Full Displacement of semi [Archive]

Portager

08-01-2003, 10:22 AM

Tdamico;

For your intended application there are many semi-displacement boats that will do just fine. The great loop is sheltered most of the way with only a few stretches of the ICW and Great Lakes that are exposed. Some (foolhardy) people have even done the great loop is a houseboat. Choose a boat that meets your budget and has the accommodations that you want/need. Your boat selection will determine if you need to wait a couple of days or a few days for good weather to cross the exposed stretches.

Full displacement trawlers are for people who want to cross oceans or cruise the West Coast of North America. The route from Seattle to Cabo is very exposed and rough. There are semi-displacement boats that could do it, but it would be more comfortable in a full-displacement boat.

With all due respect, I disagree with Gonzo’s statement. Comfort level is in heave, i.e. vertical acceleration due to wave impact is generally considered to be a function of waterline area to weight ratio with the heavier boat providing a more gentile ride than a lighter one. David Gerr has an excellent discussion of this in his book, “The Nature of Boats (Insights and Esoterica for the Nautically Obsessed)” starting on page 106 subtitle “Heave and Waterplane Loading”. Pounding generally refers to relatively flat bottom boats which tend to belly flop on the water after getting airborne. Pounding is a common problem on planning boats and racing boats in rough seas when they do not want to slow to displacement speeds. These conditions do not occur on full-displacement boats and only occur on semi-displacement boats when going too fast for the conditions. Roll stability is a more typical problem on trawlers except it doesn’t apply to most of the great loop.

If you are new to trawlers and planning such a big step, I would recommend the trawler world list and/or the great loop list. They can both be accessed at http://www.trawlerworld.com. They also have extensive archives which can be read and searched. You will find that nearly every question you have has been asked and answered many times and in many ways.

Good luck and keep us informed of your progress.

Regards;
Mike Schooley

tdamico

08-01-2003, 11:58 AM

Ahh...but eventually we do plan on making the passage to the West coast. Whether or not we ship the boat or sail the boat, in time, once experience and confidence builds. A West coast sojorn is not out of the question. I had narrowed my list down to full displacement boats like: Mirage Harbor 37 or 47, Selene 46, Krogen 39, or Nordhavn 42. I will still continue to learn, but still don't want to limit options by going for a semi for a few more creature comforts only to wish in 5 years, I could visit Alaska!

Portager

08-01-2003, 02:34 PM

I wouldn't put the Great Harbor 37 and 47 http://www.mirage-mfg.com/html/nav37b.html in the same class as the Selene 47 http://www.seleneyachts.com/47.htm, Krogen 39 http://www.kadeykrogen.com/krogen39.htm and Nordhavn 40, 43 or 46, http://www.nordhavn.com/home.htm. As a crude measure of stability, look at the above/below waterline area ratio (if you can find it) for a passagemaker it should be below 3. I can't find the A/B ratio for the Great Harbor 37 but it looks like it would be >3 to me, the Selene 47 is 2.5 full load to 2.7 light http://www.fridayharboryachts.com/selene/s47/s47-specs.html the Krogen 39 is 2.6 http://www.kadeykrogen.com/krogen39specifications.htm and the Nordhavn 40 and 46 are 2.3 http://www.nordhavn.com/40/specs.htm , http://www.nordhavn.com/46/specs.htm . A better measure of stability is the IMO offshore stability criteria, but nobody wants to provide that information. Also you will rarely find shoal draft monohull that qualify as Passagemaker.

The Selene 47 is actually a semi-displacement hull, note that maximum speed is a S/L of 1.65 and cruising speed is S/L of 1.34, but it is far more sea worthy that some full-displacement boats.

You might want to buy a boat that is adequate for your East Coast cruising and then, when you are ready to switch to the West Coast, sell it and buy a boat on the West Coast. That would avoid the time and expense of transporting the boat across country or going through the Panama Canal.

Regards;
Mike Schooley

tdamico

08-01-2003, 03:04 PM

Michael:

To me this is a wonderful discussion. Obviously I need to act like a sponge and absorb everything I can. You certainly are very knowledgeable. Can I get your reaction to the following?"

"The A/B Ratio Is Largely Meaningless

By Lou Codega
Naval Architect

Sooner or later potential trawler buyers will come across a term called the A/B ratio, as a measure of a yacht’s seaworthiness. Forget about it. The A/B ratio is, for all practical purposes, baloney.

Since its first publication in 1975, Robert Beebe’s Voyaging Under Power has been almost universally accepted as the authoritative source for information on long-distance cruising under power. This was undoubtedly a pioneering effort and, although dated, remains a wealth of practical considerations on many aspects of cruising boat mechanics. But it is not, and was never intended to be, a text on naval architecture as it applies to power craft. It is extremely weak in its treatment of many technical subjects in that it relies far too heavily on overly simplistic rules of thumb and comparisons made between a limited number of mostly similar boats.

I have tremendous respect for much of Beebe’s work, but I have a large ax to grind with his treatment of stability. There has probably never been an overused and yet so fundamentally useless a term as the A/B ratio. But it’s concept and calculation is easy for the layman to grasp, and its use has been perpetuated to some extent by those builders whose designs appear “good” by its measure. That’s too bad, as in this case a little knowledge is a terrible thing; I want to do my part to help it along a path to extinction.

Beebe proposed the A/B ratio as a measure of transverse stability, calculated simply as follows:

Projected profile area above the waterline

Projected profile area below the waterline

He then goes on to discuss ranges of this ratio that are found in then current trawler yachts, and those that he considers acceptable in boats that are, in his opinion, “qualified as ocean-crossers.” That’s it in a nutshell, and the discussion in the original text is only about twice as long as my summary. And there is no other mention of stability in the rest of the book, except to say how individual designs stack up to the A/B criteria.

This analysis is simplistic beyond credulity. The ratio is not now, and so far as I’m aware, has never been used by naval architects. It has a bit of utility when used to compare similarly proportioned and sized boats. But it neglects everything that is important to stability. The height of the boat’s center of gravity, its beam, weight, shape of the watertight boundaries, hull form, tankage and watertight integrity are all vital to an intelligent discussion of stability, but all are completely ignored. Take any boat that you want as an example. It has the same A/B ratio whether it is two feet wide or 25, whether hard chine or round bilge, if it has engine room air inlets on the side of the hull or amidships, or if it weights 100,000 pounds or 10,000.

The direct calculation of static stability has been done for 80 or 90 years, and, with the widespread use of computers, there is just no reason to simplify something so fundamentally important to the safety of the boat and its passengers into a rule of thumb ratio, and a half baked one at that.

A designer routinely models a boat’s form, calculates the weight and center of gravity, and in a matter of seconds mathematically rolls it while calculating it’s tendency to either roll upright or continue rolling to a greater angle. (In the “old days” the same calculation was done by hand, using an instrument of torture known as an integrating planimeter while seconds turned into days, but that’s another story for another time.) The complete watertight boundary, location of the center of gravity, weight, in short, all of the factors that affect intact stability are modeled exactly. The result is the so-called righting moment curve that you’ve all seen.

The example below, by the way, is not for the Navigator/Great Harbour boats and shows righting and heeling arms rather than moments. The moment is simply the arm multiplied by the boat’s displacement. The roll angle, usually zero through 180, is plotted on the horizontal axis. The vertical axis depicts the righting moment, which is the tendency of the boat to roll back upright or roll further. These typically depict a sine-like curve that starts a zero moment and zero degrees, increases to a maximum at say 50 degrees and then returns to zero at say 120 degrees. Up to 120 degrees, the so-called range of positive stability, the craft tends to return upright. Beyond that, the craft will tend to increase in roll, usually to 180 degrees or completely inverted.

