremillio looks a bit small, but would probably work for my needs. I was just thinking about making a hull similar to the F22 center cockpit hull; but with simpler lines. I want to make it out of sewn ply.

The Laser 28 is a little much for my wife. She is disabled and she has a hard time moving around; she isn't in a wheelchair, she walks with a cane.
I was hoping I could cobble together a nice little trimaran that we can sail together easily and maybe weekend on. I'll race my Laser 28 until I can start racing my F32!

The goal here is an easy tri to handle in All respects..
self tacking and furling jib
furling screecher on a sprit
easy to fold
easy to set up
easy to trailer
A porta head for the wife
a double bunk
maybe a little tent for the cockpit

 

Tri Conversion In Progress

Hi Rap,

I've started a tri conversion using H20 hulls. Received today the 5.5 inch hole saw to cut four holes into a J24 (thread is on page 3). Although it won't be a speed machine, I'm confident that some added performace will result. Ama length is almost the same as the J waterline. Your on the right track with a very workable idea. If I do it again, I'll try to use a narrower main hull. Although the J hull is only about 6 feet wide on the water. Before long I'll post pics of the progress.

Delane

 

Wow! Are you removing the lead from the J hull?

 

Yes, the keel is removed all 934 lbs. The keel stub (last 8 inches) in in tact and glassed. I wanted to go flush, but felt it was better to leave the stub as is for design built hull integrety, and makes for a great place for the bilge pump. Still in a little bit of debate as to build on a skinny center fin or use the H20 daggers not purchaced yet at about $700 for the pair. I'm leaning towards the center hull fin for all around ease of use. The daggers boards got old enough when I had a Nacra 5.2, and I'm not looking for a beachable boat.

 

Let me know how that works out... good luck and happy sailing!

 

In a perfect world...

Hello

The goal here is an easy tri to handle in All respects..
self tacking and furling jib
furling screecher on a sprit
easy to fold
easy to set up
easy to trailer
A porta head for the wife
a double bunk
maybe a little tent for the cockpit

That is a steep brief for a small trimaran - but it could be done - all except perhaps the double berth...

SH.