Discussion in 'General Catamaran Discussion' started by catmando, Mar 3, 2005.
Well well...sounds like you have inside knowledge do you not?
How many tires on that trailer?
What is the re-entry like in rough water?
Silver/back scheme gives it a very upscale, classy look. At almost 4000lbs, the C18 would not be my first choice of motor. Are there not lighter diesel motors in that HP range(that are reliable)?
Like Isotta Frachini?
Or is that what you meant by "that are reliable"?
Yes. One of our members on offshoreonly.com, a European, said that the Isotta race motors were not reliable, and I do remember the UIM Class1 diesel boats regularly blowing their turbos.
More Feather Ruffling
On another forum this interesting discussion came up:
One of the reasons I was glad to see BMcF join YF is because I believe it's important to have someone with expertise in hull design and stabilization contributing to the knowledge base. As the site publisher, I've become increasingly aware of liability issues and have curtailed my opinions, whether they be fact or fantasy.
Although hydrodynamics, stabilization & propulsion are topics I still enjoy, nowadays... my biggest limitation is time. I've got some projects underway right now that are even biting into my sleep time, hence this post is made at 4:00 AM, when I should actually be sleeping.
Thanks for understanding...
I've got my flak jacket on
That's a shame as I've always respected your knowledge in these fields. I mean as I read over your original comment (that's why I included it in the quotes), you nailed a lot of the potential problems without ever having been on one of the vessels
What are you doing up at this hour
This subject came up again with me as I just visited the Navy SeaAirSpace Show here in Wash DC yesterday and noted the such big projects as General Dynamics/Austral Ships Littoral Combat Trimaran Ship
So I was asking if anyone knew of the real results of the pilot program for a tri-hull warship, the Triton project, and how any of this test info filtered down to the latest design?? As near as I can tell there is NO input to the new design that came as a result of that pilot project??? Mysterious ways our defense contractors work:
Granted the Triton was only a 20kt vessel, but they hope for 40kts with burst to 45kts for the Littoral tri. I was particularly interested in the length of the outer sponsons on the latest vessel verses those on the Triton, especially since the Triton design was studied extensively prior to building
...good photo of Triton
Wow Brian, I can spot your posts a mile away, they are informative, thorough and often require a packed lunch.
Intersting findings. All I can add is that the Triton is currently contracted to Australian Customs as a support vesel.
Man, the short length of the outer sponsons on Triton certainly flies in the face of past practice for trimarans!
Sponson Length & Bouyancy
Lets not confuse sailing trimaran's with power ones. On sailing tri's the longer 'amas' are needed to keep the stern from squating going up wind. But note that their full bouyancy is not carried alway aft for fear of overpowering the bows
Here's a little history on Triton's development:
The initial work on trimaran warships was carried out at the University College in London where the UK MOD sponsors a department which studies warship design. In the early 90s as part of their MSc course students were given the task of designing various trimaran warships. The results of this work were so encouraging that the Royal Navy sponsors decided to fund research work at the Defence Evaluation Reasearch Agency to confirm the advantages promised by the hullform and also to understand the constraints imposed on the use of the hullform.
This work was started in 1994 and initially concentrated on the hydrodynamic aspects of the hull design and was carried out by running small-scale models of typically eight metres length in the tanks at DERA Haslar. The research was successful and the key parameters of main hull length to beam ratios, side hull length and position together with the lines were identified. As this was progressing computer design tools were developed which predicted the resistance, propulsion, seakeeping and manoeuvring characteristics of the trimaran warship.
Once the hydrodynamic design was set, DERA together with the UK MOD Procurement Executive investigated the structural design requirements. This was based on the development of load prediction computer codes in a series of numerical models which have been used to calculate the plate thickness, frame spacing and stresses which will be imposed on the ship by the onerous requirement to operate warships in the most strenuous of sea conditions. The final area of research covers survivability where any peculiarities of using a long slender hullform are being investigated through the use of scale model experiments and the development of computer based numerical models.
The results of the research have been most encouraging and to date nothing has been identified which negates any of the perceived advantages. However it is one thing to validate at small scale and then to have the confidence to build a fleet of trimaran warships. To fill this gap DERA has committed itself to fund and build an ocean going Trimaran Demonstrator - RV TRITON. During its first two years of life the ship will be used to validate the research results and resolve any risks associated with the hullform.
