Catamaran tender to replace rib?

Does anyone have any suggestions for a DIY small catamaran dinghy design to replace a rib? The emphasis is on very light weight and stability. My current 10' wood floor Achilles weighs in at around 35kg.

My idea was to have a small electric outboard for going to shore and back 95% of the time, and it would then be able to take a tohatsu 8-9.8hp 2 stroke for fast long range performance when used for exploration etc.

 

You might like to check out Craig Schionning's ripple range of tenders. The core choice dictates which models would meet your weight target:

http://www.spiriteddesigns.com.au/ripple_tenders1

 

http://www.duckworksbbs.com/plans/gumprecht/cat12/index.htm

 

This looks pretty awesome. But at $3.5K for the kit it seems a bit expensive.

 

That is also pretty cool. I guess it would be a a fraction of the cost of the Schoinning.

 

Hi Dennis, Have you considered a nester? I am building Dave Gerrs version and so far has been simple and cheap. Though not a catamaran would be easier to build. I am keeping mine whole for the time being to save weight. Also I skinnied down a bit on the bulkheads and used two inch foam sandwich for the seats. she,s pretty light, though I haven't finished and weighed her yet

http://www.boatdesign.net/forums/boat-building/kurt-hughes-daycharter-36-a-31846-22.html#post690593

There are plenty of other photos around if you google Dave Gerrs nester

 

Zap cat tender

from over on another forum....

Now I remember what it was called ....a Zap Cat
Images

https://www.youtube.com/watch?v=Dazy3BpV_Cs

https://www.youtube.com/watch?v=qKBtUf3hw7Q

...or how about this Takacat

http://takacat.com/3.html

 

Why pay for a design for such a small boat? Why not just DIY it and bend up some foam sheet material and glass it? Add some rub rails around it to prevent damage to the mother ship and voila? And you get the satisfaction of creating it entirely yourself...

 

Check out Livingston. Don't know if they are made anymore but they are a good tender - rowing or outboard

 

A small, light catamaran is not a suitable choice for a tender, imo. The inflatable would be as good as anything. And thinking you can motor around exploring at some kind of speed with a 10hp outboard in a weigh-nothing little cat, you will just have a flighty menace with it's nose pointing to the sky.

 

I would agree, if you want a tender to carry a load then don't use a catamaran. It won't have the load carrying, nor the storage space in the hulls. You are better off with a barge for a yacht tender. However if you want to go fast then it would make more sense. Even then you won't necessarily be lighter

I have just built a 10ft row/sail/motor dinghy using 2 sheets of 4mm ply, so it weighs 22kgs including the d'box, mast step. outboard bracket etc. As a plain rowboat it is lighter still

My 8ft Crayfish dinghy can safely carry three people plus their gear, and is made from 2 1/2sheets of 4mm ply (I actually built a light one once from 2.5mm ply)

In comparison a 14ft catamaran uses 6 sheets of ply yet sensibly only carries 2 people when motoring

The Livingston dinghy is very heavy. I always say the best tender is an aluminium rib with the tubes filled with helium

Richard Woods of Woods Designs

www.sailingcatamarans.com

 

Lets see, I didn't see the OP asking to carry BIG loads

So I think the cat form can certainly give him the stability that many tender owners find important. Even that little Zap cat can give good stability.


Now imagine the 'floor/hull' of the tender is nothing more than a flat plate,...pretty easy to fabricate from say a flat panel of nidacore with a suitable skin on either side.

Then why put somewhat complicated and expensive 'inflatable tubes' at either side?? Why not solid foam tubes similar to the foam collar material utilized on the 'SAFE boats'?

Then couldn't those foam tubes be provided with milled channels that would slide over the special configured ends of the flat panel floor board. Designed properly you might not even have to glue the foam tubes on, but rather secure them in place with 'commercial grade velcro' (interlocking mushrooms).

The size and cross-section of the foam tubes would determine buoyancy ...and load carrying.

If light enough, and inexpensive enough, you might even want to carry 2 such tenders

 

It gets down to whether you want something you have a level or near-level footing in, if you do, a tiny cat is a dud.

 

Key is where is the tunnel roof in relation to the water, if there is quite a bit of clearance, you will have a little boat that is somewhat sensitive to fore and aft weight shifts, if it is kissing the water, or lower, you have a boat that will slap like all heck. You can't win, so don't bother !

 

How about an outrigger?
Gary Dierking -http://homepages.paradise.net.nz/garyd
Or a design yourself - like Glenn Tiemans in the pic.