I guess that I wouldn’t be so upset if the A/B ratio was backed up by some science. I could live with it if, for example, Beebe had done some true stability calculations and came to the conclusion that the A/B ratio was a good indicator of the stability characteristics proven by the more involved calculations. But there is no evidence that he, or anyone else, ever did such a thing. I haven’t either, and frankly I’d be shocked if it were the case.

By the way, an outstanding and very accessible discussion on stability, as well as most every other aspect of boat design can be found in Preliminary Design of Ships and Boats by Cyrus Hamlin. I can heartily recommend this book to anyone wanting to further his knowledge of boat design, intended as it is for the engaged amateur or beginning professional. It is remarkably well written and goes beyond simplistic ratios and rules of thumb to give a true understanding of underlying design principles.

One more point while we’re at it. Stability calculations and criteria are intended to be comparative, not predictive. This seems perhaps to be a minor point, but it is crucial to your understanding. The righting moment curve that results from the calculations I just described result from an artificial condition that the boat will never encounter. Remember, the designer mathematically rolls the boat in still water. This same calculation, by the way, is made for most any ship around, including warships and cruise liners. This is clearly not an accurate representation of what happens when the boat is at sea.

What most folks don’t realize is that this curve is only the first step in the process. Overlaid on the righting moment curve is a curve of wind heeling moment, (as shown in the example above) or the effects of off center loading, or high-speed turns, or the firing of guns broadside, as is appropriate to the service of the ship. The two graphs are then compared against each other as well as accepted, and in many cases mandated, standards on a pass or fail basis. These standards are based on past experience for similar types of craft. What is implied by this approach is that other craft having similar stability characteristics have proven sufficiently safe in service and that by extension, so should the new craft. There is no expectation, much less a guarantee, that a boat that has a positive righting arm up a stated angle will survive a roll to that angle in a fully arisen sea. It may, it may not. But stability calculations and criteria do not claim to offer an answer.

Which returns us to the A/B ratio. It’s a rule of thumb, and like all rules of thumb it is easy to grasp and understand. But it is a gross simplification of a vitally important issue, and to my mind one that does far more harm than good. Its time, if it ever existed, has long since past. Any builder or designer worthy of your consideration will be more than happy to discuss their boat’s stability characteristics and how they relate to your anticipated cruises. But please, leave A/B ratios out of the discussion. "

Portager

08-01-2003, 04:06 PM

I agree with Lou Codega, the righting moment curve is a superior measure of stability and it should be the preferred method. Unfortunately most manufacturers will not provide that data. Since a more useful measure of stability is not available, A/B ratio is generally the best information available. I would not buy a boat without the righting moment curve and if the boat were used, I would insist on an incline test to confirm that the boat stability had not been compromised by the previous owners. Boats have a way of gaining weight over the years and this weight rarely improved stability.

What the A/B ratio is somewhat useful for is measuring the sensitivity of the boat to cross winds, although the measure should be based on the sum of each segment of area times its distance from the waterline, which would make it proportional to the disturbing moment. The righting moment curve is a measure of static stability with no wave induced disturbing moments or wind disturbance moments. A boat with a high A/B ratio and marginal stability could be in serious trouble in high winds. (I also find the trend to enclose the frybridge with eisenglass very disturbing in this regard. If you want a boat with a pilothouse you should buy a boat with a pilothouse, not enclose the flybridge.)

The righting moment curve is also used in the IMO offshore stability criteria, which is the measure of stability that I have choosen for Portager.

Here is a list of manufacturers of Ocean Voyaging Power Boats that I copied from a post by Georgs Kolesnikovs on the Trawler List http://lists.samurai.com/pipermail/trawler-world-list/1998-August/004194.html .

Branson Boats
Cape North
Cheoy Lee
Grand Banks
DeFever
FairIsle
Fleming
Kadey-Krogen
Kanter Yachts
Linssen
Nordhavn
Northern Marine
Park Isle Marine
Real Ships
Willard

Regards;
Mike Schooley

gonzo

08-01-2003, 07:48 PM

I have worked in trawlers in the North Atlantic. In rough weather it is impossible to lay in a bunk. You are airborne half the time. This is not an exageration, we use to tie ourselves. In the same conditions, thirty foot seas, a James Wharram catamaran was much more comfortable. A heavier boat has a higher bottom loading regardless of speed. Slow trawlers pound hard. Herreshoff, among others, studied the influence of hull design on roll, pitch and yaw. He found it affects the movement more than displacement or metacenter. Heavy displacement boats are slow, which keeps you in the rough weather longer. Also, they end up with all kinds of appendages and gizmos like outriggers to keep them half way livable.

tdamico

08-01-2003, 08:58 PM

Is a Power catamaran a "live aboard" boat? Is is sea worthy for extensive cruising in weather?

Portager

08-03-2003, 12:24 PM

This will probably initiate controversy, but I’ll don by flame retardant underwear and take a shot.

The short answer is yes, provided they are large enough.

Catamarans will pound in choppy seas if the height of the bridge connecting the hulls isn’t sufficient for the conditions.

Catamarans have very high initial stable and, in comparable sea states, they will have smaller roll angles than monohulls, however too much stability can be just as uncomfortable as too little stability. When a Cat is disturbed by a wake or beam seas the roll affects are lower in magnitude but higher rate, which is generally more disturbing. The motion of monohulls tends to a more gentile rolling action.

Some monohulls supporters emphasize monohulls advantage in stability range and point out that multi-hulls are stable inverted, however the higher initial stability should compensate for the reduce stability range and in a power catamaran (without the vertical close line) capsizing conditions are extremely improbable.

The practical downside of Catamarans; they are more difficult to find slips for and you are always racing to the next marina to beat others to the last end tie, almost all Cats are dual engine which increases maintenance cost and effort, they are very hard to control with one engine out or off, they are very difficult to transport over land, I have seen very few moderate sized Cats with a decent pilothouse.

The advantages of Catamarans; they can have shallower drafts than monohulls (although too shallow and they will pound), for comparable displacement they have lower specific fuel consumption and longer range at the mono-hull cruising speed and significantly higher maximum speed, Catamaran pricing is very competitive, for a comparable displacement, Cats provide more living space and are more open (although in the smaller range the narrow hulls can be a bit confining).

I’m sure this list could be expanded given more time.

Regards;
Mike Schooley

tdamico

08-03-2003, 03:27 PM

Actually a little controversy isn't always a bad thing, I enjoy different opinions.

Would you say that a Catamaran in the 45' range would qualify as being large enough?

I have seen several Catamarans in this size that have flying bridges and a "raised" look to them, sort of like a "Trawler cat" Would this design tend to reduce the pounding you mention in choppy seas?

Regarding the difficulty in finding slips, as a retired live aboard we could tend to arrange our visits to the marina during week days or times when activity is less. Storms aside, is this a solution?

Also, it was my thinking that I would go with a two screw trawler for peace of mind and better handlig, so the increased maintenance in having two engines would be a wash. I had heard that handling was much easier with two screws, than one, especially in wind. Do you have an opinion on the validity of this? Would controlling a monohull with one engine out be as difficult as handling a catamaran?

The advantages of Catamarans do seem obvious. More room for the money. With enough weight, more general stability. 45' boats can have the room of a 55' monohull. I am seriously beginning to change my thinking from a monohull to a catamaran. A month ago, I would have said a full displacement hull trawler was the only way I would go. Now...I'm not too sure.

TomD

Portager

08-04-2003, 11:35 AM

Originally posted by tdamico
Would you say that a Catamaran in the 45' range would qualify as being large enough?

