Full Displacement of semi

Discussion in 'Boat Design' started by tdamico, Jul 31, 2003.

  1. Portager
    Joined: May 2002
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    Portager Senior Member

    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
     
  2. Willallison
    Joined: Oct 2001
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    Willallison Senior Member

    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....
     
  3. Portager
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    Portager Senior Member

    Tom;

    You might find this link http://www.caracolyachts.com/new cat_new yorker.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
     
  4. Portager
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    Portager Senior Member

    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
     
  5. alanfujii
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    alanfujii New Member

    Mirage backing down?

    tdamico

    I know I'm late in getting into this discussion but I was searching the internet on this topic and found it interesting reading. I writing to see if you ever came to a conclusion on the type of boat you were seeking? I was also very interested in the Mirage Mfg's Navigator 37 and read the arguments of Mr. Codega. I found it interesting though the Mirage web site no longer has a link to this article, "The A/B Ratio Is Largely Meaningless By Lou Codega Naval Architect". I'm wondering whether this means they have backed off on the claim that this hull design was more than a coastal cruising type?
     
  6. tdamico
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    tdamico Junior Member

    This post is quite old. I can't say what Mirage's position is on the a/b ratio. I know that I am looking at only full displacement hulls based on my last 6 months of reasearch and also looking carefully at this ratio. I have ruled out the Mirage after visiting them at TrawlerFest.
     
  7. John Capuano
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    John Capuano Junior Member

    Full Displacement or Semi

    :?: I have enjoyed this discussion very much.Iam looking fof a boat along the same lines as tdamico.Several years ago I helped a friend bring a 55 footer to Seattle from Portland.The yacht was a Ocean Alaxander,a semi displacement hull.We caught an unusual summer storm,with waves 15 to 25 foot.It was impossible to run parallal with the coast.Best we could was zigzag.After 12 hours we started to hear strange sounds coming from the engine room every time we turned to port to zigzag out to sea.Turns out that the fuel tanks had no baffels to slow the fuel from sloshing side to side.We healed over so hard several times I thought we were going over.Now that Iam in the market for a boat of my own Iam reminded of that trip often.Proper fuel tank deisgn seems to be an often overlooked item.Any thoughts on this subject would be helpful. I have also posted a question under Powerboats/Dream Engines which could be helpful to tdamico and myself about prop and engine selection.
     
  8. MarkF
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    MarkF New Member

    Great Harbour N47

    Hello All,
    I realise this thread is old but I hope contributors might help me with some research. I plan to retire before reaching 60, likely around the end of 2017. I've lived and worked in Asia for 2 decades, returning to the UK. My younger years were happily spent on Moody's and similar around UK coasts and across the Bay of Biscay to Portugal. Pretty rough seas at times (no fancy GPS or digital navs in those days!).

    I'm planning to return to sea under power, around the UK and Europe initially, then consider longer destinations, possibly a crossing N. America's east coast. I've had to deal with a major health challenge since 2013, while doing OK, returning to sail isn't a good option for me (sadly).

    I've spent some time researching the rise of the "trawler" as a good way to travel long distances in relative safety. Inevitably, the decision to go with full or semi-displacment has come up, along with one engine or more, access to engines, liveability etc etc.

    So far I've decided on a LOA min of 40ft to max of 50ft, manageable size and reasonable costs to dock in marinas. I favour nearer 50ft than 40ft for practical reasons. I've studied Nordhavn, Selene and a few similar brands. But I've just not found a design that I feel completely at home. Perhaps its my mechanical design engineering nature at play but 2 full engines appeals the most. Alas there is very little choice on the market for smaller craft that have a +2000NM range with a full twin engine option.

    However, I have come across the Great Harbour N47. This design is peaking my interest. Great Harbour appear to have gone to allot of effort to design an affordable craft capable of long distances using 2 engines, relatively low superstructure, large walk-in engine room, excellent accommodation layout. However, its shallow draft (a lick under 3ft) has some arguing its not suitable for ocean crossings.

    Hence why I've posted here, as I'd like to read the thinking on the later design of craft using shallower drafts. My sea experiences is mostly with fuller displacement sailing and shallow hulled fast dinghy sailing.

    I fully accept that any vessel under 50ft in the middle of the Bay of Biscay will get tossed around should a storm brew quickly. I also accept there may be no right or wrong (best or worst) between the full and semi displacement debate. I'm more interested in learning from owners who have some experience of both types, or those who've sailed/crewed a variety of displacements in open seas. Or anyone who like me started out with sail, got older (alas) and migrated to power.

    Many thanks for your time to reply.
    M
     
  9. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Welcome to the forum.

