What makes the best offshore cruising yacht

Discussion in 'Sailboats' started by LEADGlobal, Sep 27, 2017.

  1. LEADGlobal
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    LEADGlobal Junior Member

    Yes thanks for clerifying. Definately needs to be the feathering variable pitch, usually three blade design works the best. Ewol makes a good one, although plan on checking your bank account before purchase haha
    www.ewoltech.com http://www.ewoltech.com/
     
  2. Phil Christieso
    Joined: Jun 2016
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    Phil Christieso Junior Member


    This is something you, along with many others, clearly know very little about because there is little research published on this subject.
    After some research and discussions with 2 other mechanical engineers, one being a prop designer, and some very interesting sea trials involving over 3,000 Nm's,
    I have come to realize you have to have a very good understanding of the relationship between the following:
    -Drag curve -Prop diameter -Blade area and shape -Pitch -Prop rpm as its pulled though the water -Vessel Displacement
    Have you ever seen a prop drag curve chart?
    This is a fascinating subject. It may need a new forum.
     
  3. Nick.K
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    Nick.K Senior Member

    It is interesting but drag not withstanding, the constant rumble of a free rotating prop disturbs. On the Nic we have an effective shaft brake (Borg Warner box doesn't lock the shaft) I use it even though I'm aware there is less drag with the prop turning.
     
  4. LEADGlobal
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    LEADGlobal Junior Member

    Im all ears for learning more about this. Interesting that all the feathering prop companies brag about how much more speed and efficiency they get compared to a fixed blade prop. Maybe they are exagerating? I would definately like to see some facts about this subject.

    I have seen testing comparing free spinning versus locked prop, but not so much on spinning fixed prop compared to feathering prop, and how much net drag does a free spinning prop actually have to affect actual speed of the boat. Obviously a locked 3 blade fixed prop is going to create a lot of drag.
     
  5. Nick.K
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    Nick.K Senior Member

    What problem are you trying to address here? Is it that the boat isn't balanced and needs a lot of effort to steer? What do you mean by 'power' is this autopilot power or boat drag.
    If the boat is well balanced it shouldn't be necessary to have a large rudder.
    Zero feed-back steering is horrible to steer with IMO; in a good boat you can steer with almost no effort letting the wheel turn on its own and then restraining it just at the right moment enough to make the small heading change you want.

    Rather than a large rudder, on my ideal offshore boat I'd like two rudders in the style of many racing boats. These could be skeg supported and/or could also be designed to go up and down if necessary. With two rudders, the load per rudder is less, there is redundancy in case of collision or breakage and when the boat is heeled one rudder is always well immersed reducing the tendency to ventilate at the hull surface.
     
  6. philSweet
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    philSweet Senior Member

    @ Phil Christieso , Its been discussed a few time here before. But I think it would be best to carry on over at the new thread created by Angel. Your installation is unique in several ways. Your prop shaft is level, and you have a tiny shaft diameter for the diameter of the prop. These two things are important for getting the prop generator to work. Typically, boats have a 15- 20 degree incline to freestream flow. As a propulsor, the inflow gets accelerated and the inflow angle at the prop is reduced. The prop is designed for this reduced angle. As a generator, the local flow is decelerated, the inflow skew increases, and the propeller is now very badly fitted to the flow conditions.

    But setting aside the fact that it can work on your boat, there remains the question of is it a good idea. What does it cost? There is no more expensive system to own and operate that I can imagine. On short cruises, you could pay $50/gal for fuel and be money ahead running a genset (an equivalent one, not necessarily the one you actually have), provided you could simplify the rest of the boat so as to provide equal performance under sail. On long cruises, say months between refuelings, the tankage requirements eat into the equation. Many of my arguments are about clean-sheet designs (which are relevant to this thread) and not about adapting existing designs. With existing designs, the trade-off is mostly about speed, and whether you can retain enough to still run the machine without doubling the amount of work the crew has to do to sail the boat.
     