IMHO, no. TrawlerCat Marine ( http://www.trawlercatmarine.com/index.html ) claims to have the highest waterline to forward deck clearance on the market at 7’, yet they list the 43’ model as an Island Hopper. They do not use the Passagemaker label until they get to 54’. By the way, on Yachtworld.com the new 43’ Island Hopper starts at $445K and the 53” Passagemaker starts at $689K.

I have seen several Catamarans in this size that have flying bridges and a "raised" look to them, sort of like a "Trawler cat" Would this design tend to reduce the pounding you mention in choppy seas?

I’m not sure what you mean by a “raised” look, but the only way I know of to avoid pounding is to increase the forward deck to waterline clearance and then avoid conditions that exceed the boats capacity. Increasing the clearance requires a wider beam, which requires longer length for directional stability. If you can’t avoid sea states where you pound, then your only alternative is heading into it because the aft waterline clearance is usually lower than forward and the swim steps don’t take crashing waves for very long.

Regarding the difficulty in finding slips, as a retired live aboard we could tend to arrange our visits to the marina during week days or times when activity is less. Storms aside, is this a solution?

I think you’ll have good luck in the off season, but in peak season mid week only helps a little. You will have problems in the great loop. The inland marinas are not equipped to accommodate big cats. Maneuvering will be a problem and haul outs will be very few and far in between.

Also, it was my thinking that I would go with a two screw trawler for peace of mind and better handlig, so the increased maintenance in having two engines would be a wash. I had heard that handling was much easier with two screws, than one, especially in wind. Do you have an opinion on the validity of this? Would controlling a monohull with one engine out be as difficult as handling a catamaran?

A review of boat assist records show that for diesel boats, 85% of engine out problems are fuel related and propeller/rudder damage is far more common than engine problems. In addition, electronic engine controls have made modern engines far more reliable than they were a decade ago. Most modern diesel boats are going to single main engine and single prop/rudder protected by a full length keel to reduce propeller damage. The net result is far fewer breakdowns that a twin engine boat.

On the handling issue, it is true that twin screws are more maneuverable than a single, but a single with a properly sized bow thruster is better than two props. I think if you need help maneuvering, get a bow thruster, it is far cheaper, more reliable and more effective than twin screws.

The advantages of Catamarans do seem obvious. More room for the money. With enough weight, more general stability. 45' boats can have the room of a 55' monohull. I am seriously beginning to change my thinking from a monohull to a catamaran. A month ago, I would have said a full displacement hull trawler was the only way I would go. Now...I'm not too sure.

I would argue that the disadvantages of Catamarans are more subtle. Maybe there is a reason why monohulls have such a large market share and Catamarans have so little resale value. I think this decision requires a great deal more research and ultimately I would find a way to spend several days and nights on one before buying. I can’t say I ever slept on a Catamaran, although I spend a night trying.

Regards;
Mike Schooley

Guest

08-04-2003, 12:45 PM

in my experience cats seem to be more of a hard jerking type movement compared to a monos gentle roll. but if going into wakes directly cats (especially air entapment cats on plane) provide one of the smothest rides ive had. Driving a cat is a dream as they turn like they are on tracks. But docking is an issue due to thier width. they have tons of room and are very nice to live on. They generally have much better fuel efficentcy as well as higher top speeds than monos.

tdamico

08-04-2003, 01:19 PM

I agree that much more investigation needs to be done before we are anywhere near our decision. We will also charter several boats before making our final decision. Michael, is a 7' clearence enough to counter effect the pounding you mentioned earlier. I actually communicated with the owner of the company you mentioned and he feels that the Island Hopper is not only a deep water boat, but is sailing one from China to Miami for promotional purposes. He hopes to have this boat at the powerboat show in Anapolis in October. Is the hard jerky movement analogous with the way a pontoon boat handles?

Regardless, despite all the upsides or downsides to ride, seaworthiness, etc. if you can't find a place to dock it from time to time, its worthless. From what I can see, beam for monohulls that I am looking at run around 16' and beam for the cats I am looking at run around 21', is this extra 5' really critical?

Portager

08-04-2003, 11:45 PM

Originally posted by tdamico
Is the hard jerky movement analogous with the way a pontoon boat handles?

If you are talking about the way a pontoon boat reacts when it is hit by a wave from the beam, then yes. When a wave encounters the pontoon, the water level relative to the pontoon suddenly increases causing a sudden increase in buoyancy force. When the wave hits the Catamaran head-on the affect is distributed over time, but when the wave hits broadside the force is sudden and since it has a large lever arm relative to the ships center of gravity, it creates a high angular rate.

From what I can see, beam for monohulls that I am looking at run around 16' and beam for the cats I am looking at run around 21', is this extra 5' really critical?

The beam of the Island Hopper 43’ is 22’, which is 1 foot wider than the Nordhavn 72’. Since the maximum air draft to clear a bridge in Chicago is 19’, boats the size of the Nordhavn 72’ are unable to complete the great loop. Enough said?

Next time you talk to TrawlerCat ask them what the minimum air draft of the Island Hopper 43’ is. If it is greater than 19’ then the Island Hopper 43’ and the Great loop are mutually exclusive.

Regards;
Mike Schooley

Willallison

08-04-2003, 11:54 PM

Have you considered something like our very own Tad Roberts' "Passagemaker Lite " series of designs ( http://www.tadroberts.com/ )
Air draft is low, stability, comfort, economy etc are all good..... and I'm sure Tad would be only too happy if you were to commission one!:D

Portager

08-06-2003, 09:19 PM

Did you get your questions ansered or just get anoyed?

I hope the former but if not I am sorry. I just want you to make sure the Cat is really what you want before you make a decision that cost a lot of money.

Regards;
Mike Schooley

tdamico

08-06-2003, 09:55 PM

No, Michael. I was away on a business trip and just got home this evening. Brutal trip, I'm going on about 2-3 hours of sleep in the last two days. Anyhow.

I am really torn. I can't wait until September and October to visit TrawlerFest and then the Power Boat show. I really need to climb around these boats.

I am drawn to the cat, but I wonder how hard it really will be to find a slip. Some say that 90%+ of the time is spent on the hook, so finding a slip every month or so for a few days is really not a big deal. I really have no way of knowing if this is true or not. Hopefully, at the boat show I can meet some owners. If I pick a cat that is under 19 bridge height, then am I correct in assuming that I can navigate the great circle route? Will I find anchorages along the way or will the 22' beam really be a huge factor? If I choose the monohull trawler, will the greater draft limit me when I want to explore those out of the way places?

Also, how realistic is it, really, to find free anchorage or inexpensive moorings in the islands and the east coast?

I just have so many questions!!!

Thanks to all. :confused:

Portager

08-07-2003, 01:04 AM

I think the people who spend a high percentage of their time on the hook are the ones on a tight budget. Those who can afford it tend to spend about half their time in slips. The reasons are to eat out, to gun the AC without running the generator, use shore facilities such as access to phone lines to catch up on email, …

The Catamaran I tried to sleep on was on an end tie. I never realized how unprotected end ties are until that night. Every passing boat produced enough of a wake to wake me up. Maybe that’s how it got its name? A ferry went by ever 2 hours and produced enough wake in a no wake zone that I’d go airborne. When the wake hit the first hull we would bob up, but then the wake hit the second hull the boat would reverse direction while we were still going up. I’d wake up in mid air, just an instant before impact. I spent the second night in a Motel 6.

If your air draft (with mast lowered) is less than 19’ you should be able to navigate the Great loop, although you might trouble on some of the narrower channel systems. I’m not sure how wide the locks are.

I think you can find abundant anchorages in sparsely populated areas, but the closer you get the population centers the harder anchorages will be to find. There are also long stretches on the inland rivers that have been widened and dredged for barge traffic where anchorages are rare.

