Multihull ocean rowing vessel

Discussion in 'Multihulls' started by sibosun, Apr 16, 2009.

  1. sibosun
    Joined: Jan 2009
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    sibosun Junior Member


    I'm currently engaged in a project to design a large, ocean going, multihull rowing vessel. I will be working on the foundations of Nigel Irens iLAN designs, and have a feeling (unsubstantiated as yet) that the concept will work well when applied to lower speed regime ocean going craft. I have been searching (with limited success) for parametric vessel types to start my concept models, and wondered if anyone had any experience or interest in either ocean rowing as a sport, or in the iLAN type? I am particularly concerned with low resistance hull forms at low speeds - a combination that doesn't often get addressed.

    I should probably add that my line of work is in designing equipment for Ocean Rowing, and I would be glad to add my input to any other rowing related queries.

    All the best.
  2. Chris Ostlind

    Chris Ostlind Previous Member

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  3. Guest625101138

    Guest625101138 Previous Member

    Why would anyone consider low resistance hulls for rowing in the ocean! The efficiency of rowing in all but calm water is very low. The most important criteria is a stable and safe platform to operate from.

    If you are after overall efficiency get away from rowing and go for pedal driven prop in a slender aerodynamic monohull.

    If you are stuck with rowing and a multihull then the Rocat might give you some ideas:
    An optimum cat will require 40% more power than an optimum monohull for the same speed.

    Windage is a major issue with human powered craft. It can easily exceed the hull drag. A streamline deck offers big benefits.

    This boat is presently being built:
    It is set up for single person but would also suit two up on rotating watch for long distance. The concept was tested with a less than optimised enclosed canoe and could easily achieve 5kts in rough conditions with a single pilot.

    Moksha has circled the globe using pedal power - see attached.

    It is possible to determine the lowest drag hull shape for set constraints and something I have addressed with a number of designs. This is one example:
    Rowing shells are close to optimum shape for the installed power and weight whether 1, 2, 4 or 8.

    Rick W

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  4. sibosun
    Joined: Jan 2009
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    sibosun Junior Member

    Thanks Chris - I'm well aware of Orca and his other projects. Shame she didn't fare better against Mondiale. However, the race is now on in certain quarters to innovate and improve on what we have so far. Since Mondiale's demise, I would imagine there are a few interested parties in designing to beat the records she set. Like me.

    I have discovered that there is an American team working on a vessel designed by Morelli and Melvin, though whether she will simply be a modified version of Playstation(!?) or a complete new design remains to be seen. I think the project has something to do with Roy Finlay... Any ideas?
    See this -

    Rick - are you suggesting I should be looking at a high resistance hull form? I think you may have the wrong end of the stick. When I say Ocean Rowing Boat, I mean Atlantic, Indian, potentially Pacific, to be used in record attempts with a substantial number of crew. I agree that a habitable and stable hull is required, but your assertion that an "optimum cat" will need 40 % more power than an "optimum monohull" is impossible to quantify. I agree with your comments about windage though, which is tricky to achieve with a rowing hull. I do believe that given a certain size, the multihull is the way to go.
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  5. Guest625101138

    Guest625101138 Previous Member

    The 40% increase of the drag of an optimum cat over an optimum monohull is a demonstratable fact for calm water operation. That is why all the fastest boats use a stabilised monohull form. These are called trimarans if stabilised with two outriggers or could be stabilised with a ballasted keel. The choice of method depends on the displacement of the hull and operating conditions. Either method of stabilising will add drag but is still less than what will be achieved with a catamaran. I would not recommend a single outrigger but it has lower drag than a catamaran.

    The people who purchased Rocats were generally disappointed with performance against other rowing and paddled craft. The designer/builder did not understand the fundamental problem of a catamaran versus a monohull until it was pointed out to him.

    Unless you have tried a well designed pedal craft you really cannot appreciate the advantage over stone age technology of rowing.
    The outriggers on this hull are designed to be very lightly loaded so they contributed almost nothing to drag but offer good initial stability.

    In a seaway the ability to apply power efficiently and consistently in all sorts of weather conditions with a propeller is a significant advantage over rowing.

