Multi-hull boat design

[fishingdan]

I was at a boat show recently and had the chance to climb around on a big Glacier Bay power cat. It was one of their 34' models. The boat had a 13'+ beam with a nice pilot house.

I found the accomodations very interesting. The boat had two staterooms (I think that is the right term) built into the port and starboard sponsons. The port stateroom was the main stateroom. The starboard stateroom was the secondary stateroom. Entry to either stateroom was via stairs from the pilot house. Each stateroom runs from approximately mid-ship to the bow.

As you enter the main stateroom from the pilot house, you enter the galley. Turn to the right and you will find the head built into the bow of the sponson. Just before you reach the head, one turn to the right and climb up into a queen size bed that is in the cabin area just in front of the pilot house. There is sitting headroom in that area and an entertainment system.

As you enter the secondary stateroom from the pilot house, you enter a small area that has a desk and some overhead cabinets (almost like a small office). As you turn to the left and walk toward the bow, you find 3 stacked berths stuffed into the bow of the starboard sponson. Similar to some sailboats that I have been in, you enter the berth from the head end feet first.

I thought it was a very interesting use of space. Not something I like, but fun to see.

[kiwi]

[quote=fishingdan] ... As you turn to the left and walk toward the bow, you find 3 stacked berths stuffed into the bow of the starboard sponson. Similar to some sailboats that I have been in, you enter the berth from the head end feet first.

I thought it was a very interesting use of space. Not something I like, but fun to see. [/quote]

3! Two I can understand but 3 must be like sleeping in a coffin...

Tony

[NorthWoods]

Walter,

Excellent links. I like the one Tony pointed out as well as the morellimelvin designs for general work boats.

Some of these seem to be much better looking than the ones I've found in my searches. It seems like some companies are more serious than others about finding a nice styling for the class.

Still, if you compare the hulls and power requirements, etc in the (what I would consider the amateur builder's range, and I'm no expert) 18-28' range, they seem to require more power and more construction costs than a monohull. So, I guess the question is where do you make that up in the cat design? In other words, where is the hidden value in the design that makes it prefereable over the monohull to the amateur builder/user?

Or if it is apples and oranges, how do you convert an apple lover to an orange lover without them ever tasting a sample?

On the subject of top-side designs, what about an open design contest for cat designs and invite the auto designing set to participate? I bet Pininfarina could come up with some interesting stuff. :D

[kiwi]

You're on :!:

Going to work out the details. Prize is going to be hard - going to need a serious sponsor behind this.

I think "design a power catamaran for amateur construction between 18' and 22' long" and leave all other criteria to the designer might be OK. Open in two categories: amateur or professional designer. Road transportable could be another sub class.

Guys :?:

Tony

[Toni_V]

Hey, that sounds fun. Who would be the judge?

Maybe there would be a need for more limitations? Atleast I would feel it quite difficult to judge seaworthy open planing cat with no accommodations against houseboat-style version for lakes. I would also make some limitations for building methods, making all round and such can produce nice lines but impossible to build by home builder.

However, leaving everything "open" might cause more interesting designs to surface.

[kiwi]

Us.

And yes I want to leave it open but it has to be buildable in a "home" workshop with easy to find materials.

Tony

[NorthWoods]

I like fewer restrictions my self. I do think it is important to explain that we're looking for something that would open up or connect the world of multihulls to the world of the modern amateur builder.

[Walter]

Here is my Catamaran Dream or some might call it a halucination. LOL

If we could just get the basic CC hull desiged, something close to this:

http://www.morrellimelvin.com/mm20.html

Mabe with a compromise hull, say Semi-Displacement. This creation would cut the design cost to a minimum. Depending on acceptance additional development of the basic hull could go forward adding the Cuddy, Pilot House. etc.

If possible the basic Catamaran could be offered with the option of Planing, Displacement or Semi-Displacement Hulls. Depending on the builders desires.

This minimilist approach IMHO is a good launching point for the furture of DIY Catamarans.

Would I Buy the plans? Oh ya!!

Lets get to the WHY of my obsession. ..... Comfort, Sea-Keeping, Fuel Efficiency. As stated in my original post on Bateau, I no longer desire to have my internal organs rearranged and my spinal disc compressed any further. The ride of a well designed Cat will spoil you. I no longer need to go 45 mph, 20-25 mph will do just fine.

Efficiency:
http://www.2hulls.com/archive/Gen%20Article/powerplaning.html

Catamaran Problems (this is painful).

Negative lean in turns: This can be eliminated by the hull design but I do not know what effect this has on overall performance.

Reduced Displacement: Less hull in the water naturally means less potential displacement..

Reduced Deck Space: Some designs pull the forward deck back with the 2 hulls protruding forward. This is done to miminize the effects of possible "Stuffing" caused by the reduced displacement if the front section of the boat.



Twin motors: More initial $$$$$.

They Look Different: Don't worry about this one, the looks will grow on you. They are just "different".

Mabe others more educated in this field can come up with additional down side . But at this point I would be willing to tolerate the negatives to enjoy the positives.

This is a great site for amature boat building, I know little about boat design and appreciate all who post here and at Bateau. As a rookie I have learned a lot.

Walt

[kiwi]

[quote=Walter]
If possible the basic Catamaran could be offered with the option of Planing, Displacement or Semi-Displacement Hulls. Depending on the builders desires.[/quote]

Tennant says that displacement hulls are useless under 30' because hull speed is too low. His smaller cats are planing hulls based on sailing cat hull shape.

The stock plans for the Morelli & Melvin designs are for foam core. Maybe using Farriers vertical strip in female mold method is the way forward? Using these plans and Farriers method an amateur should be able to produce a decent hull.

Tony

[Toni_V]

[quote=Walter]Here is my Catamaran Dream or some might call it a halucination. LOL

If we could just get the basic CC hull desiged, something close to this:

http://www.morrellimelvin.com/mm20.html[/quote]

Do you have any experience how this boat will handle chop? The flat part between hulls look very low (Like in the GlenL -design);
INSERT INTO phpbb_posts (old_post_id, topic_id, forum_id, poster_id, post_time, poster_ip, post_username, post_subject, post_text, enable_bbcode, enable_smilies, enable_sig) VALUES and it will surely hit the waves. The "tunnel" is quite high in bow, so the flat -part has low angle - that must help.

So, would a cat like this really be better in chop that usual monohull?

[quote]If possible the basic Catamaran could be offered with the option of Planing, Displacement or Semi-Displacement Hulls. Depending on the builders desires.[/quote]

But will the compromise be too big? It might be bad in all these.

[quote]Efficiency: [/quote]

Efficiency is all about hull shapes. A catamaran will be less efficient if the monohull is scaled to half width and two of these hulls would make a boat. Those figures look a bit marketing values, but they might be true. Just remember they are for 46 footer cat. As said before the cat's will be nice when they get big.

[quote]Negative lean in turns:[/quote]

Why would this be a problem?

[quote]Reduced Displacement:[/quote]

Actually the displacement will not be reduced so much, the cat's just have bigger draft.

[quote]Twin motors: More initial $$$$$. [/quote]

And two motors will be less efficient, require twice maintenance, maybe two gas tanks, two for many things.

But the biggest problem I see with small cat is how to make them efficient and practical. Another thing is to keep the cost and bulding time reasonable.


About the contest;

While it's fun to judge the designs, I must say I can't see how the boat will behave from the hull shape.

Like Jacques thinks about hull shape here;
http://www.amateurboatbuilding.com/articles/design/vdesign/vdesign6.html

So, maybe could we get someone professional to give their input too. i mean I would not build a boat without a pro saying it's ok.