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Old 12-07-2019, 05:44   #1
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stability re-calcalculation for pimped Trimarans

Dear fellows ! Hope to get some help from some of you who have skills to calculate "stability". - As a multihull enthusiast I am in the process to buy a Trimaran (cruising-racing type). - It will be one of the elder designs (around 1985-1990), e.g. drawn by naval architects like Norman Cross, Lock Crowther, Philippe Briand, Hedley Nicol, Phil Herting and Mick Price or Dick Newick. The size I am looking for to buy is around 40 ft.

(picture source: Foldable Trimaran for sale)

Different times (and for one concrete sales proposal) I experienced, that such Tris have been pimped by the owner (or pre-owner). E.g. stretched in length (e.g. from 39 to 42 ft), higher mast (e.g. from 16.5 to 18m), longer boom (for resizing the main sail), newly fitted with retractable or fixed mounted bow sprit (for asymmetric Spi/Reacher). Displacements have increased from original size (~4,000 kg) to remarkable heavier weights (~5.5-7.5 tons), while the cross beam size (in most cases) is the original size (e.g. Boat length 16.5 meters, total width 9.9 meters).

Actually I only can judge by watching photos or videos if such re-designed Tris (with retractable central daggerboard) are seaworthy (and trustworth). Like this one shows a Tri at 25 knots speed. "Walk through" vids like following can give an orientation of the all over conditions the boat is in, only.

(Rec.: As I live in Northern Europe, where such Trimarans are not available, I have to look overseas. Before I take the plane, I like to proof the datas as much as possible.)

Mostly video clips of Tris are done in light winds. By watching I don't get the feeling for such pimped boats how their behaviour is in rough seas/higher waves and if there is a bigger risk of nose diving (pitch poling). Such observations under perfect conditions might be impressive on first moment, but are not very trustworthy in my understanding for the abilities to go offshore / long distance cruising.

Cruising Multihulls of good performance can become dangerous as they move in higher speed ranges (16-22 knots), and I like to have a more detailed proof. Two central questions for me:
  1. Do the Amas (outrigger) have enough buoyancy / uprighting moment with the new sails plan and/or extended length of main hull (vaka) ?
  2. Can the Cross beams (aka) bear the bigger loads (e.g. by increasing displacement, higher mast and bigger main / head sails) ?

I am a professional sailor (having started with sailing more than 40 years ago), but neither I am a boat builder nor a naval architect. My skills in stability calculations are only "very bascis" (which I had to study when graduated with captain diploma for commercial sailing vessels (monohulls) up to 500 tons at Dutch Nautical Colleague in Noord-Holland).

Does exist an excel sheet or any freeware program with templates for Trimarans ? - Tks in advance giving attention. Any advice is very welcome.
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Old 12-07-2019, 05:54   #2
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Re: stability re-calcalculation for pimped Trimarans

I'm afraid I'm behind than you - I've only done stability on a displacement hull, and had coaching from a naval architect. What catches my attention is your consideration for purchase of boats that by one description have been pimped and by another have been butchered. Those boats are way outside the architect's calculations to begin with. Is there some advantage, perhaps a few extra knots, that tempts you?
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Old 12-07-2019, 05:58   #3
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Re: stability re-calcalculation for pimped Trimarans

Further thought. If someone did that to a boat, and then DIDN'T do a stability test they can show you, are you interested? This is like stuffing a big V-8 into a four banger sports car and then expecting it to be tractable to drive. Carroll Shelby, but for boats.
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Old 12-07-2019, 06:23   #4
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Re: stability re-calcalculation for pimped Trimarans

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Is there some advantage, perhaps a few extra knots, that tempts you?
Hi, tkeithlu ! ... tks for your feedback. Good question which let me start thinking about myself and abt unconciously driven motivations. Aren't we being thought (by our brain) instead thinking ?

Becoming serious: No, its not extra speed. I am an ambitious sailor, yes. But I think, cruising sailing is all about "compromises", right ? Doing 16.4 or 16.9 knots isn't really kicking me. I have some other priorities, e.g. kick-up rudder and retractable daggerboard for falling dry/beaching, headroom (I am of 1.83 m height), cutter rig etc. ...

It just happens, that I get noticed of such boats, e.g. I just got the offer by an owner of a 42 foot Norman Cross Trimaran which was pimped from 39 ft to 42ft. (Rec.: Don't search by googling, this boat is not officially in the market :-) ). The owner has no informations about the stability calculations. I could go the easy way now and just let drop such offers and look for the "perfect boat". But does such one really exist at at an affordable prize ?

