A bluewater, ocean going water ballasted matorsailer. Why not?

Thank you Crag Cay,
You read me very right !
I wonder if the elevated deck house should be of a rounded form to minimize windage, but then one should have to sacrifice usefull deck space...
I have also thought of an computerized automatic control of the engine, the batteries and the pumps, to send the right quantity of water to port/starboard tanks when the boat heels while under sail power.
The single chine hull forces the (many and heavy) pump batteries and the engine(s) to be placed higher than they should be for added stability. ..

 

Rounding the coach house, controlling the height of machinery, etc, are all several iterations away as you refine this design.

An idea such as this will require you to go round the 'design spiral' many, many times. At this stage it's essential to focus on the big issues, otherwise you'll go round and round and just get dizzy.

Pick some realistic, ball park figures and start really evaluating what you have.

 

The complexity of a trim tank, pump, electronics system drove many racers nuts! But at least they could afford to play with this (still unmature) idea. The true bluewater sailor (which you are obviously not) goes for a "no nonsense" arrangement on technical systems, never for complicating a boats propulsion.
When you are looking for professional advice, you should accept professional answers, and not only those which fit your prejudice.
I´m glad to quote Par again:

Love it or leave it, your idea has no place in bluewater sailing!

Regards
Richard

 

Thank you again apex1,

You are probably right, and that is the reason why there isn’t any such boat around, but I think that modern materials, electronic equipment AND computers could make a difference here. The operational complexity of systems is getting less and less as time passes by... Technology simplifies things, immature things are getting mature, and the cost comes down. I remember the days when autopilots, GPS, electric winches, generators, etc, were thought to be too complex for bluewater sailing... not any more.

I am sure, my dear friend, that, as a true bluewater sailor I believe you are, you can understand the nonsense of this sentence... Obviously, and fortunately, nobody, (professional or not...) can ever monopolize the knowledge and the truth of the ocean. Leaving this unfortunate remark aside, I am glad you offer me your valuable advice, together with your motto: "never forgot, that the valuation of "good" was just founded in MY knowledge only! " Now, my own knowledge is very limited and by no means on a professional level, as of many people in this forum, and that is the purpose of the threads. People like you that know more give advices and we listen! I can assure you that I always listen, and I don’t have any prejudice with anything, especially if it is only an immature vague idea!

Now, please give me some reasons why the water tanks can not be as large as we wish Reasons are always worth to discuss! In my language "reason" is synonymous to talking, speech, (Logos)

 

The concept, as Crag described it, could be a good weekender, or "island hopper" at it's best but a real bluewater cruiser.. never. To be a real blue water cruiser the ballast got to be more or less "rigid", meaning the CG staying in the centerline of the vessel thou some adjustment could be done with the amount of it..

Let's assume we take an avarage 40'er with 10t displacement and 4t ballast. Converting the ballast from iron/laed to water means 4t more displacement which means more wetted surface => more sail area => more righting moment => more water.. etc so we end up with 50'er with 40'er characteristics what comes to interior space and boat speed.. so in theory doable but not a realistic solution however..

 

Thank you Teddy,

Yes, but with shallow draft and GREATER motoring speed, as the LOA is longer and the total weight is smaller without the water ballast.

 

It won't have a shallow draft if you want to have some seekeeping ability (in a lake it would be a much simplier task) Water ballast dumped LWL either degreases or wetted surface remains. Can't gain anything without going XXL in the hull size I'm afraid..

 

Xar,

I know Par and Apex can be a bit dismissive of loony ideas like this one, but when they agree on something you can pretty much take it as gospel.

But to fill in a few of their blanks as to why it isn't that good of an idea particularly for a motorsailer... Remember Motorsailers are all designed for long distance cruising and comfort, not for performance. Now keep that in mind...

1) Motorsailers tend to be heavy and under canvased to begin with and stability is rarely their problem

2) The size of a water tank is limited by the amount of internal volume you want to dedicate to the tanks, the amount of righting moment the rig can support, and the additional loads that the hull can be designed to carry efficiently.

3) The water balast systems are incredibly complicated if done properly. You suggest using new computers, or technology but there is a real problem here. The unlimited budget racing programs stopped development on water ballast systems maybe 3 years ago. There has been no tech development since then that would allow a motorsailer where money is being budgeted to do effectively what sailing programs willing to spend 5 million a year on the boat couldn't do recently

4) Canting keels have proven to be more reliable, simpler, faster, safer, require less weight for the same righting moment, and cheaper than water ballast systems.