    Last edited: Oct 1, 2017
  7. philSweet
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    philSweet Senior Member


    Autopilot power consumption, primarily.

    I realize many people wouldn't opt for the zero feedback system, but it should be able to be fitted to a world cruiser. Just accomodate attachment for the usual suspects in the design of the steering systems.
     
  8. Nick.K
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    Nick.K Senior Member

    I don't understand the logic here. Many autopilot systems only consume power to make a rudder angle change but rudder movement is restrained while the pilot is engaged. Many pilots also have the option to manually steer via the pilot which is similar to the zero-feedback set up only with a small power consumption. Alternatively you can have the option to turn off the pilot and have a boat with good manual steering characteristics where feedback is advantageous.
     
  9. Phil Christieso
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    Phil Christieso Junior Member




    The first thing to consider is the length as that determines the choices that follow. A couple having a boat custom built for offshore cruising today will be looking for a boat between 45-50'. This is a change we have noticed over our 25 years of cruising. The following ideas fit this boat length.
    Cockpit
    1 You have to be able to board the boat easily from the stern.
    2 Davits are essential for coastal cruising. No-one wants to be putting their dinghy on the foredeck using a halyard for short hops.
    3 Aft cockpit/single helm station. So little time is spent on the helm so why have 2 wheels in the cockpit.
    4 You must be able to stand comfortably at your sheet winches.
    5 The sheeting must come directly from the tracks to the winches and not through turning blocks.

    Rudder
    1 It must be a balanced rudder. This lowers the draw on the autopilot. When going down the face of a 30' wave and the stern is picked up and thrown, you must be able to apply helm to correct this. The balanced portion of the rudder must go across the face of the propeller, therefore no bowthruster is needed when maneuvering the boat in tight situations.

    Engine
    1 Do not fit a saildrive. It is more susceptible to problems than a standard shaft and prop...electrolosis, water in the gear box, leg seal issues....the list goes on.
    2 Never fit a Volvo engine. If you want to make money have a Volvo agency, you will sell plenty of spares.
    3 Carry around 1000L fuel in 2 tanks, port and starboard, and the same for water. Using manifolds you can re-ballast for sailing to windward. We carry that amount of fuel for heating, not so much for motoring.
    4 Tanks fitted mid-ships outboard so as not to affect trim fore and aft.

    Electrical
    1 Choose an engine that can be fitted with a single large frame 250amp alternator. This will produce 150amps at idle because the battery bank is going to be 800+amp hours. Not that the boat needs this compacity, it is to do with charging and engine run time. The batteries are going to be Rolls or similar quality. Never parallel batteries, use 2 or 6volt cells. Add water every 3 months. They should last 10-12+ years.
    2 You MUST have an amp hour meter. Use BEP amp meter and switch panel.
    3 The bulk charge rate is 14.9volts.
    4 Fit 400 watts of solar panels

    Electronics
    1 Never fit electronics built for the yachting market. Use Furuno or similar.

    Galley
    1 The galley should be fitted on the starboard side.
    2 The fridge/freezer should be about 150-200L using a DB80 compressor, air-condensed. This allows it to be used when on the hard. Built correctly this will draw 35 amps a day in the tropics.

    Anchor gear
    1 100 meters of 12mm chain and a 30kg anchor. This gives more anchorage options and allows you to sleep at night.
    2 A good strong windlass with a manual override.

    Hull
    1 My peference is cold-molded 5 skins with 2 layers of 600gm double bias in expoxy and some carbon. No frames or stringers.
    2 My second choice is infused epoxy with carbon....connects the outer skin to the inside skin making it very strong and almost totally eliminates delamination.
    3 Only fit carbon chainplates.
    4 Add some sheer into the hull, raising the bow to get a dry boat when pushed hard.
    5 The stanchions and all cleats fitted on top of the toerail to give clean decks and no chaffing points.
    6 Some depth in the forward sections with no flat sections to eliminate all banging and crashing while under sail.

