Pocket cruisers

Discussion in 'Powerboats' started by Guillermo, May 13, 2006.

  1. Vega
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    Vega Senior Member

    That one is a lot better.
    Who is the designer?
     
  2. keysdisease
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    keysdisease Senior Member

  3. Vega
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    Vega Senior Member

    It seems to be a very interesting hull, but I have some doubts about the design.

    The boat looks like a sports boat, but it seems directed also to cruisers. I think that cruisers have a more conservative approach to aesthetics in what regards boat shape.

    Perhaps that hull could be suitable for two different boats:

    One, a sports boat, with the existing design, more powerful engines, and capable of 25k.

    Another, with less powerful engines, maximizing consumption economy and interior space, with a better quality interior. This one would gain in appeal with a less “modern” look. Cruisers, in what concerns aesthetics tend to be a more conservative group than Sportboaters.
     
  4. Guillermo
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    Guillermo Ingeniero Naval

    Wow! Risky business that one of yours!

    I think it's a pity the rounded dash not being able at least to be used as a 'temporary storing' surface. You always need places aboard where to leave temporarily small items such as binnacles, caps, papers, etc, etc.

    I agree with you aluminium frames to support the roof is a 'guarantee' of leakings sooner or later. There's not such a thing on boats as a roof where nobody ever climbs to....

    Please let us know results when you perform more extensive tests in Vancouver.

    fcfc: Nice posts, thanks. I had forgotten about Nimble boats. They have motorsailing versions of their boats.

    keysdisease
    : Thanks for the post. Interesting although not very paractical for a cruising boat. I had read someting about that system somewhere else but couldn't find where.
     
  5. Vega
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    Vega Senior Member

    What about about this cute 25ft?
     

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  6. fcfc
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    fcfc Senior Member

    Fine, but at 5 tonnes 4 and 2 * 200 hp, I would not call it a "pocket" cruiser. About the same weigth and power as a Beneteau Antares 980. ( And probably around the price of an Oceanis 393 :D )

    The C Ranger 25 has less than half the displacement, and only 20 % of the power. But the superstructure are ugly, probably because the hull is not deep enough to provide some headroom with a sleeker design.
     
  7. Vega
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    Vega Senior Member

    I don't see what the power or price have to do with the qualification for "Pocket Cruiser". Pocket Cruiser means small cruiser.

    About the weight, it is needed for stability and that weight is a full weight load, for light weight you would probably take a ton out. And don't forget that this is a Class B boat, like the Antares.
    About the Power 2X147kw it is just the Max power. Most of the boats have smaller engines.

    About the price, this is a high quality boat, nothing to do with Beneteau, but even so it is not as expensive as you imply.

    Look at the price of this used boat. Nice price...boat already sold:D

    http://www.eyb-boats.com/fr/recherc...Panier=JaDz4RC8W2Ud6H4bkbS3&monnaie=0&unite=m
     
  8. Guillermo
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    Guillermo Ingeniero Naval

    Nice boat with nice interiors, Who's the builder?
    Having a look at displaced water produced when under planing (as per photo), she seems to be quite heavy. fcfc talks about 5 tonnes, confirming this first thought. Going heavy for this kind of (planning) boats doesn't make a lot of sense to me.

    Although I'm fond of displacement boats, for long range motor-cruising under 30' probably fast ones are a better choice, because most of the time will be spent at marinas, ports or anchorages. With such an small boat very few will seriously consider any kind of passagemaking except the one that can be done in daylight hours and good weather (10 hours, 20 kn, 200 miles at the most?).

    Unless having a lot of spare time available (I wish I could!) displacement hulls will confine the (not retired) user to coastal pottering in his/her home waters, which is very nice, but it is what it is.

    Relatively high speeds and a low displacement combination make possible to reach pretty long distances, and then, if needed, easily bring the boat back home by truck, container, trailer, or the like. Or transported where needed.

    A plumbed bow boat, with 8.5 m (28') Lwl, 2.5 m beam, 2500 kg loaded displacement and 20º deadrise, needs a 134 HP continuous rated engine (+/-) for an 18 kn ride. New Yanmar 4BY18 engine burns 7.5 lt/h at 3600 rpm (137 HP), so with only 75 lt (10 hours) you may reach destinations 180 miles away (weather & sea permitting).

    270 kg 'wet' engine weight and, let's say, 150 lt fuel, 50 lt water, 375 kg crew (3 heavy)+stores and 125 kg 'diverse' hardware (ground tackle, batteries, other engine room appliances, etc), leaves 1550 kg for hull and its fittings & appliances, including shaft and propeller. Sounds this reasonable?

    Peter Sewell got 1350 kg for the whole thing for a 9.1 x 2.24 m boat, with a 120 lt fuel tank (WHIO), so it sounds like it should be possible. Most probably it already has been done.

    Will, Leo, Tom, others...?
     
  9. fcfc
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    fcfc Senior Member

     
  10. fcfc
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    fcfc Senior Member

  11. Vega
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    Vega Senior Member

    That boat is a Sciallino 25ft and it looks that you have not seen my post, replying to fcfc.
    The weight is 5400 kg at maximum load with 2x200hp engines.