5) Canting keels take up little interior volume.

6) Canting keels require adding significantly less weight than a water ballast system since the weight they do add generates more righting moment per pund due to longer leaver arms.

7) Water ballast tanks must either be full or empty. Any sloshing is dangerous in this type of installation. This limits the practical number of trims available. And if you go with smaller tanks it adds more complexity, creating a horrible design spiral

8) Either system are prone to breaking, seriously hampering the value of them in non-racing applications. Since at least racers know and accept the risks of gear breaking.

9) If something goes wrong with a water ballast system how do you fix it off shore? Particularly far from a high tech Marina (unless you have a support boat with paid mechanics on board)

10) Any weight savings from a water ballast system is going to be offset by the fact that motorsailers are heavy to begin with

11) in the size of boats where this would even be possible the amount of wetted surface change with full or empty tanks is minimal compared to adding the lead in a keel

12) You are still going to need a keel to provide lateral resistance, so while you can save weight here you still need the wetted surface

13) I am sure there are more, but this is off of the top of my head.


Now do you understand? There is nothing about a water ballast, or canting keel design that belongs on any cruising boat. Maybe in a few years as the complexity, cost, and reliability of canting keels gets better they will start to appear on cruising boats, but I doubt it. Water ballast was an interesting fad as it was the first real try at effective movable ballast systems, but it is a fad that has been suplanted by newer technology and practices.

 

There's a little bit of confusion here regarding water ballast. The biggest possible benefit of using water ballast in a motor sailor is to be able to vary the displacement. Lighter displacement would help efficiency under power and increased displacement would benefit both sea keeping and to a degree, sail carrry-ing ability due to an increase in the righting moment.

This is long proven technology in boats as varied as Avon Seariders through to designs for Royal Navy patrol boats we did in the late seventies that were required to be stable radar platforms at rest but be capable of high turns of speed. In both cases the plumbing was very simple and reliable. In fact it's entirely passive in seariders and required only simple pumps in the patrol craft.

This is not the same as water ballast carried asymmetrically on race boats. I'd take more convincing there was any merit in that as I think a motor sailor could achieve sufficient 'stiffness' on hull form alone.

The stumbling block for 'form stable', or lightly ballasted boats (as these would be with their internal water ballast), has traditionally been their lack of ultimate stability. That is, how to make them self righting. But by adopting the solution used by the current generation of RNLI offshore lifeboats, this again is not impossible. The large deck house that is required with this concept is not incompatible with the idea of a motor sailor. So this concept requires the making of a form stable hull in high displacement mode, with a low resistance in light displacement mode with the ultimate sea keeping and self righting ability of the RNLI life boats.

These are all proven concepts. Can they be combined in a workable package that offers real advantages for this use? I don't know. But I do know there is enough potential there for it not to be dismissed out of court.

 

Thank you Stumble.

I am not afraid to say that I am not a believer... , but of course they are right in many points they raised and I appreciate their advice very much.

We are not talking about existing motorsailers here...If a sailboat is undercanvassed, stability isn’t her problem by definition...As I have said, I think that the main advantage of the water ballast system on a motorsailer is not greater sailing stability, but greater motoring speed.

Noooo...

Good point. The hull should offer a substantial form stability, i.e. it should be quite beamy.

You don’t. You motor to the nearest harbour. The advantage of the water ballast system is that it is needed only for sailing, and with a motor sailer you can always use your reliable powerful engine. On the contrary, if the canting keel of a sailboat goes wrong...
You first say that :

And then that ;

So it is a matter of time, not engineering. And I have to tell you that canting keels and water ballast were used in a few custom made cruising sailboats already.

Why minimal ? ? ? Less than the reduction of the total weight, of course, but not minimal.
Canting keel is superior to water ballast due to its greater righting moment, but you can not leave it on the surface of the water if and when you wish, and then take it in board again ...The main advantage of the water ballast system on a motorsailer is that it is a variable displacement system that one can use effectively while sailing or motoring.

 

Having trim tanks to get some additional weight in when fuel consumption has drained the tanks can be a very sensible point, but ballast has to be solid and far down.