If your interested in gunk holing maybe you should take Willallison’s advice and consider Tad Roberts designs http://www.tadroberts.com . The Passagemaker Lite 46 has the following specifications:
LOA 46’0”
LWL 45’0”
Beam 11’6”
Draft 2’10”
Displacement 29000 lbs
Fuel 860 gals
Water 200 gals
Power (2) Perkins M65
59 HP @2600 RPM
Top Speed 11.5 Knots
Cruising Sp. 10 Knots
Vertical clearance (boat plus 14" grd. clearance) 13'2"

With a draft of only 2’ 10” it is 2” shallower draft that the TrawlerCat Island Hopper 43’ and it looks a lot better. Best of all it could be transported without a pilot car.

If that won’t do, try the Passagemaker Lite 56:
PL 56
LOA 56'0"
LWL 55'0"
Beam 13'0"
Draft 3'6"
Displacement 51000 lbs.
Fuel 1100 gals
Water 400 gals
Power (2)John Deere 4045DFM 75 HP @2400 RPM
Top Speed 11.5 Knots
Cruising Sp. 10.5 Knots

The draft is a little higher but it is much larger inside.

Regards;
Mike Schooley

tdamico

08-07-2003, 08:14 AM

[QUOTE]
I think the people who spend a high percentage of their time on the hook are the ones on a tight budget. Those who can afford it tend to spend about half their time in slips. The reasons are to eat out, to gun the AC without running the generator, use shore facilities such as access to phone lines to catch up on email, …

Wouldn't this negate the reason to live aboard a boat somewhat. I am probably wrong, but living at a slip sounds more like living in an RV park, only on a boat. Money is not the issue, peace and serenity is. Also, am I wrong in thinking that the AC will run either off batteries or off the gensat? As we have no family, phone service won't be an issue and our boat will be outiftted for high speed internet via sattelite. Can you respond to these points?

[QUOTE] The Catamaran I tried to sleep on was on an end tie. I never realized how unprotected end ties are until that night. Every passing boat produced enough of a wake to wake me up...

This point gets back to the question about marinas having slips for cats. If money wasn't the issue, wouldn't simply renting a slip for a large boat work? How limited will large slips be? I assume that gassing up and pumping out would be no issue, so, finding a large slip every few weeks, if I am willing to pay...?

[QUOTE]If your interested in gunk holing...

I have heard this term before, what in the heck is gunk holing?

Also, is pumpout available at moorings?

gonzo

08-07-2003, 10:43 AM

A large wake will move a monohull or a multihull. I can't see the difference in that situation. I suppose some people aren't able to sleep at sea. I agree that live-aboards have a setup not far from an RV park. However, most talk about sailing the seas and seeing the world. I wonder what they'll do with the plants in the cockpit and the phone connection. Anchoring out is a choice that has nothing to do with money. I prefer peace and quiet to the commotion at the marina.

Portager

08-07-2003, 10:49 AM

Originally posted by tdamico
[QUOTE]
Wouldn't this negate the reason to live aboard a boat somewhat. I am probably wrong, but living at a slip sounds more like living in an RV park, only on a boat. Money is not the issue, peace and serenity is. Also, am I wrong in thinking that the AC will run either off batteries or off the gensat? As we have no family, phone service won't be an issue and our boat will be outiftted for high speed internet via sattelite. Can you respond to these points?

It is like an RV park, only higher class. In the hot weather peace and serenity are probably better in a slip. A recurring theme on the Trawler List is people who run their generator all night in a peaceful anchorage. No A/C system that is currently available runs for an appreciable period of time off batteries. Almost all A/C systems use alternating current (AC) and therefore require the generator to be running. I am looking into running the AC off large inverters and going to all DC power, but I’m a maverick. I calculate that I can A/C the owners state room (i.e. only run 1 A/C zone) for 8 hours off the battery bank in hot weather, or I could A/C the entire boat for 4 hours, run the auxiliary engine for 1 hour and then A/C for another 4 hours off batteries, but this is revolutionary. Most boats today have to run the generator to run the A/C even while the boat is underway! Most boats generators are quite noise. Soundproofing has come a long way, but the sound shields in many older boats are absent or inadequate. In addition many older boats have larger retrofit generators and there isn’t room for a good sound shield anymore. Many boats only have soundproofing between the generator and occupied spaces and nothing to the outside. Even a quite generator sounds loud in a quiet mooring, except inside the boat with the generator and A/C running and the windows closed.

Ah, high speed internet access. I too thought I would have broadband at sea. I had dreams of video conferencing from the boat :). It turns out the two way satellite service is only available on stationary platforms :( due to the pointing requirements for the ship to satellite signal. They do have what they call mobile-stationary systems, which means you can mount it on a mobile platform but only use it while stationary, but boats in the water do not qualify even tied to a slip. The only high speed two-way satellite service I know of is INMARSAT which provides 64 kbps at a cost of $10/minute http://www.marinelog.com/DOCS/teled.html ! Check out my “Wireless Internet” presentation on my web site at http://www.portager.info/newEmail_files/frame.htm .

This point gets back to the question about marinas having slips for cats. If money wasn't the issue, wouldn't simply renting a slip for a large boat work? How limited will large slips be? I assume that gassing up and pumping out would be no issue, so, finding a large slip every few weeks, if I am willing to pay...?

When I changed my plans from a 36’ to 48’ mono-hull, I called several local (Southern California) marinas to check slip fees. More than half could not accommodate the 48’ boat at all. Now you will have the beam of a 70’ mono-hull, how many 70’+ slips do you expect to find on the inland river marinas? If you wait for the Riverboat Casino to leave you can tie up there until it returns. Install a slot machine and make a little money too. :)

I have heard this term before, what in the heck is gunk holing?

Gunk holing just means poking about in very shallow water. The term was probably originated by owners of deeper draft boats that couldn’t do it.

Also, is pumpout available at moorings?

No and also not available at anchor ether; however on most of the Coastal area you can discharge a few miles offshore.

Regards;
Mike Schooley

gonzo

08-07-2003, 10:59 AM

Is A/C really a necessity?

tdamico

08-07-2003, 11:04 AM

Gonzo, your posts are great, as a counterpoint. If you can find some time, I would love to have you elaborate on some of your opinions. Are you familiar with cats? Are there any "real" issues around finding dock space when you really need it, regardless of whether in the "Ditch" or sea? How realistic is "living on the hook" I agree with you that it has more to do with a lifestyle than it has to do with money. Is this a naieve point of view?

Michael:

As regards high speed internet access, I will be installing a KVH TRACNET Service.

This system uses a slow speed "uplink" (landline, cellular, or satphone) to request information from the internet, then the requested files from the internet are sent to the boat using a high speed connection to the DSS TV satellite. Special installation connections are made to the KVH sat TV antenna so that it will interface with the new data system. In order to use this system, the vessel will need to have both KVH satellite TV antenna, and the new Tracnet "uplink" antenna. There will be a monthly charge for the high-speed downlink service, and a per minute charge on the "uplink", which will depend upon which uplink service is needed. The "downlink" speed will be very fast: 400kbps.

gonzo

08-07-2003, 04:09 PM

I have sailed and fished the Atlantic from Argentina to Canada, worked in the islands for a while and cruised the Amazon basin. There are all kinds of different approaches to cruising, and as long as they fit your life, they are equivalent. I am sailing the Great Lakes now, where the water is frozen half the year ( iceboats are fast). Once you leave the more touristy areas, boat facilities are scarce. A problem many people have, is that their boats and lifestyle depend on continuos supplies. It is limiting as to the areas available. I think that a boat with less systems gives me more freedom. However, it is at the expense of confort. Boats designed for A/C, and I have built a few, have little or no provision for natural ventilation. In my opinion, they make poor long range cruisers. A wind scoop can cool down a boat to a confortable level. If 65-70 degrees is required at all times, then an A/C is necessary. But then, what is the use of going to the tropics?

