Thoughts on Modifying A Cross 46

[Kalagan]

Hi All,

I am considering purchasing a Cross 46 Hull and adding a 52 foot long, two foot wide Torpedo to each of the outside AMAS. Is this a good idea? See the very basic images below.

To me it seems like a good way to take the displacement Tri to the next level. It seems like it would give it more stability, longer water line (hence faster), better tracking (because of the two 52 foot Keels), it would be able to be Beached if the center Keel is removed, the Torpedoes could be used for Fuel, Water and Water Ballast if you wanted to, it would get the boat a little higher out of the water, but the center Ama would still be in the water to help disperse the Weight evenly.

It may seem like a weird modification, but it seems like it solves some of the issues inherent in Displacement Tri's.

What are your thoughts?

Thanks
Kalagan

[basildog]

With all that extra float displacement whats going to happen when sailing to windward? I would expect you would have all 3 hulls in the water all of the time. It will be near impossible to tack if that is the case.

[Kalagan]

Hi, Thanks for the input.

It was my hope that the center hull would be in the water, but just the middle maybe 12 to 15 feet. Do you think that would limit the ability to turn that much?

Would that issue change at all, if the center rudder was removed and replaced by two large rudders on the back of each AMA?

Would it be better to increase the size of the added torpedoes from 2ft to 3ft width? that would effectively lift the center hull further out of the water?

Any other suggestions would be greatly appreciated!!

Thanks
Kalagan

[jamez]

Originally Posted by Kalagan

Hi All,

I am considering purchasing a Cross 46 Hull and adding a 52 foot long, two foot wide Torpedo to each of the outside AMAS. Is this a good idea? See the very basic images below.

To me it seems like a good way to take the displacement Tri to the next level. It seems like it would give it more stability, longer water line (hence faster), better tracking (because of the two 52 foot Keels), it would be able to be Beached if the center Keel is removed, the Torpedoes could be used for Fuel, Water and Water Ballast if you wanted to, it would get the boat a little higher out of the water, but the center Ama would still be in the water to help disperse the Weight evenly.

It may seem like a weird modification, but it seems like it solves some of the issues inherent in Displacement Tri's.

What are your thoughts?

Thanks
Kalagan

Wouldn't go there. Cross designs have a good rep as is. If you want faster floats talk to Kurt Hughes who did bigger upgraded floats for a Searunner 40 (among others).

[catsketcher]

Stop right now!

Seriously what you ate thinking of is really going to wreck the boat.

Cross cruising tris have high volume floats already so you don't need the volume. As for tracking ability - if the boat does not track well it would be better to - check the rudder and keel sections for fariness, make sure you are trimming the sails well and if all else fails - add a trimming daggerboard aft.

The boat doesn't need the extra float volume and you should never load up a float with water and fuel. Tri floats should be kept light.

You won't get a Cross 46 to become an ORMA 60 with bigger floats.

Read Jim Brown's bible - The case for the cruising trimaran - it has heaps about tri design.

cheers

Phil

[Kalagan]

Hi,

I understand not wanting to change a proven design and the Cross's definitely fall into that category, which is why I am looking for one.

But what I don't understand is,
1) Why is it a bad thing to distribute the displacement of a fairly heavy and relatively slow displacement Tri-hull (like a Cross 46) from the center hull to the Amas
2) Then give the boat a longer, very aqua dynamic water line, by adding a Torpedo shaped hull to the outer Amas
3) Enabling it to head to wind better, by giving it two 52ft Keels
4) remove the vibration effect that plaining Multi-hulls are known for
5) allowing it to be safely beached, by having two hulls that are the same depth
6) make it almost impossible to sink, because each the torpedo would be separated into multiple sealed compartments, so a breach of any one compartment would not compromise any adjoining compartments or the original Hull it is attached to
7) By using the separate compartments for fuel, water and/or water ballast, the pilot could easily shift weight from one side to the other to help the boat in heavier conditions

I understand peoples concern if this boat was starting off as a light and fast plaining Tri, but since it is starting off as a pretty heavy displacement Tri, it doesn't seem to me that a modification like the one suggested would really be a very big negative. As far as I can tell, the pro's vs. the con's seems to lean towards the pro's listed above.

Am I missing something basic? Where is the flaw in the basic concept, if you take the Cross name out of the equation. The Navy designed a very seaworthy Torpedo Cat that was their first Stealth boat, it is called the "Sea Shadow" and they are trying to give it away if anyone is interested.

But seriously, it seems like a very advantageous hull design, where am I going wrong?

Thanks
Kalagan

[catsketcher]

The first question is why? There is no real reason for doing this. Tris don't vibrate and if one ever did it is almost certainly due to the foils needing a fair. Getting the main hull out won't do much and you will increase the wetted surface so the boat will be much slower in light air. You will also ruin the ability to tack. These types of things have been done before. It is tautology to say "displacement tri" All tris are displacement shapes. You won't change this. Planing floats have been done, planing main hulls done but you don't see them now. They didn't really work.

At the risk of being mean I should also ask - why hasn't it been done before? Some of us have been around long enough to see many ideas come and go. I can't think of one incredibly novel idea that was made by a newcomer to the sailing scene that worked. Farrier had a tri and made ocean passges before the Trailertri - Lexcen built and designed lovely boats before Australia 2's winged keel. Go out and do lots of sailing. Stand on the shoulders of giants - don't regard those before you as dumb. The tri you are thinking of modifying has lots of reason and history behind its design concepts.

Do it if you want but I predict you will find the modifications ruin the boat, cost you heaps of dollars and ruin the resale.

[Kalagan]

Hi,

I have the highest regard for Yacht Designers, they are designing vessels that people lives will depend on for years to come. There couldn't be any greater responsibility!

I my life and my job, I always have to ask why, why something works, why something doesn't and how can it be improved? That is all I am doing here.

The Yachting Industry is like every other, just because something has been done one way for a long time, doesn't necessarily make it the best way. Maybe the way it has been done for a long time is the best way, but what if another approach resolves lingering issues, will you and the Yachting community be at least willing to look at it, with an open mind or just dismiss it because it is different??

I was simply trying to ask what if and was completely dismissed, because it was different or out of the ordinary. While I appreciate your time and knowledge, I was hoping to get a little more constructive criticism, like why it wouldn't work or the concept is flawed because, etc.

I am not a Yacht Designer and don't claim to be, as far as I can tell, this Forum is open to everyone, including us NOVICES. I keep my eyes open and look for solutions, that what I do and when I saw the Navy Ship, see the link, I started thinking why couldn't this basic design concept be applied to a recreational boat, I haven't seen one designed that way and figured that maybe it has been overlooked.

So, HAS IT?

Thanks
Kalagan

http://www.fallingpixel.com/products...aschen_img.jpg

[jamez]

Originally Posted by Kalagan

Hi,

But seriously, it seems like a very advantageous hull design, where am I going wrong?

Thanks
Kalagan

Its been done. They're called pontoon boats and people don't generally try and sail them.

What you propose, in the context of an existing design, at the least will add drag and weight, the opposite of what you should be aiming for in any multihull sailboat.

What are the lingering issues you refer to? Trimaran design has evolved slowly, largely by trial and error since the 1960s, and not in the direction you propose. However there is nothing to stop you building a full size model to test your theory and posting your results.