    Sail plan
    1 Cutter-rig sloop
    2 Tapered carbon mast, squared spreaders, not raked. Mast rigged in column so if you do put it in the water you have more change of righting with mast intact.
    3 Track fitted to front face of mast for permanently mounted spinnaker pole. This adds at least another 5 miles a day for a cruising couple due to ease of use.
    4 Mast stepped well forward of mid-ships so it sails well wing and wing with main and genoa.
    5 Never have mast through the middle of the saloon or table.

    Decks
    1 Nothing should be stored on deck. Everything must have a place below deck.
    2 No arch. You want it to look like a boat, not a Chinese laundry.

    Performance
    1 Presently, on a 43' vessel, on ocean passages, we average 149 miles a day. This average is obtained under these conditions...we don't motor at sea. This has a huge impact on the average. The last 3 Atlantic crossings we have done 4 two hundred mile days noon to noon.
    2 We don't have light weather sails.
    3 We have no weather information available while at sea.
    A new boat would want to perform better than this or one would be pissed off.

    This a brief outline of what I consider works for long-term cruising.
     
    Last edited: Oct 1, 2017
  10. PAR
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    PAR Yacht Designer/Builder

    A well defined, if fairly subjective list Phil. I agree with much of it, though certainly have contention with others. This is the classic example of experence and actual sea miles. I've never seen two lists the same, in fact most aren't even remotely close. How much evolution have you noticed, say over the last 20 years?
     
  11. LEADGlobal
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    LEADGlobal Junior Member

    Hoek Design is another good example I believe of a good offshore cruising design, although they focus more on the larger higher end market. There is still a lot of things I am gleaning from their designs. www.hoekdesign.com

    [​IMG]
     
  12. Phil Christieso
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    Phil Christieso Junior Member

    A little background. I trained in a shipyard, both on the floor and in the design office. The foundry cast props up to 10feet in dia. After our first circumnavigation
    of 8 years on our 43' yacht Windora, the average miles under sail with no motoring on ocean passages, no light weather sails, no weather info was 135 miles per day. The prop was 22 x 17 x 3 blade and in a sad way. I went and seen Dave the prop engineer. He told me they have a new design with low drag for yachts, did the numbers 28x18.5x4 blade. I said are you sure, that's a big prop. He was so he went ahead with the job. So back to sea, do another 10,000 miles and the average with propshaft alternator fitted climbs to 139 miles per day. Now lets look at a couple of these passages going to windward ...Nelson NZ to Hobart Tasmania... 1301 in 10 days = 130 miles per day. The next one... Sydney to Vanuatu... 1135 in 7 days =162 miles per day. Dave was right - that prop ain't slowing this boat down.
    Now back home to fix a small problem, The prop was pitched for the old engine, a P6 perkins 49 hp@1500 max rpm. The new 6B cummins wouldn't pull full revs. This is where it gets interesting. Dave wasn't very keen but Warwick in the prop shop and I thought we would try taking some pitch off. He removes 3.5 " of pitch, about 2.5 degrees off the blade angle. Its now 28x15. Of course the engine rpm goes up. Great. Okay lets go for a sail. We nip up to New Caledonia and back, 3503 miles... the passage up there = 130.5 miles per day. Now what I discovered was that the yacht wouldn't sail over 8 knots. It would get to 8 knots and just stop there. In the past we would do 1 or 2 two hundred mile days a year. If you have sailed any 200 mile days you will know that you have to see the GPS hitting 10+ knots to get the 200 mile day. We had lost some serious boat speed at the top end and could definitely hear the prop spinning faster.
    Back to Nelson to sort this new problem out. I go and see Warwick again. He is a very keen sailor with lots of racing experience. He said that there was no way we should be sailing this old girl up to and over 10 knots. I tell him the boat has always done it. Spend another load of money and get the prop pitch changed from 15" to 17". He also removed the rake on the blades and stood them up more. Problem solved.
    Now I wanted to find out why this happened and what caused it. After crunching some numbers with Dave and Matt, a Scottish mechanical engineer on a circumnavigation, Matt came up with a drag curve that showed the drag generated by this prop. This took some considerable time. Unfortunately I do not have a copy of it here but it was like this......Along the bottom column is the prop rpm. On the lefthand side is the drag generated. On the righthand side is the boat speed . So after measuring the rpm of the prop at different speeds under sail to produce the graph, we found that sailing at 7 knots it was doing 250 rpm. At this rpm there is very minimal drag generated. What happens on the graph, as soon as the rpm hits around 350 rpm, the amount of drag goes through the roof. What we all learnt from this is that just about all sailing vessels are fitted with small diameter props that reach a high drag potential very quickly and at low hull speeds. The unusual thing about Dave's yacht propellers is the narrow blades and small hubs. What makes it so successful on Windora is the prop diameter ratio to the displacement and sail area. This prop would create a lot more drag on a lighter boat of the same length. Obviously the important thing is more diameter and less rpm. One of the advantages could be at surfing speeds of 15+ knots gives us some drag keeping the stern into the seas.
    Our average now for the last three years has risen to 149 a day on ocean passages.Just something to think about motoring at 7 knots the prop is being driven at 600rpm.
    I would be interested in Philsweet's thoughts on this subject.
     