Willallison

08-07-2003, 09:26 PM

This is developing into a very interesting thread, I must say. :D
Now I don't profess to know a great deal about the 'great circle' route, living on the other side of the world as I do, however much of this discussion is relative to any long-term cruise.
As far as choosing to anchor out vs berthing o/night in a marina, I'll take the anchoring out option any day. I've never understood why people who go boating to 'get away from it all' go straight to the nearest marina where there's less peace and quiet than if they'd stayed home. Sure, you might spend a night tied up here or there in order to go see the local sights, or to eat out once in a while But otherwise there's few things as pleasant as waking up in a secluded bay with nobody else around and watching the sun come up to burn the morning mist off the water. Or to step straight from the bed into the water for a morning swim.
On the other hand, if doing the circle means having to anchor close to a riverbank, whilst other boats and ferries can pass by continuously: or if that secluded bay is so full that it resembles a parking lot, then the marina starts to look pretty good!

Back to the cat / displacement / semi displacement debate. I've not spent much time aboard cruising cats - they definitely have the advantage when it comes to efficiency at higher speeds (15 - 20 knots or so). Berthing is widely regarded as a problem. Where I live there a 7 marinas nearby. A few contain largish cats, but visiting multihulls are generally forced to take end-ties. Living spaces tend to be nice and roomy, but cabins tend to be rather more confined than in a monohull. Ventilation to these cabins is often not what it could be either.....
Unless you have a very fat wallet, I'd forget the semi-displacement boat. We operate a 48ft Offshore yachtfisher. With a pair of 320hp diesels it tops out at around 18 knots. We haven't owned the boat for very long, but at that speed, I can tell you that you can visibly watch the fuel guages fall!!:!: Fine for short runs, but for any longer cruise it simply limits range too much. We usually operate the boat in the 9 - 10 knot range.
A displacement boat operating at or near these speeds will be more economical - partly as a result of hullshape and partly because its engines will be sized for the job. Further, if there's one simple rule that applies to all hulltypes, it is that the more weight you add, the more power you need to drive it at a given speed. Cats & planing hulls are most sensitive to weight, then, semi-displacement and least affected of all is the displacement vessel. As you plan on cruising long term, plan on taking lots of stuff - plan on adding lots of weight. Lastly, I gather that much of the circle is speed / wake restricted. So after all that, the displacement vessel is the one I'd go for.

Regardless of which type you choose, you must decide what kind of boater you want to be. Do you want a floating condo - where you have all the 110v domestic appliances - electric cookers, air con, heaters etc etc. If so, you'll want good shore connections and an appropriately sized, big genset. Most US boats are set up this way. Alternatively, you can go the 12 / 24 volt route. This requires more careful power management and different systems, but can generally provide most of the same comforts - just in a different way. The advantage here is that you aren't as reliant on shore power or running a generator every time you want to do something. Both have their pro's and cons, but you really need to choose one type of the other.

The most valuable advice I could give, would be to go to as many boat shows as you can. Clamber all over the boats. Forget about the shiny topsides - check out the living spaces: is the boat easy to move about on: is there sufficient storage space (you'll need at least twice as much as you think...): will you be able to handle the boat with your expected crew. The list goes on.
Talk to as many people who have completed the circle as possible. What kind of boat did they operate: what would they do differently the next time......
Lastly, don't be fooled into thinking that one boat - or type of boat - can do it all. Better to buy a boat that suits your needs now - to complete the circle if you choose - and then replace it with something more suitable for offshore cruising if and when the need arises. There's no more sure-fire way of having a mutiny than to send the wife to sea in a riverboat!;)

tdamico

08-07-2003, 09:57 PM

[QUOTE...As far as choosing to anchor out vs berthing o/night in a marina, I'll take the anchoring out option any day. I've never understood why people who go boating to 'get away from it all' go straight to the nearest marina where there's less peace and quiet than if they'd stayed home. Sure, you might spend a night tied up here or there in order to go see the local sights, or to eat out once in a while But otherwise there's few things as pleasant as waking up in a secluded bay with nobody else around and watching the sun come up to burn the morning mist off the water. Or to step straight from the bed into the water for a morning swim.

While we will want to utilize our boat for a number of diferent activities, the above statment is bang on. This is our thinking exactly, but there is a lurking doubt that this is practical. Some, not all, but quite a few boaters that lurk on the various sites all seem, somehow, to make it seem that this community of boaters is really a community of RV people, just on boats. This is NOT what we are looking for in our lifestyle change. Reading posts like this gives me hope, that I won't have to live in a marina most of the time.

[QUOTE]...Unless you have a very fat wallet, I'd forget the semi-displacement boat. We operate a 48ft Offshore yachtfisher. With a pair of 320hp diesels it tops out at around 18 knots. We haven't owned the boat for very long, but at that speed, I can tell you that you can visibly watch the fuel guages fall!!:!: Fine for short runs, but for any longer cruise it simply limits range too much. We usually operate the boat in the 9 - 10 knot range.
A displacement boat operating at or near these speeds will be more economical - partly as a result of hullshape and partly because its engines will be sized for the job.

I pretty much figured this out, but if we have the disipline to stay in the 8-10 knot range, is the fuel consumption significantly more than a displacement hull? Having the ability to get a few more knots of speed might be important, might not, but I have heard it generally stated that semi-displacement hulls with full keels, roll much less. Thoughts?

[QUOTE]...As you plan on cruising long term, plan on taking lots of stuff - plan on adding lots of weight. Lastly, I gather that much of the circle is speed / wake restricted. So after all that, the displacement vessel is the one I'd go for.

Yes, we do plan on cruising long term. Who knows, 5-10-15-20 years? The only real reason that we thought we would start with the Circle Route was to get to know our boat. How to navigate it. How to live on it. How it handles. To "really" get to know it on a "relatively" safe passage. That would be our first adventure. After that it would be all coastal cruising, island hopping, and who knows, in time maybe transocean. So we need to keep our eye on that.

[QUOTE]...Regardless of which type you choose, you must decide what kind of boater you want to be. Do you want a floating condo - where you have all the 110v domestic appliances - electric cookers, air con, heaters etc etc. If so, you'll want good shore connections and an appropriately sized, big genset. Most US boats are set up this way. Alternatively, you can go the 12 / 24 volt route. This requires more careful power management and different systems, but can generally provide most of the same comforts - just in a different way. The advantage here is that you aren't as reliant on shore power or running a generator every time you want to do something. Both have their pro's and cons, but you really need to choose one type of the other.

Now this is really the most facinating statement of all! I want to be simpler than I am, but not all the way. I won't want electric cookers, and small kitchen appliances like waffle makers, toasters etc. But it would be nice to have some AC now an then. Most especially since we will be taking our three small dogs with us. During some of those hot afternoons, I don't want to bake their brains out while I am diving the reef! Might seem weird, but none the less, they are part of my family. I have never heard the 12/24 volt route, but it is intriging. Can you point me to some sites or areas where I might do some investigation?

[QUOTE]...The most valuable advice I could give, would be to go to as many boat shows as you can. Clamber all over the boats. Forget about the shiny topsides - check out the living spaces: is the boat easy to move about on: is there sufficient storage space (you'll need at least twice as much as you think...): will you be able to handle the boat with your expected crew. The list goes on.

This is great advice. We are already registered for TrawlerFest in Solomon Island in September and the Power Boat Show in Annapolis in October. We are very excited to actually crawl around. We have our need list, want list, don't want lists as ready as we can make them, given our inexperience. TrawlerFest in interesting in that we will actually get to chat with some people who are actually doing what we want to do. I hope. Perhaps they are just glorified RVr's.