    Rick W.
  6. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect


    You are correct in your understanding about a catamaran versus a monohull. There are many aspects to consider when designing, weight being the most important. The type of vessels i design operate in the 0.8~1.3 froude range and as such a slender hull catamaran has approximately 50% less power than its equivalent monohull.
    However the hull forms my colleague are I generally use when appropriate (see caveat above) is the series 64. If you can't find or don't have access to this excellent paper i can scan it in for you. These hull forms were developed after the WWII with the intention of reducing vertical accelerations and resistance for Frigates etc, from operational experince. Downside, is their poor stability owing to their L/B range of 15~20. Hence ideal choice for a catamaran. You may well find this series to be ideal for your application.

    A stabilised monohull is not a monohull, it is a trimaran, ie multihull. Marine definitions do tend to confuse people who are not naval architects owing to clever marketing!
  7. sibosun
    Joined: Jan 2009
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    sibosun Junior Member

    Rick, thanks for your input, but I don’t believe that vessels like the RoCat or Adventures of Greg’s pedal boat are quite what I am looking for; they appear to me to have completely different design briefs. You will have to forgive my ignorance, but I don’t know what an “optimised hullform” is. Perhaps you could explain? Also, for what it’s worth, I don’t believe that oar power is a stone-age technology – with the right technique it can be a surprisingly efficient power source, and has some major advantages over propeller driven craft. Please see the following article –

    Any way, this is academic as this vessel is intended to compete in rowing races and record attempts against other oar powered craft.

    I am looking for three criteria in my brief:

    Consistency of output from the power source
    Moderate behaviour in a seaway
    Needs to operate efficiently at Froude numbers of 0.24 – 0.47

    To be of any value to the customer, this design must average 4.2 knots over 30 days on a rhumb line passage of 3000 miles. Naturally favourable weather conditions will assist this, but in reality the distance that they will travel will be greater.

    I have a provisional LOA of 12 m – 16 m, and a crew of between 14 and 16 people. Wetted surface will contribute the greatest proportion of my resistance quota, but I am sure that there must be, or have been tests carried out on hullforms designed to operate at low Fn.

    Obviously weight control is critical to the success of the design. The requirements of carrying sufficient food, water, power and ancillary equipment makes this a difficult task.

    I agree that catamaran configuration is NOT the way to do this, as I stated in my first post. As well as the drag penalty incurred at this speed, it raises serious practical snags for a rowing boat.

    Ad Hoc - I will do a little digging and see what I can unearth regarding the 64 series - it sounds like the right direction for the design. Also, whilst we are on the subject, I do appreciate that a stabilised monohull is not, technically, a monohull, however I look on the term as a subclass of the trimaran, different in that it has a much smaller percentage of overall buoyancy displacement in the outer hulls. I know this seems like a mistake on my part, but I like the term as it provides a distinction from "conventional" trimarans.
  8. Guest625101138

    Guest625101138 Previous Member

    The point of showing the world record holder is simply to point out that pedal power is the most efficient form of propulsion. It was not intended to be an ocean going boat for mutiple rowers.

    The paper you provide on rowing is very simplistic:
    1. It neglects fundamental aspects such as the biomechanical efficincy of pedalling over rowing. Pedalling is 18% more efficient biomechanically than rowing under aerobic condition.
    2. It ignores the variation in boat speed due to the long coast period in a rowing stroke. This is substantial when you analyse it and understand that power is a cube function of boat speed. Pedal power is continuous.
    3. The efficiency value provided for the propeller is based on a heavily loaded propeller. It does not relate to the lightly loaded propeller possible under human power. With single person propellers an efficiency of 86% is possible and it is possible to get up to low 90s for efficiency for props operating at higher speed.
    4. It does not count on boat motion in a seaway. If you have ever rowed in rough water you will know how difficult it is to operate efficiently. Pedalling does not lose efficiency unless the operator becomes debilitated through the motion.
    5. It ignores the windage on the paddles forcing back through the air. Scullers can reduce this by rotating the blade but this is not what happens in a seaway once the rower gets tired and becomes a significant extra drag in a headwind.

    So the paper is very limited in its analysis. It is a pity you are constrained to stone age technoilogy. The propeller quickly replaced paddle wheels on ocean going vessels although their efficiencies in calm water were similar. The most significant advantage of propellers was their ability to operate without reduction in performance once the boat started to move about.