I see it as following: Elder Tris, designed in the 80s (last century) have already a learning curve behind from the first Tri designers, who started in the 50s and 60s (e.g. Piver). Cross-Beam connections and seaworthyness are more trustworthy of that time. Compared with newer designs beginning of the 90s, the Tris of the 80s have still some bigger risks. If an owner decided to make the boat safer = better seaworthyness by stretching it, I welcome this decision and change.

But yes, its the question "how much time is it worth to spend for such pimped boats to get the upper questions answered ?" - A boat shall not become too complicated to be well balanced.
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Old 12-07-2019, 07:31   #5
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Re: stability re-calcalculation for pimped Trimarans

Hi Skip,

You are dealing with several separate issues here. One is stability. Another is structural strength. Bouyancy is a third. They should be addressed separately.

Stability: on a static level, with multis this is pretty simple. The righting moment is defined by the beam and the displacement. If the beam is increased the righting moment will increase by the same percentage as the increase in beam. Ditto displacement, righting moment will increase as the ratio of displacement increase.

When you look at dynamic stability, weight increase past a certain point will make a multi dangerous in a rough sea. When buoyancy becomes inadequate for the displacement you can get into issues like burying and tripping over the bow, the lee hull digging in and a breaking sea capsizing the boat instead of her sliding sideways, etc.

Strength: obviously this important. If the builder increases the weight of the boat without increasing the strength of the cross beams then you have a condition of more weight creating a higher righting moment (which creates higher stresses) without any increase in the strength of the beams carrying that stress. I would not consider a boat that had a significant displacement increase as you describe without increased strength in the cross beams. Without the ability to do a structural analysis of the hull structure the safe approach is to assume that the original designer knew what he was doing when he specified the original design and not accept gross variations from that without detailed analysis that shows that variation is acceptable. Very few builders are capable of that sort of work.

Bouyancy: this is a complex subject because required buoyance varies depending on how hard you drive the boat, the sea condition and how the boat is loaded. But it is easy to generalize. If the boat is significantly heavier than the design weight then she's going to have less buoyancy. So know the designers specs for his design. If the boat you are looking at is significantly heavier then you know she will have less buoyancy than the designer intended. You will need to use your own judgement to decide whether a particular boat seems reasonable.

In general, multis are happier, faster and less stressed when they are light. I would in general be skeptical of any multi built significantly heavier than the design target. There are always exceptions, but I would generalize and say that a builder who produces a grossly overweight multi doesn't know how to build that boat properly.
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Old 12-07-2019, 08:44   #6
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Re: stability re-calcalculation for pimped Trimarans

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Hi Skip,
You are dealing with several separate issues here. One is stability. Another is structural strength. Bouyancy is a third. They should be addressed separately ...
Tks Pauls for clearing. Yes, you are right. Having pimped a multihull (or any kind of boat), it addresses different issues (misleading by myself as "dummie" I summarized only as "stability risk").

I have to deal with this topic in couple of years for new examens, going back to the Nautical Colleague for the captain diploma for bigger traditional sailing ships (up to 1800 tons displacement) its not wasting time to keep warmed-up with this topic. :-)

I agree, that only some few "experts" manage it to resize a Trimaran, e.g. the 46 ft Tri Pipeline3 (original: Kurt Hughes design) is such one which got "reverse (wave piercing) bows", formerly known as Trimaran “Faamu Sami”.




(Rec.: Boat bilder company Lyman-Morse (LM) in Maine (USA) did this great job to give Pipeline3 in 2014 the wave piercing bows. Originally the boat was built in 2001 by Dick Vermeulen of Maine Cat in Bremen, ME. More pics of the refit here.)

Understanding you right, Pauls. Your advice would be: "Hands off" from such boats, right ?
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Old 12-07-2019, 09:38   #7
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Re: stability re-calcalculation for pimped Trimarans

Stability of multi-hulls = tipped beyond a point, they capsize and remain capsized. You can estimate this angle using a crane to lift the boat by the daggerboard. Then deduct about 15 degrees for rough water scenario.



Or do you ask about tripping over the ama? Which is similar even but not the same thing.