It appears as though there was considerable thought and research given to this design. And they started with a clean sheet of paper. So why didn't they consider longer sponsons, or extending more aft as in the 'littoral ship design'?? I suspect they did, and rejected it for some reason?? That's what I'm asking. I don't know the reason for their choice, but I suspsect it had something to do with diagonal stability/bow burying in big seas that might get under the sterns.
Welp, after reading this page I think I'll stick to cats.
Firstly can I say that a number of the points raised above concerning the Bladerunner are flawed. The 34 and much improved 35 do handle rough weather particular a head wind and swell very well. Look at the Video on the web site and see how flat the noise is running in what can be said is pretty choppy weather the boat is traveling at over 100mph in these shots. In fact the wind speed was high enough for the pilot not to want to go up. The 34 and 35 do have a very low free board which when traveling at slower speeds in big short swells does make for a slightly uncomfortable ride but only as much as wallowing at slow speed in a mono hull at slow speed. I have personally put 70 hours on a Bladerunner 35 and was amazed by the all round capabilities of this vessel. Every time I took it out I was always stunned at what it was capable of. At high speed it is incredibly stable to the point of belying the fact you are traveling at over 70mph. If you chose to go out in rough weather or get caught out in rough weather then i never found an occasion when I felt concerned. Plus to prove more of a point the 51 that set the world record (eclipsing Fabio Buzzi record in a mono hull) of circumnavigating the UK in just over 27 hours. Admittedly it did have to slow down in heavy seas while coming down through the north sea however this was slowing down to 50 knots!
You say that it hit a flaw in the design? That this flaw is why it stopped the first attempt at the world record around the UK. So if the design is flawed how did it manage to do it on the 2nd attempt. Was it possibly because it did hit something under water in fact possibly the Arneson’s did hit something breaking the tie bar in the process making the team have to pull into Scotland after attempts to fix the problem proved to much with limited tools and spares. Perhaps you should know what you are talking about before you start to pass potentially serious accusations.
I have had the above thread brought to my notice, and being the Bladerunner designer, feel I need to say something. The Bladerunner is described as an Air Entrapment Monohull. As most of you know, it has a narrow but low deadrise, stepped main centre hull with a tunnel each side and outer sponsons. There is aerodynamic ram lift from the tunnels, and the sponsons act as end plates to contain this pressure. At high speeds a useful amount of air lift is created. The centre hull does all the rest of the work except provide roll stability which is done by a combination of the sponsons and the tunnels.
The stepped centre hull provides lift the same way a stepped monohull would – over an appreciable length of the hull. Don’t think tippy single front wheel tricycle – the closest is a motorcycle with training wheels, or, sidecar racer with a sidecar each side. Low deadrise is efficient for lift but gives too much if the surface is too wide, so we keep it to the width necessary to carry the boat. The bow is not a needle nose which stuffs through everything, it is a wide shovel shape which gives a lot of dynamic lift when plunged into waves – at speed it is dynamic lift rather than buoyancy which lifts the bow in a sea. The BR is not a wave piercer it is designed to lift to the sea. I agree the Bladerunner 34 and 35 are fairly low freeboard and you can take the tops off waves on occasion. The 51 is very dry.
Very Tricky’s boat was the first production BR. All subsequent boats had the tunnels raised at the aft end. The problem was that the aft ends of the tunnels would act like unwanted trim tabs and lift the stern, stopping the bow from lifting to the waves which made the ride wetter. Sometimes this lift would cause a problem in roll too when a wave picked up the aft tunnel roof on one side. The newer boats don’t have this. Mr. T. has spoken to me and ICE Marine and knows all about this and we have explained that the boat can be modified to later spec if he wants it. Also, I don’t know where he gets his race statistics from –
‘They have raced with great success for one or two races - then for no real aparent reason have dumped the crew’
– that is an untrue generalisation. During racing there are accidents – the first Bladerunner rolled once during a race and a previous AEM did roll on a turn – cats and monos have often done the same when racing when, by definition, the limits are pushed. No Bladerunner has cartwheeled, to my knowledge.
The first AEM style racer (1976) was a championship winner and had quite wide sponsons. With each later design the sponsons were narrowed so that roll reactions were made less sharp and the boats improved – if there is not enough righting from the sponsons, the tunnels come into play. Neil Holmes won the 1992 4 litre World Championship in an AEM.