:cool:

gonzo

08-07-2003, 11:28 PM

Hey Will, I though you guys down under organized cruises around beer supply. Pease don't disappoint me and tell me it ain't true :)

Willallison

08-08-2003, 01:05 AM

LOL! Well to give you some idea Gonzo, I can well remember a few years back when the water police tied up next to a fairly large group of boats all rafted up. We wondered what was going on until two of them dragged a keg of beer onto the deck and spen the rest of the afternoon teaching us about the foolishness of mixing boating and alcohol!!:D
Actually, I'm not much of an example as I rarely drink anything stronger than coke!

if we have the disipline to stay in the 8-10 knot range, is the fuel consumption significantly more than a displacement hull? Having the ability to get a few more knots of speed might be important, might not, but I have heard it generally stated that semi-displacement hulls with full keels, roll much less. Thoughts?

At 10 knots we seem to manage about 1.5 nmpg. At 8, our old boat (a 36ft CheoyLee displacement 'trawler' with 2 x 120 hp) did a bit over 2.5 - so consumption was almost 1/2. Also, it's not good for big diesels to run under light load all the time as it can glaze the cylinders.
As far as the rolling goes, it's more that the motion is different as opposed to more or less. A heavy, round chined displacement hull would probably tend to roll a little further than a hard chined semi-displacement boat, but its motion would probably be more gentle - less snappy. This is what Gonzo and Mike were debating earlier in the thread. In my opinion, it comes down as much to the competency of the designer as it it does to the hullshape.

The only real reason that we thought we would start with the Circle Route was to get to know our boat. How to navigate it. How to live on it. How it handles. To "really" get to know it on a "relatively" safe passage. That would be our first adventure. After that it would be all coastal cruising, island hopping, and who knows, in time maybe transocean

Once again, I don't think that any one boat can do all these things well - or rather, I feel you'd be way better off getting to know boating in something that is relatively simple to operate. Then move on to bigger and more complicated boats as the need arises.

We are already registered for TrawlerFest in Solomon Island in September and the Power Boat Show in Annapolis in October

Wish I was coming with you!;)

tdamico

08-08-2003, 08:06 AM

Once again, I don't think that any one boat can do all these things well - or rather, I feel you'd be way better off getting to know boating in something that is relatively simple to operate. Then move on to bigger and more complicated boats as the need arises.

Actually I have some boat handling experience, albiet is a 22' boat that is used on a rather large lake in the Carolinas. But a few thoughts, if we "worked" our way up through several boats as we gained more experience, I would be too old to get much fun out the one I was really after by the time I got there! Also, I want to make sure that I understand what you are saying. I value all opinions. Are you suggesting that trying to learn and competently handle a 40+ foot boat is too much of a challange and that a much smaller boat should be selected first? Also, purely from a handling point of view. Which would be the easier task. Mono hull, full displacement, or multhull? Both power boats, NOT sail.

Thanks

Tom Lathrop

08-08-2003, 09:37 AM

tdamico,

Greetings from the coast.

In spite of all the great opinions and advice you are getting from everyone here, I am sure that the best one is to charter boats that you think you would like a couple of times to find out for yourself how things work out.

Looking over boats at a boatshow is fine IF you already know a lot about what you need. Otherwise, you can be seduced by the "next best thing" while overlooking necessities for a good experience.

I am certainly not in a position to advise you on what will work for you. Inclusion of AC, full and direct communication with the other world and three dogs place you in a different cruising category from me.

A recent cruise on part of the "great circle route" does bring out a few things though.

I saw not a single cruising power catamaran on inland waters.

Regardless of hull design, most of the owners of large power cruisers we met said that they mostly ran at displacement speed due to cost of fuel. Quite a few were well heeled enough to go faster though.

"Doing the circle" is not a short time cruise. Many take more than one season while leaving their boat on shore for the winter.

Some owners of round bilge hulls complained about rolling while I never heard this complaint from hard chine owners. Hard chine hulls far outnumbered their round chine cousins.

In the North Channel, we encountered over 90 boats almost all power) from the Great lakes Cruising Club and about 30 boats from the Trailer Sailors Association. There was quite a contrast in style and substance but both seemed to be enjoying themselves. There is a niche for everyone.

tdamico

08-08-2003, 10:02 AM

Thanks for your opinions. They are welcome. And you are right. My feeling was to learn all I could via books and the net. Make a list of what we want and don't want, keeping in mind that simplfy is the operative word. Visit boat shows to see as many different boats as we can. Crawl around them. Check the lists we have as to what they offer etc. Then step back, eliminate those that we just didn't like or that had too many "don't wants". Then charter for at least 1-2 weeks the final boats we come up with (hope to narrow it to a max of 4, hopefully 2-3) Then make a decsion, get a slot, and let the building begin. While the boat is being built, we continue to sell off household goods, and all our property. Time line for this, 1-2 years. Next step is to find a live aboard slip and put the boat there and move in. I will continue to work, thus the need for high speed internet access, and we will use the boat on weekends and 2-3 months over the course of the first year. After year one of boat ownership, I quit, and we take a full year to to the Great Circle Loop. Visit America and its inland waterways. Learn our boat even more. At the end (5 years from now) we will have two or more solid years experience under our belts, hopefully are good boat handlers. Our next goal would be to cruise the East coast extensivly and the islands. At least 2 years or more. Now we would have 4-5 years under our belts and the next step is through the canal to the West coast and Alaska. Probably spend at least 3-5 years there and now we will have 7-10 years experience. Then Transocean to ???

Financially we can make it happen if we keep the boat to around 450K-650K and keep living expenses for two under 30-40K per year. We may have to buy used, but we will see.

Portager

08-08-2003, 12:01 PM

Tom;

Sounds like a good plan, although you may find it difficult to charter the boats that you settle on. I would start the charter process earlier and consider all on boat experience useful even if it isn’t the boat you think you might buy.

As for choosing the boat for the application, Will is right to a point but I can see your point also. In addition every time you go through a buy/sell cycle you pay agents fees and spend time selling the current boat moving and prepating the new boat for cruising. If you opt for an adequate compromise you can spend more time cruising. OTOH I would concentrate on your 3 to 5 year objectives and not let the far distant future plans compromise the near future plans.

I am familiar with TracNet and I think it is a good system, however if you don’t have access to a landline or cell phone coverage, then you need to use a satellite phone which gets expensive. Cell Phone coverage on the coast is pretty good, but on the inland rivers it is only in cities and town and near freeway bridges.

In defense of semi-displacement hulls, it is true that most are configured to operate at 2 to 3 times the speed/length ratio (S/L) which requires a great deal of power and sucks fuel very fast. To make matters worse, these large engines when combined with a fixed pitch propeller, are under loaded at displacement speed to the point of being detrimental to the engine. However, it is possible to configure a semi-displacement boat to operate at about 1.6 to 1.7 times S/L without requiring too large an engine or driving fuel consumption too high. In addition, using a controllable pitch propeller allows the engine to operate on its ideal power/speed curve regardless of boat speed. Portager will use a semi-displacement hull and operate at a maximum of 1.75*S/L or 12 knots with 160 HP. Fuel consumption at 12 knots is predicted to be 0.7 gal/NMi at 3,000 RPM. At 8 knots, predicted fuel consumption is 0.27 gal/NMi requiring 40 HP the engine will run at ~1,600 RPM. Portager will be efficient and relatively quiet at displacement speed, but when I can afford the fuel and conditions allow I can increase my speed and increase my daylight passage distance by 50%.