The one you showed has the old style amas - centered and with less volume forward. You can only trip over an ama that gets submerged. Thus modern tris tend to have amas further forward and with plenty of SPARE volume in the fore part (still - distributed high to avoid drag in regular sailing conditions). Look at the last image above the mods did exactly this. But these mods do not need to be 'piercing' - look at Neel bows - all three in line, the amas very tall and very voluminous (spare volume - above wl) - this is the present day way of seeing what is best (for safety, not for speed).



Older tris need more attention from the crew. There is less margin for errors of judgement or sail trim. There is also less seaworthiness. Still, they are great boats in their own right and often beautiful ones too (like the one you have posted).


Amas are easy to mod with foam and epoxy. With help of a skilled racing naval architect you will be able to mod your boat too (should you find this necessary at any point).


Is the boat in NZ? I think I have seen an identical design in Auck.


Cheers,
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Old 12-07-2019, 11:27   #8
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Re: stability re-calcalculation for pimped Trimarans

Dear Skip Jr
Please go to the website trimaran-naga.com
I sailed for 13 years on a boat rhat you describe, kick-up.rudder, retractable centerboard, racer-cruiser trimaran, 38 feet, she could have a bowsprit for a spinnaker, we just never put it on. This Boat is a Newick Native built.to the design as designed by the designer. She doesn't bury her bows, she sailed me halfway around the world in all kinds of weather and seas and she was f***ng amazing.
After leaving Naga, I bought myself another trimaran, that is more suited to my style of sailing , she is a Jim Brown Searunner. Slower, more living space, can carry more weight, but still the magic carpet.ride of a good trimaran
But the Newick was FAST and SEXY and with the captain I sailed with, incredibly safe. Really, go to his web site. I think this is the boat you are searching for.
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Old 12-07-2019, 12:44   #9
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Re: stability re-calcalculation for pimped Trimarans

Forgot to tell you, if you go to the website, to bypass all the business stuff on the webpage, click on
Our Adventures
That will give you photos and stories and even drawings of the layout down below.
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Old 12-07-2019, 13:11   #10
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Re: stability re-calcalculation for pimped Trimarans

Skip, that first photo you posted ...that centerboard is the Condor design. Am I correct? If so that would be the Condor 40 foot. I own the 30 foot Condor. The 30 foot Condors were designed after the 40 footers. My amas are much fuller than the larger boat. My boat is trailerable so the akas are less sexy. We use round aluminum tubes.

You can see a skipper from Galveston texas area pushing his 30 footer on you tube. I think the name of his boat is “See Ya”. I have some video clips from Nov 2018 of my tri sailing west across Sea of Cortez from San Carlos to Mulege with the asymmetrical pulling us along nicely at 10 knots in 15 knots and 1-1.5 meter seas. 30 gallons of water and 10 gallons of gas with all the normal cruising shizzle. If u send me an email address I will send to you.

Skip you have way more experience and education than I when it comes to boats. But you know by now that all boats have to be learned. Because I have a boat that was designed in the mid 90’s I don’t push her too hard. But she is plenty fast. I sail remote places and I am
Strictly a coastal sailor I like retractable rudder and centerboard. My boat is trailerable. So I can break her down in a day in Mexico and be in Fort Lauderdale 3 days later or Great Lakes 3-4 days later.

Skip... the other thing... I paid 22,500 for my boat. She is plenty of boat for two people. I have two excellent sleeping berths due to the wings midship. I have a Lavac head, an Engel fridge, and a 10 hp Tohatsu. I have propane single burner and hand pump fresh water. I don’t have a lot of experience on this boat yet. But I had a Corsair 31 and plenty of time on Corsair 27’s. Because of fuller amas she is a drier and more stable ride. In lighter airs the F31 is faster. In heavier airs you would need a good crew to keep pace with the Condor. That is from Bobby Fulmer who is one of the better sailors you could ever hope to meet when it comes to race and multis.

I guess when stability rears it’s ugly head you slow the boat down and use prudent thoughts for safety and comfort. Nothing rides like a trimaran. I can beach her and walk her around in knee deep water. I couldn’t be happier. Let me know if you want sailing videos. Happy to share. Respects.
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Old 13-07-2019, 09:10   #11
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Re: stability re-calcalculation for pimped Trimarans

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Originally Posted by trimarannaga View Post
Dear Skip Jr
After leaving Naga, I bought myself another trimaran, that is more suited to my style of sailing , she is a Jim Brown Searunner. Slower, more living space, can carry more weight, but still the magic carpet ride of a good trimaran.
Thanks for the recommendation. Its very helpful to me to hear your story.