    As far as hull optimisation goes. There is very fast software for analysing the performance of slender hulls to determine total hull drag to within 2 to 3% known as Michlet. This software has an in-built iteration module called GODZILLA that iterates the hull shape at a rate of hundreds of times per second depending on the power of the computer used. It continually selects the lowest drag hull while iterating. In a few minutes it can analyse hundreds of thousands of hulls with it continuously selecting the best. After a few minutes the shape changes very little so you know you have the optimum hull. No other method will provide the optimum hull form in such a short period.

    This software and its derivative have been used for optimising many vessel types ranging from Australian olympic rowing shells to US military craft. The hull that holds the human powered distance record was optimised for the displacement, combining Greg's weight with boat build weight, and Greg's power level.

    Hence I can claim with some confidence that it is possible to design optimum hulls. The limitation is that it gives an optimum for calm conditions. This however does translate well to a seaway as well. There maye be some adjustment based on the expected prevailing weather conditions and the above waterline form needs to be designed based on operating requirements.

    There is great value in knowing what the best possible hull form looks like and what various constraints might cost in terms of performance.

    Rick W
  9. Guest625101138

    Guest625101138 Previous Member

    Just to bring home the point on pedal power over rowing. The fastest single person human powered boat achieved over 36kph. Again not highly relevant to ocean boats but demonstrated the vast performance advantage of pedal over paddles or oars. The latter cannot achieve much better than half this speed.

    Rick W
  10. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect


    Given the rough values you have, then clearly the lowest froude range is better, the 0.24, with a length of some 16m even this is pushing it at some 6knots! To obtain as minimal residuary as possible, a displacement/length ratio (to achieve this) gives an all up weight in the order of 40~80kg, not a lot!

    So this brings to the point of "optimisation". I personally detest this term and its flagrant over use owing to a lack of understanding of the "whole design". To optimise is merely an academic exercise. In other words, to focus on one, and i do stress one, aspect of the design that, for the given data is "technical ideal", ie it cannot be improved upon.

    The problem with real design, is that the are many factors that affect the design. For example. Lets say you decide upon a certain configuration of hull and decide to be made from some exotic material, as opposed to normal glass, for weight reduction. Accounting says, you're over budget, can't buy the kevlar or carbon you wanted...or when the laminator starts, he drunk too much the night before and lays down too much resin, or when you rowlocks arrive they are made from steel not ally as promised, or the oars are heavier because of costs over runs these were 'down graded', or the food supplier didn't have dried chicken curry only only beef, which is 100g heavier...and so on and so forth.

    In designing a boat there are so many factors which need to be taken into account, to focus on one as the "be all and end all", is just ignorance.

    Whilst i concede that a pure out and out speed only racer, may well benefit from such a optimised review, owing to the fact the it is ostensibly just a hull, some mechanisms and a person, there are still other influencing factors which contribute to render the "optimal" no longer optimal owing the original parameters no longer being maintained. A slight shift in the wind, or a mild attack of cramp or an ambient temperature change...everything needs to be 'perfect' for such record attempts, not easy to control. Not saying it is not worth doing because it is, but this is pushing the envelope of what is boat is designed and only one application in ideal conditions. Hardly the same SOR as yours!

    The fact that a simple rough calculation, as above, demonstrates you have a tall order, in designing your vessel. Reduction of weight is paramount, far more so than optimised hull forms. Since It is not rocket science, the longer and more slender and the less displacement for the length is better than anything else. Hull shape, actually plays a very minor role.

    Many years ago i had a nice chat with Nigel Irens at a RINA conference we were both presenting, nice bloke. He said in his experience the VCG of a "trimaran" (if that is what you are still intending) should be below the level of the cross bridging structure where it butts/joins the main hull. If above, motions are very poor. Given your SOR, i don't see how you would be able to achieve this very easily, if at all.