Regards;
Mike Schooley

Portager

08-10-2003, 03:07 PM

Tom;

So that you wouldn’t need to take my word for it and to illustrate the value of the Trawler World List and Trawler World Great Loop list, I did a Google search using [ Catamaran site:samurai.com ]. The “site:” restricts the search to the selected web site, i.e. samurai.com. This search produced 304 returns (many of them useless), but by adding additional words with a “+” sign in front, or strings of words inside “” you can further filter the returns.

One of the better posts that popped up was from Skipper Bob, an experiences Great Loop cruiser and the Author of several self published books on the subject, http://lists.samurai.com/pipermail/trawler-world-great-loop/2001-October/000130.html . Skipper Bob replied to an query regarding Catamarans on the Great Loop as follows, “Cats have the advantage of shallow draft, but the disadvantage of being quite wide. Many marinas cannot handle a 15-18' wide cat in a slip. Unless they have a T pier or alongside dock there may be no room at the inn. On the bright side, you do not have to tie up to a marina most of the time unless you want to. The wide cat also presents a problem at some marinas if you have to be hauled to be worked on. Many marinas cannot lift the wider cats. From a realistic standpoint there are no problems taking a cat around the Great Circle Route when it comes to steering or transiting canals, rivers, lakes, etc., except for height. Most catamaran masts are too high and you would have to step the mast in NY on the Hudson River and leave it down until well past Chicago on the Inland Waters. A mast on a hinge that you could manage yourself might be ideal since you could step and unstep it at will and actually sail on the Great Lakes.”

I think this addresses the slip width issue. I don’t think it would be an insurmountable problem, just a potential inconvenience.

Regards;
Mike Schooley

tdamico

08-10-2003, 04:37 PM

Michael:

I certainly appreciate the effort. This would, potentially, only leave one issue. That bridge you mentined in Chicago that is fixed and anything 19' or over can't get underneath. Some, not all, of the powercats I am looking at are higher than 19'. I am still checking into that.

On another note, I asked a question earlier about just running a semi-displacement boat at a slower speed to conserve gas. The answer was that this could potentially be damaging to the engine. But cats are rated at very high speeds. If I ran a cat as cruising speed, say 10 knots, would I not have the same issue?

Willallison

08-10-2003, 08:23 PM

As usual, I'd have to agree with all that the others have said.

Mike, so with Portager, @ 8 knots you're looking at 3.7 nmpg and at 12 you get 1.4 nmpg. The latter figure is not too dissimilar to that which we get from the Offshore 48 @ 10-11 knots. This, I think is where the cat comes into its own. You could reasonably expect 2 - 3 nmpg running at nearly twice this speed.

The July / August edition of Passagemaker magazine has two things that me be of interest to you, Tdamico:

1. Is a story about the PDQ mv34. A 34ft cruising powercat that could be of interest to you.

2. A lift out order form for an article presented at last year's 'trawlerport' on "how to choose the right boat for you".

As far as the boat size thing goes, if you've had some boating experience then you have a good head start, but it seems that every 10 foot increase in length also comes with a quantum leap in complexity. All of these systems - watermakers, generators, A/C, radar, toilets, etc, etc, etc - require maintenance. And whilst I would expect that you could find service agaents for most of these things en-route, one of the great pleasures of boating (for me at least - is to be (as far as is possible) self-sufficient and self-reliant. So the size choice also becomes a complexity choice - though less so if go the custom build route....

As far as ease of handing of the various types goes, they all have their pros and cons. For instance, as cats tend to have low draft they can be subject to windage problems. A heavy, deep drafted trawler will be less subject to windage, but once on the move will take a lot more stopping.

I may have missed it in one of your posts, but how many permanent and part time crew are you planning on having aboard?

tdamico

08-10-2003, 08:41 PM

There will be two permanent crew on board, myself and my wife. I am presently 52 and she is 46. Both in great shape and very mechanically inclined. As I said, we hope to start to build next spring, do a part time thing at a marina for a year, then full time at a marina for a year, then the great circle route for a year, and then??? We have divided up the classes. I will be taking navagation classes, and a class in maintaining diesel engines. She will be taking advanced classes in boat handling. Then we will cross train each other. I agree that part of the allure is the self sufficiency that comes with maintaining your own enviornment. That is certainly or goal. Are we crazy? Don't care, we're doing it anyway. I actually read that issue of Passagemaker. When we fit our lifestyle into a boat, it keeps coming up, full displacement trawler, but the additional space that we can get in a cat, is alluring. If we go with a traditional trawler, we are looking at 47'. If we go with a cat, we can get the same or more room at 43'. Can't wait for the boatshows this year!! Please keep all the ideas coming.

Willallison

08-10-2003, 09:05 PM

When we fit our lifestyle into a boat, it keeps coming up, full displacement trawler

For live-aboard, that's definitely the way I'd go. And 50ft is about as big as I'd choose too. I imagine that with only the two of you aboard the difficulty of navigating such a big boat through the many locks that you'll encounter will prove to be more of a hinderance than the deeper draft and slower speed that you'll have to contend with.

Portager

08-10-2003, 10:08 PM

Originally posted by tdamico
If I ran a cat as cruising speed, say 10 knots, would I not have the same issue?

It depends on how far your cruising speed is from your maximum speed, or actually the power ratio between maximum speed and cruising speed. I will have the same problem. My power level at maximum speed is 160 HP at 12 Knots and cruising power is 40 HP at 8 Knots.

The problem is the power demand curve for a fixed propeller is steeper than the engines optimum power output curve. This means that a fixed propeller can only be optimized for one engine speed. Below the optimum speed the engine in under-loaded and above the optimum the engine is overloaded. Since it is much worse for the engine to be overloaded than under-loaded, the optimum point is always selected for the maximum engine speed. Since the propeller power demand and engine ideal power output curve are at different slopes, the further you operate from the maximum speed, the more under-loaded the engine is.

The classical approach to this problem is to select your maximum speed to be only slightly higher than your typical cruising speed. The problem with this is you must give up the high speed potential.

Another approach is to break-up periods at low speed with short periods operating near maximum speed to burn the glazing off the cylinder walls. A typical approach is 1 hour at high speed for each 4 hours at low speed. The problem with this is if you are limited by speed limits or conditions such as swells for long periods of time, you may be unable to burn the glaze off the cylinder walls often enough.

If you plan a long period at low speed, you could install larger propellers that are optimized for low speed, but this is limited by propeller clearance requirements.

Another approach, and the one that I prefer, is to use controllable pitch propellers. These propellers have rotating blades so you can change their pitch, and therefore the thrust and power demand versus speed. This allows the engine to run on its ideal power output curve regardless of boat speed (provided the propeller has adequate range of travel). It does not hurt a diesel engine to run at slow speed provided it is adequately loaded. Pyrometers are the preferred sensor to adjust the pitch of the propeller blades to achieve an exhaust temperature near the ideal 850 degrees F.

The down side of controllable pitch propellers (CPP) is they are more expensive and they require a special shaft with a pitch control shaft in the center, however with a CPP you don't need a transmission which partially off sets the cost difference. Of course you would need two of them.

Have you asked the Catamaran builders about their engine out handling? Some of them are difficult to steer a straight course with one engine out.

Regards;
Mike Schooley

Willallison

08-10-2003, 11:42 PM

Have you determined the cost of variable pitched props Mike? I would have imagined that the efficiency benefits were way outweighed by the cost. Better to either put up with having to blast about for an hour every now and again, or whack an outboard on the back with a low pitch prop. But never having had the need, I really have no idea about the cost of a 'recreational' variable pitch system.....:?:

Portager

08-11-2003, 12:41 AM

That is a common misconception Will. People like to make comparisons to commercial grade CPP which exaggerates the cost difference. They also like to compare the cost of a retrofit of an existing drive train which makes the CPP less attractive because there is no transmission savings.