 

Xarax,

if you are seriously trying to reduce the amount of weight a sailboat needs to carry for some amount of righting moment, then for now the only option in my mind for something other than an all out race boat would be a telescoping keel with a big bulb at the end of it. If you really want more righting moment and to save 5K lbs in lead, then give up shallow water cruising and add another couple of feet to the keel. Heck you could even put the bulb on a lifting centerboard to get back some of the draft you gave away.

But if you are thinking that water ballast will let you motor easier... Lets take a very light weight carbon fiber racing bat, the Santa Cruiz 52' with a displacement of 21,000lbs. Lets say you could knock 5,000 off of that so you are now down to 16,000. Sure it will motor at hull speed with a smaller motor than it's 'overweight' brother. So instead of needing a 65hp diesel burning 1/2 a gallon an hour you now need a 50hp burning .45 gallons per hour. Not really a worth while savings in my mind.

So now lets look at a cruising boat, the Irwin 54' with a displacement of 46,000lbs and a ballast of 16,000lbs. Now this is truly a heavy cruising sailboat NOT a motorsailor. With a 70hp engine it motors nicely at 8.5kn sucking down a horrendous 1 gallon an hour. Again you cut the displacement by 5K lbs and you can't even tell the difference. 5Klbs on this boat is about the difference between when the boat has full and empty water tanks (450 gallons at 8.34lbs per gallon=3753lbs).

Now lets take a look at a comperable motorcruiser... The Nordhavn 56' Motorsailer sits at 70,400lbs. Almost twice the weight of the Irwin. 5k lbs off of this boat is truly meaningless at about 7% of the total ships displacement or about 2/3 the weight of a tank of fuel (750 gallons). The motorsailer also carries 17,500lbs and a draft of 6'.


Yes each of these boats goes up a slight step in size, but I couldn't think of any three more radically different boats, in roughly the same size range.

Now on a different note the Irwin normally has a 5'6" draft. To get the same righting moment out of the keel but with 5k lbs less weight you would only need to increase the draft by about two foot (assuming the center of effort for the keel is at 50 of the draft). For the Motorsailer to keep the same righting moment but to drop 5K lbs you would need to increase the draft by about 2.5 foot.

Now through all of this remember that the motor sailer despite being 100% heavier is only carrying about 10% more sail than the Irwin, where the Santa Cruiz while being the smallest, and lightest is carrying about 10% more sail area than the Motorsailor.

 

Thank you Stumble

You are absolutely right in all your points, IFF we are talking about
1.), very heavy didplacement boats, with
2.), relatively small engines,
3.), relatively undercanvassed, where
4.), the saving of the amount of the total weight is not sunstantial (at least 25-30% on boats with high ballast ratio),
AND, last but not least,
5.), their hull design remains the same it was before !.
But I am thinking of light boats, with modern powerful yet economical engines, with a hull design that will help them go much faster when much lighter !
A quite long lifting or telescopic centerboard with a really small lead bulb, or a long canting keel, would be viable alternative systems, of course. But I think they are far more complicated than water ballast and pose far more problems in reliability and safety on a bluewater cruising boat. Apex1 told it very nicely : " If your system fails, be sure it fails at 3:30 at night, ... And be sure that happens half way between Pitcairn and Ushuaia."

 

And such hull cannot hold much ballast tankage so the only obvious answer is sidetanks with their pros&cons. So it might be ok motorsailer for coastal waters but not a blue water cruiser..

 

As I read the replies to this thread, it seems that there come two completely different kinds of motorsailers on people s mind, as two different answers to two different questions.
One can ask : How I can take a bluewater, ocean going, self righting cruising sailboat, and increase its motoring speed by reducing its lead ballast weight ( by using some amount of water ballast while sailing and dispensing with it while motoring ) ? The answer to this question varies, but at the end I believe that, either we can come to the conclusion that it is not worth the added complexity of the water ballast system, or we can design a motorsailer that will not be much faster or look much different from traditional motorsailers, ( only a little more expensive )
But one can also ask : How I can take a bluewater, ocean going, self righting cruising motorboat, passagemaker, trawler, or else, and make it able to carry sails ( by using some amount of water ballast while sailing and dispensing with it while motoring)? The answer to that question is a different animal altogether, one that we cannot say right from the beginning if it will live or die at the end of the day, but one that will probably look quite different from traditional motorsailers. The main difference would be in the form of its hull, I believe, helping it to motor faster than a traditional motorsailer, while retaining their ocean going qualities, safety, reliability, comfort etc. (It is still going to be a little more expensive though...)