High Efficency Crusier, Trike or Tri?

[Zenehet]

Hey Guys,

I wanted to get some comments on a efficient power cruiser I am working on.
Specifically some thoughts on hull design, for speed and stability.

Which is better in a narrow package?
Trike or Tri?

My objective is to reach a cruising speed of 10-15 mph with as little power requirement as possible (displacement hull) while still pushing around a boat that is 30-35 feet long, (sleeps 4). I expect the boat to be 2000-3000 lbs depending how I construct it.

beginning specs:
10 mph
2500 lbs
35 feet long
8.5 feet wide (must be trailered)
?? hp (possibly small outboard or electric combo)

To reach this goal I had thought to build a trimaran. I have built a trailerable 27 foot cruising catamaran and it can achieve around 6 mph with a 4 horse engine, but a catamaran wont work for this project because I want more headroom than a low windage catamaran design can allow.

Now in making a trimaran within 8.5 feet width (with no expandable arms)which configuration will work best. A slender trimaran, 1-2 foot wide hull that is 34 feet long, flanked with only 2 feet separation by 1.5-2 foot amas. OR a Trike. That being a trimaran where a shorter forward hull is forward of the two rear amas.

I generally favor long slender hulls, so my multihulls can easily exceed hull speed without high power. But I have never built a tri and my concern was that in a standard trimaran with such small hull separation would have wave turbulence that may hinder its performance. Perhaps that is a small thing and not worth worrying about at the speeds I am targeting. But if it is a big thing I thought that putting the main hull ahead of the other two could allow a greater separation of the rear amas and reduce wave turbulence. I also wondered if just having the two hulls in the rear and widspread would give me better stability at rest than the standard trimaran layout.

What do you think, which in this 8 foot width requirement would be more efficient and stable? Trike or Tri? Or are there other considerations I should keep in mind? I have attached a rough sketch to help layout what I am considering. Also below is a link to my trailerable catamaran as reference to what I have built previously.

http://www.elementalexpeditions.com/...oteusspec.html


Thanks

[daiquiri]

Leo Lazauskas, a distinguished member of this site, has allready investigated this issue with the use of Michlet software (of which he is the author).
The results of that work can be found here:
http://www.cyberiad.net/library/mult...ep/results.htm
I'm sure that he is the most indicated person to help you in this task. You can contact him through this site or at leo@cyberiad.net .

[Guest625101138]

This thread may interest you:
Boxy, simple ~8 m electric powercat

Rick W

[alan white]

Have you investigated some narrow Bolger sharpie designs? Or Storer designs, such as this: http://www.storerboatplans.com/TC35/TC35.html
You might find that a monohull will be far cheaper to build per cubic foot of interior, and potentially lighter too. Sharpie type hulls that are long and narrow (and light) don't use much power to get up to 10 mph.
Higher speeds can be reached with twin 10 hp thruster outboards.

[Boston]

you guys are a gold mine
thanks for all the good reading
B

[Zenehet]

Hi All,

Thanks for the links and threads. They were a lot of good reading.

Obviously like many boats they must be built to many variables at once. Case in point I can not expand the width of the tri to the infinite maxium indicated in Leo's detailed work. All the same it does give me direction.

Rick, I enjoyed reading about the Faux Tri as well. It gives me a lot to think about. Like I said this would be my first tri ever, I have only owned and sailed catamarans since I was a kid.

I am going to get back to designing and will let you know if I come up with anything else.

Thanks guys

[messabout]

Alan White is telling it like it is. To achieve your stated requirements, use one of the skinny Bolger style skiffs. Cheaper, faster build, structurally superior pound for pound to anything with akas.

[Guest625101138]

Originally Posted by messabout

Alan White is telling it like it is. To achieve your stated requirements, use one of the skinny Bolger style skiffs. Cheaper, faster build, structurally superior pound for pound to anything with akas.

You cannot say this about the Faux_tri that I provided linked to and Zenehet commented on.

Rick

[messabout]

Rick; I presume that you are challenging my remark about structural rigidity. Faux-Tri does not appear to have skinny and/or complex beams sticking out from the center hull and terminating at the amas. I retract my statement about rigidity in deference to your design. I'll stand by the cheap and easy arguments. If beams, in the common interpretation of the word, are involved, I'd be obliged to hold to the original claim.

The Faux-Tri may, or may not, move with somewhat less propulsive effort than a sharpie type of the same length. Relative power absorption would make the subject of a different and perhaps stimulating discourse. Perhaps an educational one.

[Guest625101138]

Actually I was thinking more about the power requirement. Less than 1kW to do 8kts is reasonable I would have thought. It will be higher with a heavier boat but being longer it will not be much above hull speed with 10mph at 35ft long. As regards stiffness, an enclodes box is hard to beat for stiffness.

Rick W