    As you know it is not very usual to give the displacement of a boat at Max load.
    This boat is a very strong boat with an unusual load capacity.
    The boat carries 700L fuel, 8 passengers, luggage (800kg), and 150L water.

    If you take all this weight, including the weight of the two 2X200hp Yanmar (800kg), you get 2950kg for the hull and the interior, including a lot of equipment that comes standard with the boat.

    If you change those engines (that are only the max power that the boat can carry) for 2x100hp engines (a more cruising adapted motorization) and consider as displacement not the max load, but the light weight, you will have 3450kg.

    This weight is not far from the weight of the Seaward 25 (posted in another thread), that is a boat with similar characteristics, a strong and seaworthy small class B boat, as this one.

    What you say about the power of the engine needed to go at 18 kn in a 2500 kg loaded displacement does not seem right to me. You need 134 HP continuous rated engine (+/-) , but for having that speed as a cruising speed you need an engine that has that power at ¾ of the max power.

    For that you need the 6BY260. This engine can produce 260hp at 4000rpm, but only about 130hp at 3000rpm, a rotation adequate to a cruising speed (this series looks to be made for sportboaters and not cruisers. It has a lot of hp, but only at high revs).

    The load that you propose for the 18k 28ft :”270 kg 'wet' engine weight and, let's say, 150 lt fuel, 50 lt water, 375 kg crew (3 heavy)+stores and 125 kg 'diverse' hardware (ground tackle, batteries, other engine room appliances, etc)” seems completely inadequate to me.

    Who wants a cruising motorboat with only 50L of water and 150L of fuel?

    The Sciallino 25 has also a nice semi-displacement hull, have a look:

    http://www.sciallino.it/video/s25c-hull.wmv
    http://www.sciallino.it/italian/sciallino25.php?espandi=4
     
  12. Willallison
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    Willallison Senior Member

    1550 kg for a 28-odd foot boat is certainly doable, but it requires pretty careful attention to weight control. There are other things to consider too.
    For instance you are talking about a 1500 kg boat that must be capable of carrying another 1000kg of weight. A heavier payload will require a stronger - and thus heavier - structure, which may bump the weight up to over 1500 kg:( It's a never ending spiral of compromises and design descisions;)
    20 degrees of deadrise may not be the best either. Whilst it's not in the realms of a true 26 degree deep-vee, you will still have to think about whether the weight of the boat is sufficient to adequatley submerge the chines whilst at rest. If not you will have a very rocky-rolly, noisy boat. And of course you will encounter a higher trim angle. If you're prepared to slow down a little in bumpy water you'd probably be better off with something more in the region of 15 degrees in my opinion.
     
  13. Guillermo
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    Guillermo Ingeniero Naval

    Ooops! Something's very wrong, sorry. It was 7,5 gall/h not lt/h when and where I saw it. Having a second look at the engine curves in internet (quite difficult to see numbers) I realize that for 2700 rpm (135 HP?) comsumption is not even 15 lt/h, so for a 10 hours ride is enough with 150 lt. Allowing for a 10% margin we could go for a minimum tankage of 165 l to keep weight low.

    14 kn is too low to my taste, bringing the boat into a compromised region.

    Paulo:
    50 lt of water is quite enough to me as ususally trips will be from marina to marina (water available at the pontoons) and 50 lt are enough for 3 persons 3 nights when at anchor. On the Category B thing, I think Category C will be good enough for this design (It's a 'little' fast motor cruiser, and little fast motor cruisers shouldn't go out when waves are more than 2 m significative :) )
    4RY180 engine has 180 HP maximum rating at 4000 rpm and a workable 135 at 2700 rpm (aprox). Anyhow I'm using this engine for the time being only for weight and consumption purposes.

    Thanks a lot Will. Structure will be calculated and weight estimated after claryfing first the main design goals. About deadrise I still have to do more thinking on it.
     
  14. Guillermo
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    Guillermo Ingeniero Naval


  15. Guillermo
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    Guillermo Ingeniero Naval

    Well, it seems I have some trouble here:

    As per a well known estimating method (Hydrocomp) this supposed boat will not go into full plane until reaching 16.5-18.5 kn (depending on LCG position). Let's asume 20 kn, to be neatly into the planning zone.

    Estimating the BHP needed for those 20 kn using several methods, I get:
    - Barnaby: 107.7
    - Crouch-Werback: 108.4
    - Philips Birt: 108
    - Skene: 85
    - Peter du Cane: 83
    - Keith (Japanese series correction): 108

    Eliminating the two lower values, we can say 108 BHP seem to be a 'consensus' number. Allowing for 10% loses in shaft, appendages and gear, we arrive to a power of 120 BHP at its most, not the 134 I estimated before for 18 knots having used an spread sheet divulged in these forums (Bailey), that estimates wave making and friction resistances.

    fcfc, what do you think? You said 135 Hp were good for 18 kn. What computer program are you using? (My NA one uses Mercier Savitsky's method, but I'm still not using it at this stage, as I do not have forms yet)

    Other opinions, please?

    Note
    I'm working with the following:
    Displacement = 2500 kg (5500 pounds)
    Lwl = 8.5 m (27.89')
    B (knuckle) = 2.4 m (7.87')
    D/L ratio = 113,54
     
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