    The real key to seaworthiness is the skipper, not the boat. Joshua Slocum circumnavigated in an rebuilt, ragtag oyster dredger, not at all suited for deep water work. His masterful skills allowed him to carry through, which is did, just barely. On the other hand, you can take a 800' bulk carrier and manage to no brain yourself into drowning, in spite of the massive vessel you're on.

    The displacement and semi displacement debate, is an endless escape of biased discussion, with no real conclusions that can be quantified. The costs associated with the faster speed potential of the semi, might be the real deciding factor, but if you have unlimited fuel funds, well than I'd recommend the semi, so you can out run stuff and shorten passage times. On the other hand, a displacement design will likely also be more comfortable and offer more accommodations underway. In the end, it's your priority list that will make the decision for you, not our attempts at impartiality on the subject. Make up your list, with their "ranking" in terms of needs, wants, desires, etc. Find the designs that ding the most bells and then you can refine the list a bit, maybe more design specific of the few choices you have narrowed the search to.

    I'm not sure about your disabilities, but you might consider having your cake and eating it too, with a motorsailer. Modern sail handling equipment can make a 50'er a simple push button affair. Roll 'er up when you want, save fuel when wind directions are favorable and you're in the mood. I have a yacht, considerably larger than your dream 50'er and the mast is over 75' off the water. There's no thinking about handling the sails by hand on this puppy. Hell, I can't even think about stripping the main off the boom, as it weighs a lot more than me. My point is the old 500 sq. ft. rule doesn't apply anymore and we can hoist, douse, reef and furl from inside a pilothouse now, with relative safety, comfort and reliability.
     
  10. MarkF
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    MarkF New Member

    Thanks Par for your thinking.
    Yes, motorsailers are also in my sights. I was a competitive Lazer, 505 and Fireball owner/helm for several years before moving onto to windsurfing and offshore sail. Naturally I'd be keen to hear about any recommendations for easy to set-sail motorsailer rigs.

    I'm keeping reasonably fit but we're thinking about a live-on-board purchase that we hope will give us several years. Possibly a power boat remains the better choice as less potentially less demanding. My partner is reasonably practical and could possibly learn the art of sail, but is more familiar with computers, switches and most things mechanical/digital, hence the move to power. You're correct in placing the emphasis on skippering and truthfully, my better half isn't a natural sail-setting type.

    Re the full-semi displacement discourse, I much appreciate your thinking. We observe the much bigger/wider choice of semi-displacement boats. Perhaps a prudent move would be to purchase an older semi-displacement and see how we get on we shorter range trips along the coasts of the UK and Europe where a range of 1000NM should serve OK.

    While not my original choice, I would use the time to bring myself up to date in small steps. Then the search could focus on a a hunt for a robust off-shore semi-displacement boat. The downside is should we get the bug to go further (likely) we face the issue of selling an older hull...........ummmm

    Any suggestions for a robust 40 to 50ft twin engined semi with a 1000NM range, capable of handling some stiffer off-shore weather would be welcomed. Doesn't have to be a fast boat. As mentioned, not my original thinking but I must be realistic and perhaps extend my learning/planning.

    Food for thought.
    Thanks
    M
     
  11. nzboy
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    nzboy Senior Member

    There are quiet a range of 2nd hand or near new diesel ducks designed by George Buehler some steel 40-50ft and a 40ft wood at a reduced price .They are sail assisted with economical diesels and will have a resale value . A little more seaworthy than great harbours
     
  12. MarkF
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    MarkF New Member

    Thanks NZ,
    The Diesel Ducks look very interesting. I found some pictures of their sail sheets, looked easy to set and control. My heart is in sail, ummm.......lots of thinking to do.....that and some serious discussion with the other half. ;)

    When all said and done, even Nordhavn make a motor-sailer.

    But will I win the day for wind power......or do we stay on course with motor power. At 58, still fairly fit.....is it time to put my hand on throttles and forget hoisting a jib and a main....................
     
  13. PAR
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    PAR Yacht Designer/Builder

    Anyone familiar with the "Ducks" would never describe them as economical and having resale value.
     
  14. nzboy
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    nzboy Senior Member

    I agree that the wood duck being a caulked hull may have a few future resale issues But the steel ones are realistically priced compared to aluminium here 3 times the price with 500hp to keep fuelled up all because some banker wants 20knots top speed .Where our poster is happy with 7knots which only takes 70hp .
     
    Last edited: Feb 14, 2016

  15. FAST FRED
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    FAST FRED Senior Member

    I am confused a Looper is an inshore run,

    worrying about wave size to flip a cat might be a worry in the North Atlantic in winter , but on the mud run?
     
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