For new construction with comparable quality and using a single direction gearbox, the cost difference is less than 5% and break even would be about 5 years at my expected usage level and today’s interest rates, however if you compare low quality fixed pitch propellers to CPP then the initial cost savings of the FPP is closer to 40% but breakeven is sooner due to maintenance cost.

Regards;
Mike Schooley

Willallison

08-11-2003, 02:39 AM

That is surprising! What are we talking in $ terms?
Leads one to wonder why more boats aren't equipped this way....

Portager

08-11-2003, 03:12 AM

OK, Will, here is a post from Michael Kasten to the Trawler List http://lists.samurai.com/pipermail/trawler-world-list/2001-April/031596.html Sat Apr 14 11:56:10 EDT 2001.

“TW Listees,

Patrick Gerety has forwarded some recent TWL messages re: the relativecosts of a CPP installation vs an equivalent FPP installation. This question is brought up sufficiently often that I have made the following actual cost comparison.

In so doing, it's possibly best to make this kind of comparison using equipment that is suited to the requirements of a specific engine. Let's say the Lugger 6 cyl turbo: the Lugger 668-T.

CPP: Controllable Pitch Propeller Equipment

Sabb HVP 65-E as of 1999 was quoted at 60,000 NOK, ex works Bergen, Norway. At that time they were quoting a 20% discount for direct orders. The exchange is currently USD $1.00 equals NOK 9.08. This translates to a cost of USD $5,286 assuming the NOK price has not changed much, and assuming the same direct order discount remains available.

The completely assembled Helseth 60mm shaft, stuffing box, stern bearing, shaft tube, and 660mm 3 blade CPP propeller at that time were priced at NOK 25,000, with a 20% direct order discount available. This assembly translates to a cost of USD $2,203, ex works, if making the same assumptions.

______________________________________

CPP Whole Shebang: USD $7,489 plus freight of around USD $350 and import brokerage of around USD $50, for a very approximate total of around USD $7,889 with shipping, but without taxes.

FPP: Fixed Pitch Propeller Equipment

The Twin Disc MG-5050, also suited to the needs of the Lugger 668-T, retails for USD $3,570. A "builder's" 10% discount is sometimes available, so let's use approximately USD $3,213.

A comparable stern gear "assembly" is offered by Vetus and includes shaft, bearing, stuffing box, and shaft tube. I don't have a current price from Vetus for this, but we might be able to assemble the pieces one by one, again assuming a 60mm shaft and 3 blade 660mm prop (around 26 inches), and taking the retail prices:

Coupling: Usually supplied with Gear

Shaft: Aquamet approx: USD $1,500

Machining on Shaft (Both Ends): approx: USD $500

Prop: 26" 3 blade Ni Br Al prop (comparable to the Sabb / Helseth
alloy): approx USD $1,900.

Bronze Sleeved Cutless Bearing: approx USD $200

Stuffing Box: Varies, so assume approximately USD $400

Bronze Stern Tube Materials: 5' x 3" OD: USD $180

Machining on Stern Tube: Approx USD $400

Flange Fabricating on Stern Tube: Approx USD $350

___________________________________________

Tail shaft "assembly" amounts to a total of around USD $5,500
Twin Disc MG-5050 Gear comes to around USD $3,213
___________________________________________

FPP Whole Shebang: USD $8,713 without any shipping or taxes. The FPP costs given here are using current quotes from the Seattle area, and using materials of equal quality to the Sabb / Helseth system.

A few random thoughts...

These figures have factored in the miscellaneous goodies, the machining and the fabricating required to create an "equivalent" system in terms quality, and in terms of the self enclosed type of shaft arrangement offered by Sabb / Helseth. Of course one could argue that a Manganese bronze prop with an ordinary stainless shaft in a non-self-enclosed shaft tube will be less costly, but then we would not be comparing "like for like" in terms of quality and components.

The upshot of the above is that if you figure a bit of inflation on the NOK prices given above, the overall cost of the two systems are very nearly equal. If there has not been much inflation in the Sabb / Helseth costs, then the CPP arrangement is actually LESS costly than an FPP installation.

One should note that there are several CPP arrangements available from other manufacturers. Hundested equipment is excellent for example. The "break point" that I ordinarily use between Sabb and Hundested is around 200 hp. Below 200 hp, and Sabb is usual the more economical choice. Above 200 hp, and Hundested will likely be the more appropriate choice. However, Sabb is adding a new CPP gear at the upper end of their line, so this dividing line will soon move upward a bit.

With the FPP system, once it is installed you have an unknown situation in terms of whether the pitch is actually correct for your vessel, and you may need to factor in the added cost of an entire
haulout and re-pitching ceremony.

These are the economics that drive my usual recommendations in favor of the CPP system. As a further benefit, the CPP system will be more efficient in use and much more adaptable to variable vessel loadings, weather, maneuvering, etc.

I have ordered parts and spares from Sabb for my own Sabb diesel. I have usually phoned in the order using a credit card, and the parts are shipped air freight, usually the same day. I have typically received parts within a few days. That's better service than I often get when I order parts from Seattle, which is less than 80 miles away...

These thoughts are not meant to deprecate the excellent FPP equipment available, but are rather an attempt to encourage an open mind when making this choice during the course of a new vessel design.

I do not subscribe to the TWL list, so any correspondence intended for me should be sent direct.

All the best,
Michael Kasten”

Regards;
Mike Schooley

Willallison

08-11-2003, 07:29 PM

Thanks Mike - as I said before, makes you wonder why they aren't incorporated more often....perhaps, if they manage to break into the recreational market a little more, then they will be....

Portager

08-11-2003, 09:36 PM

Tom;

You might find this link http://www.caracolyachts.com/new%20cat_new%20yorker.htm interesting reading. They explain why they selected controllable pitch propellers for the "New Yorker" Catamaran Trawler. In addition to the engine loading benefits at reduced speed, they also improve single engine performance, because you can feather the prop that isn't being used, and maneuverability because you can reverse thrust without throttling the engine back and shifting gears. :cool:

Will;

I do not understand the reason for the lack of CPP popularity either, although I believe there is only one manufacturer for the recreational market and they are very far away. It seams SABB is more successful in Europe so maybe they concentrate their marketing effort in their local market? It could also be that some boat builders/buyers are not as progressive as yours truly. :D I never meet advanced technology I didn't like. ;)

Regards;
Mike Schooley

Portager

08-30-2003, 12:12 PM

Tom;

I found a report on tank testing of a trimaran that I think is relevant to the monohulls versus catamaran discussion. The entire report can be found at http://www.theyachtreport.com/PROJECT/papers2000/paper32000.pdf , but I think the abstract summarizes the relevant points very well. “This paper discusses the possible merits and disadvantages of a trimaran over a monohulls yacht. The powering performance and ship motion behaviour are evaluated for a modern 60 m monohull motor yacht and a trimaran with comparable displacement and installed power. Special emphasis is put on discomfort related to vertical and transverse accelerations. It is concluded that an increase in speed of 2 to 3 knots is possible for the trimaran. Comfort and workability on board a trimaran are superior over a monohull when sailing or at anchor in head seas. In quartering seas, the roll motions and transverse accelerations of this particular trimaran showed to be less tolerable than of the monohull. If these can be solved with special attention to the design of roll stabilising appendages, a trimaran can be a worthwhile option for owners who need a large deck area or who wish to stay onboard a longer than average period of the year.”

Obviously this report is based on much larger vessels than we were discussing and they are talking about a Trimaran instead of a Catamaran, but I believe the Catamaran, with its buoyancy further from the center of gravity plus the smaller size will only exacerbate the problems in quartering seas.

Regards;
Mike Schooley