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Old 09-07-2007, 16:10   #1
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Beau's Boat

39 ft Power/sail aluminium trimaran well underway.
I had a professional boatbuilder and a welder complete the shell in 14 working days. I helped out but I could not recommend aluminium as a DIY after watching the professionals.
I have built in fiberglass before but I am now sold on Aluminium. I believe it is less expensive and better if you run aground. You do need insulation, I have 50mm of foam. But as I said I really don't recommend it as a DIY material.
Aluminium arrived all cut out and marked and I agreed on an hourly rate with the boat yard. It did cost more than I estimated, about 20% more but I got a lot of extras done at well. Mast, Stanchions, trim tabs etc.
The outriggers and the internal fuel tanks took a lot more work, than I expected.
Christine and I are doing the fit out, ourselves.
I hope to be on the water in four weeks.
I ended up buying two Honda 30 Hp outboard which will give me a 10 knot cruise speed with one motor and 20 knots with both motors.
The Hull uses what I call a low friction "Triflection principle" below the water line, no bow wave is formed even at twenty knots.
More information is avaible if you are interested.
Beau
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Old 09-07-2007, 21:26   #2
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4 weeks to fit out???? Do you want a job?

Looks good , I hope it all goes to plan for you. 4 weeks does sound incredibly short to do a fitout though.
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Old 10-07-2007, 01:36   #3
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Your not the first one to mention that it will take a lot longer than four weeks to fit out.
The layout is fairly simple, no curves, all straight lines. We put all the 50mm foam in place in a couple of days. The plumbing, gas hot water to the kitchen sink and shower, cold water only to the hand basin took one day.
We are using New Guinea rosewood panelling for the interior. that will need a bit of time.
Everyone told me building the shell would take months and yet in four days we had the main hull nearly complete. The most time was spent on the internal fuel tanks (3 days) and the outriggers (4 days) because they were not out cut out by cnc.
i have found it very hard to estimate costs inspite of a lot of help. Some jobs just flow quickly and other bog down.
Total Costs to date, AUD$80,000 and that includes all electronics, two motors, mast and rigging.

I do think the basic design which has NO CURVES, has a lot to do with it.
I do not believe in curves on a performance boat, all they do is create friction at speed.
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Old 10-07-2007, 03:03   #4
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thats a monomaran with a couple of tiny amas to balance it (sarcasm)
sean
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Old 10-07-2007, 04:12   #5
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yes, that is probably right,
It is basically a power boat with sail assist.
In the tropics most of the time there is little wind anyway, the sea is flat so why not motor at 10 knots at 50 cents a nautical mile or 20 knots at $1.00 a n mile. However when the wind is behind use the sail.
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Old 10-07-2007, 04:25   #6
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Quote:
Originally Posted by beau
... The Hull uses what I call a low friction "Triflection principle" below the water line, no bow wave is formed even at twenty knots.
More information is avaible if you are interested.
Beau
Triflection ?
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Old 10-07-2007, 10:23   #7
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tri logic

The cross beam to the amas are going to have a massive load. I'd recommend beefing them up expecially where they connect with the hull.

I rebuilt a similar 112' tri and I'm sold on the high narow tri design. See Specifications

I'm also planing on building the next tri hull king of Sports IV using aluminum with lessons learned from the past boat.

Cheers,
SC
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Old 10-07-2007, 15:36   #8
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King of sports,

I agree with your comments.
What the drawings/photo's didnt show are two heavy wire cables that attach to the boat.
This is essentially a powerboat and is not designed to be sailed close to the wind only downwind.

"Triflection Principle" is a term I have developed to cover a number of design innovations I have been developing over ten years.
Basically it involves flat surfaces (no curves) angled (triangulated) which minimize friction along the hull surface (horizontal and vertical) to such an extent that no Bow wave is caused even at high speed.
The only friction you now have is wetted surface which is linear.

This is why multihulls become "dogs" when heavily loaded. As the hulls are submerged lower in the water the width of the hulls is substancially increased, dramatically increasing the wave making resistance. Wetted surface is also increased.
If the sides were vertical this increased wave making resistance can now be avoided with only increased wetted surface being a drag factor.
This wave making resistance is what causes the bow wave to form in the first place and has huge drag on the hull when the boat approachs the square root of the water line length etc.