    PS..if you're not a fan of the series 64, perhaps a variations of the Wiggly hull may be more your cup of tea?...bottom line is long and low displacement-length ratio wins hands down.
  11. Guest625101138

    Guest625101138 Previous Member

    I have gone into some detail in looking at the paper you linked to see how the authors arrived at their ridiculously high figure. This is the stated assumptions:
    For simplicity, we make the following assumptions:
    1. pitching and yawing motions of the boat are negligible,
    2. the oars have identical kinematics and inertial/geometric properties,
    3. air resistance on the oars is negligible,
    4. losses due to internal work (bearing friction, etc.) are negligible (Wint = 0),
    5. boat drag (Fboat) is proportional to the square of boat velocity (vb),
    6. the resultant oar blade force is perpendicular to the blade (as shown in Fig. 2), and
    7. the rotational dissipation, from torque on the oar blade multiplied by its angular velocity, is negligible
    (equivalently, we assume that for energetic purposes the forces of water on the oar are statically
    equivalent to a single force at the center of the oar blade).

    I doubt that this situation bears any relation to real rowing. There is no allowance for blade immersion. There is no allowance for the return stroke and what happens during this. The hull drag factors are scaled from rowing 8 data - a potential for favourable error. They have a fudge factor of 2.4 on the measured blade drag coefficient so the measured force data fits the model that arrives at 84% efficiency. The propeller efficiency is taken from a 1950s design for standard heavily loaded prop of the day.

    If you look at overall efficiency from oxygen uptake for rower versus pedaller of similar trained ability, using more precise hull data, you arrive at a rower achieving an overall efficiency of 14% compared with a pedaller achieving 22% - so the rower is going to expend 50% more energy to go the same distance at the same speed. That is a calm water comparison on efficient set ups. In rougher conditions the pedaller becomes even more favoured.

    Rick W
  12. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    The listed items 1~7 posted by Rick above is just QED with regards to "optimisation". Any study, to further the science, in general, needs to exclude or neglect certain aspects to enable a parametric study to be completed to proclaim....this is now optimised.

    Such as #3...considering the frontal area of the boat, rower etc, the small appendage, whilst has an effect, is in reality negligible, hence the statement. But is made so that a study of one or two "things" may be looked at in greater detail. Otherwise the research becomes very time consuming and cost prohibitive for very little real gain.

    However, the paper is no different to many others, as such all taken as interesting but not too literally. Since the paper, like an optimisation, is just one position on one aspect of the science that is being studied.

    Just more information for you to consider in your design.
  13. Guest625101138

    Guest625101138 Previous Member

    If you take 16 people working in two shifts you would expect to be able to maintain 800W on the hull continuously using oars. Assumes each rower can effectively apply 100W continuously. They would have to be capable of holding something like 150W on an ergometer to do this allowing for the rowing inefficiencies. Reasonably fite men could do this in 4 hours on, four hours off stints continuously.

    Weight of personnel is 1.28t so a well constructed hull with provisions for say 20 days might get as low as 2t.

    The linesplan for the optimum 2t hull for 8kts is attached. It will not quite achieve 8kts with 800W. It will achieve 7kts with 770W but it is reasonable to design for optimum speed slightly above what is sustainable to take full advantage of favourable sea conditions.

    You would need to go into complete detail on provisions and essentials such as water maker, comms, batteries, solar collectors etc to iterate on the weight estimate. You may also consider a more onerous rowing roster so fewer personnel and a lighter boat.

    It is quite a large boat so would be reasonably seaworthy with widely spaced outriggers. The hull is marginally stable with personnel seated on the keel but I expect you would want a self-draining cockpit for rowing so the outriggers would be required for initial stability and would be set to just caress the surface in calm conditions.

    There would be little loss in performance by shortening the bow and stern to remove the concavity evident in the plan view.

    Rick W

    Attached Files:

  14. Guest625101138

    Guest625101138 Previous Member

    I have attached the JavaProp analysis for the Opt_2t_8kts for 7.6kts based on 8 pedallers working at 150W. You will see the prop efficiency here is 86% and JavaProp has a limited range of foils. You could expect better with an optimised foil for the operating conditions.

    Rick W

    Attached Files:

  15. benjcturner
    Joined: Aug 2009
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    benjcturner New Member

    Are you still engaged in your project of building a multihull ocean rowing vessel? I'm currently seeking ways in which to do the Pacific ocean crossing E-W but exploring the idea of having a multihull vessel as apossed to the normal single hull that you see most ocean rowers use. My issue is the thought of capsize in a multihull vessel and not having the ability to turn it back over as easyily as a single hull which tends to do it automatically.
    Have you come up with any ideas thus far?

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