Please, educate me

Discussion in 'Powerboats' started by Vronsky, Apr 21, 2015.

  1. Vronsky
    Joined: Apr 2014
    Posts: 51
    Likes: 0, Points: 6, Legacy Rep: 10
    Location: Amsterdam

    Vronsky Junior Member

    Would appreciate some education here >
    I am considering this sportsfisher-model powerboat by Jeanneau, Merry Fisher 750, see example >
    http://www.aventousnautic.com/-68
    It’s 23’ long, has a 180hp inboard diesel engine, a semi-displacement hull, and weighs about 2200kg

    I’ll be singlehanding, so the size seems right, and I particularly appreciate the spacious wheelhouse in combination with the big open cockpit.
    It’s designed for sea fishing (CE safety class: B), but that’s actually irrelevant to me: I just like the looks and features :)

    My idea is to use this mobo for extended coastal cruising trips, marina hopping in the North Sea and Baltics, incl. via inland waterways perhaps to the Med.
    The plan is to cruise mostly at hull speed for fuel efficiency reasons, also because I won’t be in any hurry, doing 30-40 miles per day or so.

    My question is how the boat will behave/ride at this relatively low, hull speed, since the boat is designed for planing ??

    Also: will the relatively 'big' engine be able to cope with the small loads due to the low speeds ?

    BIG THANKS,
    V.
     
  2. rasorinc
    Joined: Nov 2007
    Posts: 1,854
    Likes: 71, Points: 48, Legacy Rep: 896
    Location: OREGON

    rasorinc Senior Member

    My 1st thought is can 2 or 3 sleep in comfort as you will have company. Does it have a Head, a shower, hot water, a large water tank? Don't worry about your engine it will be fine. You will be pulling into coves and bays and dropping anchor so comfort is everything. Remember bug netting........and a waterproof rear deck cover.
     
    Last edited: Apr 21, 2015
  3. Mr Efficiency
    Joined: Oct 2010
    Posts: 9,286
    Likes: 696, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    If you are happy to cruise at 6 knots, (which is what I assume from the opening post, and "hull speed") use a full displacement hull with a small diesel, not the one you mention. You will save more fuel, and further extend your range. There will be people here who know a whole lot more about diesels, who will say running a diesel at low revs like this is not good. And, of course, it will be dragging some transom through the water which is not ideal. If there is a decent skeg under there, it should handle OK at any speed.
     
  4. Vronsky
    Joined: Apr 2014
    Posts: 51
    Likes: 0, Points: 6, Legacy Rep: 10
    Location: Amsterdam

    Vronsky Junior Member

    There's a 'croissiere' version of this model (750 'CR') that some owners actually refer to as their "camper boat", so it appears to have all the necessary things for voyaging.
     
  5. Vronsky
    Joined: Apr 2014
    Posts: 51
    Likes: 0, Points: 6, Legacy Rep: 10
    Location: Amsterdam

    Vronsky Junior Member

    All boats are compromises, and I haven't found one yet that has a better feature package for my plan and constraints. Apart from ocean passages, I think it's capable and versatile enough to take me pretty much anywhere else that's worthwhile in a comfortable way. Simple and straightforward boat too, compared to sailing yachts.
     
  6. Mr Efficiency
    Joined: Oct 2010
    Posts: 9,286
    Likes: 696, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    In other words, you are bent on having this boat, but have some residual doubts about the suitability of it, and would like that dispelled by others agreeing what a beauty she is ! :D It just does not make a lot of sense to me to buy a boat that is designed for a different speed band than what the boat will be used for, a lot , or most of, the time. And I doubt you will really be saving much fuel by going back to "hull speed". I think the question, " for what, and where, will the boat be used, and what speed do you want to cruise at" largely decides the choice of hull type, size, and power. The accomodation aspect is a separate matter.
     
  7. tom28571
    Joined: Dec 2001
    Posts: 2,474
    Likes: 116, Points: 63, Legacy Rep: 1728
    Location: Oriental, NC

    tom28571 Senior Member

    I'm no expert on diesels but do notice lots of them that idle for hours and hours, almost never being switched off with no ill effects. Trucks, earth moving machinery and such spend a lot of time at idle. The boat itself will be fine at your projected speed although low speed can present steering issues in cross winds with lots of windage up high. If the boat suits you otherwise, there should be no real powerful negative issues and the ability to move faster when necessary or by choice is good.

    The fact that it is a planing hull only means that it is not the best at displacement speed, not that it is not adequate for you. I have seen many on longer cruises that run at displacement speed to save on fuel cost. May not give equivalent fuel mileage of a smaller engine but that may not be a big issue either.
     
  8. Mr Efficiency
    Joined: Oct 2010
    Posts: 9,286
    Likes: 696, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    Like you I profess no expertise with diesels, but you hear stories about running temps being too low, bores glazing, God knows what else going wrong, don't have any idea whether it is the case, but if it is a myth, it is a widespread one.
     
  9. Vronsky
    Joined: Apr 2014
    Posts: 51
    Likes: 0, Points: 6, Legacy Rep: 10
    Location: Amsterdam

    Vronsky Junior Member

    Thanks you for sharing your verdict.
    Believe me or not, I just like to know what the pros & cons are of this model, so I understand a bit better what I might be getting myself into.
     
  10. Vronsky
    Joined: Apr 2014
    Posts: 51
    Likes: 0, Points: 6, Legacy Rep: 10
    Location: Amsterdam

    Vronsky Junior Member

    Thank you, much appreciated.
    It's not a planing hull, but a semi-displacement type.
    And yes, I do like the idea of having extra power available. Elsewhere on this forum, I read that running diesels on low loads only gives real problems if the operating temperature gets too low.
     

  11. Mr Efficiency
    Joined: Oct 2010
    Posts: 9,286
    Likes: 696, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    Marine diesels adapted from automotive and other uses may have differences that cater to the more constant, high load characteristics of marine usage, and may vary from brand to brand. I'd want assurance from an experienced diesel mechanic who knows the particular engine, as to how long periods of low rpm will affect it.
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.