In 15 ft prototypes ( five) I have built I have proven this theory.
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Old 10-07-2007, 17:07   #9
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Curved surfaces are much stiffer than flat surfaces, which is a major reason why they are employed so much. To use largely flat surfaces means either increased skin thickness, or having frames and stringers to support them.

But if the result ofusing flats is such a quick fitout, I can see others following suit.
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Old 11-07-2007, 01:26   #10
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Yes, I agree with you on curved surfaces being stronger and I had a lot of difficulty convincing the structural engineer and the boat builder that i had to have FLAT surfaces. Yes it took more reinforcing.
It has been known for years that on a planning boat, flat surfaces are best and at a displacement speed (square root of the waterline length) curves surfaces are probably best.
However when you travel at the higher speeds possible with fast displacement curves below the water line cause high friction.

There is also a major saving in the construction, all panels were pre cut and just had to be tacked together before full welding.(no bending)As I said earlier with two professionals the main hull was up in 4 days. as per attachment photo.

The interior fitout is going well, I will post photos of progress over the next few days.
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Old 11-07-2007, 01:32   #11
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I was hoping to get some comment on my argument as to why overloaded multihulls are so slow.
Why are you all so shy?
I would love for someone to prove me wrong?
Come on, HelloSailor where are you when I need you
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Old 11-07-2007, 01:53   #12
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Quote:
Originally Posted by beau
I was hoping to get some comment on my argument as to why overloaded multihulls are so slow.
Why are you all so shy?
I would love for someone to prove me wrong?
I guess I'll jump in here, beau, and address that one. No one probably wanted to argue the point because it's a simple fact - overloaded multihulls are slow!

Your observation that the curved underwater surfaces create more friction than flat surfaces sounds logical to me, and lying deeper in the water obviously increases the wetted surface - what is there to argue about? The performance capabilities of overloaded cats and tris is definitely adversely affected by extra weight!

I very much admire your willingness to build a proof-of-concept, full-scale version of a vessel you believe in, BTW, and I appreciate the pictures you're posting here. Best of luck to you as you take it to completion.

TaoJones
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Old 11-07-2007, 04:13   #13
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Quote:
Originally Posted by beau
I was hoping to get some comment on my argument as to why overloaded multihulls are so slow.
Why are you all so shy?
I would love for someone to prove me wrong?
Come on, HelloSailor where are you when I need you
I'd suggest that if you overload ANY boat it will be slow. Slower than it would be if correctly loaded, for sure.
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Old 11-07-2007, 04:27   #14
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Although cruising cats can be designed with a reasonable anticipated payload, each pound composes a higher percentage of a light vessel's weight, so performance is affected more than on a comparable monohull.
You can compare different boats' load-carrying capacity by using pounds per inch immersion (PPI), which is the amount of weight it takes to sink the boat one inch deeper on its lines.

According to Ted Brewer: Ted Brewer Yacht Design
POUNDS PER INCH IMMERSION (PPI):
The weight required to sink the yacht one inch.
It is calculated by multiplying the LWL* area by 5.333 for sea water or 5.2 for fresh.
* LWL x 2 for Catamarans
The PPI usually increases as the hull sinks into the water as the LWL area is also increasing due to the shape of the hull above water.

To approximate PPI, multiply the hull waterline beam times its waterline length times .6 times two (for both hulls) and divide by 64.
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Old 11-07-2007, 15:00   #15
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It is not that simple.
As I said earlier there are two factors at work with speed and "overloaded" multihulls. Increased Wetted surface and Bow wave formation.
The friction formed with wetted surface is linear and follows the principle of "to double your speed reguires four times the power"

The drag caused by bow wave formation jumps 10 times as you get beyond displacement speed.
What I am suggesting is, it is the dramatic change in hull form in mutihulls when overloaded that causes a dramatic increase in drag caused by bow wave formation at speed, and not so much wetted surface drag.

With this knowledge it is possible to design multihulls that "can" carry extra weight which has little affect on performance other than the "small" increase in drag caused by extra wetted surface.
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