When turning, water is scooped around the outside tunnel by the crabbing centre hull and the craft leans on this. It is best to throttle off as you come to the turn to settle the boat, turn the wheel and then open the throttle to force the stern over and scoop the water. You can turn very quickly like this (it is a method which works for most boat shapes), but if you do push too hard the boat can let go suddenly the way a Ferrari or Aston would, once pushed past the limit. It is a bad idea, and shows lack of skill, to drive at max in a straight line and suddenly turn the wheel – how many quick boats will take that treatment? Worse again is to chicken out in the middle of the turn, throttle off and wind the wheel the opposite way. This applies not just to BRs. BRs turn well if you have just a little skill; you don’t need to push them to the limit. If you only want a slalom boat you need a vee mono – BRs are meant to cover distances in comfort in a range of sea states, not to do pin turns!
The sponsons do give the BR good directional stability – you have to work very hard to make them hook. V. Tricky says he has hooked his and, if so, the low aft tunnels in his boat have contributed – I don’t know of any other.
I have been designing fast craft – racing and non-racing - for over 35 years and, as well as the Bladerunner type and its antecedents, I have also had success with cats and monos. I wouldn’t have persisted with the BR style if I didn’t truly believe it worked and overcame many of the problems encountered with the other types. Jeremy Watts at ICE is a past World Champion racer and has a really good feel for boats. We both looked long and hard at all types of hull before ICE Marine was started.
Another fast Tri - Hull
It's time I added my two bits:
We have been working along similer paths as the Bladerunner guys.
Designing and building monohulls, cats and tri - hulls.
Perhaps the worst thing that can be said, is that we are still at the early stages of perfecting
- high speed, tri - hull vessels.
Most of the antedotal evidence put forward of
mis - behaviour - is well beyond 40 knots.
Very few recreational vessels, or yachts, operate beyond this speed.
For good reason.
As ground, or surface effect, begins to have an increasing
" effect " on proceedings - as speeds go up.
All craft will indicate some form of instability as they attempt to " fly ".
- And all vessels - pushed beyond their limits - will crash in dramatic ways.
Myself - and others - have seen test results with tri - hull forms that are, in general, positive.
Both in the wind tunnel and in sea trials.
With our design, we must have done something right.
As our boat, at higher speeds, has yet - to display any dangerous quirks.
Perhaps we need to triple the hp
- and add a " survival pod " to our test boat(s)
- before we go any further ?
In the mean time......
We can only report on our own experience.
- And to date, we see no reason, not to continue developing our tri - hull designs.
Staight up!! No Bull...
Believe it or not but when the original talks were going on for the Royal Naval "Triton" Project, the snr Naval architect asked me, at a party one night would you believe it. "What do you think young man?" Well, I was very wet behind the ears but had just spent many years messing with a lot of composite ideas.. Believe me I just cant remember why I said 'Make the outriggers from composite" I still think it was a reasonable suggestion. I left about 6 months later to work for the Dutch Royal Navy and lost touch with the project. It did however start a lot of talks and discussion.. Believe it or not, there were a few designers that loved the idea. After all, the outriggers were, at the time, purely for a more stable firing platform. After seeing the fotos here I'm really glad they went for steel though. Bought back some embarassing thoughts here. I am a keen believer in composites being used more on large yachts though. Nice info lads and poss Ladies. Nice to see it finished.
Welcome to yachtforums Mr. Campbell. It is an honor to have you posting here.
Congratulations on your RoundBritain record and will you be defending this year? The Platinum 51 is a gorgeous boat and I'm sure with an all-up weight close to 30,000lbs it takes heavy seas quite well.
Are you planning on a twin inboard 35' model for the American market?
Catmando – thanks for the welcome. There are no plans, at the moment, to up the Round Britain record – we will wait until someone else goes quicker.
The Bladerunner 35 is twin outboard only for the moment – Jeremy Watts at ICE likes the quick responses of the lightweight package. There is not room for a practical twin inboard setup but a single would fit. We would like, however, either to use a duoprop setup or split the power between twin counter rotating props to reduce the torque effect of the single.
IMCO marine has tested a new splitter with their Xtreme1000 drives. Looks promising. Now that you've moved the cabin to the bow you should have room for it behind the motor.
One nitpick I have is the 35 cannot close its roof.