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Old 27-07-2019, 09:11   #12
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Re: stability re-calcalculation for pimped Trimarans

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Originally Posted by trimarannaga View Post
Dear Skip Jr
Please go to the website trimaran-naga.com
I sailed for 13 years on a boat rhat you describe, kick-up.rudder, retractable centerboard, racer-cruiser trimaran, 38 feet, she could have a bowsprit for a spinnaker, we just never put it on. This Boat is a Newick Native built.to the design as designed by the designer. She doesn't bury her bows, she sailed me halfway around the world in all kinds of weather and seas and she was f***ng amazing.
I know this boat very well and the website. I have no doubt about that it is in good hands. Just not my personal taste (by look).

Quote:
Originally Posted by trimarannaga View Post
After leaving Naga, I bought myself another trimaran, that is more suited to my style of sailing , she is a Jim Brown Searunner. Slower, more living space, can carry more weight, but still the magic carpet.ride of a good trimaran
But the Newick was FAST and SEXY and with the captain I sailed with, incredibly safe. Really, go to his web site. I think this is the boat you are searching for.
Yes, have also noticed a while ago about your switch. :-) Congrats you made the deal. - By heart I look for a Crowther Kraken 40. (Rec.: The cruising version, Crowther Buccaneer with aft cabin might be 2nd option.) I also like the Condor 40 (but not my first option).
For now I live on a 30 foot monohull, for nearby one 1 year (inclusive cold winter). Have lived also on other boats like 17 meter 2 mast flat bottom or 15 meter aluminium catamaran (also during cold winter). Slowly I know what I like and dislike and which kind of compromises I can go.

My brain is (and can be) very lazy, scares and surprises me again and again how it can trick me to avoid work. Means, I have to push me actively out of my comfort zone, otherwise I become lame. Always need challenges and best, always on the move like a nomad. That helps me to keep awaken, focussed and feeling alive. I am not a "farmer type", I am more of "hunter nature".

So my personal formula is: Fast sailing and simple comfort.

By look - beside the F40 tris - I like also the "old racing Tris" of the 80s which had been built in the size of 40-42 ft for single hand or double handed (Transatlantic) Races . Some very view are still out there, in good and bad shape. - Like "Three Legs of a Man", "Trifle" (built in the 60s), "Côte Basque" or "Spirit of Ireland" (former Colt Cars, built 1982).
Most of these boats are in the market since years, owners do not reduce prize (irrationally). Most of these unique single built boats (images see attached) need lots of renovation, money and time. Lots of time for I don't have at all.

Rationally it does not make sense to have interests for such "old boats", as the naval architects of tris have developed since the 90s a lot with computer-based design calculations with better seaworthyness and higher saftyness.

Whatever drives me unconsciously I like the "old look". - They feel like Dinos in our modern times, isn't !
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Old 27-07-2019, 09:55   #13
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Re: stability re-calcalculation for pimped Trimarans

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Skip, that first photo you posted ...that centerboard is the Condor design. Am I correct?
Must disappoint you. Condor 40 (my 3rd choice as Tri) has no aft cabin. Two versions you see in the market, either with tiller or with wheel steering.

Only some few designs with aft cabin where built in the 80s (or earlier). Piever 39, Corsair 31 and Farriers (e.g. F-9ax/-33X, F36 and Farrier 10 meter), Chris White's Hammerhead 34, Norman Cross 38, Searunner 40 (Jim Brown/ John Marples), Crowther Buccaneer. List may not be complete. :-)

In the photo its a Crowther Buccaneer 36 which was for sale in Australia, so far I remember correctly. Here another one (built 1979) which was for sale in USA.


One is actualy for sale in Australia for less than 64KUS$ (92KAUS$)


Quote:
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I guess when stability rears it’s ugly head you slow the boat down and use prudent thoughts for safety and comfort. Nothing rides like a trimaran. I can beach her and walk her around in knee deep water. I couldn’t be happier. Let me know if you want sailing videos. Happy to share. Respects.
Shure ... share what you love to ride so much. - Always appreciate clips to learn about the behaviour under sails. :-) I think only 21 of the 40 foot size were built in Annapolis by Mick Price and Phil Hertin, right ? How many of the 30 ft condors have been built ?
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Old 31-05-2021, 13:06   #14
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Re: stability re-calcalculation for pimped Trimarans

Did you wind up buying a Trimaran... or??
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