    Last edited: Oct 2, 2017
  13. Dolfiman
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    Dolfiman Senior Member

    If that kind of classic modern cruising yachts matchs also your research, you can have a look at (I just take one example in their complete range of yachts) :
    *** Spirit yachts 47CR : Spirit 47CR cruising yacht designed for long distance cruising http://spirityachts.com/spirit-47cr/
    *** Berckemeyer Yacht Design : Berckemeyer Yacht Design | plans for modern and classic sailing yachts http://www.berckemeyer-yacht.de/yachts/New%20Yachts/BM39_arctic.html , ... for "serious" long distance cruising (and when a German say serious, you can understand very serious)
    *** Stephens and Waring yacht design :
    Deuce - Stephens Waring Yacht Design https://stephenswaring.com/yachts/deuce/
     
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  14. LEADGlobal
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    LEADGlobal Junior Member

    I sent for a quotation from EWOL and this is their response. Pretty impressive claims about drag.


    EWOL an exceptional product, really unique on the market:


    Thrust in forward: it is comparable to the thrust of a good, well calculated fix propeller

    Thrust in reverse: it is far superior to any fixed, folding or variable pitch propeller on the market and allows for exceptional directionality and strong thrust backwards from the very first moment thanks to the central pinion gear which forces the blades to the ending point, almost completely eliminating the drift

    Drastic reduction in hydrodynamic drag: under sail EWOL allows a gain between 0.5 knots and 1.5 knots of speed (folding props with 3 or 4 blades have higher drag than EWOL prop)

    As an example, a fixed propeller 17 " / 3 blades 8 knots has a drag of about 45 kg (100 Lbs)

    With a folding propeller always 17 " / 3 blades the drag is approximately 5-10 kg (11-22 Lbs) depending on brand

    With an EWOL propeller always 17 " / 3-blade the drag is about 2.5 kg (5.5 Lbs)

    Extremely light and silent in inversions: thanks to the special design and the materials used for the construction, this will avoid stresses at the gearbox, yet the props are mechanically extremely strong

    Micro-setting of pitch: it is a device allowing fine adjustments to the boat's performance, this operation can easily be performed underwater in less than 20 seconds. The pitch setting is the finest in the market, 8 to 10 times more precise than other products on the market. Pitch setting precision is a very important topic, as it allows to adjust the cruising speed as desired, enhance maximum speed and reduce fuel consumption
     

  15. Nick.K
    Joined: May 2011
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    Nick.K Senior Member

    It looks very similar to Maxprop or Darglow propellors both of which have adjustable pitch too.
     
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