Boxy Fisher Catamaran idea

Just lock the outboard straight, and steer with the rudders. Think inboard motor. The only time I find it usefull to steer with the motor is when you are going slowly and there is no flow over the rudder.

 

Model Taking Shape

Started on the model as you can see. Scale roughly 1:10, so the model is around 800mm long.

The hull shapes may still change, the bottom centre part of it will be flat so you can walk on the hull - save material, weight and head room as well as a lot of work putting a floor in.

The Boxy Cat's dimentions also changed from 8m x 5m to 8m x 6m. The cabin's dimentions has also changed some.

 

Fanie
I appreciate your taking the effort to keep us posted. The shapes look good.

You will be able to get much smarter around the transition from the hulls to bridge once you can see and feel in 3D.

One engineering aspect to keep in mind is that torsional rigidity is a function of the enclosed area of a beam. So you can get really good stiffness if you keep as much of the hull continuous as possible. A hole will have stress raisers around the edges so these areas need strengthening. Likewise with the bridge. Large enclosed sections are the best way of transmitting torsional loads.

An observation of a mechanical designer comes to mind. He pointed out that airplanes have these wonderfully strong tubular fuselages and then they go and cut holes for windows in them!

You should be able to load your model as a quartering sea would and observe the areas that flex and become highly stressed.

Rick W.

 

Hi Rick, the model is just in case we schrink and then at least I will have a boat

I'm working on that on the moment. Work is currently interfering with my boxy cat

 

That is my problem as well. I am giving a lot of thought to changing the ballance and making paid employment part time.

Rick W.

 

Good idea Rick, I didn't realise that until I was 55 Y.O. and then I fitted out a Colvic Watson hull and sailed around the Med. for 11 years. Give up regular work early if you have a skill you can sell to other sailors, I was electronics but yacht repair and deisel engines are just as good.

Cruising boats spend most of their time at anchor or tied up in Marinas so a boxy catamaran makes sense.

 

Finally the ones with good sense comes through

Rick, I've always said we fish 5 days and work two, nobody believed me

Doug, you have to admit, electronic guys can do a lot of things, eh !

Since we do fresh water lure fishing mostly, it may not be a bad idea to take boxy on some of these trips too. Be fun to check the other guys on their 'little' boats. If the wife gives you grief at home, you can just stay on the boat.

 

Hey Fanie

One quick question.

Why do you want to design and build this boat yourself?

I do believe you can do it but it will take years and cost a bit. I just want to make sure that you are not doing this to save money. If that is the case, I have some alternatives which will be cheaper and quicker.

Regards

Craig

 

Hello Craig, I always have an ear for new ideas. You've got my e-mail adress so let me hear your suggestions.

I like designing things - have done a couple of other things and it's what I do to try and stay alive...

The reason for doing it the way I do (on the moment) is to soften the wife up, get her to get used to the idea. She's unfortunately not a very positive person and the sky is going to fall on our heads, although every project I do she's the one bragging about it. I've built my boat, a cobra and built my workshop - it's been the same every time, it's just a matter of stepping through (sigh) the routine.

Anyway, the hull models. If every thing goes well a friend will help me epoxy them tomorrow night. As you can see there's some inconsistant lines on the sides caused by the tape, who knows, these may turn out to create some unexpected advantages in turbulences, which may result in a new hull design trend

 

Will send email

 

Single stand alone mast, three piece 15m, sailing area 35m2 for the Boxy Fisher. Boom 2m off the deck to clear heads, Not for racing, more like an exploration sail for simple cruising.

Please comment, I need your views on this. Mast too tall ? Sail area too small / big ?

 

Read everything at http://www.runningtideyachts.com/motorsailing/ if you haven't already.

Have you seen this? http://www.omerwingsail.com/

Pericles

 

Hello Pericles,

I've read those articles a couple of times, must admit I like the way the man thinks. I still like the aft mast configuration, I might go for it instead of the traditional mast and boom. Since I have no sailing experience and attract very little attention here to form an idea of requirements, one advantage of the aft mast setup would be you can run as big a sail as you require, I guess depends on conditions.

 

Pericles

That motorsailing article is very interesting.

Would anyone here like to comment on how motoring at 15kts would influence the apparent wind direction?

I have no experience motorsailing, but I would expect that in a number of windspeend and direction combinations, the sails would be unusable because the apparent wind would be so far forward. When would this occur?

 

tuks,

The subject of "apparent wind", in which as the vessel sails into the wind, the wind direction appears to shift forward. Ice yachts are the extreme xample of this because the ice is almost frictionless, so the runners slid effortlessly and the craft can in some cases exceed true wind speed by 20 mph with the sail sheeted in almost rigid.

If a motorsailer is headed up wind, using the engine to drive the vessel will increase the effectiveness of the sails. It seems bizarre, but the combination of both forms of propulsion saves fuel, rather than using the engine alone to achieve the 15 knots you mentioned http://en.wikipedia.org/wiki/Apparent_wind

Fanie,

Ask Brian for advice. He's a generous soul.

Pericles